| Rice is one of the most important cereal crops. Bacterial blight (BB) disease, caused by gramnegative bacteria Xanthomonasoryzae pv. Oryzae (Xoo), is one of the most serious diseases in rice. The pathogen usually invades plants by aquaporin or wound, producing a white lesion along the veins, and destroys the photosynthesis system of the leaves, resulting in poor grain yield and quality. Now, culitivating new varieties resistance to the pathogen is one of the most efficient ways to prevent bacterial blight. In recent years, great progress has been made in the research on rice bacterial blight resistance genes, and some of them have been identified and cloned from a series of resistant varieties using map-based cloning strategy. About 30 BB resistance genes have been identified recently and among them, Xa2, Xal, xa26, xa27, xa5 and xa13 have been isolated and cloned. Wild rice is found to naturally resistance to rice bacterial blight disease. Thus, it is very significant to discover new resistance genes from wild rice for the cultivation and application of the new BB resistance varieties, and it is also one of the hot researches in this field.On the basis of our previous work, the bacterial blight resistance trait from Oryza meyeriana, a wild rice species, was introduced into an elite japonica rice cultivar (Dalixiang) using asymmetric somatic hybridization method. One hundred and thirty-two independent lines were obtained by this technique. So far, four hybrid lines exhibiting high resistance to bacterial blight disease have been identified by self-crossing and identification. The rice Y73, one of the four lines, was used as the research material in this study.Resistance spectrum of Y73 was analyzed by field lesion scoring after inoculation of a range of strains of the pathogen. Genetic analysis of resistance trait was performed using F2 segregation population obtained by the cross between Y73 and IR24. High resistance population was selected from F2 for the primary mapping of resistance gene. Quantitative trait loci (QTL) associated with bacterial blight resistance was detected by using recombined inbred line as population, which was derived from the cross between Y73 and IR24 by single-seed descent methods. Single chromosome segment substitution line (SCSSL) was constructed by the cross between Y73 and the recurrent parent, cultivar IR24 to dissect QTL into single gene. The results are summarized as follow:1. Compared to Dalixiang and IR24, Y73 exhibited high resistance to the disease, and the resistance spectrum of Y73 was different from the identified genes. Meanwhile, F1 population derived from the cross between Y73 and IR24 was susceptible to Xoo. Phenotype segregation ratio of F2 was neither 1:3 nor 3:1, and did not agree with single gene controlling mode.2. Primary mapping was conducted using polymorphic markers and 50 extremely high resistance plants selected from F2 population containing 7125 plants. Three Linking intervals were located on chromosome 1, chromosome 3 and chromosome 5 respectively. While mapping population was amplified in these regions, the linking effect almost disappeared. Testifying with susceptive population in each region proved that the genotype of the three regions biased to IR24.3.308 RILs was developed for QTL mapping, and 3 QTLs (qR1, qR3 and qR5) were mapped in 3 chromosome intervals:chromosome 1 between R01D124 and RM1361 accounted for 29%of total phenotypic variation, chromosome 3 between R03D143 and R03D159 accounted for 17%of total phenotypic variation and chromosome 5 between RM7081 and RM233B accounted for 37%of total phenotypic variation.4. SCSSLs were constructed to dissect the three QTLs using the linking marker in QTL and back-cross population with high-resistant lines to IR24. At present, plants with single QTL on chromosome 1 and IR24 genetic background have been obtained, and dissecting of QTLs on chromosome 1 and 5 is underway.
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