Mapping Blast Resistance Gene And Improveing Blast Resistance And Brown Planthopper Resistance In Rice

Rice (Oryza sativa L.) is one of the important food in the word, and also a stable food in China. Blast (Magnaporthe oryzae B. Couch) and brown planthopper (Nilaparvata lugens Stal, BPH) have been the most serious disease and inset pests in rice. It has been recognized that utilization of host-plant resistance is the most desirable and economic strategy in the management of blast and BPH. The objectives of the study were to exploit and map new blast resistance genes, and incorporae blast resistance gene and BPH resistance gene into some elite rice varieties, using marker-assisted selection (MAS) system, which provided theoretical foundation and breeding materials for developing improved versions of hybrid rice with highly advanced blast and BPH resistance. The main results are as follows:1. We developed near-isogenic lines (NIL) of qBR-6a in Zhenshan97(ZS97) background using the cross between highly resistance variety CR185and susceptible variety ZS97. A BC3F3populations consisting of1900individuals were used to fine mapping qBR-6a. By combining the analysis of blast resistance and marker genotypes, we narrowed qBR-6a between markers RM527and RM19835. Recombinants were identified using a BC4F2segregating populations consisting of3568individuals, and their phenotypes were determined by progeny testing. By analysis phenotypes and marker genotypes for each recombinant, we narrowed qBR-6a to an100Kb region between markers PI2-4and HC26. Sequence comparison revealed that the allele in CR185was different from the known genes Pi2, Piz-t and Pi9. qBR-6a may be a new blast resistance gene.2. We developed NIL and pyramiding lines of four QTL qBR-la, qBR-4d, qBR-6a and qBR-12a in the background of ZS97. Blast resistance analysis showed that four QTL were have a resistance to blast and pyramiding more members of the four major QTLs in ZS97, the higher resistance to rice blast they showed.3. Three dominant genes (Pi1, Pi2and D12) were incorporated separately and pyramided into elite maintainer line Jin23B and its hybrids Jinyou402and Jinyou 207using MAS. Seven genotype combinations including single, two and three genes were developed. Gene effectiveness was evaluated on the basis of leaf blast in tillering and heading stage and neck blast in maturation stage. Blast bioassay showed that pyramiding line or hybrids with three genes expressed highest resistance. The lines pyramiding two genes had lower resistance, and resistance of single-gene lines was even lower, however, the lines with no genes had lowest resistance. In the background of maintainer lines or hybrids, the resistance of Pi2was stronger than Pil, which was stronger than D12. The lines contained Pil expressed higher resistance in the maintainer lines than in the hybrids, which indicating that Pil was a semi-dominant gene. Field trail data in Wuhan demonstrated that there were no significant differences on heading date, plant height and tillering number between improved versions and controls, and yields of improved versions were higher than or similar to that of the controls. In the disease infection condition of Xianfeng, the improved versions had higher yield than the controls.4. Six dominant genes Bph3(3), Bphl4(14), Bph15(15), Bph18(18), Bph20(20), and Bph21(21) were incorporated into elite maintainer line Jin23B using MAS. Six NIL of each gene and a pyramiding line (14/15) were developed. Gene effectiveness was evaluated on the basis of seeding and adult rice resistance, honeydew weight and survival rate of BPH. BPH bioassay showed that pyramided line with Bph14and Bph15expressed highest resistance in seeding stage, and the gene effect being14/15>15≥14≥20≥21≥3>18>none. At adult stage, the pyramided or introgression lines Jin23B (14/15), Jin23B (15) and Jin23B (14), showed resistant (R) to moderately resistant (MR) to BPH from17days after infestation (DAI) to25DAI. And Jin23B (20), Jin23B (21), Jin23B (3) and Jin23B (18) showed MR to moderately susceptible (MS) to BPH from17DAI to25DAI. Whereas Jin23B (none) showed MS to susceptible (S) to BPH from17DAI to25DAI. BPH bioassay of honeydew weight and survival rate of BPH demonstrated that gene effect of each line almost the same with seeding resistance. Results showed that pyramided line with Bphl4and Bphl5expressed highest resistance among all of them, and single gene introgression line with Bph15was stronger than other single gene introgression lines, and single gene introgression line with Bphl8have the lowest resistance. Yields of the seven improved versions were similar to the control under natural field conditions in Wuhan.