GREENHOUSE SCREENING OF CITRUS ROOTSTOCKS FOR TOLERANCE TO BICARBONATE-INDUCED IRON CHLOROSIS

Eighteen citrus rootstock seedling lines were tested for their toleran ce to Fe chlorosis using sand culture. Potassium carbonate was used to induce Fe-deficiency chlorosis. Chlorosis was quantified by 1) visual ratings, 2) SPAD-502 chlorophyll meter readings, 3) leaf chlorophyll concentration, 4) leaf active Fe, and 5) leaf total Fe. The first four criteria were well correlated among each other but not with leaf tota l Fe. Although any of the first four measurements could be used to qua ntify chlorosis, visual ratings and SPAD-502 readings were more conven ient. The rootstocks that have been reported to be tolerant or very su sceptible to Fe chlorosis in calcareous soils were rated similarly for tolerance to bicarbonate-induced Fe chlorosis. Nontrifoliate types su ch as Texas sour orange (C. aurantium L.), Cleopatra mandarin (C. reti culata Blanco), Vangasay lemon (C. limon Burm.), and Ridge pineapple x Milam 1578-201 (C. sinensis L. Osbeck x C. jambhiri) were tolerant to moderately tolerant. Although most of the trifoliate hybrids tested w ere moderately susceptible to very susceptible, Smooth Seville x Argen tine trifoliate {[C. grandis (L.) Osbeck x C. aurantium] x Poncirus tr ifoliata (L.) Raf.) and F-81-12 citrange (C. sinensis x P. trifoliata) exhibited relatively high tolerance to lime-induced Fe chlorosis.