Molecular Maker-Assisted Selection And Genetic Analysis Of Wheat Stripe Rust Resistance Genes Pyramiding

Wheat stripe rust, caused by Puccinia striiformis West. f. sp. Tritici (PST), is one of the most destructive air-borne diseases on wheat in many wheat-grown regions in the world, and it is especially heavy and popular in China. The application of resistance varieties is a most effective and economical method for the disease control. However, most of the varieties are not durable resistant, especially of some one grown on large scale, and it accelerates the specific selection on the pathogen races and population increase of another predominant race, so that the resistance varieties become susceptible grown several years later. This situation has become a common problem in the world and many plant pathologists and breeders pay more attention to it now.In recent years, many studies have shown that the different resistance genes pyramiding will improve variety resistance level and spectrum, and it is considered as an effective way to breed relatively durable resistance varieties.There are, however, many related theories and technical problems, such as the efficiency of molecular marker-assisted resistance gene selection, the multi-resistance-gene pyramiding breeding process under molecular marker-assisted selection, the marker types and genetic distance between molecular marker and the garget gene, the size of plant population used for selection, sampling methods and sample numbers, and so on, still need to be solved. Therefore, the resolution of these issues will greatly improve the wide application of molecular marker-assisted selection in plant breeding practice and contribute in raising resistance breeding level in China.In this study, Zhongzhi 1 was used as a female parent to hybridize with stripe rust resistance gene near-isogenic lines Taichung29*6/Yr5 and Taichung29* 6/YrKy2 respectively, and their F₁ plants hybridized with a male parent Taichung29*6/Yr10 and Taichung29*6/YrJu4 respectively, and then self-fertilized once time to construct two different F₂ populations. The F₂ plants were inoculated with the update predominant races. The plant resistance was scored, combined with agronomic traits. We also analyzed the F₂ Plant genotypes using related molecular markers. The main results were shown as following:(1)In the 1060-plant F₂ population of [(Zhongzhi×Taichung29*6/Yr5)×Taichung29*6/Yr10], 956 resistant plants and 104 susceptible ones were identified, therefore, it was in accord with the theoretical ratio of 231R:25S, showing that the disease resistance was under control of three resistance genes, consisting of one dominant gene and two recessive ones. In the 1114-plant F₂population of [(Zhongzhi 1×Taichung29*6/YrKy2)×Taichung29*6/YrJu4], we identified 149 resistant plants and 965 susceptible ones, and their ration was 1R:7S, so the resistance of Zhongzhi to the pathogen race used was controlled by one recessive gene.(2) Among the F₂ population of 1060 plants, 4.81 percent (51 plants) were selected with good or better agronomic traits. Among these 51 plants selected, 26 plants were of higher quality of integrated agronomic traits, and 25 plants are less high quality of agronomic traits. Their ratios were 2.45% and 2.36% respectively in the population.(3) In the F₂ population, the homozygous dominant genotype recombination ratio of Yr5 andYr10 was 3.02%.The genotype ratio for that one gene was homozygous dominant and the other was hybrid or that two genes were all hybrid, was both 32.83%.The ratio for one resistance gene with homozygous or heterozygous genotype was 56.26%. We identified that 47.26% plants contained Yr5 gene and 76.23% plants contained Yr10 gene. This result was consistent with the theory ratio.We found that nine genotypes for the two resistance genes were detected in the 1060-plant F₂ population, and the plants with four recombination genotypes were identified, taking up 35.85%. We also found that 3.02% (32 plants) were of homozygous dominant genotype.(4) The resistance plants with homozygous dominant genotype and good or better agronomic traits was 0.28% among the F₂ population. The plants with most-wanted agronomic traits was 0.094%.(5) Among the three methods used in the resistance gene pyramiding identification, we concluded that the selection efficiency of resistance identification combined with marker-assisted selection was higher than that of marker-assisted selection, the later was higher than that of resistance identification by pathogen inoculation.(6)Resistance identification assisted with molecular marker detection was an effective method used in wheat stripe rust resistance pyramiding and can speed up the pyramiding breeding process. The homozygous dominant genotypic lines with good phenotype of agronomic traits can be selected in the process. Based on the results, the size of F₂ population would be 1500-2000 plants. For two resistance genes pyramiding in one breeding process, one wheat leaf per F₂ plant was enough for genotype analysis collected at the 4th-leaf stage.