Abstract
SummaryWheat stem (or black) rust, caused by Puccinia graminis f. sp. tritici (Pgt), has been historically among the most devastating global fungal diseases of wheat. The recent occurrence and spread of new virulent races such as Ug99 have prompted global efforts to identify and isolate more effective stem rust resistance (Sr) genes. Here, we report the map‐based cloning of the Ug99‐effective SrTm5 gene from diploid wheat Triticum monococcum accession PI 306540 that encodes a typical coiled‐coil nucleotide‐binding leucine‐rich repeat protein. This gene, designated as Sr22b, is a new allele of Sr22 with a rare insertion of a large (13.8‐kb) retrotransposon into its second intron. Biolistic transformation of an ~112‐kb circular bacterial artificial chromosome plasmid carrying Sr22b into the susceptible wheat variety Fielder was sufficient to confer resistance to stem rust. In a survey of 168 wheat genotypes, Sr22b was present only in cultivated T. monococcum subsp. monococcum accessions but absent in all tested tetraploid and hexaploid wheat lines. We developed a diagnostic molecular marker for Sr22b and successfully introgressed a T. monococcum chromosome segment containing this gene into hexaploid wheat to accelerate its deployment and pyramiding with other Sr genes in wheat breeding programmes. Sr22b can be a valuable component of gene pyramids or transgenic cassettes combining different resistance genes to control this devastating disease.
Highlights
Wheat is an important cereal crop that contributes a substantial proportion of the calories and proteins consumed by humankind
To quantify the infected leaf area, we measured the percentage of the leaf area covered with Puccinia graminis f. sp. tritici (Pgt) pustules on six independent infected leaves of TmR54-3 and
We found no significant transcriptional differences between plants inoculated with Sr22b-avirulent Pgt race 34PKUSC and mock-inoculated with water at 1, 3- and 6-days post inoculation (Fig. 4), suggesting that Sr22b is not induced by the presence of the Pgt pathogen
Summary
Wheat is an important cereal crop that contributes a substantial proportion of the calories and proteins consumed by humankind. Tritici (Pgt), the causal agent of wheat stem rust (or black rust), has historically been a devastating fungal disease of tetraploid and hexaploid wheat. In the past, this pathogen was effectively controlled by growing resistant wheat varieties and eradicating alternate host (Berberis vulgaris) plants around cereal fields (Roelfs, 1985; Roelfs, 1982; Singh et al, 2015). After the year 1998, this disease became a major concern again after the emergence and spread of the Pgt race TTKSK (Ug99) and its variants ( the Ug99 race group), which were virulent on the majority of resistance genes deployed worldwide, including resistance genes Sr31 and Sr38 (Pretorius et al, 2000; Singh et al, 2011; Singh et al, 2006). Additional highly virulent Pgt races unrelated to
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