Effects of Scion Cultivar and Rootstock on Flowering in ‘Setoka’ and ‘Shiranuhi’

Abstract

In this study, the effects of the scion cultivar and rootstock on reproductive growth were investigated with ‘Setoka’ and ‘Shiranuhi’ grafted on trifoliate orange (Poncirus trifoliata L. Raf.) or ‘Hiryu’ (Flying Dragon) for three or four years. In November, which is the period of floral induction in citrus, expression of one of the flowering-related genes, citrus FLOWERING LOCUS T (CiFT), was quantified in stems of trees with each combination of scion cultivar and rootstock. In the analysis without distinction of the combination, the mRNA level of CiFT was correlated with flower numbers in the following spring. In both ‘Setoka’ and ‘Shiranuhi’, the average CiFT mRNA level in each combination was markedly changed annually when the trees were grafted on ‘Hiryu’. Yields were about 3 kg・m^–3 every year in all combinations of the scion cultivar and rootstock, and there were no significant differences in each combination among years. Two-way ANOVA of the alternate bearing index in each tree showed that the annual change in the CiFT mRNA level was significant in trees grafted on ‘Hiryu’. These results suggest that using ‘Hiryu’ as a rootstock makes flowering unstable in ‘Setoka’ and ‘Shiranuhi’, although this instability has no impact on their yield.