Study On Improving Of Bacterial Leaf Streak In Rice By Marker-assisted Selection

Molecular marker-assisted selection (MAS) has been successfully used in improving qualitive traits of crops, and gradurally used in quantitative traits. In this study, we researched the genetic improvement of bacterial leaf streak disease in rice by means of molecular marker-assisted selection. 1) On the basis of screening SSR markers closely linked to resistant QTL, we introgressed the QTL qBlsr-11-1(from rice variety Dular)for the bacterial leaf streak resistance into new genetic backgrounds of rice by means of backcross method combined with MAS or by bulk method combined with MAS,and evaluated the efficiency of MAS. 2) We analyzied the feasibility to pyramid QTLs for improving bacterial leaf streak resistance by the use of marker-assisted selection, and explored some issues concerning breeding of bacterial leaf streak resistance. The main results are as follows:1. On the basis of located QTL qBlsr5a, qBlsr3d, qBlsr5b and qBlsr-11-1 for bacterial leaf streak resistance and the rice genome information published before, we obtained two SSR markers RM153 and RM17769 closely linked to the qBlsr5a, two SSR markers RM523 and RM231 closely linked to the qBlsr3d, and two SSR markers RM440 and RM173 closely linked to the qBlsr5b. These six SSR markers perform polymorphisms between the donor parents Dular and H359R. We also got three SSR markers RM120, RM26267and RM552 linked to the qBlsr-11-1. The markers RM120 and RM26267 exist polymorphisms between two donor parents Dular and H359R and the recipient parentⅡ-32B; the markers RM26267 and RM552 exist polymorphisms between the donor parental Dular and the recipient parent Minghui 2155. Their distances from the markers to the target QTLs estimated at 0.4-4.9cM, which will meet the basic requirements for MAS.2. In the prosess of introgressing qBlsr-11-1 into II-32B by combining backcross method with MAS, both of selection methods are efficiency by use either duoble side markers RM120 and RM26267or one side marker RM120 closely linked the qBlsr-11-1 to select the resistantly heterozygous marker genotypes; but selection is not efficiency by use the marker RM26267 only.3. In the F3:4 population derived from Dular×Minghui 2155, the difference was not significant in average lesion lengths of homozygous resistant genotypes (BB, CC and BBCC) selected by use both double side markers RM552 and RM26267 or one side marker. But the average lesion lengths were significantly difference between the homozygous resistant genotypes (BBCC,CC and BB) and infectious parent Minghui 2155, the heterozygous marker genotypes (BbCc, Bb and Cc), and the susceptibly homozygous marker genotypes (cc, bb and bbcc). The average lesion lengths were significantly difference between heterozygous marker genotype (BbCc and Cc) and the susceptibly homozygous marker genotypes (cc, bb and bbcc) and the infectious parent Minghui 2155 too. The difference was not significant in average lesion lengths between heterozygous marker genotype selected by RM26267 marker and the infectious parent Minghui 2155.4. We could obtain resistant plants with 4 resistant QTLs, 3 resistant QTLs and 2 resistant QTLs respectively, by means of the methods both through identifing disease resistance first and then select the marker genotype or direct select the marker genotype, but the efficiency is different. We obtained homozygous marker genotypes 3 plants and 4 plants which were with 4 resistant QTLs and 3 resistant QTLs respectively, in the 30 extremely resistant plants. And by the method of direct marker genotypes selection,we obtained homozygous marker genotype 1 plants and 7 plants with 4 resistant QTLs and 3 resistant QTLs respectively, in the population comprises 300 plants. Above results indicated that,it would be an ideal method to identify disease resistance first and then select the marker genotype, in improving the quantitative traits such as bacterial leaf streak resistance, as this could select more ideal plants and greatly reduce work and costs.5. The plants(lines)containing more than 2 resisitant QTLs were significantly higher than susceptible parent H359 in resistant level. The difference was not significant in average lesion lengths among the plants carrying 4 resistant QTL (L1), 3 resistant QTL (L2 and L3), 2 resistant QTL (L6) and their resistant donor parents Acc8558 and Dular. The results indicating that, we can breed a new rice variety similar with their resistant donor parents in resistant level, as long as 2 ~ 4 resistant QTL been pyramided.