Study on molecular mechanisms of fruit abscission and evaluation of parthenocarpy in citrus

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The method of detached fruit let incubation on agar medium is useful for induction of fruit abscission to confirm the mechanisms of fruit abscission process during physiological fruit drop in citrus. Abscission layers are rapidly formed in the fruit abscission zone after the induction of abscission and fruit abscission occurs in primary fruitdrop system. However, it is confirmed that no abscission layer is formed in the fruit abscission zone and fruit abscission occurs in secondary fruit drop system. It was evaluatedthat a potential parthenocarpic level is low in ponkan, navel -orange and iyokan, and high in Satsuma mandarin, hyuganatsu and ‘ Hirado’ pummel. It would be possible to evaluate a potential parthenocarpic level by a check of the abscission pattern of detached fruitlet on agar medium during secondary fruit drop. It is supposed that sugar metabolism related genes would be associated to fruit abscission “Decision” process and that β-galactosidase and β-xylosidase would be closely associated to fruit abscission “Performance” process in secondary fruit drop system. It is indicated that an endogenous ethylene is not related to a fruit abscission process and the process of Satsuma mandarin is probably unique.