Pietrusińska A., Czembor P.Cz., Czembor J.H. (2013): Lr39 + Pm21: a new effective combination of resistance genes for leaf rust and powdery mildew in wheat. Czech J. Genet. Plant Breed., 49: 109–115. Two effective resistance genes were introduced, one for leaf rust (Lr39) and the other for powdery mildew (Pm21), into the susceptible German wheat cv. Lexus. Molecular selection of plant material was carried out us-ing closely linked markers to the introduced genes (foreground selection). In addition, for the BC 1 F 1 population, background selection was carried out using AFLP markers that were distributed randomly throughout the wheat genome. Moreover, resistance tests were conducted using natural pathogen populations of Puccinia triticina and Blumeriagraminis. The use of molecular markers for foreground selection in combination with pathology tests enabled 66 homozygous lines to be obtained that were simultaneously resistant to leaf rust and powdery mildew.

Wild Triticum and Aegilops species are increasingly used in wheat breeding programmes around the world as donors of genes conferring resistance to biotic and abiotic stresses, as well as of genes that contribute to the improvement of grain quality. In the present study, thirty-nine accessions of diploid species with the A genome (Triticum boeoticum and T. urartu) were evaluated for the presence of the genes conferring resistance to powdery mildew (Blumeria graminis) and leaf rust (Puccinia recondita) using both inoculation tests and sequence tagged sites (STS) marker analyses in order to find correspondence between STS markers and resistance as a trait. The most resistant entries were T. boeoticum accessions. All the marked Lr and Pm resistance genes (Pm1, Pm2, Pm3, Lr10, Lr47, Lr25 and Lr28) were identified in the check T. aestivum cultivar Bezostaya 1. The resistance to powdery mildew in the material studied was conferred by the combination of the Pm1 gene with either Pm2 or Pm3. The Pm1 and Pm3 markers appeared to be suitable for tracking these powdery mildew resistance genes, while the Pm2 gene marker cannot be considered as usable in various genetically different wheat accessions. The presence of the genes Lr25, Lr28 and Lr47 seems to be particularly useful for obtaining leaf rust resistance in T. boeoticum and T. urartu species.

Breeding for resistance is an efficient strategy to manage wheat leaf rust (Lr) caused by Puccinia triticina f. sp. tritici. However, a prerequisite for the directed use of Lr genes in breeding and detection of new races virulent is a detailed knowledge on these genes present in wheat cultivars. Molecular markers are ideal for the identification of resistance genes in wheat genotypes with unknown genetic background. Therefore, molecular markers were conducted using specific SSR primers to screen ten out of fifteen Egyptian wheat cultivars which exhibited high resistance against P. triticina f. sp. tritici in four locations (Dakahlia, Kafr el-Sheikh, Beheira and Sharqia) during seasons 2010/2011 and 2011/2012. The obtained results showed that Lr9 was present in two cultivars namely Sids-12 and Sids-13, while Lr25 was found in all ten tested cultivars except Gemmeiza-11 cultivar. Lr28 was found in five cultivars, that is, Giza-168, Sids-12, Misr-2, Sakha-94 and Misr-1. On the other ha...

The wheat powdery mildew resistance gene Pm40, which is located on chromosomal arm 7BS, is effective against nearly all prevalent races of Blumeria graminis f. sp tritici (Bgt) in China and is carried by the common wheat germplasm PI 672538. A set of the F1, F2 and F2:3 populations from the cross of the resistant PI 672538 with the susceptible line L1034 were used to conduct genetic analysis of powdery mildew resistance and construct a high-density linkage map of the Pm40 gene. We constructed a high-density linkage genetic map with a total length of 6.18 cM and average spacing between markers of 0.48 cM.Pm40 is flanked by Xwmc335 and BF291338 at genetic distances of 0.58 cM and 0.26 cM, respectively, in deletion bin C-7BS-1-0.27. Comparative genomic analysis based on EST-STS markers established a high level of collinearity of the Pm40 genomic region with a 1.09-Mbp genomic region on Brachypodium chromosome 3, a 1.16-Mbp genomic region on rice chromosome 8, and a 1.62-Mbp genomic reg...

Leaf and stripe rusts, caused by Puccinia triticina and P. striiformis, respectively, are globally important fungal diseases of wheat that cause significant annual yield losses. A gene that confers slow rusting resistance to leaf rust, designated as Lr46, has recently been located on wheat chromosome 1B. The objectives of our study were to establish the precise genomic location of gene Lr46 using molecular approaches and to determine if there was an association of this locus with adult plant resistance to stripe rust. A population of 146 F5 and F6 lines produced from the cross of susceptible ‘Avocet S’ with resistant ‘Pavon 76’ was developed and classified for leaf rust and stripe rust severity for three seasons. Using patterns of segregation for the two diseases, we estimated that at least two genes with additive effects conferred resistance to leaf rust and three to four genes conferred resistance to stripe rust. Bulked segregant analysis and linkage mapping using amplified fragme...

Host-plant resistance is the most economically viable and environmentally responsible method of control for Puccinia triticina, the causal agent of leaf rust in wheat (Triticum aestivum L.). The identification and utilization of new resistance sources is critical to the continued development of improved cultivars as shifts in pathogen races cause the effectiveness of widely deployed genes to be short lived. The objectives of this research were to identify and tag new leaf rust resistance genes. Forty landraces from Afghanistan and Iran were obtained from the National Plant Germplasm System and evaluated under field conditions at two locations in Texas. PI 289824, a landrace from Iran, was highly resistant under field infection. Further evaluation revealed that PI 289824 is highly resistant to a broad spectrum of leaf rust races, including the currently prevalent races of leaf rust in the Great Plains area of the USA. Eight F1 plants, 176 F2 individuals and 139 F2:3 families of a cross between PI 289824 and T112 (susceptible) were evaluated for resistance to leaf rust at the seedling stage. Genetic analysis indicated resistance in PI 289824 is controlled by a single dominant gene. The AFLP analyses resulted in the identification of a marker (P39 M48-367) linked to resistance. The diagnostic AFLP band was sequenced and that sequence information was used to develop an STS marker (TXW200) linked to the gene at a distance of 2.3 cM. The addition of microsatellite markers allowed the gene to be mapped to the short arm of Chromosome 5B. The only resistance gene to be assigned to Chr 5BS is Lr52. The Lr52 gene was reported to be 16.5 cM distal to Xgwm443 while the gene in PI 289824 mapped 16.7 cM proximal to Xgwm443. Allelism tests are needed to determine the relationship between the gene in PI 289824 and Lr52. If the reported map positions are correct, the gene in PI 289824 is unique.