Molecular Mapping And Allelism Test Of Leaf Rust Resistance Gene In Two Chinese Wheat Lines

Wheat leaf rust, caused by Puccinia triticina, is one of the most important and widespread diseases in China. It is adapted to a wide range of climates, occurs wherever wheat is grown, and can cause significant yield and economic losses. Given favorable conditions, the disease can cause yield losses of up to 40%. As climate warming, the harm of the wheat leaf rust may be more severe. Resistant cultivars are the most efficient, economic and environmentally-friendly way for reducing the losses caused by the disease. Genetic resistance to leaf rust can be most fully utilized by information about the identity of resistance genes in current leading resistance resources and newly released cultivars. It is, therefore, very important to research genetics of leaf rust resistance and map new leaf rust resistance genes for wheat breeding resistance cultivars and disease control. Neijiang 977671 developed by Neijiang Agricultural Science institute, showed high resistance to leaf rust in the field. In this study, F₁, F₂ plants and F₃ lines from a cross between resistant line Neijiang 977671 and susceptible line Zhengzhou 5389 were used for molecular mapping leaf rust resistance genes in Neijiang 977671 by gene postulation, genetic analysis and SSR markers. The other objective of this study is to map LrBi16 in Bimai 16 using AF_LP markers, and to test the allelism of LrBi16 with Lr14a. The results were showed as following .1) Neijiang 977671 and 19 near-isogenic lines with known leaf rust resistance genes were inoculated with 12 pathotypes of Puccinia triticina for postulation of leaf rust resistance genes effective at the seedling stage. The result showed that the response pattern of Neijiang 977671 was different with the 19 known Lr resistance genes used in the test and Neijiang 977671 may carry new leaf rust resistance gene （s）.2) Neijiang 977671, Zhengzhou 5389, and their F_l, F₂ populations and F₃ families were tested for wheat leaf rust resistance with Chinese Puccinia triticina pathotype FHNQ in greenhouse. The results showed that Neijiang 977671 was resistant to FHNQ and Zhengzhou 5389 was susceptible to FHNQ, F₂ population segregated for a single gene, fitting 3:1 ratio and F₃ lines also segregated monogenically, fitting 1:2:1 ratio. Results from the F₂ and F₃ populations indicated that a single dominant gene, tentatively designated LrNJ97, conferred resistance to P. triticina pathotype FHNQ in Neijiang 977671.3) SSR primers were used to test the parents and their resistant and susceptible bulks. The polymorphic SSR markers between the resistant and susceptible bulks were used for analying the F₃ lines. Linkage analysis was conducted with the software MapManager QTXb20. Results indicated that Neijiang 977671 carries a single dominant resistance gene LrNJ97, located on chromosome 2BL. The resistance gene LrNJ97 was closely linked to the five known SSR loci on the 2BL with genetic ranging from 2.2 cM to 25.4 cM. The two closest flanking SSR loci were Xbarc159 and Xwmc317 with genetic distances of 2.2 cM and 4.2 cM, respectively.4) Two formally named leaf rust resistance genes Lr50 and Lr58 were located on chromosome 2BL. In the seedling tets the reaction pattern of LrNJ97 was different from that of Lr50, and origin of LrNJ97 was also different with Lr50 and Lr58, indicating LrNJ97 is a new leaf rust resistance gene.5) Three hundred AF_LP primers were used to test Bimai 16, Tathcher and their F₂ population. The polymorphic AF_LP marker P-ATT/M-CGC173bp between the resistant and susceptible bulks was used for analying the F₂ population. Linkage analysis was conducted with the software MapManager QTXb20. Results indicated that the resistance gene LrBi16 was closely linked to P-ATT/ M-CGC_173bp with genetic distances of 0.5 cM, shortening the linkage distance between marker reported before and LrBi16 as 2.4 cM.6) A total of 809 F₂ plants from Bimai 16/RL6013 （Lr14a） were inoculated with pathotype FHNQ to test the allelism of Lr14a and LrBi16. All 809 F₂ plants were resistant to FHNQ （IT;-2）, indicating that Lr14a and LrBi16 were likely to be allelic or closely linked.