Issue 1 (201)/2025

ALSE and ACS Style
Amponsah, J.; Kumah, P.; Appiah, F.; Idun, I.A.; Tandoh, P.K. Influence of paclobutrazol concentrations, soil types and production seasons on physicochemical attributes of Keitt mangoes. Journal of Applied Life Sciences and Environment 2025, 58 (1), 85-120.
https://doi.org/10.46909/alse-581167

AMA Style
Amponsah J, Kumah P, Appiah F, Idun IA, Tandoh PK. Influence of paclobutrazol concentrations, soil types and production seasons on physicochemical attributes of Keitt mangoes. Journal of Applied Life Sciences and Environment. 2025; 58 (1): 85-120.
https://doi.org/10.46909/alse-581167

Chicago/Turabian Style
Amponsah, Justice, Patrick Kumah, Francis Appiah, Irene Akua Idun and Paul Kweku Tandoh. 2025. “Influence of paclobutrazol concentrations, soil types and production seasons on physicochemical attributes of Keitt mangoes.” Journal of Applied Life Sciences and Environment 58, no. 1: 85-120.
https://doi.org/10.46909/alse-581167

Influence of paclobutrazol concentrations, soil types and production seasons on physicochemical attributes of Keitt mangoes

Justice AMPONSAH^*, Patrick KUMAH, Francis APPIAH, Irene Akua IDUN and Paul Kweku TANDOH

Department of Horticulture, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

*Correspondence: justiceauspy@gmail.com 

Received: Jan. 24, 2025. Revised: Mar. 26, 2025. Accepted: Apr. 02, 2025. Published online: May 05, 2025

ABSTRACT. Mango is an important fruit with nutritional and economic benefits. However, the impact of varying paclobutrazol (PBZ) concentrations, soil types, and production seasons on its quality is less known in the literature. This study investigated the effects of varying PBZ concentrations, soil types, and production seasons on the quality of Keitt mangoes, aiming to optimise fruit attributes for both domestic and export markets. Conducted over three years in the Eastern Region of Ghana, this study had a 5×3×3 factorial design, with 5 PBZ concentrations (0, 10, 12.5, 20, and 25 mL), 3 soil types (Agawtaw, Akuse, and Baraku), and 3 production seasons (major, minor, and off-season). PBZ application had a concentration-dependent influence on the physical attributes of Keitt mango fruit, particularly fruit size, density, and firmness. Lower PBZ concentrations (0–12.5 mL) improved fruit size and total soluble solids (TSS) content, while higher concentrations (20–25 mL) reduced these parameters. Soil fertility played a key role, with fertile soils, such as Agawtaw, producing larger, heavier fruit with higher TSS and moisture contents. Seasonal variations also influenced the outcomes, with the major season favouring optimal fruit development due to favourable climatic conditions. Non-treated trees (0 mL PBZ) produced the largest and heaviest fruit, while the 25 mL PBZ treatment increased fruit firmness and extended the shelf life by reducing the total titratable acidity. The study emphasises the need to tailor PBZ applications to soil fertility and seasonal factors to achieve the desired fruit quality. These findings offer valuable insights for mango growers, promoting sustainable practices that enhance yield, quality, and economic viability in Keitt mango production to meet the growing global demand.

Keywords: Agawtaw soil series; Baraku soil series; Keitt mango; paclobutrazol.

 

INTRODUCTION

Mango (Mangifera indica L.) is a highly valued tropical fruit known for its exceptional taste, nutritional benefits, and culinary versatility (Mwaurah et al., 2020). The Keitt variety stands out due to its large size, vibrant colour, and superior flavour, making it a top choice for both local and export markets (Bura et al., 2023). Producing high-quality mangoes necessitates optimised agronomic practices, including the use of growth regulators (Bisht et al., 2018), soil fertility management (Liu et al., 2022), and seasonal adjustments in production (Pérez et al., 2018). These strategies are crucial for ensuring consumer satisfaction and maintaining postharvest quality in competitive global markets (Alfarisi et al., 2024).

Paclobutrazol (PBZ), a widely used plant growth regulator, plays a vital role in managing vegetative growth and promoting reproductive development in fruit trees, including mango (Kishore et al., 2015). PBZ functions by inhibiting gibberellin biosynthesis and redirecting assimilates toward fruit production, which enhances yield and fruit quality (Malhotra et al., 2018).

However, its effectiveness is influenced by factors such as soil type and production season, requiring calibration to avoid negative effects, such as reduced fruit size, weight, and physicochemical properties (Zanamwe, 2014). This study examines how different PBZ concentrations interact with soil types and seasonal variations to affect Keitt mango quality, aiming to optimise these parameters for improved fruit production.

Keitt mangoes are highly valued for their sensory appeal, nutritional benefits, and economic importance (Datir and Regan, 2022). Rich in vitamins A and C, antioxidants, and dietary fibre, they play a crucial role in combating malnutrition and oxidative stress-related disorders (Lenucci et al., 2022; Yahia et al., 2011). Economically, mango cultivation supports smallholder farmers and serves as a key export commodity, driving rural development and income generation in tropical regions (Akrong, 2020; Mitra, 2016). Additionally, their versatility extends beyond fresh consumption to processed products, such as juices, jams, and dried slices, underscoring their significance in global food systems and value chains (Ambuko and Owino, 2023).

Despite the significant potential of Keitt mangoes in promoting food security, nutrition, and economic growth, several challenges impede their production and postharvest quality (Onyango et al., 2023). Variability in soil fertility (Kumar et al., 2012) and fluctuating seasonal conditions often compromise fruit development (Cavalcante, 2022). Moreover, inconsistent PBZ application has been linked to reductions in fruit size, weight, and sweetness (Babu et al., 2022). These challenges highlight the need for targeted research to optimise PBZ application while considering soil and climatic variability to ensure consistent production of high-quality Keitt mango. This study explores the interaction between PBZ concentrations, soil types, production seasons, and their combined effects on the physicochemical quality of Keitt mango. Given the growing global demand for premium-quality mangoes, refining production practices is essential FOR enhancing their competitiveness in export markets. Additionally, this research provides actionable insights for mango growers, promoting evidence-based practices to optimise yield, quality, and profitability.

The main objective of this research was to evaluate the effects of the PBZ concentration, soil type, and production season on the physicochemical quality attributes of Keitt mango. By examining the interactions among these factors, this study aimed to identify optimal conditions for maximising the quality and market value of Keitt mango, thereby contributing to the development of sustainable and economically viable mango production systems.

 

MATERIALS AND METHODS

This study was conducted in two distinct phases. The first phase involved a field experiment in which PBZ was applied to randomly selected Keitt mango trees cultivated on various soil types across different production seasons. The second phase comprised laboratory analyses aimed at evaluating how varying PBZ applications influenced the quality attributes of Keitt mango fruit grown under these differing soil and seasonal conditions.

Study Area

The study took place in Ghana’s Eastern Region (Figure 1), specifically within the Manya Krobo and Yilo Krobo municipalities. Yilo Krobo Municipality encompasses approximately 594 km² and had a population of 122,705 in 2021. The municipal capital, Somanya, is located about 69 km from Accra and 50 km from Koforidua.

This region experiences a bimodal rainy season, with annual rainfall of 750–1600 mm, temperatures of 24.9–29.9°C, and relative humidity levels of 60–93%. The ecological landscape transitions between semi-deciduous rainforests and coastal savannah.

Laboratory analyses were conducted at the Kwame Nkrumah University of Science and Technology (KNUST) in Kumasi, utilising facilities from the Departments of Horticulture, Crops, and Soil Science, Pharmacology, and the Central Laboratory.

 

Location and extent of the mango farms

The following three mango farms in Ghana’s Eastern Region were selected for the study, each geo-referenced at specific soil profile pits: Farm 1 in Lower Manya, located at latitude 6°07’21.70”N and longitude 0°00’57.20”E and characterised by the Agawtaw soil series (Calcic Vertisol); Farm 2 in Lower Manya, situated at latitude 6°06’54.0”N and longitude 0°01’14.60”E and identified as the Akuse soil series (Calcic Vertisol); and Farm 3 in Somanya, positioned at latitude 6°02’51.70”N and longitude 0°00’52.50”W and characterised by the Beraku soil series (Gleyic Cambisol).

Experimental design

A 5×3×3 factorial design, with 5 PBZ concentrations (0, 10, 12.5, 20, and 25 mL), 3 soil types (Agawtaw, Akuse, and Baraku), and 3 production seasons (major, June–August; minor, January–February; and off-season, April–May). Each factor combination was replicated 3 times, resulting in 135 experimental units. The three dominant soils identified on the mango farms were Agawtaw series, Akuse series, and Beraku series, representing Farms 1, 2, and 3, respectively. A total of 540 mature mango fruits were used per year for this analysis, resulting in 1620 fruits overall.

Experiment planning, tree selection, and randomisation

This study involved the systematic selection and randomization of 135 ten-year-old Keitt mango trees across 3 farms representing the Agawtaw, Akuse, and Baraku soil series, with 45 trees from each farm. Trees were chosen based on their uniform size, canopy width, and vigour, with buffer zones established to prevent edge effects. Unique alphanumeric identifiers reflecting soil type, production season, and PBZ concentration (e.g., AGMJC0 for Agawtaw, major season, PBZ concentration 0) were assigned to each tree. Randomisation was achieved through the lottery method, in which identifiers were drawn from a container to allocate treatments impartially.

Treatment identifiers varied by soil series and season (major, minor, and off-season) and included PBZ concentrations ranging from 0 to 25 mL. Identifiers for trees in each soil series, such as AGMJC0 for Agawtaw, AKMJC0 for Akuse, and BKMJC0 for Baraku, ensured comprehensive categorisation. To maintain accuracy, trees were reviewed for duplicates and conformity to experimental criteria, with durable plastic tags attached for identification. A database and data collection sheet were created to record each tree’s details, facilitating organised data collection and ensuring reliable experimental tracking. The HPW manual for commercial mango farmers was followed for all three years of production. 

PBZ characterisation and determination of heavy metal content using the sample digestion method

In this study, PBZ (trade name: Cultar) was characterised, and its heavy metal content was determined through a sample digestion method. A 5 mL sample of Cultar solution was accurately measured in a Kjeldahl digestion tube. A mixture of perchloric acid, nitric acid, and hydrochloric acid in a 1:2:3 volumetric ratio was added. The mixture was heated to 450°C until the solution turned whitish, indicating the completion of digestion, which typically occurred in 30–60 min. After cooling, the digest was diluted to 100 mL with deionised water. The clear supernatant was analysed for heavy metals, including zinc (Zn), copper (Cu), manganese (Mn), iron (Fe), cadmium (Cd), mercury (Hg), lead (Pb), arsenic (As), and nickel (Ni), using atomic absorption spectrophotometry (AAS). This method allowed the precise quantification of heavy metals, providing insights into the chemical profile and potential environmental implications of PBZ.

Database and field documentation

A spreadsheet was designed to log tree information, including soil type, season, PBZ concentration treatments, and unique identifiers. Data entry protocols were established to ensure accuracy and consistency. A detailed schematic was created to indicate the spatial distribution of the experimental trees within each farm. The map included tree ID, soil type, and PBZ concentration of treatment allocations.

Harvesting, cleaning, packaging, and transportation to laboratory for analysis and data collection

A total of 270 treated Keitt mango fruits were randomly harvested by hand at the hard green stage of maturity from three farms, ensuring each treated tree was represented. The fruit was carefully washed with chlorinated water (200 ppm sodium hypochlorite) to eliminate microorganisms and remove foreign matter, such as dust and dirt. Efforts were made to select fruits that were uniform in size, of good quality, and free of injury or disease. The orchard management practices were adapted from HPW’s guidelines for commercial mango farmers and were consistently applied in subsequent productions for the second and third years.

Evaluated parameters

Determination of the respiration rate of treated Keitt mango after harvest

The respiration rate was measured by determining the amount of carbon dioxide (CO₂) released by the fruit over time. Mango fruit was placed in an airtight 1-L glass jar, sealed with a rubber septum, and incubated at 25 ± 2°C for 1–2 h. A 1-mL gas sample was extracted from the headspace using a gas-tight syringe and injected into a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD) and a stainless-steel column packed with Porapak Q. The GC was operated with an injector temperature of 100°C, a column temperature of 60°C, and a detector temperature of 200°C, using helium or nitrogen as the carrier gas at a flow rate of 40 mL min⁻¹. The CO₂ concentration was quantified using a calibration curve generated from standard CO₂ gas concentrations.

The respiration rate (mgCO₂ kg⁻¹ h⁻¹) was calculated using Equation (1), as follows:

where C is the CO₂ concentration in the headspace; V is the headspace volume; 44 is the molecular weight of CO₂; M is the fruit mass; T is the incubation time.

Determination of ethylene production of treated Keitt mango after harvest

Ethylene production was measured in mango fruit using the closed-system GC method. An individual mango was placed in an airtight 1-L glass jar, sealed with a rubber septum, and incubated at room temperature (25 ± 2°C) for 1–2 h to allow ethylene accumulation. A 1-mL gas sample was then extracted from the headspace using a gas-tight syringe and injected into a gas chromatograph equipped with a flame ionisation detector and a stainless-steel column packed with Porapak Q.

The GC operating conditions were as follows: injector temperature of 100–120°C, column temperature of 80°C, and detector temperature of 200°C, with nitrogen or helium as the carrier gas at a flow rate of 30 mL min⁻¹. Ethylene concentrations were quantified by comparing peak areas with standard calibration curves, and the ethylene production rate (µL kg⁻¹ h⁻¹) was calculated accordingly (Equation 2).

where C is the ethylene concentration in the headspace; V is the headspace volume; M is the fruit mass; and T is the incubation time.

Determination of fruit geometrical diameter (cm) of treated Keitt mango after harvest

The geometric diameter (D_g, cm) was derived using Equation (3), as given by Mohsenin (1986), using the length (L), width (W), and thickness (T):

Determination of fruit solid density of treated Keitt mango trees

A 100-mL beaker was filled with distilled water to the 50-mL mark. The mass of the mango fruit was weighed on a digital balance. The new volume was recorded after the fruit was suspended in the water in the beaker. The displaced volume was then determined. This was repeated three times. The solid density (ρ_s, g cm⁻³) was calculated using Equation (4) (Shittu et al., 2012):

where M_gs is the mass of the mango fruit; and V_dw is the volume of water displaced by the fruit.

Determination of eaten ripe fruit firmness (N) of treated Keitt mango tree

The firmness of ripe Keitt mango fruit was assessed non-destructively using a Shore C digital durometer. Each mango was placed on a horizontal laboratory bench, and measurements were collected at three points: the middle, stem end, and blossom end.

The durometer’s pressure needle was gently pressed against the fruit’s surface at each location, and the firmness readings were recorded in triplicate. The average of these readings was calculated and expressed in Newtons (N). This method allowed for consistent firmness evaluation without damaging the fruit.

Determination of the dry matter content (%) of ripened Keitt mango fruit pulp

The mango was weighed, placed in a moisture can or dish, and dried to constant weight at 70°C in a drying oven for 72 h. The sample was then placed in the desiccator and weighed again. Fruit dry matter was then calculated using Equation (5).

Determination of the moisture content (%) of ripened fruit pulp of treated Keitt mango

The moisture content (MC) was determined by weighing 2 g of the sample in a pre-weighed moisture can, drying it at 60°C for 24 h, cooling it in a desiccator, and reweighing. This process was repeated until a constant weight was achieved. The MC (%) was calculated using Equation (6):

where A is the crucible weight; B is the sample weight; C is the dry sample weight; and D is the moisture weight.

Determination of the total soluble solids content of ripened Keitt mango fruit pulp

To determine the total soluble solids (TSS) content (°Brix) of treated ripe Keitt mangoes, 30 g of peeled pulp was blended with 90 mL of distilled water. The mixture was filtered, and a few drops of the filtrate were placed onto the prism of a calibrated refractometer (HI 96801, Germany). After each measurement, the prism was cleaned with methanol and distilled water to ensure accuracy for subsequent readings.

Data analysis

The laboratory results were analysed with Statistix software version 9. When there were significant differences, treatment means were separated using the honestly significant difference (HSD) at the 1% probability level.

 

RESULTS AND DISCUSSION

Respiration rate of treated Keitt mango fruit after harvest

The respiration rate is a vital physiological parameter in climacteric fruit, such as mango, directly influencing the postharvest shelf life, metabolic activity, and ripening kinetics. as shown in Tables 1–3, a consistent trend of respiration rate suppression was observed in Keitt mango treated with increasing PBZ concentrations over 3 years. The findings confirm that PBZ application significantly reduced the respiration rate (p < 0.01), with notable interactions among the PBZ concentration, soil type, and season.

Across all 3 years, non-treated mango exhibited the highest respiration rate, while fruit treated with the highest PBZ concentration showed the lowest values. In the first year, the respiration rate decreased from 38.2 (0 mL PBZ) to 29.7 mgCO₂ kg⁻¹ h⁻¹ (25 mL PBZ). A similar pattern was observed in the second (43.3 to 26.8 mgCO₂ kg⁻¹ h⁻¹) and third years (39.7 to 27.6 mgCO₂ kg⁻¹ h⁻¹). This concentration-dependent decline aligns with previous research showing that PBZ reduces respiration by inhibiting gibberellin biosynthesis, thereby limiting ethylene synthesis and delaying climacteric ripening (Gill et al., 2023).

PBZ primarily reduces respiration in mangoes by inhibiting gibberellin biosynthesis, which slows cell expansion and carbohydrate metabolism, thereby lowering the energy demand and CO₂ evolution (Rossouw et al., 2024). By suppressing ethylene biosynthesis through the downregulation of 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), PBZ prevents the climacteric respiration peak, further reducing the metabolic activity (Li et al., 2020; Sebastian et al., 2019). Additionally, PBZ alters mitochondrial function by inhibiting key respiratory enzymes, such as cytochrome oxidase and succinate dehydrogenase, leading to lower ATP production and oxygen consumption (Shan et al., 2023).

PBZ also affects carbohydrate metabolism by inhibiting starch degradation and amylase activity, restricting glycolysis and the TCA cycle function (Santos et al., 2021). Furthermore, it enhances the antioxidant activity, reducing reactive oxygen species (ROS) production and oxidative stress, which stabilises cellular metabolism and delays senescence (Kamran et al., 2020). Another key mechanism is the PBZ-induced accumulation of abscisic acid (ABA), which suppresses ethylene synthesis and decreases fruit transpiration, reducing the respiratory activity (Maheshwari et al., 2022). These combined mechanisms explain the observed reduction in respiration rates from 34.5 in non-treated mango to 29.7 mgCO₂ kg⁻¹ h⁻¹ in fruit treated with 25 mL PBZ.

Soil type significantly influenced the respiration rate, with mangoes grown in Agawtaw soil consistently exhibiting higher respiration rates compared to Akuse and Baraku soils. This suggests that soil fertility, water-holding capacity, and organic matter content influence fruit’s metabolic activity (Kumar et al., 2021). Agawtaw soil, which is potentially richer in nutrients, may have promoted higher respiration, while the relatively compact or less fertile Baraku and Akuse soils may have imposed slight physiological constraints, leading to lower CO₂ emissions in PBZ-treated mango (Medina and Aguiar, 2017).

Seasonal variability also played a crucial role, with off-season mangoes exhibiting the highest respiration rates across all three years. In the first year, off-season fruit had a mean respiration rate of 34.3 mgCO₂ kg⁻¹ h⁻¹ compared to 34.0 mgCO₂ kg⁻¹ h⁻¹ in the major season and 33.4 mgCO₂ kg⁻¹ h⁻¹ in the minor season.

A similar trend was observed in the second (34.6, 34.9, and 32.1 mgCO₂ kg⁻¹ h⁻¹ for off-season, major, and minor seasons, respectively) and third years (34.5, 34.1, and 33.5 mgCO₂ kg⁻¹ h⁻¹ for off-season, major, and minor seasons, respectively).

The elevated respiration rate in off-season mango is likely due to increased temperatures and humidity, which accelerate metabolic activity and ethylene production, thus expediting ripening (Wang et al., 2022). Additionally, environmental stressors, such as irregular water availability and fluctuating diurnal temperatures, may have contributed to increased respiration rates, as previously reported in mango postharvest physiology studies (Adak et al., 2016).

The PBZ-induced reduction in respiration rate offers significant benefits for postharvest management, as lower metabolic activity translates to delayed ripening, extended shelf life, and improved storage potential. This is particularly advantageous for mango exporters, as PBZ-treated fruit may be better suited for long-distance transportation and extended market availability (Singh and Singh, 2019).

However, excessive respiration suppression may lead to undesirable textural changes or altered sensory attributes, necessitating careful optimisation of PBZ application.

Ethylene production (30 µL kg⁻¹ h⁻¹) of treated Keitt mango fruit after harvest

Ethylene production, a critical determinant of fruit ripening, was significantly influenced by PBZ application, soil type, and seasonal fluctuations (p < 0.01). PBZ consistently reduced ethylene emissions in a concentration-dependent manner across all 3 years (Tables 4–6), with higher concentrations (20 and 25 mL) resulting in the most substantial suppression. This finding aligns with the established role of PBZ as a gibberellin biosynthesis inhibitor, which indirectly restricts ethylene synthesis by disrupting the mevalonate pathway (Bai et al., 2021; Rademacher, 2016). The suppression of ethylene by PBZ can also be attributed to its direct impact on the ethylene biosynthesis pathway. By downregulating ACS and ACO (Mohapatra and Sahu, 2022), PBZ reduces the conversion of S-adenosylmethionine (SAM) to aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene (Sutaoney et al., 2023).

Studies on mango and other fruit crops, including apple (Malus domestica), pear (Pyrus communis), and tomato (Solanum lycopersicum), have confirmed that PBZ-treated plants exhibit decreased ACS and ACO activity, leading to delayed ripening and prolonged shelf life (Babu et al., 2022).

 

Table 1
Respiration rate (mgCO₂ kg^-1 h^-1) of harvested treated Keitt mango fruits with varied PBZ concentrations applied on different soil types during different production seasons for year one

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	40.2a	37.2abcdefg	34.6bcdefghij	30.7ijklm	31.1hijklm	34.7a
Agawtaw	Minor	37.6abcdef	37.8abcdef	32.9efghijkl	30.0jklm	28.3lm	33.3a
	Off-season	38.5abc	38.7abc	35.9abcdefgh	31.6hijklm	30.2jklm	35.0a
Means		38.8a	37.9a	34.5bc	30.8d	29.9d	34.3a
	Major	37.4abcdefg	35.7abcdefghi	33.6cdefghijk	30.4jklm	32.4ghijklm	33.9a
Akuse	Minor	40.0a	35.7abcdefghi	32.8fghijkl	30.6ijklm	28.4lm	33.5a
	Off-season	38.0abcde	39.2ab	34.6bcdefghij	29.2klm	29.5jklm	34.1a
Means		38.5a	36.9ab	33.7c	30.1d	30.1d	33.8a
	Major	37.4abcdefg	35.7abcdefghi	33.6cdefghijk	30.4jklm	30.3jklm	33.5a
Baraku	Minor	37.1abcdefg	38.4abcd	33.3defghijkl	30.6ijklm	27.5m	33.4a
	Off-season	37.3abcdefg	39.2ab	34.6bcdefghij	29.2klm	29.5jklm	34.0a
Means		37.3a	37.8a	33.8c	30.1d	29.1d	33.6a
Concentrations Grand means 38.2a			37.5a	34.0b	30.3c	29.7c
Seasons Mean	Major	38.3ab	36.2bcd	33.9de	30.5fgh	31.3fg	34.0ab
	Minor	38.2ab	37.3abc	33.0ef	30.4fgh	28.1h	33.4b
	Off-season	37.9ab	39.0a	35.0cde	30.0gh	29.7gh	34.3a
CV 4.07
HSD (0.01); PBZ concentrations =1.2652; seasons=0.8734; soil types=0.8734; PBZ concentration*seasons=2.6219; season*soil= 1.8819; PBZ concentration*soil types=2.6219; PBZ concentrations*seasons*soil types=5.1597.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 2
Respiration rate (mgCO₂ kg^-1 h^-1) of harvested treated Keitt mango fruits with varied PBZ concentrations applied on different soil types during different production seasons for year two

Soil Type	Seasons	Concentrations						Means
		0	10	12.5		20	25
Agawtaw	Major	44.3ab	35.3bcdef	41.6abc		34.1bcdef	27.4f	36.5a
	Minor	40.7abcd	35.1bcdef	31.7cdef		28.2ef	25.8f	32.3ab
	Off-season	41.2abc	35.9bcdef	36.1bcdef		31.8cdef	29.0def	34.8ab
Means		42.1ab	35.4cd	36.5bc		31.4cdef	27.4ef	34.6a
Akuse	Major	44.3ab	35.3bcdef	31.8cdef		33.3bcdef	27.4f	34.4ab
	Minor	40.0bcde	34.1bcdef	30.0cdef		27.8f	25.8f	31.5b
	Off-season	52.2a	33.3bcdef	36.4bcdef		30.5cdef	26.4f	35.8ab
Means		45.5a	34.2cd	32.7cde		30.5cdef	26.5f	33.9a
Baraku	Major	44.3ab	35.3bcdef	31.8cdef		30.5cdef	27.4f	33.9ab
	Minor	42.0abc	35.6bcdef	31.9cdef		27.8f	25.8f	32.6ab
	Off-season	40.3abcde	33.3bcdef	36.4bcdef		30.5cdef	26.4f	33.4ab
Means		42.2ab	34.7cd	33.4cde		29.6def	26.5f	33.3a
Concentrations Grand means       43.3a			34.8b	34.2b	30.5c		26.8d
Seasons Mean	Major	44.3a	35.3bc	35.1bc		32.6cd	27.4de	34.9a
	Minor	40.9ab	34.9bc	31.2cde		27.9de	25.8e	32.1b
	Off-season	44.6a	34.2c	36.3bc		30.9cde	27.3de	34.6a
CV 9.57; HSD (0.01); PBZ concentrations =2.9709; Seasons=2.0510; Soil types=2.0510; PBZ concentration*seasons=6.1568; season*Soil= 4.4191; PBZ concentration*soil types=6.1568; PBZ concentrations*seasons*soil types=12.116.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 3
Respiration rate (mgCO₂ kg^-1 h^-1) of harvested treated Keitt mango fruits with varied PBZ concentrations applied on different soil types during different production seasons for year three

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
Agawtaw	Major	38.7abc *	37.5bc	38.6abc	29.5ef	29.4ef	34.7a
	Minor	40.0abc	37.0bcd	37.2bcd	28.4ef	26.3f	33.8ab
	Off-season	40.47ab	37.9abc	37.3bcd	30.2ef	28.8ef	34.9a
Means		39.7a	37.5abc	37.7abc	29.4e	28.2e	34.5a
	Major	38.7abc	37.5bc	35.3cd	29.5ef	27.5ef	33.7ab
Akuse	Minor	37.9abc	37.5abc	32.4de	29.5ef	26.2f	32.7b
	Off-season	42.5a	36.8bcd	36.2bcd	28.9ef	28.3ef	34.5a
Means		39.7a	37.3 abc	34.6d	29.3e	27.3e	33.6b
Baraku	Major	38.7abc	37.5bc	35.6bcd	29.5ef	27.5ef	33.8ab
	Minor	40.6ab	37.1bcd	36.5bcd	29.5ef	26.2f	34.0ab
	Off-season	39.3abc	36.8bcd	36.2bcd	28.9ef	28.3ef	33.9ab
Means		39.5ab	37.1cd	36.1cd	29.3e	27.3e	33.9ab
Concentrations Grand means 39.7a			37.3b	36.1b	29.3c	27.6d
Seasons Mean	Major	38.7abc	37.5bcd	36.5cd	29.5e	28.1ef	34.1ab
	Minor	39.5ab	37.2bcd	35.3d	29.1e	26.2f	33.5b
	Off-season	40.8a	37.2bcd	36.6cd	29.3e	28.5ef	34.5a
CV 3.92; HSD (0.01); PBZ concentrations =1.2189; seasons=0.8415; soil types=0.8415; PBZ concentration*seasons=2.5261; season*Soil= 1.8132; PBZ concentration*soil types=2.5261; PBZ concentrations*seasons*soil types=4.9712.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

In addition to ethylene biosynthesis inhibition, PBZ interacts with other plant hormones to further suppress ethylene production. One such interaction occurs with ABA, a key phytohormone known to counteract ethylene synthesis. PBZ treatment enhances ABA accumulation, which inhibits ACS and ACO activity and further reduces ethylene biosynthesis (Kumar et al., 2021). Additionally, PBZ mitigates oxidative stress, which is a known inducer of ethylene production. Reactive Oxygen Species (ROS), particularly hydrogen peroxide (H₂O₂), enhance ACS and ACO activity under stress conditions, accelerating fruit ripening (Khan et al., 2023). By reducing ROS accumulation and enhancing antioxidant enzyme activity, PBZ indirectly suppresses ethylene synthesis and prolongs fruit storage life (Patel et al., 2022). Furthermore, PBZ delays fruit softening by inhibiting ethylene-induced expression of cell wall-degrading enzymes, such as polygalacturonase, cellulase, and pectin methylesterase, thereby preserving fruit firmness and preventing postharvest deterioration (Elad, 1997). In addition to PBZ application type played a significant role in ethylene production (Khan et al., 2020), with mangoes grown on Agawtaw soil consistently exhibiting higher emissions than those grown on Akuse and Baraku soils. This suggests that soil properties, such as organic matter content, nutrient availability, and moisture retention, influence ethylene biosynthesis (Spokas et al., 2010). The likely higher organic matter and nutrient content in the Agawtaw soil may have promoted greater metabolic activity, leading to increased ethylene production. In contrast, Baraku and Akuse soils, which are potentially more compact or nutrient-deficient, may have imposed mild physiological constraints on ethylene biosynthesis, leading to lower ethylene emissions (Medina and Aguiar, 2017). Seasonal variability further impacts ethylene production (Li et al., 2022), with off-season mangoes exhibiting signify-scantly higher ethylene emissions com-pared to those harvested in the major and minor seasons. This trend was observed consistently over the 3-year study period and was attributed to climatic fluctuations, particularly changes in temperature and humidity, which are known to influence ethylene biosynthesis and accelerate fruit ripening (Biale et al., 2018). Additionally, environmental stressors, such as irregular water availability and fluctuating diurnal temperatures, likely triggered stress-induced ethylene production, a phenome-non commonly reported in studies on tropical fruit physiology (Riaz et al., 2024).

Physical attributes of treated Keitt mango trees 

Geometrical diameter of treated Keitt mango fruit

This study revealed a significant (p ≤ 0.01) inverse relationship between PBZ concentration and mango fruit geometrical diameter, with non-treated trees producing the largest fruit, while those treated with the highest PBZ concentration (25 mL) yielded the smallest (Tables 1–3). This reduction in fruit size is primarily due to PBZ’s inhibition of gibberellin biosynthesis, which restricts cell elongation and carbohydrate allocation, thereby limiting fruit expansion (Reddy and Kurian, 2008; Sebastian et al., 2019; Yeshitela et al., 2004).

 

Table 4
Ethylene production (µL kg^-1 h^-1) of harvested treated Keitt mango fruits with varied PBZ concentrations applied on different soil types during different production seasons for year one

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	92.4abc	91.6abc	86.9c	76.5d	69.5d	83.4a
Agawtaw	Minor	99.7a	97.1abc	94.4abc	70.0d	68.3d	85.9a
	Off-season	98.8ab	95.2abc	90.0abc	72.1d	70.3d	85.3a
Means		97.0a	94.6ab	90.4b	72.9c	69.4c	84.8a
	Major	92.4abc	91.6abc	88.9bc	70.5d	69.5d	82.6a
Akuse	Minor	93.8abc	90.6abc	95.2abc	66.5d	68.8d	83.0a
	Off-season	98.3ab	94.3abc	95.2abc	72.3d	69.8d	86.0a
Means		94.8ab	92.2ab	93.1ab	69.8c	69.4c	83.8a
	Major	92.4abc	91.6abc	88.9bc	70.5d	69.5d	82.6a
Baraku	Minor	95.5abc	92.3abc	88.9bc	66.5d	68.8d	82.4a
	Off-season	96.5abc	94.3abc	95.2abc	72.3d	69.8d	85.6a
Means		94.8ab	92.7ab	91.0b	69.8c	69.4c	83.5a
concentration Grand means 95.5a			93.2ab	91.5b	70.8c	69.4c
Seasons Mean	Major	92.4bc	91.6bc	88.2c	72.5d	69.5d	82.8b
	Minor	96.3ab	93.3abc	92.8abc	67.7d	68.6d	83.8b
	Off-season	97.9a	94.6ab	93.5ab	72.2d	70.0d	85.6a
CV= 3.27; HSD (0.01); PBZ concentrations =2.5153; soil types=1.7365; seasons= 1.7365; PBZ concentrations * seasons= 5.2127; PBZ concentrations * soil types=5.2127; seasons *soil types= 3.7415; PBZ concentrations *seasons *soil types= 10.258.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 5
Ethylene production (µL kg^-1 h^-1) of harvested treated Keitt mango fruits with varied PBZ concentrations applied on different soil types during different production seasons for year two

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	103.4ab	97.9abcdef	85.2hi	68.8jk	66.8jk	84.4cde
Agawtaw	Minor	102.2abc	90.6defgh	88.9efgh	67.9jk	63.1k	82.6de
	Off-season	107.5a	90.8defgh	91.0defgh	76.17ij	66.7jk	86.4abc
Means		104.4a	93.1bc	88.4c	71.0d	65.5e	84.5a
	Major	105.4ab	102.4abc	85.2hi	65.8k	66.8jk	85.1bcd
Akuse	Minor	100.7abcd	88.3fgh	87.3gh	64.9k	62.8k	80.8e
	Off-season	99.2abcde	95.7bcdefg	92.2cdefgh	88.5fgh	66.3jk	88.4ab
Means		101.8a	95.5b	88.2c	73.1d	65.3e	84.8a
	Major	105.4ab	102.4abc	85.2hi	65.8k	66.8jk	85.1bcd
Baraku	Minor	105.4ab	91.4defgh	87.3gh	64.9k	62.8k	82.3de
	Off-season	103.0ab	95.7bcdefg	92.2cdefgh	88.5fgh	66.3jk	89.2a
Means		104.6a	96.5b	88.2c	73.1d	65.3e	85.5a
concentration Grand means       103.6a			95.0b	88.3c	72.4d	65.4e
	Major	104.7a	100.9a	85.2de	66.8f	66.8f	84.9b
Seasons Mean	Minor	102.8a	90.1bcd	87.8cde	65.9f	62.9f	81.9c
	Off-season	103.2a	94.1b	91.8bc	84.4e	66.4f	88.0a
CV= 3.27; HSD (0.01); PBZ concentrations =2.5396; soil types=1.7533; seasons= 1.7533; PBZ concentrations * seasons= 5.2630; PBZ concentrations * soil types=5.2630; seasons *soil types= 3.7777; PBZ concentrations *seasons *soil Types= 10.357.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 6
Ethylene production (µL kg^-1 h^-1) of harvested treated Keitt mango fruits with varied PBZ concentrations applied on different soil types during different production seasons for year three

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	103.3abc	96.7abcde	96.1abcde	87.8abcdefghi	69.3hijk	90.6a
Agawtaw	Minor	105.8ab	96.3abcde	85.7bcdefghijk	69.3hijk	65.4jk	84.5a
	Off-season	108.2a	95.1abcdef	87.1abcdefghij	81.4cdefghijk	67.0ijk	87.8a
Means		105.8a	96.0ab	89.6bc	79.5cd	67.2e	87.6a
	Major	105.3ab	98.2abcd	88.9abcdefghi	75.4efghijk	64.3k	86.4a
Akuse	Minor	103.3abc	98.4abcd	88.0abcdefghi	78.7defghijk	73.7fghijk	88.4a
	Off-season	98.4abcd	98.8abcd	92.3abcdefg	75.3efghijk	64.4k	85.8a
Means		102.3a	98.8ab	89.7bc	76.5de	67.5e	86.9a
	Major	103.9ab	96.7abcde	89.7abcdefgh	68.8hijk	67.3ijk	85.3a
Baraku	Minor	105.8ab	92.0abcdefg	85.3bcdefghijk	70.4ghijk	64.3k	83.6a
	Off-season	106.7ab	97.4abcde	88.5abcdefghi	75.2efghijk	68.5hijk	87.3a
Means		105.5a	95.4ab	87.8bc	71.5de	66.7e	85.4a
concentration Grand means 104.5a			96.6b	89.1c	75.8d	67.1e
Seasons Mean	Major	104.2a	97.2ab	91.6b	77.3cd	67.0d	87.4a
	Minor	105.0a	95.6ab	86.3bc	72.8d	67.8d	85.5a
	Off-season	104.4a	97.1ab	89.3b	77.3cd	66.6d	86.9a
CV= 6.87; HSD (0.01); PBZ concentrations =5.4479; soil types=3.7611; seasons= 3.7611; PBZ concentrations * seasons= 11.290; PBZ concentrations * soil types=11.290; seasons *soil types= 8.1037; PBZ concentrations *seasons *soil types= 22.218.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Gibberellins play a crucial role in fruit growth by promoting cell division, elongation, and sugar mobilization from leaves to developing fruit. PBZ application disrupts this process, causing carbohydrate accumulation in vegetative tissues rather than in fruit, slowing fruit development (Bai et al., 2021). Furthermore, PBZ suppresses cell wall-loosening enzymes, such as expansions and pectinases, increasing rigidity and further restricting fruit expansion (Medina and Aguiar, 2017).

Additionally, PBZ enhances ABA accumulation, which counteracts gibberellin activity, reducing the fruit growth potential and photosynthetic efficiency and further contributing to a smaller fruit size (Maheshwari et al., 2022).

 

Soil type significantly influences the fruit diameter, with mangoes grown in Agawtaw soil being the largest, followed by those from Akuse and Baraku soils. The superior performance of Agawtaw soil may be attributed to its higher fertility and water-holding capacity, which supports fruit expansion, whereas Baraku soil, which has a lower fertility, amplified PBZ’s growth-suppressing effects, further reducing fruit size (Fosu and Tetteh, 2008; Yeshitela et al., 2004).

Seasonal variations also played a crucial role, with mangoes harvested in the major season, exhibiting larger fruit diameters due to optimal climatic conditions, including adequate rainfall and moderate temperatures, which enhanced photosynthesis and nutrient uptake. Conversely, minor and off-season fruit was smaller due to water stress and reduced nutrient availability (Litz, 2009; Taiz and Zeiger, 2018).

The interaction among PBZ concentration, soil type, and season further highlights the complexity of fruit development. The largest mangoes were observed in non-treated trees on Agawtaw soil during the major season, while the smallest were recorded in mango treated with 25 mL PBZ on Agawtaw soil in the off-season. This suggests that PBZ effectiveness is highly dependent on environmental conditions (Malhotra et al., 2018), emphasising the need for site-specific PBZ application strategies. Adjusting PBZ concentrations based on soil fertility and seasonal conditions is essential for balancing vegetative growth regulation and optimal fruit development.

At higher concentrations, PBZ suppresses fruit cell division by downregulating cyclin-dependent kinases (CDKs) and mitotic regulators, leading to fewer total cells and permanently smaller fruit (Patel et al., 2022). It also disrupts the gibberellin–auxin balance, causing abnormal fruit morphology compared to non-treated mango, which exhibit normal hormone interactions that support optimal fruit growth (Singh and Singh, 2019).

These findings suggest that although PBZ is effective in managing vegetative growth, its excessive use may negatively impact fruit size, necessitating careful concentration optimisation to prevent undesirable reductions in mango fruit quality.

 

Table 7
Fruit geometrical diameter (cm) of treated Keitt mango tree with varied PBZ concentrations applied on different soil types during different production seasons for year one

Soil type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	21.7a*	19.9abc	18.6abcde	17.4abcdef	16.0cdef	18.7a
Agawtaw	Minor	19.8abc	18.5abcdef	17.8abcdef	15.5cdef	15.1cdef	17.3abc
	Off-season	19.4abc	18.6abcde	17.7abcdef	15.6cdef	13.7f	17.0abc
Means		20.3a	19.0ab	18.1abc	16.2cde	14.9e	17.7a
	Major	21.4ab	19.0abcde	18.1abcdef	17.3abcdef	16.4cdef	18.4ab
Akuse	Minor	19.3abcd	18.8abcde	17.0abcdef	16.3cdef	15.0cdef	17.3abc
	Off-season	19.5abc	16.8bcdef	16.2cdef	16.0cdef	14.1ef	16.5c
Means		20.0a	18.2abc	17.1bcde	16.5bcde	15.2de	17.4a
	Major	18.8abcde	16.7bcdef	16.6bcdef	15.3cdef	14.4def	16.4c
Baraku	Minor	17.4abcdef	18.2abcdef	15.8cdef	15.3cdef	15.0cdef	16.3c
	Off-season	18.6abcde	17.4abcdef	16.5bcdef	16.0cdef	15.4cdef	16.8bc
Means		18.3abc	17.4bcd	16.3cde	15.5de	14.9e	16.5b
concentration Grand means 19.5a			18.2b	17.2bc	16.1cd	15.0d
Seasons Mean	Major	20.6a	18.5abc	17.8bcd	16.7cdef	15.6def	17.8a
	Minor	18.8abc	18.5abc	16.9bcde	15.7def	15.0ef	17.0b
	Off-season	19.2ab	17.6bcd	16.8bcdef	15.9def	14.4f	16.8b
CV= 7.64
HSD (0.01); PBZ concentrations =1.2030; soil types=0.8306; seasons= 0.8306; PBZ concentrations * seasons= 2.4932; PBZ concentrations * soil types=2.4932; seasons *soil types= 1.7895; PBZ concentrations *seasons *soil types= 4.9064.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 8
Fruit geometrical diameter (cm) of treated Keitt mango tree with varied PBZ concentrations applied on different soil types during different production seasons for year two

Soil type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	21.1a*	18.9abc	17.1abcdefgh	17.4abcdefg	14.9cdefgh	17.9a
Agawtaw	Minor	18.4abcd	16.8bcdefgh	17.7abcdef	14.9cdefgh	14.0efgh	16.3abc
	Off-season	17.8abcdef	16.9bcdefgh	16.6bcdefgh	15.8bcdefgh	13.7efgh	16.2bc
Means		19.1a	17.5ab	17.2abc	16.0bcde	14.2de	16.8a
	Major	20.0ab	17.4abcdefg	16.7bcdefgh	15.5cdefgh	14.1efgh	16.8ab
Akuse	Minor	18.6abcd	17.5abcdefg	15.8bcdefgh	15.4cdefgh	14.5defgh	16.4abc
	Off-season	17.7abcdef	17.0abcdefgh	14.7cdefgh	14.6defgh	13.2gh	15.4bc
Means		18.8a	17.3abc	15.7bcde	15.2cde	14.0e	16.2a
	Major	16.9abcdefgh	15.5cdefgh	15.9bcdefgh	14.4defgh	13.1h	15.2c
Baraku	Minor	17.6abcdef	16.7bcdefgh	15.2cdefgh	13.6fgh	13.3gh	15.3bc
	Off-season	17.9abcde	16.6bcdefgh	15.1cdefgh	14.5defgh	15.3cdefgh	15.9bc
Means		17.5ab	16.3bcd	15.4bcde	14.2de	13.9e	15.4b
concentration Grand means 18.4a			17.0b	16.1bc	15.1c	14.0d
Seasons Mean	Major	19.4a	17.3abcd	16.6bcdef	15.8cdefgh	14.0h	16.6a
	Minor	18.2ab	17.0bcde	16.2bcdefg	14.6fgh	13.9h	16.0ab
	Off-season	17.8abc	16.8bcde	15.5defgh	14.9efgh	14.1gh	15.8b
CV= 7.08; HSD (0.01); PBZ concentrations =1.0453; soil types=0.7216; seasons=0.7216; PBZ concentrations * seasons= 2.1662; PBZ concentrations * soil types=2.1662; seasons *soil types= 1.5548; PBZ concentrations *seasons *soil types= 4.2629.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 9
Fruit geometrical diameter (cm) of treated Keitt mango tree with varied PBZ concentrations applied on different soil types during different production seasons for year three

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	21.4a*	19.2abcde	17.0bcdefghijkl	15.8defghijklm	15.1efghijklm	17.7a
Agawtaw	Minor	20.8abc	17.6abcdefghijk	15.3efghijklm	14.5hijklm	13.0lm	16.2abc
	Off-season	17.6abcdefghijk	14.5hijklm	15.0efghijklm	14.1jklm	12.7 m	14.8c
Means		19.9a	17.1bcde	15.8defgh	14.8fghi	13.6i	16.2a
	Major	21.0ab	19.1abcde	17.1bcdefghijkl	15.8defghijklm	13.4klm	17.3a
Akuse	Minor	19.1abcde	17.9abcdefghij	15.9defghijklm	14.6ghijklm	13.4klm	16.2abc
	Off-season	18.8abcdefg	17.6abcdefghijk	15.9defghijklm	15.2efghijklm	14.2jklm	16.4ab
Means		19.6a	18.2abc	16.3cdef	15.2efghi	13.7hi	16.6a
	Major	18.7abcdefgh	18.2abcdefghij	16.6cdefghijklm	14.7fghijklm	13.9jklm	16.4ab
Baraku	Minor	18.9abcdef	16.9bcdefghijklm	15.6defghijklm	13.1lm	13.4klm	15.6bc
	Off-season	18.5abcdefghi	18.5abcdefghi	16.1defghijklm	14.3ijklm	13.5klm	16.5ab
Means		19.2ab	17.9abcd	16.1cdefg	14.1ghi	13.5i	16.2a
concentration Grand means   19.6a			17.7b	16.1c	14.7d	13.6e
Seasons Mean	Major	20.4a	18.8abc	16.9cd	15.4def	14.1efg	17.1a
	Minor	19.6ab	17.5bcd	15.6def	14.1efg	13.2g	16.0b
	Off-season	18.7abc	16.9cd	15.7de	14.5efg	13.5fg	15.9b
CV= 7.03; HSD (0.01); PBZ concentrations =1.0506; soil types=0.7253; seasons=0.7253; PBZ concentrations * seasons= 2.1773; PBZ concentrations * soil types=2.1773; seasons *soil types= 1.5628; PBZ concentrations *seasons *soil types= 4.2847.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Density of treated Keitt mango fruit

PBZ application significantly reduced mango fruit density, with non-treated trees consistently producing denser fruit than PBZ-treated trees. Over 3 years, mean densities of 1.71, 1.53, and 1.55 gcm^–³ were recorded in non-treated trees, whereas those treated with the highest PBZ concentration (25 mL) had the lowest densities (1.25–1.33 gcm^–³). This inverse relationship between PBZ concentration and fruit density is linked to its effects on gibberellin inhibition, carbohydrate metabolism, cell wall modification, and water retention (Singh and Singh, 2019). PBZ suppresses gibberellin biosynthesis by inhibiting ent-kaurene oxidase, limiting cell division and expansion and leading to smaller, denser cells. However, at higher PBZ concentrations, excessive gibberellin suppression restricts intercellular expansion, increasing air spaces, and reducing the overall fruit density (Rademacher, 2016). Additionally, PBZ alters carbohydrate partitioning by diverting sugars to vegetative tissues instead of fruit development, thus reducing dry matter accumulation and fruit density (Bai et al., 2021). Research has shown that PBZ-treated mango trees exhibit increased leaf carbohydrate retention at the expense of fruit growth, contributing to decreased pulp firmness (Lalel et al., 2020). Soil type significantly influenced fruit density, with Agawtaw soil producing the densest fruit across all 3 years (1.54, 1.33, and 1.49 gcm^–³), while Baraku soil yielded the lowest, especially in PBZ-treated trees. Agawtaw soil’s high organic matter and superior water retention supported optimal root function and fruit development, enhancing carbo-hydrate accumulation and improving fruit density (Brady and Weil, 2017). However, Baraku soil, with low fertility and poor nutrient retention, exacerbated PBZ’s negative effects by further restricting sugar accumulation in fruit tissues (Scholtz, 2020). Akuse soil, which exhibited intermediate density values, likely had moderate nutrient availability, limiting its capacity to support fruit growth under PBZ application (Lal and Stewart, 2015). Seasonal variations also played a crucial role, with fruit from the major season consistently exhibiting higher densities (1.56, 1.40 and 1.42 g cm^–³ across 3 years) compared to that from the minor season and off-season. The higher densities in the major season were due to favourable climatic conditions, including adequate rainfall, moderate temperatures, and high solar radiation, which enhanced sugar accumulation and strengthened cell walls (Litz, 2009). Conversely, minor and off-season fruit had lower densities due to irregular rainfall and temperature fluctu-ations, which restricted carbohydrate translocation. However, in the third year, off-season fruit (1.46 g cm^–³) was slightly denser than minor-season fruit (1.38 g cm^–³), suggesting improved environmen-tal conditions or adaptive physiological responses (Yadav et al., 2013). PBZ also impacts fruit density by influencing cell wall composition and water retention. Gibberellins regulate enzymes, such as expansions and pectinases, which facilitate cell wall loosening. PBZ downregulates these enzymes, increasing cell rigidity but also creating more air pockets and reducing fruit density (Medina and Aguiar, 2017). Additionally, PBZ-induced ABA accumulation reduces stomatal conductance, limiting water uptake and further decreasing fruit density (Maheshwari et al., 2022). At the cellular level, PBZ suppresses mitotic activity by inhibiting CDKs, leading to fewer, loosely packed cells, increasing fruit porosity, and reducing density (Patel et al., 2022).

 

Table 10
Fruit density (g cm^–³) of treated Keitt mango tree with varied PBZ concentrations applied on different soil types during different production seasons for year one

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	2.07a*	1.75ab	1.51ab	1.39ab	1.36ab	1.61a
Agawtaw	Minor	1.85ab	1.83ab	1.82ab	1.30b	1.32b	1.62a
	Off-season	1.50ab	1.55ab	1.39ab	1.27b	1.19b	1.38ab
Means		1.81a	1.71ab	1.57abcde	1.32cde	1.29de	1.54a
	Major	1.79ab	1.72ab	1.67ab	1.27b	1.21b	1.53a
Akuse	Minor	1.60ab	1.64ab	1.48ab	1.25b	1.31b	1.46ab
	Off-season	1.60ab	1.55ab	1.34b	1.21b	1.17b	1.38ab
Means		1.67abc	1.64abcd	1.49abcde	1.25e	1.23e	1.45ab
	Major	1.84ab	1.51ab	1.56ab	1.45ab	1.35b	1.54a
Baraku	Minor	1.45ab	1.24b	1.17b	1.21b	1.14b	1.24b
	Off-season	1.65ab	1.48ab	1.52ab	1.37ab	1.23b	1.45ab
Means		1.65abcd	1.41bcde	1.42bcde	1.34bcde	1.24e	1.41b
concentration Grand means          1.71a			1.59ab	1.49b	1.30c	1.25c
	Major	1.90a	1.66ab	1.58abcd	1.37bcde	1.31bcde	1.56a
Seasons Mean	Minor	1.63abc	1.57abcd	1.49bcde	1.26de	1.26de	1.44ab
	Off-season	1.58abcd	1.53bcde	1.41bcde	1.29cde	1.20e	1.40b
CV= 13.17; HSD (0.01); PBZ concentrations =0.1771; soil types=0.1223; seasons= 0.1223; PBZ concentrations * seasons= 0.3670; PBZ concentrations * soil types=0.3670; seasons *soil types= 0.2634; PBZ concentrations *seasons *soil types= 0.7223.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 11
Fruit density (g cm^–³) of treated Keitt mango tree with varied PBZ concentrations applied on different soil types during different production seasons for year two

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	1.91a*	1.62ab	1.17b	1.10b	1.30ab	1.42a
Agawtaw	Minor	1.45ab	1.30ab	1.13b	1.24ab	1.22ab	1.27a
	Off-season	1.49ab	1.25ab	1.17b	1.36ab	1.24ab	1.30a
Means		1.62a	1.39abc	1.16c	1.23bc	1.25bc	1.33a
	Major	1.62ab	1.39ab	1.30ab	1.10b	1.26ab	1.33a
Akuse	Minor	1.34ab	1.32ab	1.23ab	1.34ab	1.12b	1.27a
	Off-season	1.40ab	1.22ab	1.24ab	1.17b	1.12b	1.23a
Means		1.45abc	1.31abc	1.26bc	1.20bc	1.17bc	1.28a
	Major	1.77ab	1.59ab	1.35ab	1.34ab	1.22ab	1.46a
Baraku	Minor	1.40ab	1.49ab	1.37ab	1.24ab	1.22ab	1.34a
	Off-season	1.39ab	1.41ab	1.34ab	1.24ab	1.17b	1.31a
Means		1.52ab	1.49abc	1.35abc	1.27abc	1.20bc	1.37a
concentration Grand means 1.53a			1.40ab	1.26bc	1.24bc	1.21c
Seasons Mean	Major	1.77a	1.53ab	1.27b	1.18b	1.26b	1.40a
	Minor	1.40b	1.37b	1.24b	1.27b	1.19b	1.29ab
	Off-season	1.43ab	1.29b	1.25b	1.26b	1.18b	1.28b
CV= 14.30; HSD (0.01); PBZ concentrations =0.1734; soil types=0.1197; seasons= 0.1197; PBZ concentrations * seasons= 0.3594; PBZ concentrations * soil types=0.3594; seasons *soil types= 0.2580; PBZ concentrations *seasons *soil types= 0.7073.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 12
Fruit density (g cm^–³) of treated Keitt mango tree with varied PBZ concentrations applied on different soil types during different production seasons for year three

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	1.71a*	1.45a	1.37a	1.41a	1.56a	1.47a
Agawtaw	Minor	1.91a	1.45a	1.30a	1.27a	1.41a	1.47a
	Off-season	1.56a	1.30a	1.51a	1.63a	1.60a	1.52a
Means		1.73a	1.40ab	1.34ab	1.44ab	1.52ab	1.49a
	Major	1.73a	1.37a	1.22a	1.26a	1.44a	1.43a
Akuse	Minor	1.32a	1.29a	1.19a	1.46a	1.57a	1.36a
	Off-season	1.45a	1.26a	1.27a	1.27a	1.49a	1.35a
Means		1.50ab	1.31b	1.28b	1.33b	1.50ab	1.38a
	Major	1.54a	1.35a	1.29a	1.30a	1.29a	1.35a
Baraku	Minor	1.38a	1.24a	1.32a	1.21a	1.31a	1.29a
	Off-season	1.33a	1.53a	1.54a	1.66a	1.54a	1.52a
Means		1.42ab	1.37ab	1.38ab	1.39ab	1.38ab	1.39a
concentration Grand means 1.55a			1.36ab	1.33b	1.39ab	1.47ab
Seasons Mean	Major	1.66a	1.39a	1.29a	1.32a	1.43a	1.42a
	Minor	1.54a	1.33a	1.27a	1.31a	1.43a	1.38a
	Off-season	1.45a	1.36a	1.44a	1.52a	1.54 a	1.46a
CV= 14.80; HSD (0.01); PBZ concentrations =0.1924; soil types=0.1328; seasons= 0.1328; PBZ concentrations * seasons= 0.3987; PBZ concentrations * soil types=0.3987; seasons *soil types= 0.2862; PBZ concentrations *seasons *soil types= 0.7846.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

These findings highlight the complex interactions between PBZ, soil properties, and seasonal conditions in regulating mango fruit density. Although PBZ effectively controls vegetative growth, excessive concentrations may compromise fruit quality by reducing the density. Optimising the PBZ concentration based on soil fertility and seasonal conditions can help mitigate these negative effects and sustain fruit quality.

Ripe fruit firmness of treated Keitt mango

PBZ application significantly enhanced fruit firmness across all 3 years, with higher concentrations (25 mL) consistently producing firmer fruit (46.0–46.3 N). In contrast, non-treated trees produced the least firm fruit, with values ranging from 39.9 to 41.0 N. The increase in firmness with PBZ application can be attributed to several physiological mechanisms. PBZ inhibits gibberellin biosynthesis, leading to reduced cell expansion and enhanced lignification, which strengthens the fruit structure (Kumar, 2023). Furthermore, PBZ increases calcium and pectin deposition, fortifying cell walls and delaying enzymatic degradation during ripening (Reddy and Kurian, 2008). PBZ-treated mangoes have also been reported to exhibit reduced polygalacturonase and pectin methylesterase activities, which are responsible for breaking down cell wall components during ripening (Lobo and Sidhu, 2017). The findings of this study align with those of previous research showing that PBZ improves firmness in fruit crops by promoting cell wall reinforcement and delaying ethylene-mediated softening (Srivastava and Dwivedi, 2000). However, while PBZ enhances fruit firmness, excessive concentrations may lead to stress-induced metabolic imbalances, necessitating precise concentration optimisation for maintaining fruit quality without compromising plant physiology. The soil type significantly influenced firmness outcomes, with variations observed across the years. In the first year, Akuse soil yielded the firmest fruit (42.8 N), while Baraku soil produced the firmest fruit in the second and third years, with values of 43.0 N and 43.9 N, respectively. Agawtaw soil produced consistently high firmness values across all years, indicating its ability to support optimal fruit development under PBZ treatments.

The role of soil fertility in modulating fruit firmness is well established. Well-structured soils rich in organic matter, such as Agawtaw, facilitate efficient calcium uptake, which is essential for stabilising pectin within the fruit’s middle lamella, thereby enhancing firmness (Brady and Weil, 2017). Calcium plays a crucial role in cross-linking pectin molecules, strengthening cell walls, and reducing enzymatic degradation during ripening (White and Broadley, 2003). Baraku soil, despite its lower fertility compared to Agawtaw soil, exhibited improved firmness levels under higher PBZ concentrations. This suggests that in nutrient-limited soils, PBZ may enhance firmness by improving resource allocation efficiency and compensating for deficiencies in organic matter and micronutrients (Scholtz, 2020). However, Akuse soil, which initially produced firmer fruit, was outperformed by Baraku soil in later years. This could be attributed to Akuse soil’s moderate cation exchange capacity (CEC), which may have limited the long-term availability of calcium and potassium, both of which are essential for maintaining fruit firmness (Sebastian et al., 2019). These findings highlight the importance of tailoring PBZ application to specific soil conditions to optimise fruit firmness outcomes. Nutrient management strategies, including calcium supplementation, may be necessary to sustain long-term firmness improvements, particularly in soils with lower fertility. Seasonal variations significantly influenced fruit firmness, with the off-season producing the firmest fruit in the first and second years (42.8 and 43.6 N, respectively). However, in the third year, the major season yielded the highest mean firmness (43.9 N). The minor season consistently exhibited intermediate firmness values, reflecting a transitional effect between the favourable conditions of the major season and the environmental stressors of the off-season.

The increased firmness observed during the minor season and off-season can be attributed to slower vegetative growth, which allows for extended cell wall thickening and structural reinforcement. Cooler temperatures and reduced growth rates during these seasons promote the accumulation of structural carbohydrates, such as cellulose and hemicellulose, leading to firmer fruit (Patanè and Cosentino, 2010). In contrast, fruit harvested during the major season, characterised by rapid growth and higher temperatures, exhibited slightly reduced firmness due to accelerated ripening and increased enzymatic softening (Litz, 2009).

 

Table 13
Ripe fruit firmness (N) of treated Keitt mango tree with varied PBZ concentrations applied on different soil types during different production seasons for year one

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	39.9cde*	43.6abcde	42.3abcde	41.4abcde	44.7abcde	42.4a
Agawtaw	Minor	39.6cde	41.2abcde	41.8abcde	40.9bcde	47.9a	42.3a
	Off-season	40.2cde	41.6abcde	45.2abcde	44.0abcde	45.2abcde	43.2a
Means		39.9bc	42.1bc	43.1ab	42.1bc	45.9a	42.6a
	Major	41.7abcde	43.9abcde	42.0abcde	42.1abcde	46.0abcd	43.1a
Akuse	Minor	40.2cde	41.4abcde	41.3abcde	43.2abcde	46.2abcd	42.5a
	Off-season	39.4de	40.8bcde	43.4abcde	43.4abcde	46.4abc	42.7a
Means		40.4bc	42.1bc	42.3bc	42.9ab	46.2a	42.8a
	Major	39.8cde	40.6cde	40.1cde	41.1abcde	44.1abcde	41.2a
Baraku	Minor	38.9e	42.8abcde	43.6abcde	43.6abcde	47.1ab	43.2a
	Off-season	39.5de	42.6abcde	42.6abcde	42.0abcde	46.2abcd	42.6a
Means		39.4c	42.0bc	42.1bc	42.3bc	45.8a	42.3a
concentration Grand means 39.9c			42.1b	42.5b	42.4b	46.0a
Seasons Mean	Major	40.5def	42.7bcdef	41.5cdef	41.5cdef	44.9abc	42.2a
	Minor	39.7f	41.8cdef	42.3cdef	42.6bcdef	47.1a	42.7a
	Off-season	39.7ef	41.7cdef	43.7abcd	43.1bcde	45.9ab	42.8a
CV= 4.32; HSD (0.01); PBZ concentrations =1.6836; soil types=1.1623; seasons= 1.1623; PBZ concentrations * seasons= 3.4891; PBZ concentrations * soil types=3.4891; seasons *soil types= 2.5044; PBZ concentrations *seasons *soil types= 6.8663.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 14
Ripe fruit firmness (N) of treated Keitt mango tree with varied PBZ concentrations applied on different soil types during different production seasons for year two

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	41.9ab*	42.3ab	46.0ab	42.4ab	44.3ab	43.4a
Agawtaw	Minor	39.2b	41.3ab	42.3ab	42.5ab	46.4ab	42.3a
	Off-season	40.2ab	45.6ab	41.4ab	42.6ab	47.5a	43.5a
Means		40.4c	43.0abc	43.2abc	42.5bc	46.1ab	43.1a
	Major	21.4ab	41.7ab	42.7ab	42.3ab	46.3ab	42.8a
Akuse	Minor	41.0ab	43.8ab	42.9ab	41.8ab	46.4ab	43.2a
	Off-season	40.4ab	43.4ab	45.6ab	44.7ab	47.1ab	44.2a
Means		40.9c	43.0abc	43.8abc	42.9abc	46.6a	43.4a
	Major	39.5b	43.2ab	41.4ab	142.3ab	43.8ab	42.0a
Baraku	Minor	40.2ab	43.7ab	42.6ab	44.4ab	47.9a	43.8a
	Off-season	40.8ab	42.0ab	42.5ab	43.8ab	46.2ab	43.1a
Means		40.2c	43.0abc	42.2bc	43.5abc	46.0ab	43.0a
concentration Grand means   40.5c			43.0b	43.1b	43.0b	46.2a
	Major	40.9bc	42.4bc	43.4abc	42.3bc	44.8ab	42.6a
Seasons Mean	Minor	40.1c	42.9abc	42.6bc	42.9abc	46.9a	43.1a
	Off-season	40.5c	43.7abc	43.2abc	43.7abc	46.9a	43.6a
CV= 4.95; HSD (0.01); PBZ concentrations =1.9561; soil types=1.3505; seasons= 1.3505; PBZ concentrations * seasons= 4.0539; PBZ concentrations * soil types=4.0539; seasons *soil types= 2.9098; PBZ concentrations *seasons *soil types= 7.9778.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 15
Ripe fruit firmness (N) of treated Keitt mango tree with varied PBZ concentrations applied on different soil types during different production seasons for year three

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	43.5ab*	43.7ab	43.8ab	44.1ab	46.1ab	44.2a
Agawtaw	Minor	40.8ab	43.6ab	41.7ab	44.5ab	46.1ab	43.3a
	Off-season	39.9b	41.9ab	43.4ab	41.5ab	47.1ab	42.8a
Means		41.4de	143.1bcde	43.0bcde	43.4abcde	46.4ab	43.4a
	Major	42.0ab	43.3ab	43.7ab	44.3ab	45.8ab	43.8a
Akuse	Minor	40.5ab	41.8ab	42.3ab	42.0ab	45.0ab	42.3a
	Off-season	42.0ab	41.8ab	41.0ab	42.7ab	44.7ab	42.4a
Means		41.5de	42.3cde	42.3cde	43.0bcde	45.2abcd	42.9a
	Major	39.9b	43.3ab	46.4ab	42.2ab	46.9ab	43.7a
Baraku	Minor	40.4ab	43.5ab	46.0ab	43.1ab	47.8a	44.2a
	Off-season	39.7b	43.2ab	46.2ab	43.1ab	46.9ab	43.8a
Means		40.0e	43.3bcde	46.2abc	42.8bcde	47.2a	43.9a
concentration Grand means          41.0c			42.9b	43.8b	43.1b	46.3a
	Major	41.8cd	43.4abcd	44.6abc	43.5abcd	46.3ab	43.9a
Seasons Mean	Minor	40.6d	43.9abcd	43.3abcd	43.2abcd	46.3a	43.3a
	Off-season	40.5d	42.3cd	43.5abcd	42.4bcd	46.2ab	43.0a
CV= 4.70; HSD (0.01); PBZ concentrations =1.8671; soil types=1.2890; seasons= 1.2890; PBZ concentrations * seasons= 3.8694; PBZ concentrations * soil types=3.8694; seasons *soil types= 2.7774; PBZ concentrations *seasons *soil types= 7.6147.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

The observed seasonal variations in firmness also suggest an interaction between PBZ application and climatic conditions. Studies indicate that PBZ is more effective in enhancing fruit firmness under moderate climatic conditions, in which slower fruit growth rates allow for the prolonged accumulation of cell wall-strengthening compounds (Kishore et al., 2015). In contrast, high temperatures and rapid fruit expansion during the major season may dilute the effects of PBZ by accelerating metabolic processes that contribute to softening (Yadav et al., 2013).

Chemical parameters of treated Keitt mango trees

Moisture content (%) of treated Keitt mango fruit

PBZ application consistently reduced the MC across all 3 years, with non-treated trees producing the highest MC values (80.9–81.5%) and trees treated with 25 mL exhibiting the lowest MC (76.7–77.6%). The suppressive effect of PBZ on MC was most pronounced in fruit grown on Baraku soil during the minor season, in which the lowest MC values were recorded (74.6% in the first year and 73.1% in the third year) (Tables 16–18). The observed reduction in MC aligns with PBZ’s physiological effects on plant water relations. By inhibiting gibberellin biosynthesis, PBZ limits vegetative growth and reduces transpiration, decreasing water uptake and movement to fruit tissues (Kumar, 2023). PBZ has also been reported to suppress xylem differentiation, further restricting water transport to reproductive structures (Reddy and Kurian, 2008). Similar trends have been observed in other fruit crops, in which PBZ-induced reductions in hydraulic conductivity lead to lower fruit hydration levels (Srivastava and Dwivedi, 2000). Despite PBZ’s overall suppressive effect on MC, moderate application rates (10–15 mL) maintained relatively higher hydration levels while still controlling vegetative growth. Lobo and Sidhu (2017) reported that moderate PBZ concentrations balanced water conservation and fruit firmness, thereby improving postharvest quality. These findings suggest that optimising PBZ concentrations is essential for sustaining fruit moisture and achieving growth regulation benefits. Soil fertility and water retention significantly influenced MC across all PBZ treatments and seasons. Akuse and Agawtaw soils consistently supported the highest mean MC values (79.3–79.7%), while Baraku soil yielded the lowest values (77.0–77.8%). The higher MC levels observed in fruit grown on Akuse and Agawtaw soils could be attributed to their superior organic matter content and water-holding capacity, which facilitate sustained water availability for fruit development (Brady and Weil, 2017). These results align with those of White and Broadley (2003), who emphasised that well-structured soils enhance root hydraulic conductivity, improving water absorption and translocation within plants. In contrast, Baraku soil, characterised by a lower water retention and reduced CEC, amplified PBZ’s restrictive effects on fruit hydration. Lal and Stewart (2015) and Sebastian et al. (2019) showed that nutrient-poor soils exacerbated water stress conditions, limiting fruit moisture retention. The lowest MC values (73.1%) were recorded in fruit grown on Baraku soil under 25 mL PBZ, underscoring the compounded effects of soil infertility and growth regulator-induced water limitations on fruit hydration. Seasonal variations significantly influenced MC, with the major season generally producing the highest values, while the off-season consistently yielded the lowest values. In the first and second years, the major season recorded the highest MC (79.3 and 78.7%, respectively), while in the third year, the minor season marginally surpassed the major season (79.2 and 79.0%). The off-season consistently recorded the lowest MC (78.2–78.4%). The higher MC values observed in the major and minor seasons were attributed to favourable climatic conditions, including optimal rainfall and humidity, which enhance water absorption and retention in fruit pulp (Litz, 2009). Increased soil moisture during these periods facilitated sustained xylem flow, leading to higher fruit hydration levels. Conversely, off-season fruit exhibited lower MC values due to cooler temperatures, lower light intensity, and reduced soil moisture availability, all of which limit water uptake and translocation (Patanè and Cosentino, 2010). The persistent impact of PBZ on fruit MC was particularly evident in Baraku soil, in which fruit treated with 25 mL exhibited consistently lower hydration levels across all seasons. These results align with those of Srivastava and Dwivedi (2000), who reported that high PBZ concentrations induced prolonged water stress by modifying the xylem vessel structure and reducing the transpiration efficiency. However, the gradual convergence of MC values over time suggests that these residual effects may diminish with improved soil fertility management.

 

Table 16
Moisture content (%) of ripened fruit pulp of Keitt mango trees treated with varied PBZ concentrations on different soil types during different production seasons for year one

Soil Type	Seasons	Concentrations						Means
		0	10		12.5	20	25
	Major	82.7a*	79.9abcdefgh		78.5cdefghi	79.2abcdefghi	78.1cdefghij	79.7ab
Agawtaw	Minor	82.7ab	80.3abcdefg		78.6cdefghi	78.9bcdefghi	77.5efghij	79.6ab
	Off-season	81.8abc	79.5abcdefghi		77.5efghij	76.6ghij	78.4cdefghij	78.8bcd
Means		82.4a	79.9bc		78.2bcd	78.2bcd	78.0cdef	79.3a
	Major	82.5ab	81.2abcde		79.2abcdefghi	79.6abcdefgh	79.3abcdefghi	80.4a
Akuse	Minor	82.6ab	80.0abcdefgh		78.6cdefghi	77.7efghij	78.6cdefghi	79.5ab
	Off-season	81.6abcd	78.9abcdefghi		76.9fghij	81.3abcde	77.9defghij	79.3abc
Means		82.2a	80.0b		78.3bcd	79.5bcd	78.6bcd	79.7a
	Major	80.2abcdefg	78.2cdefghij		78.5cdefghi	75.7ij	77.1fghij	77.9cde
Baraku	Minor	80.6abcdef	78.5cdefghi		77.3fghij	76.5ghij	74.6j	77.5de
	Off-season	78.5cdefghi	77.5efghij		77.2fghij	76.1hij	76.9fghij	77.3e
Means		79.8bc	78.1cde		77.7def	76.1f	76.2ef	77.6b
Concentrations Grand means 81.5a				79.3b	78.0c	77.9c	77.6c
Seasons Mean	Major	81.8a	79.7bc		78.7bcde	78.1cde	78.1cde	79.3a
	Minor	82.0a	79.6bcd		78.2cde	77.7de	76.9e	78.9ab
	Off-season	80.6ab	78.6cde		77.2e	78.0cde	77.7de	78.4b
CV=1.30HSD (0.01); PBZ concentrations =0.9370; seasons=0.6469; soil types=0.6469; PBZ concentration*seasons=1.9419; season*soil= 1.3939; PBZ concentration*soil types=1.9419; PBZ concentrations*seasons*soil types=3.8216.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 17
Moisture content (%) of ripened fruit pulp of Keitt mango trees treated with varied PBZ concentrations on different soil types during different production seasons for year two

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	81.1abcd*	79.2bcdefghijk	77.2ghijklmnop	79.0bcdefghijkl	78.6cdefghijklm	79.0ab
Agawtaw	Minor	81.4abc	78.1defghijklmno	77.4fghijklmnop	77.6fghijklmno	76.4klmnop	78.2bc
	Off-season	81.0abcde	78.2defghijklmn	76.9ijklmnop	78.1defghijklmno	76.6jklmnop	78.2bc
Means		81.2ab	78.5de	77.2efg	78.2de	77.2efg	78.5b
	Major	82.6a	80.3abcdef	79.2bcdefghijk	78.1efghijklmno	77.3ghijklmnop	79.5a
Akuse	Minor	81.9ab	80.1abcdefgh	78.6cdefghijklm	76.3klmnop	77.0hijklmnop	78.8ab
	Off-season	81.7ab	80.2abcdefg	77.7fghijklmno	79.7abcdefghi	79.6abcdefghij	79.8a
Means		82.1a	80.2bc	78.5de	78.0de	78.0def	79.4a
	Major	79.8abcdefghi	78.8bcdefghijklm	77.2ghijklmnop	76.8ijklmnop	75.2op	77.6cd
Baraku	Minor	79.2bcdefghijk	77.5fghijklmno	76.2klmnop	76.1lmnop	74.4p	76.7d
	Off-season	79.1bcdefghijkl	76.7jklmnop	75.8mnop	76.2klmnop	75.4nop	76.6d
Means		79.4cd	77.7efg	76.4gh	76.4gh	75.0h	77.0c
Concentrations Grand means 80.9a			78.8b	77.4cd	77.5c	76.7d
Seasons Mean	Major	81.2a	79.5bc	77.9def	78.0cdef	77.0defg	78.7a
	Minor	80.8ab	78.6cd	77.4defg	76.6fg	75.9g	77.9b
	Off-season	80.6ab	78.3cde	76.8efg	78.0cdef	77.2defg	78.2ab
CV=1.05; HSD (0.01); PBZ concentrations =0.2231; seasons=0.5179; soil types=0.5179; PBZ concentration*seasons=1.5547; season*soil= 1.1159; PBZ concentration*soil types=1.5547; PBZ concentrations*seasons*soil types=3.0596.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 18
Moisture content (%) of ripened fruit pulp of Keitt mango trees treated with varied PBZ concentrations on different soil types during different production seasons for year three

Soil Type

Seasons

Concentrations

Means

0

10

12.5

20

25

Major

82.9a *

78.7abcdefg

78.1abcdefgh

78.5abcdefg

77.5cdefgh

79.1abc

Agawtaw

Minor

82.7ab

80.3abcdefg

78.8abcdefg

79.9abcdefg

78.8abcdefg

80.1a

Off-season

81.9abcd

79.6abcdefg

77.5bcdefgh

75.9gh

78.5abcdefg

78.7abc

Means

82.5a

79.5bc

78.2cde

78.1cde

78.3cd

79.3a

Major

82.5abc

81.3abcdef

78.8abcdefg

78.6abcdefg

78.5abcdefg

79.9a

Akuse

Minor

82.3abc

79.9abcdefg

78.3abcdefg

78.4abcdefg

78.7abcdefg

79.5ab

Off-season

81.6abcde

78.2abcdefgh

78.9abcdefg

79.6abcdefg

77.9abcdefgh

79.3abc

Means

82.1ab

79.8bc

78.7cd

78.9c

78.4cd

79.6a

Major

80.2abcdefg

78.6abcdefg

78.8abcdefg

75.7gh r

76.9defgh

78.0bc

Baraku

Minor

80.5abcdefg

81.8abcde

77.4cdefgh

76.7efgh

73.1h

77.9bc

Off-season

78.7abcdefg

77.8abcdefgh

77.4cdefgh

76.3fgh

76.8defgh

77.4c

Means

79.8bc

79.4c

77.9cde

76.2de

75.6e

77.8b

Concentrations Grand means     81.5a

79.6b

78.2c

77.7c

77.4c

Seasons Mean

Major

81.8a

79.5abc

78.6bcd

77.6cd

77.6cd

79.0a

Minor

81.8a

80.7ab

78.2bcd

78.3bcd

76.9d

79.2a

Off-season

80.8ab

78.6bcd

77.9cd

77.2cd

77.8cd

78.4a

CV=1.75; HSD (0.01); PBZ concentrations =1.2632; seasons=0.8721; soil types=0.8721; PBZ concentrations* seasons = 2.6178; seasons*soil types=1.8790; PBZ concentrations*soil types= 2.6178; PBZ concentration*season*soil type=5.1516.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other. 
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Total ash content (%) of treated Keitt mango fruit

PBZ significantly influenced the total ash content in Keitt mango pulp over 3 years (Tables 19–21), with higher PBZ concentrations (20–25 mL) consistently enhancing mineral accumulation. The highest ash content was observed in fruit treated with 25 mL PBZ, recording 8.40% in the first year and 8.44% in the second year, while non-treated fruit exhibited the lowest values, decreasing from 7.02 to 6.62%. By the third year, the effect of PBZ stabilised, with the highest mean ash content (6.57%) recorded under 10 mL PBZ treatment and the lowest (6.42%) under 12.5 mL PBZ, suggesting a diminishing residual effect over time.

The observed increase in ash content with PBZ application aligns with its role in modifying the hormone balance, which enhances root activity and nutrient uptake efficiency (Rademacher, 2016; Scholtz, 2020). By inhibiting gibberellin biosynthesis, PBZ limits vegetative growth, directing more nutrients to fruit tissues, particularly in the first two years, during which time mineral translocation is most pronounced. However, by the third year, metabolic adjustments likely normalised nutrient partitioning, reducing the impact of PBZ on mineral accumulation (Patel et al., 2020). Additionally, the genetic buffering capacity of the Keitt mango cultivar may have contributed to maintaining nutrient homeostasis despite continued PBZ application (Yahia et al., 2011). Soil type played a crucial role in determining the ash content, with Akuse and Agawtaw soils consistently yielding fruit with a higher mineral composition. Akuse soil recorded the highest mean ash content across the study period, ranging from 6.77% in the third year to 8.73% in the first year, followed closely by Agawtaw soil (6.59–8.49%). Conversely, Baraku soil consistently produced the lowest ash content (5.11–6.35%), likely due to its lower organic matter content and reduced CEC, which restricts nutrient absorption (Brady and Weil, 2017). These findings reinforce previous research on soil fertility’s impact on fruit mineral composition, emphasising that well-fertilised soils improve nutrient uptake of the roots and mineral deposition, while less fertile soils limit nutrient availability, reducing the total ash content (Lal and Stewart, 2015; Sebastian et al., 2019). Seasonal variations also influenced the ash content, with the off-season and minor season producing fruit with higher mineral accumulation. In the first year, the off-season recorded the highest mean ash content (8.43%), followed by the minor season (8.29%), while the major season had slightly lower values (7.76%). Similar trends were observed in the second year, with the minor season yielding the highest ash content (8.38%). By the third year, seasonal differences narrowed, with the off-season producing the highest ash content (6.66%), followed by the minor (6.54%) and major seasons (6.51%). The higher ash content during the off-season and minor seasons may be attributed to reduced metabolic competition for nutrients due to slower vegetative growth, allowing greater mineral allocation to fruit tissues. In contrast, the major season, characterised by rapid growth, higher temperatures, and increased transpiration, may have prioritised vegetative development over reproductive allocation, thereby limiting nutrient retention in fruit pulp (Litz, 2009).

PBZ-induced increases in ash content can be directly linked to its effects on nutrient absorption and accumulation. Ash content represents the total mineral matter present in fruit, including essential macro- and micronutrients, such as K, Ca, Mg, P, Fe, Zn, and Mn (Yadav et al., 2018). PBZ application enhances root biomass and modifies root architecture, improving the root-to-shoot ratio, which increases the nutrient uptake efficiency (Basak, 2021). As a result, minerals crucial for fruit firmness, structural integrity, and enzymatic functions become more concentrated. PBZ-treated trees exhibit higher Ca and Mg levels due to enhanced root uptake and reduced shoot growth, minimising competition for mineral resources (Babu et al., 2022). Additionally, PBZ facilitates K translocation into fruit, improving sugar transport and enzyme activity, indirectly enhancing the ash content (Shinde et al., 2020). PBZ reduces the transpiration rate, limiting overall water loss and having a concentration effect in fruit tissues. With reduced fruit expansion and water content, minerals and organic matter become more concentrated, contributing to the observed increase in ash content (Monti et al., 2008).

PBZ application also triggers several metabolic changes that further support increased mineral deposition in fruit. Elevated antioxidant enzyme activity, including that of peroxidase, catalase, and superoxide dismutase, in PBZ-treated mangoes enhances secondary metabolism, influencing membrane permeability and ion transport, which promotes mineral accumulation (Verma et al., 2021). Moreover, PBZ enhances carbohydrate accumulation in mango pulp by improving source–sink dynamics, which is closely linked to increased mineral retention, as K and Mg play crucial roles in sugar transport and enzymatic regulation (Singh et al., 2023).

 

Table 19
Total ash (%) of ripened fruit pulp of Keitt mango trees treated with varied PBZ concentrations on different soil types during different production seasons for year one

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	6.32de*	7.60abcde	8.05abcd	7.92abcd	8.46abc	7.67ab
Agawtaw	Minor	7.16abcde	7.65abcde	8.01abcd	8.14abcd	8.35abcd	7.86ab
	Off-season	7.74abcde	7.87abcde	8.14abcd	8.32abcd	8.50abc	8.12ab
Means		7.07cd	7.71abc	8.07abc	8.13ab	8.44ab	7.88ab
	Major	7.69abcde	7.78abcde	7.92abcd	8.55abc	9.09a	8.21a
Akuse	Minor	7.69abcde	7.78abcde	7.92abcd	7.96abcd	8.46abc	7.96ab
	Off-season	7.51abcde	7.69abcde	7.74abcde	8.23abcd	8.64ab	7.96ab
Means		7.63bc	7.75abc	7.86abc	8.25ab	8.73a	8.04a
	Major	6.55cde	7.54abcde	7.52abcde	7.38abcde	7.96abcd	7.39b
Baraku	Minor	6.68bcde	7.98abcd	7.93abcd	8.11abcd	8.05abcd	7.75ab
	Off-season	5.82e	7.65abcde	7.83abcde	7.96abcd	8.14abcd	7.48ab
Means		6.35d	7.72abc	7.76abc	7.82abc	8.05abc	7.54b
Concentrations Grand means        7.02c			7.73b	7.89b	8.06ab	8.40a
Seasons Mean	Major	6.86d	7.64abcd	7.83abcd	7.95abc	8.50a	7.76a
	Minor	7.18bcd	7.80abcd	7.95abc	8.07ab	8.29a	7.86a
	Off-season	7.02cd	7.74abcd	7.90abc	8.17ab	8.43a	7.85a
CV 7.06; HSD (0.01); PBZ concentrations =0.5056; seasons=0.3491; soil types=0.3491; PBZ concentration*seasons=1.0479; season*soil= 0.7521; PBZ concentration*soil types=1.0479; PBZ concentrations*seasons*soil types=2.0621.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 20
Total ash (%) of ripened fruit pulp of Keitt mango trees treated with varied PBZ concentrations on different soil types during different production seasons for year two

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	6.74cd*	7.92abc	7.96abc	8.29abc	8.24abc	7.83ab
Agawtaw	Minor	7.19abcd	7.78abcd	7.69abcd	8.52ab	8.73a	7.98ab
	Off-season	6.93bcd	7.48abcd	7.91abc	8.01abc	8.51ab	7.77abc
Means		6.96d	7.72bcd	7.85abc	8.27abc	8.49ab	7.86b
	Major	7.91abc	7.83abcd	8.05abc	8.42ab	8.86a	8.23a
Akuse	Minor	7.87abcd	8.05abc	8.24abc	8.38abc	8.47ab	8.20a
	Off-season	7.61abcd	8.01abc	8.10abc	8.19abc	8.69a	8.12a
Means		7.80bcd	7.96abc	8.13abc	8.33abc	8.67a	8.18a
	Major	6.21de	7.49abcd	7.72abcd	7.68abcd	8.26abc	7.47bcd
Baraku	Minor	4.70ef	7.69abcd	7.78abcd	7.46abcd	7.94abc	7.11d
	Off-season	4.43f	7.51abcd	7.69abcd	8.10abc	8.28abc	7.20cd
Means		5.11e	7.56cd	7.73bcd	7.74bcd	8.16abc	7.26c
Concentrations Grand means   6.62c			7.75b	7.90b	8.12ab	8.44a
Seasons Mean	Major	6.95bc	7.75ab	7.91a	8.13a	8.45a	7.84a
	Minor	6.59c	7.84a	7.90a	8.12a	8.38a	7.76a
	Off-season	6.32c	7.67ab	7.90a	8.10a	8.50a	7.70a
CV 5.79; HSD (0.01); PBZ concentrations =0.4117; seasons=0.2842; soil types=0.2842; PBZ concentration*seasons=10.8532; season*soil= 0.6124; PBZ concentration*soil types=0.8532; PBZ concentrations*seasons*soil types=1.6791.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 21
Total ash (%) of ripened fruit pulp of Keitt mango trees treated with varied PBZ concentrations on different soil types during different production seasons for year three

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
Agawtaw	Major	6.56a*	6.56a	6.41a	6.57a	6.74a	6.57ab
	Minor	6.50a	6.58a	6.47a	6.55a	6.50a	6.52ab
	Off-season	6.85a	6.55a	6.69a	6.75a	6.50a	6.67ab
Means		6.64ab	6.56abc	6.52abc	6.62ab	6.58abc	6.59a
Akuse	Major	6.44a	6.78a	7.12a	6.83a	6.58a	6.75ab
	Minor	6.78a	6.77a	6.73a	6.94a	6.80a	6.80a
	Off-season	6.87a	6.81a	6.88a	6.84a	6.45a	6.77a
Means		6.70ab	6.79ab	6.91a	6.87ab	6.61abc	6.77a
Baraku	Major	6.30a	6.45a	5.86a	6.13a	6.33a	6.21bc
	Minor	6.02a	6.73a	5.92a	6.34a	6.52a	6.31abc
	Off-season	6.26a	5.88a	5.72a	5.86a	5.77a	5.90c
Means		6.19abc	6.35abc	5.83c	6.11bc	6.20abc	6.14b
Concentrations Grand means    6.51a			6.57a	6.42a	6.53a	6.46a
Seasons Mean	Major	6.43a	6.59a	6.46a	6.51a	6.55a	6.51a
	Minor	6.43a	6.69a	6.38a	6.61a	6.61a	6.54a
	Off-season	6.66a	6.41a	6.43a	6.48a	6.24a	6.45a
CV 6.31; HSD (0.01); PBZ concentrations =0.3755; seasons=0.2592; soil types=0.2592; PBZ concentration*seasons=0.7781; season*Soil= 0.5585; PBZ concentration*soil types=0.7781; PBZ concentrations*seasons*soil types=1.5312.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Additionally, PBZ-treated fruit often exhibits higher phenolic compounds and organic acid content, particularly citric and malic acids, which act as chelators, improving mineral solubility and facilitating nutrient accumulation in fruit tissues (Sarker and Rahim, 2019).

The increased ash content in PBZ-treated mangoes has important implications for fruit quality. Higher mineral availability improves fruit firmness, extending postharvest life and making fruit more resistant to mechanical damage (Sarkar et al., 2021).

Additionally, elevated mineral concentrations, particularly K and Mg, enhance sugar metabolism and acid balance, improving flavour and sweetness perception in Keitt mangoes (Verghese et al., 2023).

Total soluble solids content (°Brix) of treated Keitt mango fruit

PBZ application significantly influenced TSS content across all 3 years, with higher concentrations (20–25 mL) consistently enhancing fruit sweetness. The 25 mL PBZ treatment yielded the highest TSS values, peaking at 19.78°Brix in the first year and 20.30°Brix in the second year. In contrast, non-treated trees consistently produced fruit with the lowest TSS content, ranging from 17.48 to 17.65°Brix. These results suggest that PBZ enhances sugar accumulation by altering source–sink dynamics and redirecting photosynthates from vegetative tissues to fruit development (Sebastian et al., 2019).

The physiological basis of this response lies in PBZ’s inhibition of gibberellin biosynthesis, which reduces shoot elongation and increases assimilate availability for reproductive growth (Reddy and Kurian, 2008). Additionally, PBZ has been shown to increase starch accumulation in developing mango fruit, which are later hydrolysed into soluble sugars during ripening, thereby elevating the TSS content (Patel et al., 2020). The effect of PBZ on TSS was particularly pronounced in the first two years, while in the third year, interactions among PBZ, soil type, and season became statistically non-significant.

This reduction in variability indicates a diminishing residual impact of PBZ on sugar metabolism, as observed by Patel et al. (2020). The stabilisation of the TSS content suggests that sustained PBZ application may have a cumulative effect in the early years, gradually normalising as metabolic adjustments occur within the plant system.

Soil fertility emerged as a key factor influencing the TSS content. Akuse and Agawtaw soils consistently supported the highest mean TSS content in the first and second years, with values exceeding 19.30°Brix. By the third year, the TSS content in these soils remained comparable (18.34 and 18.24°Brix), indicating their capacity to sustain high sugar biosynthesis under varying PBZ treatments. In contrast, Baraku soil consistently produced the lowest TSS values, ranging from 17.37 to 18.01°Brix across the study period.

The superior performance of Akuse and Agawtaw soils can be attributed to their higher organic matter content, improved CEC, and efficient nutrient cycling, which collectively enhances carbohydrate metabolism and photosynthate allocation to fruit tissues (Brady and Weil, 2017). In contrast, Baraku soil’s lower fertility and poor water retention likely constrained sugar accumulation, reducing TSS levels (Lal and Stewart, 2015).

These findings align with those of Falchi et al. (2020), who reported that soil nutrient availability plays a pivotal role in fruit sugar synthesis by modulating key enzymatic pathways involved in starch hydrolysis and sucrose metabolism.

Therefore, optimising soil fertility through targeted amendments can complement PBZ treatments and enhance fruit sweetness. Seasonal variations had a moderate but consistent influence on TSS accumulation. In the first and second years, the minor and major seasons generally recorded higher TSS contents compared to the off-season. In the first year, the minor season produced the highest mean TSS content (18.68°Brix), while in the second year, the major season exhibited the highest TSS content (18.74°Brix). By the third year, seasonal differences diminished, with the TSS content stabilising across all treatments.

The observed seasonal patterns align with the established physiological mechanisms governing sugar biosynthesis.

Optimal temperatures and adequate rainfall during the major and minor seasons enhance photosynthetic efficiency, promoting carbohydrate synthesis and translocation to fruit (Prasad et al., 2015).

In contrast, the off-season, characterised by cooler temperatures and reduced light intensity, exhibited slightly lower TSS levels due to slower enzymatic activity and reduced starch-to-sugar conversion (Litz, 2009).

 

Table 22
Total soluble solids (°Brix) of ripened fruit pulp of Keitt mango trees treated with varied PBZ concentrations on different soil types during different production seasons for year one

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	17.57abcde*	17.83abcde	17.90abcde	19.93abcde	19.70abcde	18.59abc
Agawtaw	Minor	17.23bcde	17.60abcde	18.57abcde	20.93a	20.53abcd	18.97ab
	Off-season	17.40abcde	19.50abcde	19.07abcde	20.70abc	20.13abcd	19.36ab
Means		17.40de	18.31bcde	18.51bcde	20.52a	20.12ab	18.97a
	Major	18.10bcde	19.23abcde	19.27abcde	19.93abcde	20.77ab	19.46ab
Akuse	Minor	18.50abcde	19.27abcde	19.33abcde	20.10abcde	20.80ab	19.60a
	Off-season	18.03abcde	18.77abcde	18.57abcde	19.07abcde	19.73abcde	18.83ab
Means		18.21cde	19.09abcd	19.06abcd	19.70abc	20.43a	19.30a
	Major	17.07cde	18.13abcde	18.87abcde	18.77abcde	19.20abcde	18.41abc
Baraku	Minor	16.43e	17.00de	17.40abcde	17.87abcde	18.57abcde	17.45c
	Off-season	16.97de	17.9abcde	18.87abcde	18.87abcde	18.53abcde	18.18bc
Means		16.82e	17.69de	18.38bcde	18.39bcde	18.79abcd	18.01b
Concentrations Grand means 17.48d			18.36cd	18.65bc	19.54ab	19.78a
Seasons Mean	Major	17.58cd	18.40abcd	18.68abcd	19.54ab	19.89a	18.82a
	Minor	17.39d	17.96bcd	18.43abcd	19.63ab	19.97a	18.68a
	Off-season	17.47d	18.73abcd	18.83abcd	19.43abc	19.49ab	18.79a
CV 5.27; HSD (0.01); PBZ concentrations =0.9046; seasons=0.6245; soil types=0.6245; PBZ concentration*seasons=1.8746; season*soil= 1.3456; PBZ concentration*soil types=1.8746; PBZ concentrations*seasons*soil types=3.6891.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 23
Total soluble solids (°Brix) of ripened fruit pulp of Keitt mango trees treated with varied PBZ concentrations on different soil types during different production seasons for year two

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	16.97ab*	18.13ab	18.07ab	19.13ab	19.47ab	18.35ab
Agawtaw	Minor	17.47ab	17.40ab	18.17ab	19.43ab	19.97ab	18.49ab
	Off-season	16.73ab	17.53ab	18.67ab	19.37ab	19.67ab	18.39ab
Means		17.06de	17.69cde	18.30abcde	19.31abc	19.70ab	18.41b
	Major	19.33ab	19.60ab	19.40ab	19.93ab	19.73ab	19.60a
Akuse	Minor	18.60ab	18.77ab	19.20ab	19.53ab	20.10a	19.24a
	Off-season	18.63ab	18.90ab	19.13ab	19.93ab	20.30a	19.38a
Means		18.86abcd	19.09abc	19.24abc	19.80ab	20.04a	19.41a
	Major	16.83ab	18.93ab	18.23ab	18.97ab	18.40ab	18.27ab
Baraku	Minor	16.70ab	17.10ab	16.73ab	18.63ab	19.00ab	17.63b
	Off-season	16.20b	17.80ab	17.73ab	18.03ab	18.40ab	17.63b
Means		16.58e	17.94bcde	17.57cde	18.54abcde	18.60abcd	17.85b
Concentrations Grand means 17.50c			18.24c	18.37bc	19.22ab	19.45a
Seasons Mean	Major	17.71bc	18.89abc	18.57abc	19.34ab	19.20ab	18.74a
	Minor	17.59bc	17.76abc	18.03abc	19.20ab	19.69a	18.45a
	Off-season	17.19c	18.08abc	18.51abc	19.11abc	19.46ab	18.47a
CV 5.62; HSD (0.01); PBZ concentrations =0.9538; seasons=0.6585; soil types=0.6585; PBZ concentration*seasons=1.9765; season*soil= 1.4187; PBZ concentration*soil types=1.9765; PBZ concentrations*seasons*soil types=3.8897.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

Table 24
Total soluble solids (°Brix) of ripened fruit pulp of Keitt mango trees treated with varied PBZ concentrations on different soil types during different production seasons for year three

Soil Type	Seasons	Concentrations					Means
		0	10	12.5	20	25
	Major	18.03a*	18.50a	16.93a	18.93a	18.93a	18.27a
Agawtaw	Minor	17.60a	18.30a	18.73a	17.93a	18.83a	18.28a
	Off-season	18.13a	18.60a	17.90a	17.47a	18.73a	18.17a
Means		17.92a	18.47a	17.86a	18.11a	18.83a	18.24a
	Major	18.30a	19.00a	17.77a	18.17a	18.97a	18.44a
Akuse	Minor	17.97a	18.00a	18.43a	18.57a	18.53a	18.30a
	Off-season	18.23a	19.23a	17.70a	17.57a	18.73a	18.29a
Means		18.17a	18.74a	17.97a	18.10a	18.74a	18.34a
	Major	17.63a	16.97a	16.63a	17.50a	17.60a	17.27a
Baraku	Minor	16.60a	17.60a	17.20a	18.00a	17.73a	17.43a
	Off-season	17.40a	17.40a	17.53a	17.77a	16.97a	17.41a
Means		17.21a	17.32a	17.12a	17.76a	17.43a	17.37b
Concentrations Grand means     17.77a			18.18a	17.65a	17.99a	18.34a
	Major	17.99a	18.16a	17.11a	18.20a	18.50a	17.99a
Seasons Mean	Minor	17.39a	17.97a	18.12a	18.17a	18.37a	18.00a
	Off-season	17.92a	18.41a	17.71a	17.60a	18.14a	17.95a
CV 6.44; HSD (0.01); PBZ concentrations =1.0606; seasons=0.7322; soil types=0.7322; PBZ concentration*seasons=2.1979; season*soil= 1.5776; PBZ concentration*soil types=2.1979; PBZ concentrations*seasons*soil types=4.3253.

*Mean followed by the same alphabets are not significantly different (p>0.01) from each other.
CV: Coefficient of Variation; HSD: Honet Significant Difference; PBZ: Paclobutrazol

 

The gradual convergence of TSS values by the third year suggests that PBZ’s residual effects on sugar metabolism decrease over successive growing seasons. This aligns with the results of Patel et al. (2020), who observed that PBZ-induced metabolic shifts in mango trees tended to stabilise over time, necessitating periodic adjustments in application rates to maintain optimal fruit quality.

 

CONCLUSIONS

This study demonstrated that PBZ application significantly affected the physical and chemical attributes of Keitt mangoes, with outcomes influenced by the application rate, soil fertility, and seasonal conditions. Higher PBZ concentrations (20–25 mL) reduced the fruit size and density by inhibiting gibberellin biosynthesis, which restricts cell elongation and carbohydrate translocation. This effect was more pronounced in less fertile soils, such as Baraku, in which nutrient limitations amplified PBZ’s growth-suppressing effects.

Conversely, fruit grown in fertile soils, such as Agawtaw, exhibited superior size and density due to better nutrient availability. Major-season mangoes were larger and had higher densities due to favourable rainfall and temperatures, while off-season fruit was smaller and less dense. Despite size reductions, PBZ enhanced fruit firmness by promoting lignification and calcium deposition, particularly in the minor season and off-season, when slower vegetative growth enabled greater structural reinforcement.

Higher PBZ concentrations reduced the MC by limiting transpiration and water uptake, with the effect being most pronounced in Baraku soil due to its poor water retention capacity. Fruit from Akuse and Agawtaw soils exhibited a higher MC and ash content, reflecting better soil fertility and water-holding capacity. Seasonally, major-season fruit retained more moisture due to increased rainfall, while off-season fruit had lower hydration levels. PBZ application increased the TSS content and enhanced fruit sweetness. Higher PBZ concentrations redirected photosynthates from vegetative growth to fruit development, increasing sugar biosynthesis. This effect was particularly pronounced in the minor season, when reduced vegetative competition allowed greater carbohydrate allocation to fruit. Soil fertility further influenced the TSS content, with mangoes from Akuse and Agawtaw soils exhibiting higher values due to superior nutrient cycling.

PBZ significantly suppressed the respiration rate and ethylene production, delaying ripening and extending the shelf life. Higher PBZ concentrations reduced CO₂ evolution and ethylene biosynthesis by inhibiting gibberellin pathways and ethylene-related enzymes and slowing metabolic activity and postharvest deterioration.

Seasonal and soil variations also contributed, with off-season mangoes and those from nutrient-rich soils exhibiting higher respiration and ethylene emissions. In conclusion, when carefully managed considering soil fertility and seasonal factors, PBZ application can effectively enhance Keitt mango quality and postharvest longevity, offering significant benefits for producers and exporters.

 

RECOMMENDATION

It is recommended that PBZ application be carefully managed to balance its growth-regulating effects with potential negative impacts on fruit size, weight, and MC, especially on less fertile soils. Lower concentrations (0–12.5 mL) are recommended for fertile soils to promote larger fruit, while marginal soils may require additional soil fertility management, such as organic matter or fertiliser supplementation.

Additionally, excessive PBZ concentrations (above 20 mL) should be avoided in nutrient-deficient soils. Seasonal variations should guide PBZ application, with moderate concentrations during the major production season to enhance fruit quality, and higher concentrations during the off-season to improve firmness and the shelf life. Improving soil fertility through sustainable practices, such as organic fertilisers and soil conservation measures, will amplify PBZ’s positive effects and improve fruit quality across seasons.

 

Author contributions: Conceptualization, methodology, data curation: AAA; Writing: AA; Review: AA; Supervision: ASA. All authors declare that they have read and approved the publication of the manuscript in its present form.

Funding: This study did not receive any external funding.

Acknowledgements: The authors extend their sincere gratitude to all field staff of the Institute of Agricultural Research and Training for their invaluable support during the field trial.

Conflicts of Interest: The authors affirm that no conflicts of interest are associated with this publication. 

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