Leaf rust resistance gene Lr34 is likely the most important leaf rust gene characterized to date. It has been characterized as an adult plant resistance gene and is known to enhance the resistance of other leaf rust resistance genes and to condition resistance to a number of other diseases. Located on chromosome 7D, this gene was identified to be one of six co-located genes of which, an ABC transporter was shown to be the only valid candidate. Ten new molecular markers were developed spanning the Lr34 locus, including six novel microsatellite markers (cam), one insertion site-based polymorphism marker (caISBP), two single nucleotide polymorphisms (caSNP), and one gene-specific marker (caIND). Using these new markers and others that were previously published, a comparative fine map of the locus was constructed from five segregating populations representing 1,742 lines. Identification of a susceptible line with a recombination in the 4.9 kb interval between caSNP4 located in the ABC transporter gene and cam8 located just upstream of this gene provided further evidence to support the identity of the ABC transporter as Lr34 by ruling out four of the adjacent genes. Originally, three mutations forming two haplotypes had been described for the ABC transporter gene. A third combination of the three mutations and an additional rare mutation in exon 22 were subsequently described. We identified an additional novel mutation in exon 10 that would cause a frameshift and is likely non-functional. This mutation was only found in Lr34- lines and constituted a novel molecular haplotype. Characterization of two germplasm collections of 700 Triticum aestivum lines permitted us to gain an understanding of the frequency of the ABC haplotypes characterized to date and their distribution in germplasm from and around the world. In addition to the four haplotypes previously described, a fifth haplotype was found in two of the 700 lines from the germplasm collections. These lines displayed the deletion in indel 11 characteristic of Lr34+ lines, but are likely susceptible to leaf rust. Mapping and haplotyping data suggest that of all the markers described herein, marker caIND11 is the best diagnostic marker for marker-assisted selection of Lr34 because it is co-dominant, robust and with the exception of 2/700 lines, it is highly diagnostic. Other markers are also described to provide alternatives for laboratories with different technologies.

Two cabbage (Brassica oleracea) cultivars ‘Tekila’ and ‘Kilaherb’ were identified as resistant to several pathotypes of Plasmodiophora brassicae. In this study, we identified a clubroot resistance gene (Rcr7) in ‘Tekila’ for resistance to pathotype 3 of P. brassicae from a segregating population derived from ‘Tekila’ crossed with the susceptible line T010000DH3. Genetic mapping was performed by identifying the percentage of polymorphic variants (PPV), a new method proposed in this study, through bulked segregant RNA sequencing. Chromosome C7 carried the highest PPV (42%) compared to the 30–34% in the remaining chromosomes. A peak with PPV (56–73%) was found within the physical interval 41–44 Mb, which indicated that Rcr7 might be located in this region. Kompetitive Allele-Specific PCR was used to confirm the association of Rcr7 with SNPs in the region. Rcr7 was flanked by two SNP markers and co-segregated with three SNP markers in the segregating population of 465 plants. Seven genes encoding TIR-NBS-LRR disease resistance proteins were identified in the target region, but only two genes, Bo7g108760 and Bo7g109000, were expressed. Resistance to pathotype 5X was also mapped to the same region as Rcr7. B. oleracea lines including ‘Kilaherb’ were tested with five SNP markers for Rcr7 and for resistance to pathotype 3; 11 of 25 lines were resistant, but ‘Kilaherb’ was the only line that carried the SNP alleles associated with Rcr7. The presence of Rcr7 in ‘Kilaherb’ for resistance to both pathotypes 3 and 5X was confirmed through linkage analysis.

Genetic resistance is the most effective approach to managing wheat leaf rust. The aim of this study was to characterize seedling and adult plant leaf rust resistance of a world wheat collection. Using controlled inoculation with ten races of Puccinia triticina, 14 seedling resistance genes were determined or postulated to be present in the collection. Lr1, Lr3, Lr10 and Lr20 were the most prevalent genes around the world while Lr9, Lr14b, Lr3ka and/or Lr30 and Lr26 were rare. To confirm some gene postulations, the collection was screened with gene-specific molecular markers for Lr1, Lr10, Lr21 and Lr34. Although possessing the Lr1 and/or Lr10 gene-specific marker, 51 accessions showed unexpected high infection types to P. triticina race BBBD. The collection was tested in the field, where rust resistance ranged from nearly immune or highly resistant with severity of 1 % and resistant host response to highly susceptible with severity of 84 % and susceptible host response. The majority of the accessions possessing the adult plant resistance (APR) gene Lr34 had a maximum rust severity of 0–35 %, similar to or better than accession RL6058, a Thatcher-Lr34 near-isogenic line. Many accessions displayed an immune response or a high level of resistance under field conditions, likely as a result of synergy between APR genes or between APR and seedling resistance genes. However, accessions with three or more seedling resistance genes had an overall lower field severity than those with two or fewer. Immune or highly resistant accessions are potential sources for improvement of leaf rust resistance. In addition, some lines were postulated to have known but unidentified genes/alleles or novel genes, also constituting potentially important sources of novel resistance.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-013-9899-8) contains supplementary material, which is available to authorized users.