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United States Department of Agriculture

Agricultural Research Service

Research Project: Genetic Improvement of Durum and Spring Wheat for Quality and Resistance to Diseases and Pests

Location: Cereal Crops Research

Title: Characterization of Thinopyrum species for seedling resistance to stem rust and variability in ploidy level

Authors
item Zheng, Q -
item Klindworth, Daryl
item Friesen, Timothy
item Liu, A.-F -
item Li, Z.-S -
item Zhong, S -
item Jin, Yue
item Xu, Steven

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 19, 2014
Publication Date: N/A

Interpretive Summary: In the relative species of wheat, several wild species under genus Thinopyrum (common name: wheatgrass) have been used as sources of resistance to rusts and other major diseases in wheat. For stem rust resistance, at least five stem rust resistance (Sr) genes (i.e. Sr24, Sr25, Sr26, Sr43, and Sr44) were transferred from tall wheatgrass (Thinopyrum ponticum) and intermediate wheatgrass (Th. intermedium). In an effort to identify novel sources of resistance to stem rust race Ug99, we evaluated and characterized the stem rust resistance of 241 lines belonging to five wheatgrass species currently maintained at the USDA-ARS Western Regional Plant Introduction Station, including Thinopyrum bessarabicum, Th. elongatum, Th. intermedium, Th. junceum, and Th. ponticum. These lines were evaluated for seedling reactions to nine stem rust races (RTQQC, QFCSC, TCMJC, TPMKC TMLKC, TPPKC, TTTTF, TRTTF, and TTKSK) and analyzed with molecular markers linked to the five Sr genes from Thinopyrum species. The results showed that all lines but one (Th. elongatum PI 531718) were resistant to all or most of the stem rust races. Among the five species, Th. elongatum and Th. ponticum exhibited the highest level of resistance and most of the lines of the two species showed near-immunity to all of the races tested. The lines 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. The results from this study demonstrate that these wheatgrass species are a rich source of stem rust resistance for wheat improvement.

Technical Abstract: 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.

Last Modified: 8/22/2014
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