The Use Of Dna Marker-assisted Selection Polymerization Bacterial Blight Resistance Gene Modified Hybrid Rice

Bacterial blight, a bacterial disease of rice worldwide, affects the yield and quality of rice seriously. It is considered that breeding resistant cultivars is the most effective and economical strategy for controlling the disease. Marker assisted breeding, which is a grown-up and efficient technology, has been appling for the improvement of genetic of various of crops and traits. The objectives of this study were to improve and elongate the bacterial blight (BB) resistance of Minghui63, a elite restorer line of hybrid rice, by pyramiding two BB resistance genes:Xa7 and Xa21, using MAS in the process of the crossing-selfcrossing; and to evaluate the effects of such aggregation on the resistance and agronomic performance of the restorer lines and their hybrids. The main results are as follows:1. Making sure that Xal and Xa21 were two genes that were highly resistant to a broad-spectrum of the pathogen races according to the comparision of the resistance between Minghui63(Xa7) and Minghui63(Za21).2. Two Xoo strains were used to judge of the resistance performance of segregant population of Minghui63(Xa7) crossing Minghui63(Xa27/Bt), and to conclude that pyramiding of the bacterial blight resistant genes increased remarkably the BB resistance of rice by comparing the resistance between individual gene and their aggregation.3. The F3 ratio of the lesion length with two isolates inoculation in the population, composed of 166 lines from individuals without Xa21 gene in F2, approximated to the expected 1:2:1. It was said that Xa7 gene exhibited incomplete dominance.4. A local linkage map of the Xal genomic region on chromosome 6 was constructed based on 166 individuals of the F2 population excluding Xa21 from Minghui 63(Xa7)/Minghui63(Xa21/Bt) cross, from which a MAS system was established. A dominant PCR marker linked closely to Xal and two PCR markers flanked both sides of the Xal locus were used for the presence of the Xal gene.5. Thirty homozygous lines for Xal were obtained from the sections (part of F4 population) in which Xa21 showed homozygous using the molecular markers tightlylinked to Xa7. Further analysis showed that four homozygous lines for Bt were selected from the above 30 homozygous lines conferring bacterial blight resistance.6. Compared with the original restorer lines or hybrids, pyramiding shows greatly potential of resistance, and the BB resistance of Minghui63(Xa7/Xa21) or Shanyou63(Xa7/Ya27) were improved remarkably according to the results of inoculation with a total 10 BB strains; Simultaneously, the result displayed that the level of resistance of hybrids with genes pyramided was inclined to that of corresponding restorer lines.7. In the field without artificial inoculation, the contribution of resistance gene pyramiding to the yield and its components is not significant. Whereas under bacterial blight inoculation, Shanyou63(Xa7/Xa21) shows higher grains per panicle and grain weight than Shanyou63, as Minghui63(Xa7/Xa21) against its control class.