| Rice (Oryza sativa L.) is one of the most important food and commercial crops in China; and its yield is very important to Chinese economic development and to the Chinese livelihood. Brown planthopper (Nilaparvata lugens Stal, BPH), one of typical sap-sucking insects, is one of the most endanger to rice production. The large amount of BPH insects occurrence tend to be accompanied with serious damage for large rice area, and would led to great reduce of rice yield. The most economic and effective way to reduce suffer from BPH is to excavate resistance genes from BPH resistance varieties, and by means of conventional breeding and molecular techniquel to transfer the resistance gene to cultivated rice varieties. In the present study, rice variety Ptb33 is the donor parent; and varieties TB5 and 9311 are receptor parent. The F2 population was constructed by Ptb33 and TB5, and seedling bulk test were used to identify the resistant score of F2 families. Then the BSA was used to screen the polymorphism markers between resistant and susceptible pools. Total 114 SSR markers were found obvious polymorphism between Ptb33 and TB5 from 433 pairs of SSR markers. As a result, three SSR markers were found to be polymorphic between the resistant and susceptible pools. The polymorphic SSR markers, RM5757, RM5626 and RM586, were located on chromosome 4,3 and 6 respectively. Then more flanking markers were found which show polymorphism between Ptb33 and TB5 closed to the detected markers; and local genetic linkage map were constructed based on the F2 individuals genotypes of the polymorphic SSR markers Combined the results of F2 individuals phenotype and genotype, QTL scanning was performed to find the quantitative resistance loci. The results indicated three major BPH resistance loci in the resistance rice variety Ptb33. One major resistance QTL was located between RM5626 and RM168 on the long arm of chromosome 3. The biggest LOD score is 3.96 and it can explain 26.7% of the phenotypic variation. The second major resistance QTL was located between RM5757 and RM3643 on the long arm of chromosome 4. Its biggest LOD score is 5.66 and it can explain 32.4% of the phenotypic variation. The third major resistance QTL was located close to RM586 on the short arm of chromosome 6, and the biggest LOD score is 3.03, and it can explain 21.8% of the phenotypic variation.By using the detected BPH resistance QTLs and tightly linked molecular markers, we obtained the F3 population from F2 inbred lines which posses the one or more QTLs. The further resistance identification showed that these separate populations still have certain resistance to BPH even though the resistance loci were separated from Ptb33. And the ability of resistant will enhance when more than one resistance loci exist in the rice. On the other hand,172 accumulated lines of Ptb33 were cultivated through backcross and hybridization. Including the advanced backcross population (Ptb33/9311) which only possess the single QTL of chromosome 4 was obtained by marker assisted selection. The presence of the resistant site was further verified by QTL scan analysis. After the seedling survival rate of these accumulated lines, a number of high resistant strains were obtained. These materials will provide the new resources for rice cultivation in the future. |
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