Application Of Marker-assisted Selection To The Genetic Improvement Of Disease Resistance In Rice

To promote the application of the technology of marker-assisted selection to rice breeding, some issues concerning the genetic improvement of disease resistance in rice using molecular markers were studied: 1) on the basis of screening molecular markers closely linked to disease resistant genes, the disease resistant genes were introgressed into elite parental varieties of hybrid rice, and the efficiency of marker-assisted selection was evaluated; 2) the feasibility of using the method of marker-assisted backcross to breed new disease resistant varieties during the process of pedigree breeding was investigated; and 3) previously mapped QTLs conferring the resistance to bacterial leaf streak were verified using isogenic lines. Main results are as follows:1. Using the published information of rice genome, a SSR marker (MRG4766) , which was closely linked to the rice blast-resistant gene Pi-I with a distance of 1.3 cM was obtained; and three SSR markers, SRM22, SRM24 and SRM91, which were closely linked to the rice blast-resistant gene Pi-2 (Pi-9) with distances of 0.73, 0.08 and 1.09 cM, respectively, were obtained.2. The correctness rate of selection for Pi-1 using SSR marker RM224 was over 90%, while that using MRG4766 was as high as 98%. The correctness rate could reach 100% when RM224 and MRG4766 were used simultaneously. The correctness rate of selection for Pi-2 was from 97.9% to 100% when using SSR marker RM24; the correctness rate of selection for Pi-9 could reach 100% when two SSR markers, SRM22 and SRM91, were used simultaneously.3. Using LAC23, 5173 and 75-1-127 as the donor of the resistant gene Pi-1, Pi-2 and Pi-9, the three blast genes were introgressed into several elite parents of three-line or two-line hybrid rice, respectively via marker-assisted backcross breeding. Eight near-isogenic lines (NILs) of Zhenshan 97B with Pi-1 introgressedwere obtained, of which the recovery rates of the recurrent parent's genetic background were from 93.1% to 97.5%; and ten NILs of Zhenshan 97B with Pi-2 introgressed were obtained, of which the recovery rates of the recurrent parent's genetic background were from 93.0% to 98.3%. In addition, a number of BC1F1 and BC2F1 plants carrying one of the three resistant genes were obtained using Jinshan B-1 and Jinshan S-1 as recurrent parents.4. Our study showed that it is feasible to use the method of marker-assisted backcross to breed new disease resistant varieties during the process of pedigree breeding, and the speed of breeding new CMS line can be accelerated. Six NILs of JSB9, a good quality maintaining line, carrying the bacterial blight disease resistant gene Xa2] were obtained. The recovery rates of Jinshan B-l's genetic background were from 92.7% to 97.3% with an average of 94.8%.5. A NIL of H359 exhibiting a high level of resistance to bacterial leaf streak similar to the resistance donor parent Acc8558 was obtained via the traditional backcross breeding method. Graphic genotype analysis indicated that the NIL carried three chromosomal segments from the donor parent, on which major QTLs were located, confirming the reliability of the QTLs detected previously. The study also indicted that a new variety with high resistance to bacterial leaf streak could be bred by pyramiding four to five favorable resistant alleles.