Endogenous hormonal status in citrus flowers and fruitlets: relationship with postbloom fruit drop

Abstract

Gibberellin accumulation in citrus ovaries has been proposed as an activating signal for fruit set in citrus. Our data under tropical conditions associate pollination-dependent fruiting of ‘Valencia’ orange with high ratios of growth promoters to inhibitors ( G/ I) in floral organs. Lower values of G/ I were found in the parthenocarpic ‘Marsh Seedless’ grapefruit and ‘Ortanique’ tangor, the latter a self-incompatible, seedless hybrid. In all the varieties, two kind of fruitlets were identified at the early stages of fruit development: (1) normal developing fruits, with high peel chlorophyll content, firmly attached to the stem (2) non-growing fruits with lower peel chlorophyll content, prone to early abscission. G/ I values of firmly attached fruitlets were higher than those of non-growing, early abscising fruits during the fruit set period. In addition, higher absicisic (ABA) and ABA-like inhibitor accumulation as well as lower growth promoting substances were found in proximal abscission zones of abscising fruits. Furthermore, higher contents of jasmonic acid-like compounds in floral organs and in developing fruits were found in the cultivars with stronger early fruit abscission, which suggest that ABA-like and jasmonic acid-like substances could play a shared role in fruit set and early fruit abscission.