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Key message: The novel, leaf rust seedling resistance gene, Lr81, was identified in a Croatian breeding line and mapped to a genomic region of less than 100 Kb on chromosome 2AS. Leaf rust, caused by Puccinia triticina, is the most common and widespread rust disease in wheat. Races of Puccinia triticina evolve rapidly in the southern Great Plains of the USA, and leaf rust resistance genes often lose effectiveness shortly after deployment in wheat production. PI 470121, a wheat breeding line developed by the University of Zagreb in Croatia, showed high resistance to Puccinia triticina races collected from Oklahoma, suggesting that PI 470121 could be a leaf rust resistance source for the southern Great Plains of the USA. Genetic analysis based on an F2 population and F2:3 families derived from the cross PI 470121 × Stardust indicated that PI 470121 carries a dominant seedling resistance gene, designated as Lr81. Linkage mapping delimited Lr81 to a genomic region of 96,148 bp flanked by newly developed KASP markers Xstars-KASP320 and Xstars-KASP323 on the short arm of chromosome 2A, spanning 67,030,206–67,132,354 bp in the Chinese Spring reference assembly (IWGSC RefSeq v1.0). Deletion bin mapping assigned Lr81 to the terminal bin 2AS-0.78–1.00. Allelism tests indicated that Lr81 is a distinctive leaf rust resistance locus with the physical order Lr65-Lr17-Lr81. Marker-assisted selection based on a set of markers closely linked to leaf rust resistance genes in PI 470121 and Stardust enabled identification of a recombinant inbred line RIL92 carrying Lr81 only. Lr81 is a valuable leaf rust resistance source that can be rapidly introgressed into locally adapted cultivars using KASP markers Xstars-KASP320 and Xstars-KASP323. [ABSTRACT FROM AUTHOR]

Key message: The recessive Hessian fly resistance gene h4 and flanking SNP markers were located to a 642 kb region in chromosome 1A of the wheat cultivar 'Java.' Hessian fly (HF), Mayetiola destructor, is one of the most destructive insect pests in wheat worldwide. The wheat cultivar 'Java' was reported to carry a recessive gene (h4) for HF resistance; however, its chromosome location has not been determined. To map the HF resistance gene in Java, two populations of recombinant inbred lines (RILs) were developed from 'Bobwhite' × Java and 'Overley' × Java, respectively, and were phenotyped for responses to infestation of HF Great Plains biotype. Analysis of phenotypic data from the F1 and the RIL populations confirmed that one recessive gene conditioned HF resistance in Java. Two linkage maps were constructed using single-nucleotide polymorphism (SNP) markers generated by genotyping-by-sequencing (GBS). The h4 gene was mapped to the distal end of the short arm of chromosome 1A, which explained 60.4 to 70.5% of the phenotypic variation for HF resistance in the two populations. The GBS-SNPs in the h4 candidate interval were converted into Kompetitive Allele-Specific Polymerase Chain Reaction (KASP) markers to eliminate the missing data points in GBS-SNPs. Using the revised maps with KASP markers, h4 was further located to a 642 kb interval (6,635,984–7,277,935 bp). The two flanking KASP markers, KASP3299 and KASP1871, as well as four other closely linked KASP markers, may be useful for pyramiding h4 with other HF resistance genes in breeding. [ABSTRACT FROM AUTHOR]

Key message: A new powdery mildew resistance gene conferring a wide spectrum of resistance toBgtisolates in the USA,Pm63, was identified in Iranian wheat landrace PI 628024 and mapped to the terminal region of the long arm of chromosome 2B. Powdery mildew is a globally important wheat disease causing severe yield losses, and host resistance is the preferred strategy for managing this disease. The objective of this study was to characterize a powdery mildew resistance gene in Iranian landrace PI 628024, which exhibited a wide spectrum of resistance to representative Blumeria graminis f. sp. tritici (Bgt) isolates collected from different regions of the USA. An F2 population and F2:3 lines derived from the cross PI 628024 × CItr 11349 were used in this study, and genetic analysis indicated that a single dominant gene, designated Pm63, conferred resistance to Bgt isolate OKS(14)-B-3-1. Linkage analysis located Pm63 to an interval of about 13.1 Mb on the long arm of chromosome 2B, spanning 710.3–723.4 Mb in the Chinese Spring reference sequence. Bin mapping assigned Pm63 to the terminal bin 2BL6-0.89-1.0, 1.1 cM proximal to STS marker Xbcd135-2 and 0.6 cM distal to SSR marker Xstars419. Allelism tests indicated that Pm63 is a new powdery mildew resistance gene, which differs from other genes in the terminal bin by origin, genomic location, and responses to a set of 16 representative US Bgt isolates. Pm63 can be widely used to enhance powdery mildew resistance in the Great Plains, western, and southeastern regions of the USA. [ABSTRACT FROM AUTHOR]