Fruit-load-induced starch accumulation causes leaf chlorosis in 'off' ‘Nadorcott’ mandarin trees

Leaf chlorosis often develops in low-fruiting (“off”) trees of healthy, severely alternate bearing ‘Nadorcott’ mandarin (Citrus reticulata Blanco) trees in commercial orchards in South Africa, whereas leaves of heavily-fruiting (“on”) trees maintain a healthy green colour. This study investigated the role of fruit load and leaf carbohydrate content on the development of leaf chlorosis in “off” trees under a broad spectrum of source/sink relationships. Leaf chlorosis in “off” trees was mediated by low sink activity, and leaf total chlorophyll content strongly correlated with leaf starch content [r2 = (−)0.74 (P