[Show abstract][Hide abstract] ABSTRACT: Leaf rust (LR), caused by Puccinia triticina, is one of the most widespread diseases of common wheat (Triticum aestivum L.) worldwide. The LR resistance gene LrBi16 has been mapped on chromosome arm 7BL in Chinese wheat cultivar Bimai 16 and was closely linked to SSR loci Xcfa2257 and Xgwm344 with genetic distances of 2.8 cM and 2.9 cM, respectively. In the present study, a total of 304 AFLP primer pairs were used to screen Bimai 16 and Thatcher and resistant and susceptible DNA bulks. The polymorphic AFLP marker P-ATT/M-CGC173bp was used to genotype F2 and F3 populations to identify markers more closely linked to LrBi16. Marker P-ATT/M-CGC173bp was tightly linked to LrBi16 with a genetic distance of 0.5 cM. As LrBi16 was mapped near the Lr14a locus, 809 F2 plants from the Bimai 16/RL6013 (Lr14a) cross were inoculated with the Pt pathotype FHNQ to test the allelism of Lr14a and LrBi16. All of the F2 plants were resistant to FHNQ (IT between ; and 2), suggesting that Lr14a and LrBi16 are allelic.
[Show abstract][Hide abstract] ABSTRACT: Leaf rust and powdery mildew, caused by Puccinia triticina and Blumeria graminis f. sp. tritici, respectively, are widespread fungal diseases of wheat (Triticum aestivum L.). Development of cultivars with durable resistance is crucially important for global wheat production. This paper reviews the progress of genetic study and application of adult plant resistance (APR) to wheat leaf rust and powdery mildew. Eighty leaf rust and 119 powdery mildew APR quantitative trait loci (QTL) have been reported on 16 and 21 chromosomes, respectively, in over 50 publications during the last 15 yr. More important, we found 11 loci located on chromosomes 1BS, 1BL, 2AL, 2BS (2), 2DL, 4DL, 5BL, 6AL, 7BL, and 7DS showing pleiotropic effects on resistance to leaf rust, stripe rust, and powdery mildew. Among these, QTL on chromosomes 1BL, 4DL, and 7DS also correlate with leaf tip necrosis. Fine mapping and cloning of these QTL will be achieved with the advent of cheaper high-throughput genotyping technologies. Germplasm carrying these potential resistance genes will be useful for developing cultivars with durable multidisease resistance. In addition to its non-NBS-LRR (nucleotide binding site-leucine rich repeat) structure, the senescence-like processes induced by Lr34 could be the reason for durability of resistance; however, more information is needed for a full understanding of the molecular mechanism related to durability. Adult plant resistance genes have been used by CIMMYT for more than 30 yr and have also been transferred to many Chinese wheat varieties through shuttle breeding.
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Six QTL for adult plant resistance to leaf rust, including two QTL effective against additional diseases, were identified in a RIL population derived from a cross between Shanghai 3/Catbird and Naxos. Leaf rust is an important wheat disease and utilization of adult-plant resistance (APR) may be the best approach to achieve long-term protection from the disease. The CIMMYT spring wheat line Shanghai 3/Catbird (SHA3/CBRD) showed a high level of APR to Chinese Puccinia triticina pathotypes in the field. To identify APR genes in this line, a mapping population of 164 recombinant inbred lines (RILs) was developed from a cross of this line and Naxos, a moderately susceptible German cultivar. The RILs were evaluated for final disease severity (FDS) at Baoding, Hebei province, and Zhoukou, Henan province, in the 2010-2011 and 2011-2012 cropping seasons. QTL analysis detected one major QTL derived from SHA3/CBRD on chromosome 2BS explaining from 15 to 37 % of the phenotypic variance across environments. In addition one minor resistance QTL on chromosome 1AL from SHA3/CBRD and four minor QTL from Naxos on chromosomes 2DL, 5B, 7BS, and 7DS were also detected. SHA3/CBRD also possessed seedling resistance gene Lr26, and Naxos contained Lr1 based on gene postulation following tests with an array of P. triticina pathotypes and molecular marker assays. These seedling resistance and APR genes and their closely linked molecular markers are potentially useful for improving leaf rust resistance in wheat breeding programs.
[Show abstract][Hide abstract] ABSTRACT: Leaf rust, caused by Puccinia triticina, is one of the major wheat diseases worldwide and poses a constant threat to common wheat (Triticum aestivum L.) production and food security. Results from the F2 and F2:3 populations derived from a cross between resistant line Fundulea 900 and susceptible cultivar Thatcher indicated that a single dominant gene, tentatively designated LrFun, conferred resistance to leaf rust. In order to identify other possible genes in Fundulea 900, nine P. triticina pathotypes avirulent on Fundulea 900 were used to inoculate F2:3 families. The results showed that at least two leaf rust resistance genes were present in Fundulea 900. A total of 1,706 pairs of simple sequence repeat (SSR) primers were used to test the parents and resistant and susceptible bulks. Eight polymorphic markers from chromosome 7BL were used for genotyping the F2 and F2:3 populations. LrFun was linked to eight SSR loci on chromosome 7BL. The two closest flanking SSR loci were Xgwm344 and Xwmc70, with genetic distances of 4.4 and 5.7 cM, respectively. At present four leaf rust resistance genes, Lr14a, Lr14b, Lr68 and LrBi16, are located on chromosome 7BL. In a seedling test with 12 P. triticina isolates, the reaction patterns of LrFun were different from those of lines carrying Lr14a, Lr14b and LrBi16. Lr68 is an adult plant resistance gene, and it is different from the seedling resistance gene LrFun. Therefore, we concluded that LrFun is a new leaf rust resistance gene.
[Show abstract][Hide abstract] ABSTRACT: Yellow or stripe rust, caused by Puccinia striiformis f. sp. tritici, is an important disease of common wheat (Triticum aestivum L.) worldwide. A recombinant inbred line (RIL) population, derived from the cross PBW343 9 Kenya Kudu, was pheno-typed for yellow rust reaction in the field at the CIMMYT research station near Toluca, Mexico, during 2010 and 2011. Segregation results indicated the presence of a race-specific resistance gene, temporarily designated as YrKK, in Kenya Kudu that conferred immunity to adult plants in field trials, despite conferring only slight reductions in seedling reactions in greenhouse tests with three Mexican pathotypes. A minimum of four minor genes having additive effects also segregated in the population and were likely derived from both parents. A total of 635 simple sequence repeat (SSR) primers were screened for polymorphism surveys on the parents, and resis-tant (YrKK-possessing RILs) and susceptible (YrKK-lacking RILs) bulks identified four polymorphic markers. These markers were located on the short arm of chromosome 2B. Genotyping of the entire RIL population identified Xgwm148 and Xwmc474 as the most closely linked proximal and distal flanking SSR markers, with respective genetic distances of 3.6 and 1.8 cM from YrKK. Four yellow rust resistance genes (Yr27, Yr31, Yr41, and YrP81) are located on chro-mosome 2BS; however, their specificity to pathogen pathotypes and host reactions in seedling and adult plants indicate that YrKK is a new resistance gene.
[Show abstract][Hide abstract] ABSTRACT: 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 reaction pattern of Neijiang 977671 differed from those of the lines with known leaf rust resistance genes used in the test, indicating that Neijiang 977671 may carry a new leaf rust resistance gene(s). With the objective of identifying and mapping the new gene for resistance to leaf rust, F1 and F2 plants, and F2:3 families, from Neijiang 977671 × Zhengzhou 5389 (susceptible) were inoculated with Chinese P. triticina pathotype FHNQ in the greenhouse. Results from the F2 and F2:3 populations indicated that a single dominant gene, temporarily designated LrNJ97, conferred resistance. In order to identify other possible genes in Neijiang 977671 other eight P. triticina pathotypes avirulent on Neijiang 977671 were used to inoculate 25 F2:3 families. The results showed that at least three leaf rust resistance genes were deduced in Neijiang 977671. Bulked segregant analysis was performed on equal amounts of genomic DNA from 20 resistant and 20 susceptible F2 plants. SSR markers polymorphic between the resistant and susceptible bulks were used to analyze the F2:3 families. LrNJ97 was linked to five SSR loci on chromosome 2BL. The two closest flanking SSR loci were Xwmc317 and Xbarc159 at genetic distances of 4.2 and 2.2 cM, respectively. At present two designated genes (Lr50 and Lr58) are located on chromosome 2BL. In the seedling tests, the reaction pattern of LrNJ97 was different from that of Lr50. Lr50 and Lr58 were derived from T. armeniacum and Ae. triuncialis, respectively, whereas according to the pedigree of Neijiang 977671 LrNJ97 is from common wheat. Although seeds of lines with Lr58 were not available, it was concluded that LrNJ97 is likely to be a new leaf rust resistance gene.
[Show abstract][Hide abstract] ABSTRACT: Stripe rust and leaf rust, caused by Puccinia striiformis Westend. f. sp. tritici Erikss. and P. triticina, respectively, are devastating fungal diseases of common wheat (Triticum aestivum L.). Chinese wheat cultivar Bainong 64 has maintained acceptable adult-plant resistance (APR) to stripe rust, leaf rust and powdery mildew for more than 10 years. The aim of this study was to identify quantitative trait loci/locus (QTL) for resistance to the two rusts in a population of 179 doubled haploid (DH) lines derived from Bainong 64 × Jingshuang 16. The DH lines were planted in randomized complete blocks with three replicates at four locations. Stripe rust tests were conducted using a mixture of currently prevalent P. striiformis races, and leaf rust tests were performed with P. triticina race THTT. Leaf rust severities were scored two or three times, whereas maximum disease severities (MDS) were recorded for stripe rust. Using bulked segregant analysis (BSA) and simple sequence repeat (SSR) markers, five independent loci for APR to two rusts were detected. The QTL on chromosomes 1BL and 6BS contributed by Bainong 64 conferred resistance to both diseases. The loci identified on chromosomes 7AS and 4DL had minor effects on stripe rust response, whereas another locus, close to the centromere on chromosome 6BS, had a significant effect only on leaf rust response. The loci located on chromosomes 1BL and 4DL also had significant effects on powdery mildew response. These were located at the same positions as the Yr29/Lr46 and Yr46/Lr67 genes, respectively. The multiple disease resistance locus for APR on chromosome 6BS appears to be new. All three genes and their closely linked molecular markers could be used in breeding wheat cultivars with durable resistance to multiple diseases.
[Show abstract][Hide abstract] ABSTRACT: Leaf rust, caused by Puccinia triticina, is one of the most widespread diseases in common wheat (Triticum aestivum L.) globally. With the objective of identifying and mapping new genes for resistance to leaf rust, F1, F2 plants and F3 lines from a cross between resistant cultivar Bimai 16 and susceptible cultivar Thatcher were inoculated with Chinese Puccinia triticina pathotypes FHTT and PHTS in the greenhouse. In the first seedling test, Bimai 16, Thatcher, 20 F1 plants, 359 F2 plants and 298 F3 lines were inoculated with pathotype FHTT. A set of 1,255 simple sequence repeat (SSR) primer pairs were used to test the
parents, and resistant and susceptible bulks. Seven polymorphic markers on chromosome 7BL were used for genotyping the F2 and F3 populations. The results indicated that Bimai 16 carried a single dominant resistance gene, temporarily designated LrBi16, closely linked to SSR markers Xcfa2257 and Xgwm344, with genetic distances of 2.8 and 2.9 cM, respectively. In the second seedling test, two dominant resistance genes were
identified in Bimai 16 based on seedling reactions of 254 F2 plants inoculated with pathotype PHTS. One of the genes was LrBi16, and the other was likely to be LrZH84, which is located in chromosome 1BL. The seedling reaction pattern of plants with LrBi16 was different from that of the Thatcher lines, with Lr14a and Lr14b located on chromosome 7BL. It was concluded that LrBi16 is likely to be a new leaf rust resistance gene.