| Leaf rust caused by Puccinia triticina, is an airborne foliar fungal disease of wheat that can seriously disturb plant photosynthesis and ultimately result in significant loss of production. Leaf rust occurs in wheat growing areas all over the world. Selection and deployment of resistant cultivar is the most economic and effective measure used for wheat leaf rust control. Study of resistance genes in wheat cultivar is a prerequisite for disease resistance breeding and crop improvement.In the present study, CIMMYT line 19HRWSN-122, Zhengzhou5389, and their F1, F2 and F2:3 lines were tested for wheat leaf rust resistance. Based on the chromosomal location, gene postulation, the genetic analysis and SSR technique, it can be concluded that 19HRWSN-122 carried leaf rust resistance gene. In order to make use of the leaf rust resistance gene in LB0288 effectively, F1 and F2 populations from the cross LB0288/Thatcher were tested with pathotype THTT for following marker analysis. To identify leaf rust APR genes in the Chinese wheat lines W014204, one mapping populations with 215 F2:3 lines from the cross W014204/Zhengzhou 5389, were phenotyped for leaf rust severities during the 2010-2011, 2011-2012 and 2012-2013 cropping seasons in the field at Baoding, Hebei province. A total of 1,215 SSR markers were used to identify the quantitative trait loci(QTL) for leaf rust APR in the populations. To identify leaf rust APR genes in the Chinese wheat line Pingyuan50, one mapping populations with 148 DH lines from the cross Pingyuan50/Mingxian169, respectively, were phenotyped for leaf rust severities during the 2010-2011, 2011-2012 cropping seasons in the field at Baoding, Hebei province and Zhoukou, Henan province. A total of 1,215 SSR markers were used to identify the quantitative trait loci(QTL) for leaf rust APR in the populations. 1. CIMMYT line 19HRWSN-122 and 36 lines with known Lr(leaf rust resistance) genes were inoculated with 13 Chinese P. triticina pathotypes for postulation of Lr genes at the seedling stage. Line 19HRWSN-122 showed high resistance to all 13 P. triticina pathotypes in the greenhouse, indicating that it may carry a new leaf rust resistance gene. With the objective of mapping the putatively new gene for resistance to leaf rust,20 F1, 280 F2 plants and 254 F2:3 lines from the cross 19HRWSN-122 × Zhengzhou5389(susceptible) were inoculated with P. triticina pathotype THJP in the greenhouse. Results based on the F1 and F2 and F2:3 lines indicated that a single dominant gene,temporarily designated Lr HR122, was present in 19HRWSN-122. Bulked segregant analysis(BSA) was performed on equal amounts of genomic DNA from 10 resistant and 10 susceptible F2:3 lines. Molecular markers polymorphic between the resistant and susceptible bulks were used to genotype F2:3 lines. Lr HR122 was linked to one SSR marker, one STS marker, one SCAR marker and three EST markers on chromosome 3DL. Marker SCS1302609 co-segregated with Lr HR122, and the closest flanking markers were BE442875 and STS24-16 at genetic distances of 0.4 and 1.6 c M, respectively. Lr24 was known to be located on chromosome 3DL near Lr HR122. In seedling tests, lines with both Lr HR122 and Lr24 showed high resistance to all 13 Chinese P. triticina pathotypes. According to the pedigree and chromosome position Lr HR122 should be Lr24.Lr HR122(Lr24) was closely linked to 1 SSR marker and 3 EST markers in the terminal region of 3DL. These markers should be useful for marker assisted selection in breeding leaf rust resistant wheat cultivars. 2. To identify and map the leaf rust resistance gene in the LB0288 line, F2 plants from a cross between LB0288 and Thatcher(susceptible) were inoculated in the greenhousewith the Chinese P. triticina pathotype, THTT. Results from the F2 populations indicate that a single dominant gene conferred resistance, temporarily designated Lr LB88. Using the molecular marker method, Lr LB88 was located on the 5DL chromosome. It was closely linked to the STS markers of Lr1 and SSR marker Xbarc144, with genetic distances of 0 c M and 5.3 c M, respectively. 3. The wheat line W014204, Zhengzhou 5389 and 36 lines with known Lr genes wer inoculated with 14 Chinese P. triticina pathotypes for postulation of Lr genes at the seedling stage. Based on the gene postulation and molecular markers co-segregated with Lr26, it can be concluded that W014204 carried resistance gene Lr26 and other new leaf rust resistance genes.In the W014204/Zhengzhou 5389 population, three QTLs were located on 1BL, 2BS and 7DS, respectively. They were designated as QLr.hbu-1BL.1, QLr.hbu-2BS.1 and QLr.hbu-7DS. They explained 2.9-8.4%,11.5-38.3% and 8.5-44.5% of the phenotypic variance, respectively. All the resistance alleles at these loci were derived from W014204. Based on chromosome positions and molecular marker tests, QLr.hbu-1BL.1 is Lr46 and QLr.hbu-7DS is Lr34. Based on chromosome positions, pedigree and field reactions the 2BS QTL are different from all the known APR genes and are likely to be new APR QTL for leaf rust. These QTL and their closely linked markers are potentially useful for improving leaf rust resistance in wheat breeding. 4. The DH populations from the cross Pingyuan50/Mingxian169 were inoculated with mixed P. triticina pathotypes in the field. Variance analysis of MDS showed that the difference of the plants of this population and locations were significant, while the difference was not significant between the repeats, indicating that expression of wheat leaf rust resistance were influenced by genotypes and environments. The MDS of offspring lines showed a continuous variation in multiple environments. These results showed that the adult plant leaf rust resistance was controlled by quantitative trait genes, there are several QTL sites. Five APR QTLs were identified in the QTL mapping for adult-plant resistance to leaf rust in wheat cultivar Pingyuan 50 with durable resistance, located on 4A, 5D, 7B, 7D and 7DS, respectively, and five QTLs explained 6.73%, 5.30%, 6.06%, 6.69-9.60% and 4.00-6.24% of the phenotypic variation, respectively. The QTL on 7DS is Lr34. |
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