No reproducible and efficient transformation system has been developed, despite many attempts made to obtain transformed plants in tea (Camellia sinensis). This is because no efficient and stable tissue culture system for tea has been developed yet. In order to develop such a system, it is essential to analyze the materials used for tissue culture as well as tissue culture conditions. The National Research Institute of Vegetable and Tea Science in Makurazaki maintains a collection of various tea clones (var. sinensis, var. assamica) from Japan, China, India, and other Asian countries. We tested 130 strains by cotyledon culture to identify strains with a high potential for somatic embryogenesis. Cotyledons in immature seeds derived from natural crosses were used as explants. Embryos were cut out, then both cotyledons derived from each seed were placed onto solid MS medium containing 3.0 mg/L BA, 3% sucrose, and 0.2% gellan gum for somatic embryo induction. The medium was adjusted to pH 5.8 prior to autoclaving. Cotyledons were cultured in the dark at 25°C. Thirteen strains formed somatic embryos directly on the surface of the cotyledons. The Chinese strain ‘Makura-Ck2’ showed the highest frequency of somatic embryo formation, with clusters consisting of large numbers of somatic embryos.

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The Xinjiang-Uygur Autonomous District (abbreviated as Xinjiang) is situated in the northwestern most part of China and is equivalent in latitude to the area extending from the southern part of Japan to southern Sakhalin. The continental, cool and dry climate of the Xinjiang district is in sharp contrast with the oceanic, warm and humid climate of the Far East including Japan. Although presently, rice is not an important staple food crop in Xinjiang, there are historical records of rice cultivation covering 1400 years or longer in the southern part of Xinjiang. In the present study, various morphological, physiological, agronomical, biochemical traits as well as grain quality and components of the Xinjiang rice cultivars, including 16 landraces and 13 improved ones, were investigated to characterize the Xinjiang rice cultivars compared with rice cultivars from other regions like Japan, China etc. Furthermore, genotypes of esterase isozymes were identified to analyze the genetic characteristics of the Xinjiang rice cultivars. The results revealed that the Xinjiang rice cultivars displayed specific features of extreme earliness, including longer panicles, fewer tillers, larger grains and very large flag leaves. And most of the landraces were highly susceptible to pre-harvest sprouting. Most interestingly, all the Xinjiang rice cultivars displayed esterase isozyme genotypes identical with those of the Japanese cultivars.

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To determine the characteristics of cultivated rice in ancient Japan and the origin of Japanese rice, polymorphism analysis using microsatellite markers was carried out on 73 landraces of Japanese rice which were considered to conserve genetic diversity. Four upland Chinese varieties and eight landraces from Asia were used as standards, which had been classified into Indica and Japonica based on morphological and physiological characteristics. Eight microsatellite markers (RM1, RM20A, RM20B, RM30, RM164, RM167, RM207 and RM241) were used. Japanese landraces were classified into 2 major groups, Indica and Japonica. The 8 landraces belonged to Indica while the others belonged to Japonica. Japonica was classified into 3 minor groups; upland rice group (J-A), combined group of upland- and paddy rice (J-B) and paddy rice group (J-C). Group (J-B) was further divided into two subgroups, upland (J-B₁) and paddy rice (J-B₂) which correspond to tropical and temperate Japonica respectively. As the results show, “Furuwase”, “Fukubouze” and “Sekitori” upland rice are closely related to paddy rice of the temperate Japonica group that may have been derived from paddy rice. The eight microsatellite markers used in this study were found to be effective indices for the classification and discrimination of the rice landraces cultivated in Japan.

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Tea anthracnose is one of the major diseases in tea cultivation in Japan. Since the leading cultivar ‘Yabukita’ is susceptible to the fungus, it is important to develop cultivars resistant to the disease. In the present study, 5 vegetative propagated lines as parents and F₁ lines from reciprocal diallel crosses were used as materials. Scores of 1 (no) to 5 (severe) were used to express the degree of disease infection. Diallel analysis was conducted using computer software “DIAL98” developed by Ukai (2002). Additive effect was highly significant, while the dominance effect was negligible. The value of broad and narrow sense heritability were very high, 0.947 and 0.943, respectively. There were no significant differences between the reciprocal crosses and between the replications. Epistasis was not recognized. The (Vr, Wr) graph indicated that ‘Sayamakaori’ harboured mostly dominant alleles, and ‘Yamatomidori’ mostly recessive alleles.

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Molecular marker-assisted selection (MAS) was conducted for recurrent backcross breeding with a cytoplasmic male sterility line to develop Koshihikari near-isogenic lines harboring the resistance genes, Stvbi and Pb1, to rice stripe virus and panicle blast respectively. The two resistance genes were linked at a distance of 5.2cM on chromosome 11 in a donor line St.No.1. Koshihikari enjoys a high repuration for its cooking quality, but lacks the two resistance genes. The recurrent backcross was conducted with a high level of accuracy by using a molecular marker ST10 linked to Stvbi within 0.0 cM and four molecular markers closely linked to Pb1 for the resistance to panicle blast, which can not be easily tested under field conditions. In particular, early fixation of the blast resistance was obtained by using a CAPS marker B4 for Pb1 which differentiated homozygotes. The authors were able to breed a Koshihikari near-isogenic line, “Koshihikari Aichi SBL” that was resistant to both rice stripe virus and panicle blast and displayed a set of characters similar to them of Koshihikari. Efficiency of MAS was demonstrated in terms of cost and time required for the breeding.

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