Improving Blast Resistance Of Indica Rice Lines Using Pigm Gene And Molecular Marker-assisted Selection

Rice blast, caused by the fungal pathogen of Magnaporthe oryzae, is one of the most devastating diseases of rice throughout the world, which causes great grain loss each year. Breeding resistant varieties is the most economical, effective and environment-friendly method to control this disease. Conventional breeding methods are low efficiency and easily affected by environments in contrast to molecular breeding methods, especially for quality-quantity traits such as rice blast resistance. The molecular breeding technology, including transgenic technology and molecular marker-assisted selection (MAS) technology, is being employed for directionally improving some specific characters by pyramiding multiple genes. MAS technology, based on genotypic identification and selection by gene-tightly-linked molecular markers, is more accurate and efficient, comparing with conventional breeding methods.A dominant broad-spectrum blast resistance gene, Pigm, which was identified from the local rice cultivar Gumei4of Sichuan province and has been finely mapped within a120kb interval at the Pi2/9locus of chromosome six. Other broad-spectrum blast resistance genes such as Pi-z, Pi-2, Pi-9, Piz-t, Pi-22(t), Pi-26(t), Pi-40(t) and Pi-50(t) were also localized at the same locus. In this study, we aim to improve the blast resistance of24indica rice lines based on the Pigm gene fine mapping informations, by means of developing effective, stable and polymorphic molecular markers and marker-assisted selection breeding. The main results are as follows:1. Resistance spectra of24receptor rice lines, Gumei4, susceptible control CO39and resistant control75-1-127were investigated through indoor inoculation assay. The resistance rates of24receptor lines to28M.oryzae isolates were in the range of25.9%～57.1%, which implied that all of them need to improve the blast resistance. Resistance rates of Gumei4, CO39and75-1-127are96.4%,0.0%and85.7%, respectively. Gumei4is only susceptible to isolate E2007046A2from Hubei province. And75-1-127, which harbors another broad-spectrum blast resistance gene Pi9, is susceptible to4M.oryzae isolates, ROR1from Korea, KOH from Japan, Xiang2007A-7and95097AZC13from China. 2. Two codorminant polymorphic InDels markers, S29742and T9E4, were screened from20Pigm-closely-linked markers including14CAPS markers,3SSR markers and3InDels markers. S29742and T9E4showed obvious and stable polymorphism, and polymorphic rates are20.8%and100.0%respectively.3. Marker-assisted selection efficiency of T9E4was proved above95%through corresponding genotypic and phenotypic datas of randomly sampled individuals from3BC1F1populations of T98B×Gumei4, R640xGumei4and XWX11×Gumei4, which showed that T9E4is an effective molecular marker for MAS breeding.4. BC3F1populations of12combinations between R996,1701, FYB, XWX11, XWX13, Ⅱ32B, E32, T98B, R198, R527, R640,25H003and Gumei4were developed, and BC2F1populations from12crosses between316B, Jin23B, LH422, R207, R228, R288, TLX103, XF187, R389, MH63, MH86, R747and Gumei4were obtained. These results paved a solid way for breeding stable blast resistant rice varieties.