Exploitation of latent cool-injury resistance genes among rice cultivars grown in warm region.

本研究旨在开发水稻孕穗期耐冷新基因(以下简称耐冷基因)。为寻找新的耐性基因，开展了耐冷性基因分析和新的耐冷性测定系的选育。对来自EG3(感病品系)和EG5(Aikoku：耐性品系)杂交的F3和F4品系的分离分析表明，EG5携带两个互补的显性耐性基因。EG3/Aikoku3(耐性品种)与EG3/CTH5(从Hayakogane引入耐性)杂交的结果表明，两个耐性亲本都携带至少两个耐性基因。与EG3/Rikuu20和EG3/Shinriki杂交组合获得的F3株系相比，前者的F3植株大多耐受，后者的F3植株大多感病。这表明Aikoku来源的耐性基因是显性的，而Shinriki来源的耐性基因是隐性的。同时，利用高耐性品种Silewah耐性基因的CTH5和Kirara397近等基因系进行了耐性基因功能的研究。在抽穗前1个月将植株置于冷水浴中，观察冷水对花药长度、花粉育性和种子育性的影响。不考虑耐性的基因型，所有品系的花药长度都分别减少了。此外，冷处理植株的花药变白变薄，而对照植株的花药变黄变厚。在相对花药长度方面，携带抗病基因的品系比不含抗病基因的品系表现出较小的降幅。在花粉育性方面，前者表现出较高的育性，后者表现出较高的育性。由此可见，耐性基因的作用不仅表现在花粉育性上，还表现在雄性生殖器官的生长发育上。

Exploitation of new genes for cold tolerance at booting stage of rice (Hereafter these genes are called tolerance genes for simplicity) was intended. To identify new tolerance genes, gene analyses for cold tolerance and development of new tester lines for cold tolerance were carried. Segregation analysis using F3 and F4 lines derived from the cross between EG3 (susceptible line) and EG5 (Aikoku : tolerant line) revealed that EG5 carried two complementary dominant genes for tolerance. Results from crosses of EG3/Aikoku3 (tolerant variety) and EG3/CTH5 (introduced tolerance from Hayakogane) suggested that both tolerant parents carried at least two tolerance genes. Comparing F3 lines derived from the cross combinations of EG3/Rikuu20 and EG3/Shinriki, most of the F3 plants were tolerant in the former combination while most of them were susceptible in the latter combination. This indicated that tolerance gene of Aikoku origin was dominant and that of Shinriki origin was recessive. Also, function of tolerance gene was investigated using CTH5 and near isogenic lines of Kirara397 for tolerence gene of Silewah (highly tolerant variety). Plants were put into the cold bath one month before the heading time (cold treatment) and effect of cold water on anther length, pollen fertility and seed fertility were observed. Irrespective of genotype for tolerance, all lines were severally reduced in anther length. Furthermore, anthers of plants grown under cold treatment become white and thin, while those of control plants were yellow and thick. For the relative anther length, lines with tolerance gene showed less reduction in it than the ones without tolerance gene. In pollen fertility, the former lines showed higher fertility than the later. Thus, it was suggested that effect of tolerance gene was expressed not only in pollen fertility but also in the growth of male reproductive organs.