Mode of Leaf Shedding from Avocado Cuttings and the Effect of its Delay on Rooting

Abstract

Leaf shedding (LS) of 3 avocado ( Persea americana Mill.) clones (‘Northrop 28/5’, ‘Fuchs 20’ and ‘Nahlat 7’) differing in rooting ability was studied. Two distinct processes, leaf blade senescence and formation of the abscission layer, were found to be associated with LS. The rate of these processes differs among the 3 clones, and their combination determines the speed of LS. Leaf senescence was simulated by measuring chlorophyll destruction over time in leaf discs incubated in the light. The speed of abscission layer formation was estimated by measuring the time required for petioles to shed from incubated internodes. The results obtained in these tests were in agreement with the behavior of LS from cuttings of the 3 clones under mist. Auxin and cytokinin alone, or in combination, as measured in the 2 test systems, affected these leaf blade senescence and abscission layer formations at different rates. Six cuttings of the clone ‘Fuchs 20’ were sprayed weekly with combinations of NAA and BA. The optimal combination (1.10 -4 m NAA + 5.10 -4 m BA) caused a significant delay in LS and improvement in rooting. Relatively simple tests of leaf senescence and petiole abscission are discussed as potential methods for predicting rooting ability of leafy cuttings.