Molecular Mapping Of Leaf Rust Resistance Gene LrZH84 In Chinese Wheat Line Zhou 8425B

Wheat leaf rust, caused by Puccinia triticina, is one of the most important and widespread diseases in wheat. 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%. 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 for wheat resistance breeding and disease control to search for genetic law of leaf rust resistance, to identify and map new leaf rust resistance genes. Zhou 8425B developed in 1984, continues to be resistant to leaf rust and strip rust. It has at least thirty hybrid derivatives which have covered over six million hectares totally. In this study, using Zhou 8425B as an experiment material, through genes postulation, the genetic analysis of resistance, and SSR technique did some researches on Zhou 8425B. The following results regarding its leaf rust resistance were obtained.1) The resistance genes in Zhou 8425B were identified by comparing the reaction of Zhou 8425B to 20 Puccinia triticina races with 37 near-isogenic lines with known resistance genes. The result showed that the reaction patterns of Zhou 8425B were different from the 37 known Lr resistance genes used in the test and therefore Zhou 8425B may carry one or more new leaf rust resistance genes.2) Zhou 8425B, Chinese Spring, and their F₁, F₂ populations and F₃ families were tested for wheat leaf rust resistance with Chinese Puccinia triticina races THTT in greenhouse. The results showed that the resistance of Zhou 8425B was controlled by one dominant gene to Puccinia triticina race THTT, temporarily designated LrZH84.3) To confirm influence of temperature on expression of leaf rust resistance gene LrZH84, Zhou 8425B were inoculated with four different Puccinia triticina races (FKJS, PKQQ, PHQS, THTT) and placed in three different growth chambers with night-day temperatures of 5-10℃, 15-20℃and 25-30℃, respectively. No significant difference exited among infection types of all race-line-temperature combinations, indicating that LrZH84 was not sensitive to temperature changes used in the test.4) A total of 793 pairs of 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 F₂ and F₃ populations. Linkage analysis was conducted with the software MapManager QTXb20. Results indicated that Zhou 8425B carries a single dominant resistance gene LrZH84, located on chromosome 1BL. The resistance gene LrZH84 was closely linked to the seven known SSR loci on the 1B with genetic ranging from 3.9 cM to 12.0 cM. Gwm582 and barc8 with genetic distances of 3.9 cM and 5.2 cM, respectively. Gwm582 and barc8 were screened on DNA bulks from each of the 136 F₃ lines, providing comparative linkage of 4.9 and 7.7 cM, respectively. Neither value was significantly different from the results based on F₂ plants.5) Zhou 8425B, Chinese Spring, TcLr26, and 136 F3 lines were inoculated with races THTT and MBHP. Zhou 8425B was moderately resistant with THTT and highly resistant with MBHP. TcLr26 was susceptible to THTT and resistant with MBHP. On the other hand each F₃ line was assayed with two gene-specific markersω-secalin and Glu-B3. Results indicated that the Xbarc8 allele co-segregated with Lr26 in the F₃ population and therefore LrZH84 is linked to Lr26 with 7.7 cM, So LrZH84 was different from Lr26.6) Six formally named leaf rust resistance genes Lr26, Lr33, Lr44, Lr46, Lr51 and Lr55 are located on chromosome 1B. Zhou 8425B and the lines carrying Lr26, Lr33, Lr44 were inoculated with 20 Puccinia triticina races in a seedling test. The result showed that reaction patterns of LrZH84 to the races was different from those of lines with Lr26, Lr33, Lr44. Former study showed that Lr46 is an adult plant resistance gene, and origin of LrZH84, Lr44, Lr51 and Lr55 are different, that suggests LrZH84 is likely to be a new leaf rust resistance gene.7) Inoculating Zhou 8425B, Chinese Spring, Zhou 78A, Annong 7959, Predgornaia 2, Lianfeng 1 with leaf rust race THTT, the result indicated Zhou 78A, Zhou 8425B and Predgornaia 2 were resistant, whereas Chinese Spring, Annong 7959 and Lianfeng 1 were susceptible. SSR analyses with gwm582 and barc8 closely linked to LrZH84 confirmed that Zhou 78A and Predgornaia 2 possessed the same alleles as Zhou 8425B, whereas Annong 7959 carried the same alleles as Chinese Spring. It seems likely, however, that LrZH84 is originated from Predgornaia 2.