Induction and Characterization of Fruit Abscission during Early Physiological Fruit Drop in Citrus

A new method of inducing fruit abscission by incubating detached ovaries and fruits in agar medium was developed in citrus. Ovary and fruit abscission in the satsuma mandarin, 'Kiyomi', hyuganatsu, and ponkan during early physiological fruit drop was characterized using this method. For primary physiological fruit drop, the abscission of detached ovaries could be divided into three patterns, including an early type in hyuganatsu, a medium type in 'Kiyomi', and a late type in satsuma mandarin and ponkan. The cumulative abscission ratio of four species and cultivars was over 80% at 96 h after treatment. However, for secondary physiological fruit drop, the initiation of fruit abscission was earliest in hyuganatsu, and latest in satsuma mandarin. The cumulative abscission ratio was highest in ponkan at 84% and lowest in hyuganatsu at 6%. The pattern of abscission was different for primary and secondary physiological fruit drop in the four species and cultivars. High temperature promoted the abscission of detached ovaries and fruits in satsuma mandarin and ponkan. Leaf attachment suppressed fruit abscission in 'Kiyomr', hyuganatsu, and ponkan at 7 weeks after anthesis in 2012 and ponkan at 5 weeks after anthesis in 2013. Ovary and fruit abscission in four species and cultivars during early physiological fruit drop was characterized by incubating detached ovaries and fruits in agar medium.