ffect of plant bio- regulators and micro-nutrients on chemical attributes of mango (Mangifera indica L) cv Amrapali

Introduction

Mango (Mangifera indica L.) is one of the oldest and most extensively cultivated fruit crops in tropical and subtropical regions of the world. It is grown in more than 100 countries and is recognized as the second most widely cultivated tropical fruit and the sixth most important fruit crop globally (Ahmad et al., 2018 [2] ; Masroor et al., 2016 [15] ; UNCTAD, 2016). Owing to its adaptability to diverse agro-climatic conditions and its resilience to changing climatic scenarios, mango continues to be a highly sustainable fruit crop (Munir et al., 2015) [16] . Mango is widely appreciated for its attractive appearance, unique flavor, pleasant aroma, and exceptional nutritional value. The fruits are rich in carotenoids and vitamins such as vitamin C, A, E, and B-complex, including riboflavin, niacin, and thiamine. In addition, they contain appreciable amounts of phenolic compounds, carbohydrates, and essential mineral nutrients such as iron (Fe), phosphorus (P), calcium (Ca), and potassium (K), making mango an important component of a healthy and balanced diet (Maldonado et al., 2019) [14] . Because of its high nutritional and economic value, mango plays a significant role in ensuring food and nutritional security. Despite its commercial importance, mango production is often constrained by several factors, including micronutrient deficiencies, physiological disorders, poor fruit retention, and inadequate fruit quality, which collectively reduce productivity and limit export potential (Elsheery et al., 2020) [7] . The judicious application of plant growth regulators and micronutrients has emerged as an effective strategy to overcome these constraints and improve both yield and fruit quality (Zargar et al., 2019) [25] .Among the plant growth regulators, Naphthalene Acetic Acid (NAA) has been reported to promote flowering when applied at concentrations ranging from 50 to 100 ppm (Davenport, 2007) [5]. It also reduces flower and fruit drop, enhances fruit set, improves fruit size, and ultimately increases yield and fruit quality. Similarly, GA₃ application has been shown to significantlyenhance fruit retention per panicle, resulting in increased fruit size and fruit weight in mango as well as in several other fruit crops (Kumar et al., 2018) [12] . Boron, an essential micronutrient, plays a crucial role in reproductive development by promoting ovule formation, pollen germination, pollen tube growth, and fruit set. It also contributes significantly to improving the physical and biochemical quality of mango fruits. Therefore, pre-harvest foliar application of suitable plant growth regulators and micronutrients represents an effective management practice for reducing fruit drop and enhancing the yield as well as the overall quality of mango fruits.

Materials and methods

The present investigation was carried out during the 2022-2023 growing season at the Main Experiment Station, Department of Fruit Science, Acharya Narendra Deva University of Agriculture and Technology, Narendra Nagar (Kumarganj), Ayodhya, Uttar Pradesh. The study was undertaken to assess the influence of Gibberellic acid (GA₃), Naphthalene Acetic Acid (NAA), and Borax on fruit quality of mango (Mangifera indica L.) cv. Amrapali. Thirty healthy, uniform, and bearing mango trees were selected for the experiment. The experiment was laid out in a Randomized Block Design (RBD) comprising ten treatments with three replications. The treatments included foliar viz., T 1 -GA 3 @20 ppm, T 2 -GA 3 @40 ppm, T 3 -GA 3 @60 ppm, T 4 -NAA @15 ppm, T 5 -NAA @20 ppm, T 6 -NAA @25 ppm, T 7 -Borax @0.2 ppm, T 8 -Borax @0.4 ppm, T 9 -Borax @0.6 ppm and T 10 -Control (water spray). Foliar sprays were applied twice during the experimental period, with the first application in the second fortnight of March and the second application in the second fortnight of April, following fruit set. Observations were recorded at 15-day intervals until harvest. The study focused on evaluating the effects of the treatments on the chemical quality attributes of the fruits, including total soluble solids (TSS), ascorbic acid, reducing sugars, non-reducing sugars, total sugars.

Total soluble solids percentage:

The total soluble solids (TSS) content of the fruit was determined using a hand refractometer with a measurement range of 0-32°Brix. For analysis, a small portion of fruit pulp was wrapped in a muslin cloth and gently squeezed to extract the juice. Before taking the measurements, the prism of the refractometer was cleaned thoroughly with a moist muslin cloth. A few drops of the extracted juice were then placed on the prism, and the TSS reading was recorded. The observed values were corrected to the standard temperature of 20°C using the temperature correction table recommended by A.O.A.C. (1980). The TSS content was expressed as a percentage.

Ascorbic acid (Vitamin C):

The ascorbic acid content of the fruit pulp was estimated by homogenizing 5 g of fresh pulp with 3.0% metaphosphoric acid, which served as the extracting and stabilizing solution. The homogenate was filtered, and the filtrate volume was made up to 100 ml with the same solution. An aliquot of 5 ml of the extract was titrated against a standard 2,6dichlorophenol indophenol dye solution until the appearance of a light pink endpoint. The ascorbic acid content was calculated and expressed as milligrams per 100 g of fresh fruit pulp (mg 100 g⁻¹ pulp).

To estimate the reducing sugar content, 100 g of fruit pulp was crushed with distilled water, filtered through a muslin cloth, and the volume was adjusted to 100 ml. A 5 ml aliquot of the extract was mixed with 5 ml each of Fehling's 'A' and 'B' solutions and titrated against a 1.0% glucose solution under boiling conditions, using Methylene Blue as an indicator. A blank sample containing 5 ml each of Fehling's 'A' and 'B' solutions was also prepared. The results were expressed as a percentage of reducing sugars.

𝑅𝑒𝑑𝑐𝑢𝑖𝑛𝑔 𝑠𝑢𝑔𝑎𝑟𝑠(%) = (𝐵𝑙𝑎𝑛𝑘 𝑡𝑖𝑡𝑟𝑎𝑡𝑒 𝑣𝑎𝑙𝑢𝑒 -𝑠𝑎𝑚𝑝𝑙𝑒 𝑡𝑖𝑡𝑟𝑒 𝑣𝑎𝑙𝑢𝑒) 𝑥 𝑉𝑜𝑙𝑢𝑚𝑒 𝑚𝑎𝑑𝑒 𝑢𝑝 𝐴𝑙𝑖𝑞𝑢𝑜𝑡 𝑡𝑎𝑘𝑒𝑛 𝑥 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 𝑡𝑎𝑘𝑒𝑛 × 100

To determine the non-reducing sugar content, the value of reducing sugars was subtracted from the total sugar content, and the result was multiplied by 0.95. The following formula was used for the calculation of non-reducing sugars (AOAC, 1980): Non-reducing sugar = (Total sugar %-Reducing sugar %) × 0.95

The sum of reducing and non-reducing sugars was expressed as total sugars. Total sugars (%) = Reducing sugar (%) + Non-reducing sugar (%)

Results and discussion Total soluble solids ( 0 Brix)

The data presented in Table 1 revealed that the highest total soluble solids (18.4°Brix) content in mango fruits was recorded at GA₃ @ 20 ppm, followed by the NAA treatment (18.3 °Brix), whereas the lowest TSS (16.2°Brix) was observed in the control. The increase in total soluble solids (TSS) may be attributed to the enhanced photosynthetic activity and carbohydrate accumulation induced by micronutrients. Gibberellins play an important role in the breakdown of sucrose and starch by enhancing the activity of the enzyme invertase, which converts sucrose into glucose and fructose (Majumder et al., 2017) [13] .

Ascorbic acid content

The data presented in Table 1 revealed that the highest ascorbic acid (37.5 mg/100 g pulp) observed in GA₃ @ 20 ppm, closely followed by NAA @ 25 ppm (37.1 mg/100 g pulp), whereas the lowest ascorbic acid (29.2 mg/100 g pulp) was recorded at control. The increase in ascorbic acid content may be attributed to the role of micronutrients such as boron and zinc, which activate several enzymes involved in physiological and biochemical processes. These findings are in agreement with those reported by Gill and Bal (2013) [8] in mango, Bankar and Prasad (1990) [3] in ber, Kaur et al. (2009) in guava, and Singh and Singh (2015) [19] in aonla following the application of GA₃, NAA, and other growth regulators. Similar results were reported by Tripathi and Shukla (2010) [22] , who observed an increase in ascorbic acid content in strawberry following GA₃ application. The findings presented in Table 2 reveal that maximum reducing sugar (4.66%) recorded GA₃ at 20 ppm, closely followed by NAA at 25 ppm (4.38%), while minimum reducing sugar (3.64%) recorded at control. The increase in reducing sugar content may be attributed to the conversion of organic acids into sugars during fruit ripening. These findings are consistent with the reports of Hammam et al. (2001) [9] , Singh et al. (2003) [21] , Patel and Valia (2004) [17] , Sarkar and Ghosh (2004) [18] , Singh and Banik (2011) [20] , and Yadav et al. (2011) [24] .

The data presented in Table 2 shows significant differences among the treatments. The highest non-reducing sugar content (8.90%) was observed in GA₃ @ 20 ppm, followed by NAA at 25 ppm (7.40%). The lowest non-reducing sugar content (7.40%) was recorded in the water spray (T 10 ) treatment. The present findings are in close agreement with those reported by Singh et al. (2003), Patel and Valia (2004) [17] , Bhowmick and Banik (2011) [4] , Moazzam et al. (2011), and Yadav et al. (2011) [24] and Kaur et al. (2015).

Total sugars

The data presented in Table 2 indicate that highest total sugar content (14.12%) was recorded with the foliar application of GA₃ @20 ppm followed by NAA @ 25 ppm (13.28%) whereas, the lowest total sugar content (11.04%) was observed at control. The higher total sugar content may be due to the enhanced conversion of organic acids into sugars, coupled with improved nutrient absorption and the regulatory influence of plant growth regulators on carbohydrate synthesis and accumulation in the fruits. Results are agreed with the finding reported by Hammam et al. (2001) [9] , Dutta and Dhua (2002) [6] , Singh et al. (2003) [21] , Patel and Valia (2004) [17] , Sarkar and Ghosh (2004) [18] , Bhowmick and Banik (2011) [4] , Singh and Banik (2011) [20] , Yadav et al.

Conclusion

The present investigation concluded that foliar application of plant growth regulators and micronutrients significantly influenced the chemical quality attributes of mango (Mangifera indica L.) cv. Amrapali. Among the treatments, GA₃ at 20 ppm (T₁) proved to be the most effective, recording the highest total soluble solids (18.4 °Brix), ascorbic acid (37.5 mg 100 g⁻¹ pulp), reducing sugars (4.66%), non-reducing sugars (8.90%), and total sugars (14.12%). The NAA at 25 ppm (T₆) treatment ranked second for most of the quality parameters, whereas the control consistently recorded the lowest values. The improvement in fruit quality may be attributed to the beneficial effects of GA₃ on carbohydrate metabolism, sugar accumulation, and the synthesis of biochemical constituents during fruit development. Therefore, foliar application of GA₃ at 20 ppm, applied twice during the second fortnight of March and April, can be recommended for improving the chemical quality of mango cv. Amrapali under the agro-climatic conditions of Eastern Uttar Pradesh.

References

1. Association of Official Analytical Chemists. Official methods of analysis. 13th ed. Horwitz W, editor. Washington (DC): Association of Official Analytical Chemists; 1980. p. 617-623.
2. Ahmad I, Bibi F, Ullah H, Munir TM. Mango fruit yield and critical quality parameters respond to foliar and soil applications of zinc and boron. Plants. 2018; 7:97.
3. Bankar GJ, Prasad RN. Effect of gibberellic acid and NAA on fruit set and quality of fruits in ber cv. Gola. Progressive Horticulture. 1990; 22:60-62.
4. Bhowmick N, Banik BC. Influence of pre-harvest foliar application of growth regulators and micronutrients on mango cv. Himsagar. Indian Journal of Horticulture. 2011;68(1):103-107.
5. Davenport TL. Reproductive physiology of mango. Brazilian Journal of Plant Physiology. 2007;19(4):363-376.
6. Dutta P, Dhua RS. Improvement of fruit quality of Himsagar mango through application of zinc, iron and manganese. Horticultural Journal. 2002;15(2):1-9.
7. Elsheery NI, Helaly MN, El-Hoseiny HM, Alam-Eldein SM. Zinc oxide and silicone nanoparticles to improve the resistance mechanism and annual productivity of saltstressed mango trees. Agronomy. 2020; 10:558.
8. Gill KS, Bal JS. Impact of application of growth regulators on Indian jujube. Acta Horticulturae. 2013; 993:119-124.
9. Hammam MS, Abdallah BM, Mohamed SG. The beneficial effects of using ascorbic acid with some micronutrients on yield and fruit quality of Hindy Bisinnara mango trees. Assiut Journal of Agricultural Sciences. 2001;32(5):181-193.
10. Iqbal M, Khan MQ, Rehman K, Muni M. Effect of foliar application of NAA on fruit drop, yield and physicochemical characteristics of guava (Psidium guajava L.) red flesh cultivar. Journal of Agricultural Research. 2009;47(3):259-269.
11. Kaur S. Effect of micronutrients and plant growth regulators on fruit set, fruit retention, yield and quality attributes in litchi cultivar Dehradun. Chemical Science Review and Letters. 2017;6(22):982-986.
12. Kumar R, Tripathi VK, Tomar S, Chaudhary M. Effect of best plant bioregulator and micronutrients for achieving higher yield and quality of mango (Mangifera indica L.) fruits cv. Amrapali. Journal of Plant Development Sciences. 2018;10(11):599-604.
13. Majumder I, Sau S, Ghosh B, Kundu S, Roy D, Sarkar S. Response of growth regulators and micronutrients on yield and physico-chemical quality of ber (Zizyphus mauritiana Lamk.) cv. BAU Kul-1. Journal of Applied and Natural Science. 2017;9(4):2404-2410.
14. Maldonado-Celis ME, Yahia EM, Bedoya R, Landázuri P, Loango N, Aguillón J, Restrepo B, Guerrero Ospina JC. Chemical composition of mango (Mangifera indica L.) fruit: Nutritional and phytochemical compounds. Frontiers in Plant Science. 2019; 10:1073.
15. Masroor HM, Anjum MA, Hussain S, Ejaz S, Ahmad S, Ercisli S, Zia-Ul-Haq M. Zinc ameliorates fruit yield and quality of mangoes cultivated in calcareous soils. ErwerbsObstbau. 2016; 58:49-55.
16. Munir TM, Perkins M, Kaing E, Strack M. Carbon dioxide flux and net primary production of a boreal treed bog: Responses to warming and water-table-lowering simulations of climate change. Biogeosciences. 2015; 12:1091-1111.
17. Patel PM, Valia RZ. Effect of foliar application of plant growth regulators and urea on yield and quality of mango cv. Langra. In: Proceedings of the First Indian Horticulture Congress for Improving Productivity, Quality, Postharvest Management and Trade in Horticultural Crops; 2004 Nov 69; New Delhi, India. p. 288.
18. Sarkar S, Ghosh B. Effect of growth regulators on biochemical composition of mango cv. Amrapali. In: Proceedings of the First Indian Horticulture Congress for Improving Productivity, Quality, Postharvest Management and Trade in Horticultural Crops; 2004 Nov 6-9; New Delhi, India. p. 289.
19. Singh A, Singh HK. Application of plant growth regulators to improve fruit yield and quality in Indian gooseberry (Emblica officinalis Gaertn.). Journal of Agricultural Search. 2015;2(1):20-23.
20. Singh SR, Banik BC. Response of integrated nutrient management on flowering, fruit setting, yield and fruit quality in mango (Mangifera indica L.) cv. Himsagar. Asian Journal of Horticulture. 2011;6(1):151-154.
21. Singh YP, Tiwari JP, Mishra KK. Effect of micronutrients on fruit yield and physico-chemical characters of mango cv. Dashehari. Progressive Horticulture. 2003;35(1):34-37.
22. Tripathi VK, Shukla PK. Influence of plant bioregulators, boric acid and zinc sulphate on yield and fruit characters of strawberry cv. Chandler. Progressive Horticulture. 2010;42(2):186-188.
23. United Nations Conference on Trade and Development. Mango: An Infocom commodity profile. Geneva (Switzerland): United Nations; 2016. p. 21.
24. Yadav AK, Singh JK, Singh HK. Studies on integrated nutrient management in flowering, fruiting, yield and quality of mango cv. Amrapali under high-density orchard. Indian Journal of Horticulture. 2011;68(4):453-460.
25. Zargar M, Tumanyan A, Ivanenko E, Dronik A, Tyutyuma N, Pakina E. Impact of foliar fertilization on apple and pear trees in reconciling productivity and alleviation of environmental concerns under arid conditions. Communications in Integrative Biology. 2019;12(1):1-9.