Efficacy of foliar feeding of micronutrients and growth regulators on yield and quality attributes of litchi (Litchi chinensis Sonn.) cultivar ‘China’

Introduction

Litchi (Litchi chinensis Sonn.) belongs to the family Sapindaceae, and is one of the important sub-tropical fruit crops of India. Litchi is native to Southern china, particularly the provinces of Kwantung and Fukien. From China it was introduced in India by the end of the 17 th century (Knight, 1980; Liang, 1981) [39,47] , where it has acclimatized so much that India is now the second largest producer of litchi, after its native place China. It is highly specific to climatic requirements, as it required cool dry winters and warm wet summers and due to this reason its cultivation is restricted to few states in our country. Litchi is grown mainly in the Litchi is well known for its dietic attributes such as higher content of sugars, vitamins, organic acids, phenolic acids, phytochemicals, anthocyanin, minerals etc. It provides good return to growers of Punjab state of India. The problems responsible for low economic potential of litchi cultivation in various litchi growing regions include poor fruit set (Sarkar et al., 1984) [76], heavy fruit drop (Singh and Phogat, 1984) [81] , fruit cracking (Bhat et al., 1997) [10] and inferior fruit quality (Brahmachari and Rani, 2001) [11] .The litchi based cropping system is affected with physiological disorder, fruit drop and fruit cracking (Lal et al., 2017) [44] . Although the litchi tree flowers profusely, but fruit setting in specific litchi cultivar varies from 1 to 50 percent, which is far higher than fruits retained till maturity (Nath et al., 2021) [57] .Around 90-95 percent fruit drop occurs up to third week after pollination (Gharge et al., 2025) [25] . The initial wave of fruit drop is mainly due to improper pollination, poor fertilization and embryo abortion. But fruit drop, during later fruit developmental stages, is ascribed to the lack of assimilates, irrigation, environmental factors, nutrient deficiency, insect attack and hormonal imbalances (Lal et al., 2021) [44] . The higher level of growth promoters and lower abscisic acid content are prerequisite for fruit set and afterward for fruit growth, development, and retention. The foliar application of growth regulators and micronutrients are effective in improving fruit yield and quality (Hitesh et al., 2025; Piyadarshi et al., 2018) [31,65] . Lower ratio of growth promoters to abscisic acid and ethylene concentrations may induces the formation of pre-mature abscission layer in pedicel that results in more loss of fruit productivity (Yuan and Carbaugh, 2007) [91] . Therefore, plant growth regulators and micronutrients have been used for many years to alter the fruit plant behaviour for the economic benefits such as to control the vegetative growth, increase in flowering and fruit set, stimulation of maturity and ripening and improving fruit quality. It is also reported that growth substances like gibberellic acid (GA 3 ), borax, 1naphthalene acetic acid(NAA) and 2,4-D (2,4-Dichlorophenoxyacetic acid) have great influence on litchi and proved beneficial in reducing the cracking and dropping of fruits and enhancing the quality of fruits along with delay in harvest(Kaur, 2017) [38] . Gibberellic acid has been found to offer suitable means of controlling ripening process in litchi and improving fruit quality (Ray and Sharma, 1986) [70] and other fruit crops (Lavon et al., 1982) [46] . The foliar application of nutrients and growth regulators in specific plant developmental and critical stages improves the yield and quality. Foliar application of micronutrients has gained importance because it is a well-established operation to complete and boost plant nutrition. Foliar application can meet the expense of nutrients where absorption of nutrients from the soil is unavailable due to plant stress or in adverse soil conditions (Marschner, 2012) [52] .Application of plant growth regulators results in increased flowering, fruiting and fruit retention. Yield and quality of litchi fruit have been positively influenced by application of nutrients and plant growth regulators (Singh and Phogat, 1984) [81] .Reduced flower induction and fruit set, leading to inferior fruit quality are caused by zinc and boron deficiency (Menzel and Simpson, 1987) [53] . Micronutrients applied in optimum concentrations results in better plant growth which causes better flowering, higher fruit set that ultimately leads to higher yield (Ram and Bose, 2000) [67] . Micronutrients plays specific role in improving the growth, yield and quality of litchi even though these elements are needed in small quantities. Zinc and boron take part in various enzymatic reactions and helps in sugar accumulation in fruit from source to sink (Priyadarshi et al., 2018) [65] . Boron is the only micronutrient not only specifically associated with either photosynthesis or enzyme function, but it is also associated with the carbohydrate chemistry and reproductive system of the plant. Micronutrients such as zinc, boron and copper play an important role in litchi nutrition, especially with regard to increase the flowering, fruit setting, fruit retention, fruit size and quality.Zinc plays a vital role in the metabolic activities of plants. The principal function of zinc in plants is as a metal activator of enzymes like dehydrogenase (pyridine nucleotide, glucose-6 phosphodiesterase, carbonic anhydrase etc.). It is involved in the synthesis of tryptophane, a precursor of indole-3acetic acid. It is associated with water uptake and water retention in plant bodies (Kumar et al., 2009) [41] . Boron is also required for photosynthetic activities, cellular differentiation, hormone metabolism and water absorption in plants. It is essentially required during reproduction phase, i.e., germination of pollen tube and fertilization, because boron deficiency produced less number of flowers which resulted in mostly sterile, deformed fruit and such type of fruits are commercially useless (Ruby et al., 2001) [71] . Plant growth regulators signalling the various metabolic processes in plants such as apical dominance, inhibition of apical dominance, regulating flowering and early ripening by using ethrel in less amounts, is very effective and significantly improves yield and quality of fruit (Choudhary et al., 2013) [16] . Plant growth regulators can also increase the ascorbic acid content in fruits by synthesis of catalytic activity of several enzymes and coenzymes which are essential in ascorbic acid synthesis (Suman et al., 2017) [83] . Although the effect of micronutrients and growth regulators in enhancing yield and quality in litchi have been investigated over the years, but the studies on the effect of foliar feeding of nutrients and growth regulators on yield and quality attributes of litchi cultivar 'China' in particular is scarce especially in the sub-mountaneous zone of Punjab. Keeping in view, the present investigation was undertaken to evaluate the efficacy of foliar feeding of micronutrients (zinc and boron) and growth regulators (GA 3 , 2, 4-D and NAA) on yield and quality attributes of litchi (Litchi chinensis Sonn.) cultivar 'China'.

Material and Methods

Experimental site

The present investigation on "Efficacy of foliar feeding of micronutrients and growth regulators on yield and quality attributes of litchi (Litchi chinensis Sonn.) cultivar 'China'" was conducted during the years 2023-24 and 2024-25 at Punjab Agricultural University, Regional Research Station, Gurdaspur. This region is sub-montaneous zone of Punjab which is situated between 32°3′ N latitude, 75°22′ E longitude and has an altitude of about 257 m from mean sea level having humid subtropical and dry winter climate. The sub-montaneous zone of Punjab (kandi region) features hilly topography with shiwalik foothills, undulating terrains, and deep, coarse-textured sandy loam to silt loam coarse textured soils.

Selection of plants and treatments detail

Litchi plants (25-30 years old) grown in the orchard were selected for this experiment on the basis of their uniformity in appearance, growth habit, free from visual symptoms of pests and disease occurrence. Different doses of borax (0.8%, 1.0%), zinc sulphate (0.8%, 1.0%), 2,4dichlorophenoxyacetic acid (2,4-D) (10 ppm, 20 ppm), gibberellic acid (GA 3 ) (10 ppm, 20 ppm), 1naphthaleneacetic acid (NAA) (10 ppm, 20 ppm), along with control were tested. Zinc sulphate (ZnSO 4 ) and borax were sprayed on new growth flushes before initiation of inflorescence, whereas 2,4-D, GA 3 and NAA were sprayed after fruit setting in litchi. The experiment was planned out in a randomized block design and each treatment was replicated thrice with a single tree as a treatment unit. The spray solution was prepared by dissolving the calculated dose of growth regulators (laboratory grade) in alcohol, then made the final volume in water along with spreader Tween-20(0.01%). The control trees were sprayed with plain water without any micronutrients and growth regulators. The cultural practices were adopted as per 'Package of Practices for Cultivation of Fruit Crops', Punjab Agricultural University, Ludhiana (2025).

Observations recorded

Twenty terminal flowering shoots per plant were randomly selected in each direction of tree canopy and tagged for recording various observations viz. fruit set(%), fruit drop(%), fruit cracking(%), fruit colour, fruit yield (kg/tree), fruit weight (gm), fruit length(cm) & fruit breadth (cm), nut length (cm) & breadth (cm), nut weight (gm), pulp weigh t(gm), peel weight (gm), TSS (%), acidity (%), sugars(%), ascorbic acid (mg/100 ml) and anthocyanins (mg100 g-1 pericarp). Number of fruits in each tagged panicles were counted after fruit set before the plants sprayed and the percentage was worked out after counting the final fruit set, fruit drop and fruit cracking about one week prior to harvesting. Fruit yield was estimated by weighing all fruits during harvesting and was expressed in kg/plant. The fruit weight, pulp weight, stone weight and peel weight were measured using digital balance and expressed in gram. Fruit length &breadth and nut length& breadth were measured with digital vernier's calipers' and expressed in cm. Total soluble solids percentage of fruit juice was recorded using digital hand refractometer (Atago, Japan) at 20 °C with necessary correction factor, while acidity percentage was determined by titrating fruit juice with N/10 NaOH using phenolphthalein (1%) as an indicator. The acidity was expressed in maleic acid content. Juice sugars and ascorbic acid were analyzed as per (AOAC, 2005) [4] . Pericarp anthocyanin content was determined as per spectroscopy method suggested by Ranganna (1991) [69] . The technique involves extraction of anthocyanin using ethanolic hydrochloric acid and measurement of colour at 535 nm wavelength against ethanolic hydrochloric acid (used as blank).

Statistical analysis

The recorded experimental data were statistically analyzed by using one-way analysis of variance (ANOVA) with Randomized Block Design (RBD) as suggested by Gomez and Gomez (2010) [28] by using SPSS software.

Results and Discussion

3.1 Fruit set Significant higher fruit set(92.62%) in caparison with other treatments including the control were noticed in plants sprayed with borax 1.0%, where as the control treatment had the lowest fruit set (60.25%) (Table 1). According to Liu (1986) [48] , levels of naturally occurring auxins are drastically reduced in litchi fruits during embryo development after 4-5 to weeks of fertilization. As a result, disintegration of cell wall and middle lamella of abscission zone occurs in pedicel due to more activity of hydrolytic cellulase and polygalacturonase enzymes (Kaur et al., 2021) [36] . Borax response was more positive due to boron, which play an important role in translocation of carbohydrates, auxin synthesis and increased pollen viability and fertilization. Similarly, maximum fruit set, fruit retention, fruit size, fruit weight and fruit yield were observed in foliar application of 0.4% borax in litchi culivar 'Dehradun'(Kaur, 2017) [38] .Borax on increasing the fruit setting with reduced fruit drop on date palm cultivar 'Barhi' (El-Sharabasy and Ghazzawy, 2019) [21] .

Fruit drop

The trees sprayed with NAA 20 ppm registered lowest fruit drop (8.26%) compared to rest of treatments (Table 1) and maximum fruit drop (48.21%) was observed in control treatment. The reduction of fruit drop by NAA 20 ppm application is mainly due to the effect of auxin which helps to reduce the disintegration of cells and thereby reduces fruit drop (Noggle and Fritz, 1989) [58] . Generally auxin helps in cell division, cell enlargement, cell elongation and reduction in abscission layer (Salisbury and Ross, 1992) [75] . Similarly Sahay et al., (2018) [73] also reported minimum fruit drop with the use of NAA 20 ppm in litchi cultivar 'Purbi'. These findings align with the results of Badal et al., (2021) [6] in guava, Tripathi et al., (2022) [86] in aonla and Kumar et al., (2023) [40] in ber.

Fruit Cracking

1-naphthalene acetic acid plays a significant role in reduction of pericarp fruit cracking. The fruit cracking was minimum (3.51%) with application of borax 1.0% and maximum fruit cracking (46.18%) was noted in control treatment(Table1). The reducing of fruit cracking by foliar application of borax might be attributed to the fact that boron is important nutrient for plant growth/development, flowering and fruiting. Borax plays major role in cell wall membrane function, cell wall strength and development, cell division, fruit and seed development, sugar transport. The reducing effect on fruit cracking percent in response to application of boron was mainly attributed to its important role in the extension of plant cell walls through building of pectins and water uptake. This might be due to beneficial effect of boron in general improvement and extension of plant cell wall through its association with cell wall pectins. The role of boron application in reducing fruit cracking may probably be due to translocation of sugars and synthesis of cell wall material. Similarly Haqmal et al., (2022) [29] reported that foliar application of 0.3% borax was quite effective in minimizing fruit cracking in pomegranate cv. Mridula. Likewise Singh et al., (2022) [79] also reported minimum fruit cracking with borax (0.4%) in litchi cultivar 'Dehradun'. Similarly Baloda et al., (2023) [9] noted that four sprays of borax 0.3% during the 3rd week of April, Ist week of May, and last week of May and 2nd week of June proved to be the best treatment in reducing the fruit cracking in pomegranate.

Fruit yield

Litchi plants sprayed with GA 3 20 ppm had highest fruit yield (150.52kg/tree) as compared to rest of the treatments (Table1).Exogenous application of gibberellic acid (GA 3 ) increases cell size and intercellular spaces coupled with more accumulation of water and nutrients in greater amount. This may have improved the fruit size and weight which ultimately enhanced yield. The above results were in accordance with Parauha and Pandey (2019) [61] in mango and Singh et al., (2021) [80] & Purohit et al., (2019) [66] in guava. Pre-harvest spray of GA 3 100 ppm recorded significantly maximum fruit weight and fruit yield of sapota cultivar 'Kalipatti' (Bagul et al., 2021) [7] . Maximum fruit set, retention and yield of rambutan fruit were obtained by preharvest foliar spray of GA 3 300 ppm (Uddin et al., 2024) [87] . Gibberellic acid with various concentrations at the different developmental stages, increases both quality and yield in grapes (Pahi et al., 2020) [59] .

Fruit length& fruit breadth (fruit size) and fruit weight

From the Table1, it has been noted that with the foliar spray of GA 3 20 ppm, the maximum fruit length (4.75 cm), fruit breadth (4.15 cm) and fruit weight (25.32 gm) were observed in litchi fruits as compared to other treatments

The study showed that concentration of gibberellic acid 250 ppm, it helped to increase the fruit size (fruit length & fruit breadth), fruit weight, total soluble solids and ascorbic acid level in cape gooseberry (Kumar et al., 2017) [42] .These results are in close conformity with the findings of Tohamy et al., (2012) [85] and Kaur et al., (2013) [37] in Cape gooseberry. Also fruit size and pulp weight were increased with GA 3 300 ppm preharvest foliar spray in Rambutan fruits (Uddin et al., 2024) [87] .Gibberellic acid is one of the critical regulators for carbohydrate translocation to the sink from the source. As a result of this partitioning, the growth of sink tissues is induced (Iqbal et al., 2011) [34] , resulting in higher fruit size and weight. Cell division, elongation, and enlargement are major effects of gibberellin in plants. In the present study, GA 3 might have played critical roles in raising sink potential through boosting cell quantity or controlling cell division, such as plastid biogenesis and DNA amplification, or by altering the duration or speed of dry mass deposition of developing fruits (Davies, 1995) [18] . These observations are comparable with the findings of Kaur (2017) [38] in litchi, where preharvest GA 3 application resulted in increased fruit length, width and weight compared to control. Similar effects were obtained by applying GA 3 on the other fruits viz. pear (Canli and Pektas, 2015) [13] , sweet cherries (Sabir et al., 2021) [72] , pineapple (Li et al., 2011) [46] , Japanese plum (Erogul and Sen, 2015) [22] , custard apple (dos Santos et al., 2016) [19] , blueberry (Zang et al., 2016) [92] and mango (Ahmed et al., 2012; Vishwakarma et al., 2022) [1,88] .

Nut length& Nut breadth (nut size) and Nut weight

From Table1 and 2, It has been noted that minimum nut size in terms of nut length (1.31cm) nut& breadth (1.12 cm) and nut weight (2.32 gm) were observed in GA 3 20 ppm spray and maximum vales of these parameters were noticed in control treatment. The present findings of reduced nut/seed weight and size can be attributed to and supported by the effectiveness of gibberellic acid in inducing parthenocarpy in many fruits, including apples (Galimba et al., 2019) [24] , pears (Liu et al., 2018) [49] , cherries (Sabir et al., 2021) [72] , loquats (Mesejo et al., 2010) [54] and custard apples (dos Santos et al., 2016) [18] . dos San tos et al., (2016) [19] also observed a considerable reduction in the total seed weight and number of seeds in custard apple with the application of gibberellic acid. Ahmed et al., (2012) [1] also noted minimization of stone weight in mango due to the use of GA 3 . Similarly, litchi seed weight was also reduced with GA 3 100 mglitre -1 application (Chen et al., 2014) [15] . Likewise reduction in seed weight was observed with gibberellic acid spray treatment in litchi as reported by Kaur (2017) [38] and also reported in sugar apples by Pereira et al., (2019) [62] .

Pulp weight (gm) and peel weight (gm)

The litchi sprayed with GA 3 20 ppm had significantly maximum fruit pulp weight (21.65 gm) with minimum peel weight (1.35 gm) as compared to rest of treatments (Table 2). Fruits obtained from panicles treated with GA 3 20 ppm had a maximum pulp weight of rambutan fruits (Uddin et al., 2024) [87] . Increase in pulp weight after GA 3 treatment was obtained by Pereira et al., (2014, 2019) [63,62] in atemoya and sugar apple, by dos Santos et al., (2016) [19] in custard apple, by Sahay et al., (2018) [73] in litchi, by Ahmed et al., (2012) [1] in mango, by Saleem et al., (2007) [74] in sweet orange and by Ramezani and Shekafandeh (2009) [68] in olive. Pulp weight increased with GA 3 application and the fruit size increasing even after reaching physiological ripeness until harvest maturity, causing local swelling of the pericarp, ultimately reducing the thickness of the skin. The opposite process occurred for control fruits, where further low fruit size with minimal fruit surface area did not reduce skin thickness. The present results are consistent with the findings of Chang and Lin (2006) [14] in litchi, Pozo et al., (2000) [64] in mandarin, and Fidelibus et al., (2002) [23] in orange.

Total soluble solids (TSS) (25.46%) and total sugars (22.65%) contents of litchi fruits significantly highest in GA 3 20 ppm application on the panicles (Table2) and the control treatment had lowest values. Similarly, maximum value of total soluble solids and total sugars were reported in preharvest foliar spray of GA 3 300 ppm treatment to rambutan fruit (Uddin et al., 2024) [87] . As gibberellic acid is closely related to the carbohydrate partitioning in the reproductive organ (Wang et al., 2020) [89] , exogenous application of GA 3 probably increased the total soluble solids contents of fruits under treatment compared to control. The study showed that increasing the concentration of gibberellic acid 250 ppm it helped to increase the fruit size, fruit weight, total soluble solids and ascorbic acid level of cape gooseberry (Kumar et al., 2017) [42] . The results are in line with the findings of Hifny et al., (2017) [30] in washington navel orange, Li et al., (2011) [46] in pineapple and Mishra et al., (2017) [55] litchi fruits. Gibberellic acid induced TSS increment was also observed in mango (Ahmed et al., 2012) [1] , litchi (Kaur, 2017) [38] , blueberry (Zang et al., 2016) [92] , and sweet cherry (Canli and Orhan, 2009) [12] . The increase in TSS by the application of GA 3 might be due to the effect of enhanced photosynthetic efficiency, more dry matter accumulation in plants and better partitioning of photo assimilates and nutrients from leaves to the developing sink organs (Sharma and Singh 1990) [77] .The improvement in sugar content in fruits due to GA 3 spraying can be explained by the fact that the application of this hormone probably enhanced the physiological functions of the plant, which resulted in the acceleration of the translocation of essential components in the fruits and the subsequent photosynthesis by the growing rambutan fruits (Ghosh et al., 2009) [26] . Possibly, Kaur (2017) [38] showed an 18.5% increase in sugar levels in GA 3 treated litchi panicles compared to the control.

Gibberellic acid treatment showed significant changes in the titratable acidity (TA) content of litchi fruits (Table 2). Lowest fruit acidity value 0.35%) was noted in foliar spray of GA 3 20 ppm to litchi plants and highest acidity value (0.49%) was observed in control treatment. Similarly, minimum value of acidity were reported in GA 3 300 ppm treatment to rambutan fruits (Uddin et al., 2024) [87] . The lowering titratable acidity trends in the fruits of GA 3 treated panicles may be due to conversion of organic acids into soluble sugars during fruit development and maturation as observed by Souza et al., (2019) [82] in cashewnut. Likely, minimum TA contents in fruits of Pyrus communis L. resulted in GA 3 application (Gilani et al., 2021) [27] . Almost identical phenomena in TA accumulation in the sink after preharvest gibberellic acid were also noted by Yadav et al., (2022) [90] in mango, by Moradinezhad et al., (2020) [56] in pomegranate, and by Talat et al., (2020) [84] in kinnow mandarin fruits.

Higher vitamin C content imparts higher nutritive value to fruits. Data in Table 2 shows that the content of vitamin C was recorded higher (41.36 mg/100 ml) in the GA 3 20 ppm treated fruits than in non-treated control (24.18 mg/100 ml). These results were in line with the findings of Sindhu and Sighrot (1993) [78] who reported maximum ascorbic acid content in GA treated fruits. Foliar application of different concentrations of gibberellic acid significantly increased the ascorbic acid content of cape gooseberry fruits (Kumar et al., 2017) [42] . Awad and Al-Qurashi (2012) [5] used gibberellic acid in the cultivation of date palms of the 'Barhee' variety and showed a positive influence of hormonisation on the vitamin C level in the fruit. Application of GA 3 significantly increased the vitamin C content in grapes (Kaplan et al., 2019) [35] .

3.11 Fruit colour and anthocyanins (mg 100 g -1 pericarp) It has been observed that litchi plants sprayed with NAA 20 ppm produced fruits having dark red peel colour with highest anthocyanin content (25.53 mg100 g -1 pericarp)) as compared to rest of treatments (Table 2). This is due to the transcript levels of key anthocyanin regulatory, biosynthetic and transport genes were significantly up regulated upon fruit exposure to NAA (Clayton-Cuch et al., 2021) [17] . Similarly, Balbontin et al., (2018) [8] noted a decrease in hue angle with increase in anthocyanin content among sweet cherry subjected to different hormonal treatments. Dutta et al., (2011) [20] also found the impact of plant growth regulators on anthocyanin content of litchi fruits. The chroma value indicates the quantitative measure for colourfulness or purity of colour. The present results indicated higher chroma value in NAA treated fruits over the control. Pericarp colour gradually changed from green to pink and finally red during fruit maturation. These transitions are not uniform across fruit surface which might be responsible for the comparative decrease in chroma values. Plant growth regulators effectively improved fruit yield and quality due to better supply of nutrients, water and other compounds required for their growth and development that in turn produced fruits of superior size, quality and ultimately greater yield (Pandey, 1999) [60] .Ripening and anthocyanin production was enhanced by the synthetic auxin 1-naphthaleneacetic acid (NAA) application to sweet cherry trees during the straw-color stage of fruit development (Clayton-Cuch et al., 2021) [17] . Ma et al., (2021) [50] also reported that NAA treatments accelerated the colour changes from green to orange in the gibberellin (GA) and prohydrojasmon (PDJ) treated citrus fruit during the ripening process.

Conclusion

The present investigation concluded that among the eleven different concentrations of growth regulators and micronutrients applied at new growth flushes before initiation of inflorescence and after fruit setting in litchi, the foliar application of NAA 20 ppm after fruit setting significantly managed the fruit drop and also improved the fruit colour and pericarp anthocyanin pigments. Borax 1.0% spray increased fruit set and also reduced fruit cracking. Also foliar spray of GA 3 20 ppm improved physical and chemical quality attributes of litchi cultivar 'china' growing under submountaneous zone of Punjab.

Acknowledgments

References

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