Crosstalk effect of brassinosteroids and gibberelic acid affects plant phenology, yield and fruit quality traits in sugar apple (Annona squamosa L.) cv. Balanagar

Introduction

Custard apple (Annona squamosa L.) is an important minor fruit of tropical and subtropical, which belongs to the family Annonaceae. The 100 g pulp contains 70.5 g moisture, 23.5 g carbohydrate, 1.6 g protein, 0.9 g minerals, 1.5 mg iron, 17 mg calcium, 47 mg phosphorus and 37 mg vitamin C (Dashora et al., 2004) [5] . Besides, pulp of custard apple is used to prepare different processed products like nectar, RTS, ice-cream and frozen chips. Custard apple is generally used as table fruit, known for its pleasant distinctive texture of pulp, subacid and aromatic flavour. Unripe fruits are directly baked on fire and eaten. Custard apple bears flower during April to August depending upon the variety, geographical condition and climate (Kumar et al., 1977; Sahoo et al., 2000) [10] . The greenish yellow flowers arise in extra axillary position usually in clusters and rarely solitary. The flowering is observed mostly on new shoots as well as on old shoot. Flowers consist around six petals are in two whorls and hermaphrodite. However, protogynous dichogamy reported in which the female part matures before the male. In custard apple plant, low fruit set is a major constraint. Several well-known factors such as high and low atmospheric humidity during flowering, moisture stress, dichogamy and competition among developing parts have been reported to have low flower and fruit setting Kumar et al., 1977. [10] . Flowering is highly correlated with defoliation and there after emergence of new growth. Fruit set takes place after the onset of monsoon coupled with high relative humidity, however late vegetative growth delays flowering and fruit set. In custard apple, only about two per cent of the flower set and bear fruit. In order to increase fruit set, certain measures like hand pollination, nutrient and water management and use of certain chemicals and plant growth regulators (PGRs) could be used. Plant growth regulators serve as a means for enhancing flowering, fruit set, fruit drop control, yield enhancement and fruit quality in different horticultural crops. They regulate various plant growth and developmental processes by synchronizing flowering, improving fruit set, decreasing pre-harvest fruit drop and thinning of excessive flowers or young fruits (Singh et al., 1976; Bhatia and Yadav, 2003; Singh et al., 2007) [3,21,22] .

In this concern, recently use of brassinosteroids (BRs) and gibberellic acid (GA 3 ) in horticultural crops has been standardized and has gained significant importance. Brassinosteroids (BRs) are a group of naturally occurring plant steroids known for its pleiotropic effects. It is a new group of polyhydroxyl steroids which have been recognized as a class of phytohormones has been conferred as novel hormone and hormone of the 21st century, due to its involvement in large number of physiological processes (Khripach et al., 2000) [9] . The foliar application of Epi-Bl (45 and 60ng/g fruit weight) enhanced the ripening, fruit softening and colour development with increased ethylene and respiration rate in mango crop. The results revealed that foliar application of 3 µM 24-epibrassinolide favours vegetative growth enhances yield and thereby improves quality of strawberry fruit. Watanabe et al. (1997) [26] . reported increased fruit set in Japanese persimmon when applied BRs exogenously. Mostafa and Kotb (2018) [13] . reported maximum fruit set, retention, number of fruits/tree and yield and fruit physicochemical quality in BRs treated trees of custard apple with 1mg/l. Similarly, Gibberellins (GA3) control fruit development in various ways and at different developmental stages. Gibberellins are known to influence both cell division and cell enlargement application of GA3 is also standardized as it helps in increasing the fruit setting number of fruits per tree, fruit weight and ultimately increase the fruit yield (Shinde et al., 2008) [20] . Santos et al., (2016) [19] . reported that of GA3 (1500 ppm) improved fruit physicochemical quality of sugar apple and also produced seedless fruits. Likewise, Pereira et al. (2014) [17] . found that GA3 application on "Gefner" custard apple (Annona cherimola x Annona squamosa) produced fruit with good pulp proportion, high TSS and imparted seedlessness. Ingle et al., (2001) [18] . revealed that foliar application of GA3 @ 25 ppm increased the fruit weight, volume, TSS, ascorbic acid. Eid et al. (2016) [4] . revealed the effect of foliar sprays application of Milagrow on yield and fruit quality of Avocado tree cv." Fuerte". The foliar application of milagro (0.2% Brassinolide) increased fruit weight of avocado tree cv. Fuerte. Therefore, the present investigation was undertaken for comparative study with the following objectives: - To study the individual effects of Brassinosteroids and gibberellic acid on growth and yield of custard apple.  To find out the combined effect of Brassinosteroids and gibberellic acid on growth and yield of custard apple.

Materials and Methods

The present experiment was carried out during 2021-22 on 10 year old trees of custard apple cv. balanagar at the Fruit Instructional Farm, Department of Fruit Science, College of Horticulture and Forestry, Jhalarapatan city, Jhalawar (Agriculture University, Kota). The experiment was laid out in a Randomized Block Design with Nine treatment combinations viz., T 0: Control (Water spray), T 1: BRs (0.5ppm) T 2: BRs (1.0ppm) T 3: GA3 (25ppm) T 4: GA3 (50ppm) T 5: BRs + GA3 (0.5ppm + 25 ppm) T6: BRs + GA3 (0.5ppm + 50ppm) T 7: BRs+ GA3 (1.0ppm + 25ppm) T 8: BRs + GA3 (1.0ppm + 50 ppm) keeping three replications The treatments were applied first spray at the time of initiation of flowering and second at the time of fruiting (fruit set).

The height of plant was measured from the base of soil to the highest tip of the plant with the help of measuring scale.

The spread of the plants was recorded in East-West and North-South directions separately with the help of a measuring tape and the average for each direction was calculated.

The initial girth of rootstock was measured separately by using digital Vernier Calipers before treatment application in the first week of August. Thereafter, the final observation on rootstock girth was measured at the end of experiment.

The per cent increase in girth of rootstock was computed based on the cumulative increase in initial value. (Mostafa and Hatem 2018) [13] .

For measuring scion girth, the custard apple plants under different treatments were marked at a fix point with white paint. Initial observations on scion girth were taken during first week of August and final observations were recorded at the end of experiment. The per cent increase in scion girth was calculated on the basis of cumulative increase in initial value. (Mostafa and Hatem 2018) [13] .

Number of shoots per branch

The number of shoots per branch was counted manually at before foliar application of treatments and thereafter at the end of experiment. The per cent increase in number of shoots per branch was calculated on the basis of cumulative increase on the basis of initial values recorded during August.

Number of leaves per shoot

The number of leaves per shoot under different treatments of Custard apple was counted manually before foliar application of treatments and thereafter at the end of experiment. The per cent increase in number of leaves was estimated on the basis of cumulative increase in initial values of August.

For measuring leaf length, selected tagged leaves under various treatments of Custard apple were measured initially during August before foliar application of treatments and final values were recorded towards the end of experiment. The per cent increase in leaf length was calculated on the basis of cumulative increase in initial values. (Pujari et al. 2021) [16] .

Leaf width (cm): For measuring leaf width, selected tagged leaves under various treatments of Custard apple were measured initially during August before foliar application of treatments and final values were recorded towards the end of experiment. The per cent increase in leaf width was calculated on the basis of cumulative increase in initial values. (Pujari et al. 2021) [16] . ) [13] .

Number of flowers per plant

Days taken to fruit set

It was recorded by time interval between flowering to fruiting. (Kavati, 1992).

It was recorded by number of days taken from flowering to fruit set. (Mostafa and Hatem 2018) [13] .

No of fruits per plant

It was recorded by counting manually the number of fruits per tree at the time of harvesting. (Bansidharrao 2016) [2] .

It was calculated according to the formula. (Bansidharrao 2016) [2] .

No of stone fruits

It was calculated by total number of fruits that got converted into hard fruits at the maturity stage.

 Yield per plant (Kg): Mature fruits were harvested periodically in each treatment separately and the weight was recorded with the help of electronic balance. Then the total estimated yield (kg / plant) was calculated.

(Pujari et al. 2021) [16] .  Statistical analysis: The data collected as a part of experiment will be analysed by following analytical method as followed for Randomized Block Design (RBD) as per method as suggested by Panse and Sukhatme (1995) [27] .

Results

Table The data shows that the maximum Rootstock girth percentage increase in rootstock growth with value (4.81%), scion girth (5.75%), plant height (6.02%), E-W spread (6.45%), N-S plant spread (6.52%) was measured in T5 (BRs @ 0.5 ppm + GA3 @ 25 ppm), Likewise the minimum per cent increase in rootstock growth of Custard apple cv. Balanagar trees with value (2.11%), scion girth (5.75%), plant height (2.70%), E-W spread (0.92%), N-S spread (3.37%) was recorded in T0 treatment (control). Table 2 revealed that of different treatments significantly influenced the growth attributes such as, number of shoots per branch, number of leaves per shoot, leaf length, leaf width and no of flowers/plant. The highest per cent increase in number of shoots per branch (71.23%) was recorded in T 3 (GA3 @ 25ppm), number of leaves per shoots (75.54%), leaf length (36.20%), leaf width (40.45) and no of flowers (265.33) was estimated in T 5 treatment consisting (BRs @ 0.5ppm + GA3 @ 25 ppm). However, minimum per cent increase in number of shoots/branches was recorded in T0 treatment (control) with value (51.96%), number of leaves/shoot (43.12%), leaf length (31.97%), leaf width (25.01%), no of flowers/plant (226.66) was recorded in T 0 treatment (control) in custard apple cv. Balanagar. The data exhibited non-significant effect of brassinosteroids and GA3 on flower retention percentage in custard apple cv. Balanagar trees are presented in table 4.3. Maximum flower retention (67.69%) was recorded in T5 treatment, flower retention (67.69%), Minimum number of days taken to fruit set (53.66), fruit set (76.16%) was estimated in T5 (BRs @ 0.5 ppm + GA3 @ 25 ppm) under vertisols of Jhalawar district. However, the maximum number of fruits/ plant (83.90) was obtained in T8 treatment consisting (BRs @ 1.0 ppm + GA3 @ 50 ppm). The results determined that maximum fruit retention (43.81%) comprising (BRs @ 0.5 ppm + GA3 @ 25 ppm), minimum number of stone fruits (0.66) was estimated in T 2 treatment consisting (BRs @ 1.0 ppm) and maximum yield (18.51kg/plant) was obtained in T 5 treatment consisting (BRs @ 0.5 ppm + GA3 @ 25 ppm) Similary the minimum fruit retention (40.22%), maximum number of stone fruits (5.00), minimum yield (11.42 kg/plant) was recorded in T0 treatment (control).

Discussion

The plant growth parameters of custard apple cv. treatment consisting (BRs @ 0.5 ppm + GA3 @ 25 ppm) and these parameters were observed significantly higher and relatively better as compared with application of other treatments. However, maximum per cent increase in (North-South plant spread) with value (9.12%) was recorded in T 6 treatment (BRs @ 0.5 ppm + GA3 @ 50 ppm), number of shoots/branch (71.23) was measured in T3 treatment (GA3 @ 25 ppm) days taken to fruit and number of fruits per plant (83.90) were set (70.34) in T 8 treatment (BRs @ 1.0 ppm + GA3 @ 50 ppm). Similarly, minimum per cent increase in plant height (2.70%), east-west spread (0.92%), north-south spread (3.37%), no of shoots/branch (51.96), no of leaves/shoot (43.12), leaf length (31.97%), leaf width (25.01%), number of flowers/plant (226.66), flower retention (61.70%), fruit retention (40.22%) yield/plant (11.42 kg) were measured in T0 treatment (control).

The relatively better increase in growth and yield attributes recorded in T 5 treatment may be attributed to the beneficial response of BRs and GA3 in terms of improved carboxylation efficiency, protein synthesis and better integration of various bio-chemical and physiological responses within the plant system of custard apple. The overall better response in T 5 treatment could be ascribed to improved developmental processes including cell elongation, pollen tube growth, flowering, ontogenical fruit development and maturation. The results of present finding are in conformity to those reported by Kalinich (1985) [8] , Mahorker et al. [13,16] .

Conclusions

The effect of study involving foliar spray of brassinosteroids and giberellic acid in custard apple cv. Balanagar revealed that maximum per cent in growth parameters viz. plant height (8.48%), E-W plant width (6.45%), rootstock girth (4.40%), scion girth (6.09%), no. of leaves/shoot (75.54%), leaf length (36.20%), leaf width(40.45%), number of flowers/ branch (265.33), flower retention (67.69%), fruit set (77.49%), fruit retention (43.81%) and yield/plant (18.51 kg) was measured in T 5 treatment consisting (BRs @ 0.5 ppm + GA3@ 25 ppm).

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