Identification And Mapping Of Broad-spectrum Blast Resistance Genes In Rice Cultivars Jefferson And Gumei2

Rice (Oryza sativa) is one of the most important food crops in the world. Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is one of the most devastating diseases in rice. It has been proved that breeding the disease-resistant varieties is considered as the most effective and economical strategy to solve this problem. Identification and utilization of the resistance genes are the key for disease-resistant breeding. More resistance genes identification will help us further understand the molecular mechanism of the resistance in rice. Meanwhile, it has huge and practical value for the disease-resistant breeding.Ten rice lines were collected from different countries and regions.Their resistant spectra were analyzed and resistance genes of 2 candidate lines were mapped by allelic analysis and utilizaiton of molecular markers.1. Ten resistant rice lines from 4 countries were selected for this research.32 isolates collected from 7 different regions were used for evaluating the performance of the resistant lines. Amber, Gumei2, Jefferson, Mowanggu, Xiangzi3150 and Tianjin wild rice were selected as candidate lines for the further study because of their broader spectra.2. F2 populations derived from the cross of three candidate lines (Amber, Jefferson, Gumei2) with 75-1-127 respectively, which is the donor of Pi9, were inoculated by the isolate 318-2. The results showed that resistance genes in Gumei2, Jefferson, which involved in the resistance to isolate 318-2, were allelic to Pi9 and resistance gene in Amber was not.3. F2 mapping populations derived from the cross of Gumei2, Jefferson with CO39 (susceptible parental line) were also inoculated by the isolate 318-2.102 plants and 127 plants were anayzed respectively.The segregation ratio between resistant and susceptible plants is 3:1 in the two populations. It suggested that the genetic mechanism of resistance to isolate 318-2 in the two candidate lines was controlled by single dominant blast resistance gene. The resistance of Jefferson was co-segregated with molecular markers RM7311,RM7178,RM6836,AP4791,AP5659-5,AP5695-1,AP5413 and it was co-segregated with AP4791,AP5930,AP5659-5,AP4007 in Gumei2.4. Homologs of Pi9 gene were amplified by RT-PCR in Jefferson and Gumei2. The homologous sequences showed high identity with three cloned resistance genes (Pi2, Pi9 and Piz-t). It also showed that NBS domain was more conservative than LRR domain. There were 46 amino acids difference between Gumei2's seqences and Pi9.6 of them were in NBS domain and 31 were in LRR domain.Between Jefferson's and Pi9, there were 18 amino acids difference and they were all in LRR domain.