Preharvest application of plant growth regulators extends harvest window and improves yield and quality of mandarin orange cv. Khoku Local

Mandarin Orange (Citrus reticulata Blanco) is among the most widely cultivated citrus fruits globally. The preharvest fruit drop and seasonal glut remain major challenges for mandarin growers. The preharvest application of plant growth regulators (PGRs) is a crucial agronomic practice in mandarin for managing fruit drop, maturity, and quality. Therefore, in this study, we evaluated the effects of preharvest application of 2,4-D (20 mg L-1, 40 mg L-1, 60 mg L-1), GA3 (20 mg L-1, 40 mg L-1, 60 mg L-1), and NAA (20 mg L-1, 40 mg L-1, 60 mg L-1) on fruit drop, maturity, and quality in mandarin orange cv. Khoku Local. All concentrations of GA3 and 60 mg L-1 NAA significantly extended the harvest window of mandarin. The PGRs application markedly reduced the preharvest fruit drop and improved fruit retention. 60 mg L-1 NAA and 60 mg L-1 GA3 resulted in significantly lower fruit drop, while 60 mg L-1 NAA resulted highest fruit retention. The greatest increase in diameter was observed in fruits treated with 60 mg L-1 GA3. At harvest, GA3 at 40 mg L-1 and 60 mg L-1 resulted in the highest total soluble solids (TSS), NAA at 60 mg L-1 exhibited the highest titratable acidity (TA), while GA3 at 60 mg L-1 yielded the highest TSS: TA ratio. During the storage, the qualitative parameters varied: TSS remained higher in GA3 at 20 and 40 mg L-1, TA was lowest in NAA at 60 mg L-1, vitamin C was highest in GA3 at 60 mg L-1, Physiological Loss in Weight (PLW) was lower in NAA at 20 mg L-1, and decay loss was lowest in GA3 at 20 mg L-1. Linear regression showed that the extended maturity positively correlated with fruit diameter and TSS, while a negative correlation with TA and decay loss. The Linear Mixed Model indicated that 20 mg L-1 2,4-D, 60 mg L-1 2,4-D, 20 mg L-1 GA3, and 60 mg L-1 GA3 exhibited a much slower decay progression and a lower value for decay index. Overall, the preharvest application of GA3 at 60 mg L-1 was most effective in extending fruit maturity, minimizing fruit drop, improving fruit retention, enhancing qualitative traits, and reducing postharvest decay.