Wheat stem rust, caused by Puccinia graminis Pers. f. sp. tritici (Pgt), is a devastating fungal disease threatening global wheat production. The present paper reports the identification of stem rust resistance gene Sr60, a race-specific gene from diploid wheat Triticum monococcum L. that encodes a protein with two putative kinase domains. This gene, designated as WHEAT TANDEM KINASE 2 (WTK2), confers intermediate levels of resistance to Pgt. WTK2 was identified by map-based cloning and validated by transformation of a c.10-kb genomic sequence including WTK2 into susceptible common wheat variety Fielder (Triticum aestivum L.). Transformation of Fielder with WTK2 was sufficient to confer Pgt resistance. Sr60 transcripts were transiently upregulated 1 d post-inoculation with Pgt, but not in mock-inoculated plants. The upregulation of Sr60 was associated with stable upregulation of several pathogenesis-related genes. The Sr60-resistant haplotype found in T. monococcum was not found in polyploid wheat, suggesting an opportunity to introduce a novel resistance gene. Sr60 was successfully introgressed into hexaploid wheat, and we developed a diagnostic molecular marker to accelerate its deployment and pyramiding with other resistance genes. The cloned Sr60 also can be a useful component of transgenic cassettes including other resistance genes with complementary resistance profiles.
Work at East Malling, Kent, between 1952 and 1963 on the biology of Harpalus rufipes (Deg.) (Carabidae), the strawberry seed beetle, is described in detail, and briefer notes are given on the life-histories of H. aeneus (F.), Feronia melanaria (Ill.) and F. madida (F.), which are less abundant but may also damage strawberries. Soil samples for larvae were washed over suitable sieves, those for pupae and adults were carefully searched in the field. Soil sampling showed that adults of H. rufipes colonised strawberry fields only during the fruiting period, weedy arable land and grassy situations being preferred at other times. By soil sampling, it was found that larvae of H. rufipes hatched from eggs laid in weedy soil in late summer, and evidence from pitfall trapping showed that the first two instars were sometimes active on the soil surface from August to December, before penetrating to a depth of 6–18 in. to overwinter. Development was resumed in April, but the larvae remained and the pupae were subsequently found at the overwinter depth in the soil, the larvae presumably feeding on the seed of fat hen (Chenopodium album) lodged in worm burrows. Third-instar larvae occurred from April to July, and adults emerged soon after. In the laboratory, adults lived for a further two years, hibernating in winter, and becoming active and breeding each summer. Laboratory observations on oviposition periods, fecundity and feeding were also made. Larvae, which in the field were mostly found associated with plants of fat hen, fed on germinating seeds of several plants in the laboratory but growth was most rapid when they were reared on the germinating seed of fat hen.The life-cycles and habits of the three other species are briefly described and compared with those of H. rufipes, the seasonal occurrence of the different stages in the life-cycles of all species being shown in a table.
Key messageThe new stem rust resistance gene Sr60 was fine-mapped to the distal region of chromosome arm 5AmS, and the TTKSK-effective gene SrTm5 could be a new allele of Sr22. AbstractThe emergence and spread of new virulent races of the wheat stem rust pathogen (Puccinia graminis f. sp. tritici; Pgt), including the Ug99 race group, is a serious threat to global wheat production. In this study, we mapped and characterized two stem rust resistance genes from diploid wheat Triticum monococcum accession PI 306540. We mapped SrTm5, a previously postulated gene effective to Ug99, on chromosome arm 7AmL, completely linked to Sr22. SrTm5 displayed a different race specificity compared to Sr22 indicating that they are distinct. Sequencing of the Sr22 homolog in PI 306540 revealed a novel haplotype. Characterization of the segregating populations with Pgt race QFCSC revealed an additional resistance gene on chromosome arm 5AmS that was assigned the official name Sr60. This gene was also effective against races QTHJC and SCCSC but not against TTKSK (a Ug99 group race). Using two large mapping populations (4046 gametes), we mapped Sr60 within a 0.44 cM interval flanked by sequenced-based markers GH724575 and CJ942731. These two markers delimit a 54.6-kb region in Brachypodium distachyon chromosome 4 and a 430-kb region in the Chinese Spring reference genome. Both regions include a leucine-rich repeat protein kinase (LRRK123.1) that represents a potential candidate gene. Three CC–NBS–LRR genes were found in the colinear Brachypodium region but not in the wheat genome. We are currently developing a Bacterial Artificial Chromosome library of PI 306540 to determine which of these candidate genes are present in the T. monococcum genome and to complete the cloning of Sr60.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-017-3024-z) contains supplementary material, which is available to authorized users.
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