Abstract
To identify the cause of poor fruit set in the triploid Japanese plum ‘Kiyo’ (Prunus salicina Lindl.), we performed morphological observation of the inside of ovules using histological techniques. Early fruit drop of ‘Kiyo’ occurred at a higher rate than that of ‘Taiyo’. The fruit drop rates of ‘Taiyo’ and ‘Kiyo’ at 42 days after hand pollination (DAHP) were 77.8 and 88.0%, respectively. Even during the flowering time, the embryo sac of 60% or more of ‘Kiyo’ remained undifferentiated. Regarding the plums with embryo sacs other than those undifferentiated, while many ‘Kiyo’ managed to develop in the same manner as ‘Taiyo’, we observed a higher rate of ‘Kiyo’ embryo sacs with developmental delay and/or degeneration compared with ‘Taiyo’. With regard to the development of the embryo and endosperm at 14 DAHP, we observed a higher rate of developmental delay as well as problems such as embryo sacs without a zygote and/or endosperm nucleus in ‘Kiyo’. In the observation at 35 DAHP, the rate of ovules with both a proembryo and endosperm nucleus was 91.7% in ‘Taiyo’, whereas it was 75.0% in ‘Kiyo’. Moreover, while most of the ovules of dropping fruits in ‘Taiyo’ were merely undifferentiated, those of ‘Kiyo’ also had the problems of embryo sacs with developmental delay and/or degeneration as well as a non-divided zygote and/or endosperm nucleus.
