A comparison of IAA and ABA levels in leaves and roots of two citrus cultivars with different degrees of alternate bearing

The IAA and ABA contents in the leaves and roots in alternate-bearing citrus were compared in defruited and nondefruited (control) trees. Two satsuma mandarin cultivars, 'Aoshima', a highly alternate bearer and 'Miyagawa', a slightly alternate bearer, were used. Defruiting increased the IAA content in roots, but not in leaves, and increased the ABA contents in leaves of 'Aoshima', but not in roots. The IAA content in the roots of the control trees was lower from September to November ('Aoshima') and October to November ('Miyagawa'), including the floral initiation period (from early-September to early-December). The ABA content in the leaves of the defruited trees of 'Aoshima' was higher than that in the control trees from September to December excluding October. There was no difference in the ABA content in the leaves of 'Miyagawa' between the defruited and control trees. From the comparison of the ratio of sprouting nodes and the type of shoots;generative, mixed or vegetative' between cultivars, it is concluded that the high degree of alternate bearing in 'Aoshima' is due to the low ratio of sprouting nodes, and high ratio of vegetative shoots. The above results suggest that the ABA content in leaves may be related to sprouting and floral initiation, which determines the degree of alternate bearing.