Histological and cytological study of ‘Mukaku Kishu'-derived female sterility in pummelo.

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The results of this study in which seed formations and chromosome constructions were investigated using 'Hirakishu', 'Mukaku Kishu', 'Southern Yellow', Bul-7 pummelo and BSYs seedlings from Bu1-7 crossed by 'Southern Yellow' were summarized below.1. The seedlessness of 'Mukaku Kishu' and its progenies can not attributed to abnormal embryo sacs and unfertilized ovules.2. Small seeds with filling in center and undeveloped seed coat (call A type seed tentatively) were specifically observed in all seedless cultivars and BSY seedlings and the seedlessness should be attributed to A type seeds.3. The embryos in almost A type seeds only developed to the zygote or proembryo while the endospermes was not aborted. The development of embryo in some seedless cultivars varied by years and the embryos developed to hart-shape embryos or small cotyledons suggesting that arrested embryo development would not be resulted from genotypes of embryos.4. The embryos of seedless cultivar 'Southern Yellow' developed to hart-shape embryos or small cotyledons under high temperature condition and A type seeds were formed in seedy cultivar 'Hirakishu' by GA_3 treatments. The results suggested that plant growth regurators and temperature and/or some stresses would influence to the gene expressions concerned with A type seed formation.5. DNA marker linked to Fs gene which dominate seedlessness was detected in seedless 'Mukaku Kishu', 'Southern Yellow' and BSY18, and also detected in seedy BSY3, BSY15 and BSY29. This indicated that BSY3, BSY15 and BSY29 have Is gene which dominantly suppress the Fs gene expression.6. The results from chromosome constitution based on PI(+) band patterns and GISH signals suggested that Fs gene would locate on D1(Green) type chromosome or E type chromosome except E1 and E5 among 'Mukaku Kishu' chromosomes, and that Is gene would locate on C1(Red/Red) type, D1(Red) type or E type chromosome except E1 type among Bu1-7 pummelo chromosomes.