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Most rust resistance genes thus far isolated from wheat have a very limited number of functional alleles. Here, we report the isolation of most of the alleles at wheat stem rust resistance gene locus SR9. The seven previously reported resistance alleles (Sr9a, Sr9b, Sr9d, Sr9e, Sr9f, Sr9g, and Sr9h) are characterised using a synergistic strategy. Loss-of-function mutants and/or transgenic complementation are used to confirm Sr9b, two haplotypes of Sr9e (Sr9e_h1 and Sr9e_h2), Sr9g, and Sr9h. Each allele encodes a highly related nucleotide-binding site leucine-rich repeat (NB-LRR) type immune receptor, containing an unusual long LRR domain, that confers resistance to a unique spectrum of isolates of the wheat stem rust pathogen. The only SR9 protein effective against stem rust pathogen race TTKSK (Ug99), SR9H, differs from SR9B by a single amino acid. SR9B and SR9G resistance proteins are also distinguished by only a single amino acid. The SR9 allelic series found in the B subgenome are orthologs of wheat stem rust resistance gene Sr21 located in the A subgenome with around 85% identity in protein sequences. Together, our results show that functional diversification of allelic variants at the SR9 locus involves single and multiple amino acid changes that recognize isolates of wheat stem rust.

Faba bean (Vicia faba L.) is one of the oldest grain legumes and is grown in many countries for both human consumption and animal feed. Faba bean rust, caused by Uromyces viciae-fabae, is a serious disease of faba beans in the subtropical agricultural region of Australia. Experiments were conducted to assess the genetic variation for rust resistance in Australian faba bean germplasm and to determine the genetic basis of rust resistance in selected germplasm. Resistant lines were identified, subsequently crossed to agronomically suitable parents and the ensuing progeny were evaluated for resistance. Many derived lines showed a higher level of resistance than the current cultivars, although none were rated immune. This level of resistance was considered adequate for reliable crop production when combined with limited fungicide application. Genetic studies from the seedling test of F2 and F3 progenies derived from two crosses based on two different sources of resistance showed three distinct responses; highly resistant, moderately resistant and susceptible. However, no homozygous family with a moderate response was found in the F3 progeny test, hence, this infection type could not be attributed to independent gene(s). The segregation ratio in both F2 and F3 in the population derived from Doza#12035, a selection from the commercial cultivar Doza, indicated a single dominant gene was responsible for conferring resistance. In the other population developed from the resistant parent Ac1655, it is likely that also a single dominant gene confers resistance even though the F3 segregation ratio deviated significantly from a one gene hypothesis. An allelism test revealed that each of the resistant parents (Doza#12035 and Ac1655) carried a single and independent gene for resistance, thus providing at least two genes for breeders to choose or pyramid for improving the rust resistance in faba bean. [ABSTRACT FROM AUTHOR]

Key message: Wheat–Aegilops speltoides recombinants carrying stem rust resistance genesSr32 andSrAes1t effective against Ug99 and PCR markers for marker-assisted selection.Wild relatives of wheat are important resources for new rust resistance genes but underutilized because the valuable resistances are often linked to negative traits that prevent deployment of these genes in commercial wheats. Here, we report ph1b-induced recombinants with reduced alien chromatin derived from E.R. Sears’ wheat– Aegilops speltoides 2D-2S#1 translocation line C82.2, which carries the widely effective stem rust resistance gene Sr32. Infection type assessments of the recombinants showed that the original translocation in fact carries two stem rust resistance genes, Sr32 on the short arm and a previously undescribed gene SrAes1t on the long arm of chromosome 2S#1. Recombinants with substantially shortened alien chromatin were produced for both genes, which confer resistance to stem rust races in the TTKSK (Ug99) lineage and representative races of all Australian stem rust lineages. Selected recombinants were back crossed into adapted Australian cultivars and PCR markers were developed to facilitate the incorporation of these genes into future wheat varieties. Our recombinants and those from several other labs now show that Sr32, Sr39, and SrAes7t on the short arm and Sr47 and SrAes1t on the long arm of 2S#1 form two linkage groups and at present no rust races are described that can distinguish these resistance specificities. [ABSTRACT FROM AUTHOR]

Stripe rust is one of the most destructive diseases of wheat. Breeding for resistance is the most economical and environmentally acceptable means to control stripe rust. Genetic studies on resistance sources are very important. Previous inheritance studies on Triticum aestivum subsp. spelta cv. album and wheat cultivar Lee showed that each possessed a single dominant gene for stripe rust resistance, i.e., Yr5 and Yr7, respectively. Both were located on the long arm of chromosome 2B, but due to the complexities caused by genetic background effects there was no clear evidence on the allelism or linkage status of these genes. Our study, involving an intercross of Avocet S near-isogenic lines possessing the genes, provided clear evidence for allelism or extremely close linkage of Yr5 and Yr7 based on phenotypic and molecular studies. [ABSTRACT FROM AUTHOR]