Optimising Kinnow mandarin productivity under rainfed conditions through foliar application of plant growth bioregulators

Citrus, particularly Kinnow mandarin, holds a prominent position in the fruit industry worldwide. The study evaluated the effects of plant bioregulators on Kinnow mandarin at different stages of fruit development. The experiment was laid out in a factorial randomised block design with 14 treatment combinations and three replications. The 7 levels of hormonal applications were as follows: H1: naphthalene acetic acid (NAA) at 50 µM, H2: NAA at 100 µM, H3: gibberellic acid (GA3) at 150 µM, H4: GA3 at 300 µM, H5: methyl jasmonate (MeJA) at 200 µM, H6: MeJA at 400 µM, H7: Control and two stages of hormonal application [S1= at full spray flowering stage (FSFS) and cell division stage and S2 = at full spray flowering stage and cell elongation stage]. Among the treatment combinations evaluated, H₄S₂ (GA₃ at 300 µM applied at full-spray flowering stage (FSFS) and cell elongation stages) demonstrated the most pronounced improvement in reproductive attributes, notably enhancing FSFS, number of fruits per plant, total fruit yield (FY) and yield efficiency (YE). Additionally, this treatment also resulted in the lowest fruit drop (FD) percentage, indicating improved fruit retention. It was also superior in improving the physico-chemical properties of fruit, total soluble solids (TSS), acidity (Ac) balance, ascorbic acid (AA) content, sugars (total, reducing, non-reducing), phenolic compounds, carotenoids and antioxidant activity. Moreover, physiological responses such as relative water content (RWC), chlorophyll concentration and proline accumulation were also maximised under the H₄S₂ treatment regime, signifying improved plant health and tolerance to stress. In contrast, untreated control plants recorded the lowest values across all parameters. Overall, the study demonstrates that foliar application of GA₃ at critical growth stages, particularly FSFS and cell elongation, enhances both the yield and quality of Kinnow mandarin fruits while also improving the physiological resilience of the plant. These findings provide a practical framework for hormone-based spray scheduling aimed at sustainable citrus production in the rainfed region.