Molecular Mapping Of Bacterial Blight Resistance Gene Xa30(t) And Pyramiding Genes Resistant To Both Disease And Insect Pest In Rice

Rice is an important food crop in the world and threatened seriously by diseases and insect pests.Bacterial blight and brown planthopper endangered rice product seriously and caused huge loss of production of rice,which could even cause complete loss of rice yield in the worst situation.Through practice, it was confirmed that to breed varieties harboring resistance gene was the most effective and economical way of controlling diseases and insect pests, which was accordance with demand of sustainable development of agriculture too.The rice bacterial blight(BB)was caused by Xanthomonas oryzae pv. Oryzae.The over 30 rice bacterial blight resistance genes have been identified so far.But few genes were applied in the breeding practice because most resistance genes were either of narrow-spectrum resistance or recessive.At present,Xa3 and Xa4 which were ever used in the breeding broadly have lost resistance to BB.So scientists in and outside my country dedicate to find out new resistance genes.Wild rice harbored plenty of excellent genes resistant to disease and sustaining adversity due to grow under very awful environment for long time so it became important genebank in which promising genes could be found out.Wang chun-liang et al found out and identified a new gerplasm which showed high and broad-spectrum resistance to BB,called as Y238,from wild rice in Guangxi.It was proved that resistance of Y238 is controlled by a new dominant gene through genetic analysis.Wang chun-lian et al transferred the resistance gene into rice varieties Jin-gang 30 and IR24 respectively and bred near-isogenic line CBB30 successfully using cross and back-cross method.This new resistance gene was nominated as Xa30(t) temporarily.In order to research molecular mechanism of resistance deeply and make it application in breeding effectively,it appear important to map and clone Xa30(t).In 2006,Jin xu-wei et al used F₂ population of back-cross progeny of Jin-gang 30/Y238 as mapping population and initially mapped Xa30(t)on the long arm of chromosome 11 by molecular marker method.In this study,a line of BC₆F₁ generation of IR24/Y238 was used as mapping population and mapping of Xa30(t)would be carried out by molecular marker method so that location of Xa30(t)on the rice chromosome would be determined further.Rice suffered threat from not only disease but also insect pest,especially brown planthopper.Brown planthopper distributed widely and was very dangerous to rice.Brown planthopper often broke out in most area where rice was grown including China.For a long time,breeder and geneticist worked hard to find out new genes among different germplasm and introduced these into cultivar to breed new varieties resistant to pest.But development of breeding new varieties resistant to brown planthopper was slow due to difficulty of identifying resistance of rice and long duration of selecting and breeding varieties.Moreover,major bio-population of brown planthopper in China has changed to type 2 from type 1 gradually,leading to resistance loss of varieties expressing resistance to brown planthopper initially.In order to raise efficiency of selection and speed up development of breeding,Xa23 expressing high resistance to BB and Bph18(t)resistant to bio-type of brown planthopper in China were pyramided into restore line of hybrid rice 9311 and Ce253 using marker assistance selection so that good-quality rice accession expressing high resistance to BB and brown planthopper could be bred in this study.The main results were summarized as follows:1,BC₆F₂ population of IR24/Y238 was constructed and identified with P6.Segregation ratio of resistance/susceptible plants in population was equal approximately to 3:1.Result of genetic analysis showed that resistance of plant was controlled by a dominant gene.So this population was determined as mapping population of Xa30(t).SSR,EST,STS and special PCR markers distributed evenly on the 12 pairs of chromosomes of rice were screened between resistance-pool and susceptible-pool of mapping population using BSA method.In the end,6 molecular markers,03STS,Lj74/Y02W1R, A83b4,Lj112,Lj121and RM206,were found to be linked with Xa30(t). Xa30(t)was located within an interval about 412 kb flanked by 2 markers 03STS and Lj112 on the long arm of chromosome 11 covering 2 complete BAC clone AC137588,AC104847 and part sequence of 2 BAC clone AC 137589 and AC 136148.Marker A83b4 was co-segregate with Xa30(t).2,Based on sequence information of marker 7312.T4A co-segregating with Bph18(t),3 PCR markers,KC5,KC1F/7312.T4A and 7312.T4AF/KC2R, linked closely to Bph18(t)were developed using bio-information analysis technology.As recurrent parent,restore line of hybrid rice 9311 and Ce253 crossed and back-crossed respectively for some generations with Indica 4064 harboring Bph18(t).At last,both Xa23 and Bph18(t)were pyramided into recurrent parent using maker assistance selection in combination with identification with P6 each generation and BC₃F₁ generation with genetic background of 9311 and Ce253 harboring both Xa23 and Bph18(t)was obtained.