Genetic analysis for the rice stripe resistance of Japanese upland rice [Oryza sativa] varieties and wild rice species

Rice stripe disease is one of the most important viral diseases affecting the rice (Oryza sativa L.) production in the temperate regions of East Asia, especially in China, Korea and Japan. The small brown planthopper, Laodelphax striatellus Fallen, transmits the rice stripe virus (RSV), a causal agent of the disease. This disease spread in the 1960s in Japan, and an estimated over 600,000 hectares of paddy field was damaged. Screening of RSV-resistant rice varieties was initiated in the early 1960's, and some Indica type rice varieties and Japanese upland rice varieties showed high resistance. An incompletely dominant gene, Stvb-i, controls RSV resistance in Indica type varieties. Resistance in Japanese upland rice varieties was controlled by two complementary genes, Stva and Stvb. Breeding program of RSV-resistant rice was started using Stvb-i gene in Pakistan variety, Modan. Many resistant varieties have been cultivated widely in Japan and these resistant varieties have shown a stable resistance against RSV during the last 40 years. Consequently, almost all the resistant paddy rice varieties cultivated in Japan were expected to harbor this gene. Varieties with a single resistance gene may lose their resistance once the strain of virus changes virulence. For that reason, the other resistant genes should be introduced to the breeding programs of RSV-resistant rice. Some resistant paddy lines were introduced the resistance genes, Stva and Stvb, from Japanese upland rice varieties. However, these lines were also introduced inferior characteristics of grains and eating qualities from the donor parents. In this study, the QTL analysis for rice stripe resistance in the Japanese upland rice Kanto72 (URK72) was performed. Detected QTLs were evaluated and characterized their resistance to RSV using near-isogenic lines (NILs). DNA marker-assisted selection system for rice stripe resistance was examined. Furthermore, novel resistant genes of wild species Oryza rufipogon and O. officinalis were studied.