The cultivar 'Yubeni' was discovered as a mutant of Meiwa kumquat (Fortunella crassifolia Swingle) in Kushima city, Miyazaki. According to the results of flow cytometry analysis and morphological investigation of several tissues and organs, 'Yubeni' was supposed to be a ploidy periclinal chimera with diploid (2n = 2X = 18) in the outermost layer (histogenic layer L-I) and tetraploid (2n = 4X = 36) inner layer (histogenic layer L-II and L-III) in the shoot apical meristem. Compared with the diploid line, it showed similar morphology to the tetraploid line such as larger leaves, flowers and pollen grains. The weight and size of the fruit were both greater than those of the diploid line. Furthermore, this cultivar has desirable traits for kumquat such as smaller number of developed seed and thicker pericarp.
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.
We investigated the cause of poor fruit set in Japanese plum 'Kiyo' (Prunus salicina Lindl.). Early fruit drop of 'Kiyo' was heavier than that of 'Taiyo'. Fruit drop of 'Taiyo' and 'Kiyo' in 56 days after full bloom was 80.4 and 95.5%, respectively. There was little difference between 'Kiyo' and 'Taiyo' in the incidence of imperfect flower and 'Holly wood' pollen tube elongation on the style. However, 'Kiyo' demonstrated pollen grains that were nonuniform in size and shape. 'Taiyo' showed 91.6% stainability and 47.6% pollen germination rate, respectively, whereas those of 'Kiyo' were 70.4 and 3.2%, respectively. Furtheremore, developed seeds obtained from 'Kiyo' varied in weight from 0.02 to 0.59 g, and the percentage of developed seed of 'Kiyo' (71.3%) was less than that from 'Taiyo' (93.0%). Chromosome observation of immature leaflets demonstrated that 'Kiyo' was triploid with 24 chromosomes.
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