Demonstration and induction of apomixis in the genus Diospyros and its utilization for polyploidy breeding

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1. To demonstrate the occurrence of apomixis, intra- and interspecific (D.kaki) pollinations were conducted using Diospyros lotus and D. virginiana as seed parents. One strain of D. lotus showed fruit setting and seed formation by not only intra- but interspecific pollination. In the banding pattern of DNA anlyses (RAPD and AFLP) of the seedlings derived from these seeds, those derived from interspesific pollination showed the same banding pattern as seed parent, but did not show that as pollen parent, suggesting apomictic seed formation. On the other hand, the seedlings from inraspecific pollination mostly showed the same banding pattern as that specific to pollen parent but some showed apomictic seed formation. D. virginiana did not manifest apomixis.2. Morphological observation of D. lotus showed that most embryogensis normally proceeded but in some cases meiosis failed at a dyad stage, one of the resultant dyads degenerated while the other proceeded normal embryogenesis. This suggests that the apomixis in this species is diplospory type as seen in Compositae family.3. Pollination with γ-ray irradiated pollen of D. kaki did not induce apomictic seed formation in this species. To search for the possibility of natural occurrence of apomixis in D. kaki, ploidy determination of many seedlings derived from 10 cultivars was conducted by using a ploidy analyzer. High frequency of polyploid variation, such as nonaploid, dodecaploid and their aneuploids as well as hexaploid, was specifically found in cv. Fujiwaragosho. It was needed to reveal whether or not they derived from apomixis. However, such polyploids could be used as novel germplasms for breeding of D. kaki in the future.