Management of Pre-harvest Fruit Drop and Ultrastructural Studies of 'Kinnow' Mandarin Under Subtropical Conditions

Fruit drop is a major concern to 'Kinnow' mandarin-growing farmers worldwide. 'Kinnow' growers suffer great economic loss when physiological fruit drop is accelerated by pathogenic infection and their combinations were tested for management of fruit drop during the year 2019-2020. Based on physical parameters and biochemical attributes of the fruits, azoxystrobin (18.2%) + difenoconazole (11.4%) at 0.1% concentration and 2,4-D sodium salt at 10 ppm emerged as effective treatments in checking the fruit drop and enhancing fruit quality as well as yield of 'Kinnow' mandarin. Pre-harvest fruit drop has a negative association with yield and antioxidants. Exogenous application of fungicides and growth regulators significantly reduced fruit drop percentage, leading to an increase in total number of fruits per plant, fruit weight, total soluble solids, titratable acidity, vitamin C, flavonoids, phenols and sugars. Structural components of abscised and non-abscised fruit stalks were assessed by using a scanning electron microscope (SEM). The ultrastructure of longitudinal sections showed the absence of an abscission layer in the fruit stalk of non-abscised fruits. The present study concludes that the application of azoxystrobin (18.2%) + difenoconazole (11.4%) at 0.1% concentration in combination with 2,4-D sodium salt at 10 ppm may have the ability to reduce pre-harvest fruit drop in 'Kinnow' mandarin with a significant increase in fruit yield and biochemical characteristics.