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Characterization of Species for Wheat Stem Rust Resistance and Ploidy Level

Zheng, Qi, Klindworth, Daryl L., Friesen, Timothy L., Liu, Ai-Feng, Li, Zhen-Sheng, Zhong, Shaobin, Jin, Yue, Xu, Steven S.
Crop Science 2014 v.54 no.6 pp. 2663-2672
Puccinia graminis, Thinopyrum bessarabicum, Thinopyrum elongatum, Thinopyrum intermedium, Thinopyrum junceum, Thinopyrum ponticum, Triticum aestivum, disease resistance, genes, genetic markers, genotype, intergeneric hybridization, introduced plants, plant breeding, ploidy, races, seedlings, stem rust, wheat
In the tribe Triticeae, several wheatgrass species within the Thinopyrum genus have been used as sources of resistance to rusts and other major diseases in wheat (Triticum aestivum). For stem rust resistance, at least five Sr genes (i.e. Sr24, Sr25, Sr26, Sr43, and Sr44) were transferred from Thinopyrum species into wheat. Numerous wheat-Thinopyrum species derivatives developed by various programs were recently identified to be resistant to Ug99 lineage races of stem rust. In an effort to identify novel sources of resistance to Ug99, we evaluated and characterized the stem rust resistance of 242 accessions belonging to five Thinopyrum species currently maintained at the USDA-ARS Western Regional Plant Introduction Station, including Th. bessarabicum, Th. elongatum, Th. intermedium, Th. junceum, and Th. ponticum. These accessions were evaluated for seedling reactions to nine stem rust races (RTQQC, QFCSC, TCMJC, TPMKC TMLKC, TPPKC, TTTTF, TRTTF, and TTKSK), genotyped with molecular markers linked to the five Sr genes from Thinopyrum species, and examined for ploidy levels. The evaluation result showed that all accessions but one (Th. elongatum PI 531718) were resistant to all or most of the stem rust races tested. Among the five species, Th. elongatum and Th. ponticum exhibited the highest level of resistance and most of the accessions of the two species showed near-immunity to all of the races. The accessions belonging to the other three species (Th. bessarabicum, Th. intermedium, and Th. junceum) had varied levels of resistance ranging from near-immunity to moderate resistance. Molecular marker analysis showed that some markers appeared to be species or genus specific rather than linked to a gene of interest and thus haplotyping analysis was of limited value. Comparisons of ITs of accessions based on ploidy level suggested that higher ploidy level was associated with higher levels of stem rust resistance. The results from this study substantiate that the Thinopyrum species are a rich source of stem rust resistance.