Characterization of Seedling Infection Types and Adult Plant Infection Responses of Monogenic Sr Gene Lines to Race TTKS of Puccinia graminis f. sp. tritici

Abstract

Stem rust, caused by Puccinia graminis f. sp. tritici, historically was one of the most destructive diseases of wheat and barley. The disease has been under effective control worldwide through the widespread use of host resistance. A number of stem rust resistance genes in wheat have been characterized for their reactions to specific races of P. graminis f. sp. tritici. Adult plant responses to race TTKS (also known as Ug99) of monogenic lines for Sr genes, a direct measurement of the effectiveness for a given gene, have not been investigated to any extent. This report summarizes adult plant infection responses and seedling infection types for monogenic lines of designated Sr genes challenged with race TTKS. High infection types at the seedling stage and susceptible infection responses in adult plants were observed on monogenic lines carrying Sr5, 6, 7a, 7b, 8a, 8b, 9a, 9b, 9d, 9g, 10, 11, 12, 15, 16, 17, 18, 19, 20, 23, 30, 31, 34, 38, and Wld-1. Monogenic lines of resistance genes Sr13, 22, 24, 25, 26, 27, 28, 32, 33, 35, 36, 37, 39, 40, 44, Tmp, and Tt-3 were effective against TTKS both at the seedling and adult plant stages. The low infection types to race TTKS observed for these resistance genes corresponded to the expected low infections of these genes to other incompatible races of P. graminis f. sp. tritici. The level of resistance conferred by these genes at the adult plant stage varied between highly resistant to moderately susceptible. The results from this study were inconclusive for determining the effectiveness of resistance genes Sr9e, 14, 21, and 29 against race TTKS. The understanding of the effectiveness of individual Sr genes against race TTKS will facilitate the utilization of these genes in breeding for stem rust resistance in wheat.

Fine mapping and characterization of Sr21, a temperature-sensitive diploid wheat resistance gene effective against the Puccinia graminis f. sp. tritici Ug99 race group

“…Subsequent genetic analyses determined those Sr21 gene postulations were accurate, confirming the reduced infection of race TTKSK isolate 04KEN156/04 to plants carrying Sr21 (Rouse and Jin 2011a). Variable reactions of race TTKSK and related races to monogenic lines with Sr21 were reported by different laboratories in the United States, Canada, and South Africa (Jin et al 2007;Visser et al 2011;Pretorius et al 2010). Since the Sr21 resistance gene is part of the North American differential set, these variable reactions affect the five-letter designation of the Ug99 race group isolates.…”

“…This isolate was classified as race TTKSK according to the North American system for Pgt race nomenclature (Jin et al 2007;Jin et al 2008). The unique virulence combination of race TTKSK allows this race to overcome resistance in the majority of wheat cultivars in Asia , the United States , and Canada (Fetch 2007) and is considered a threat to global wheat production.…”

“…Conflictive or inconclusive results were reported regarding the effectiveness of Sr21 resistance against race TTKSK (Jin et al 2007). Accession 'Einkorn' (CI 2433) and other T. monococcum accessions were postulated to have Sr21 based on their reduced infection in response to race TTKSK relative to susceptible controls (Rouse and Jin 2011b).…”

Genetic analysis of rust resistance genes in global wheat cultivars: an overview

“…To date, approximately 58 stem rust resistance (Sr) genes have been identified [88,89] and numerically designated as Sr1 to Sr58 as part of the International Wheat Genetics Symposium Gene Catalog [26,90]. Among these genes, at least 27 genes, including Sr2 (Yr30), Sr13, Sr21, Sr22, Sr24, Sr25, Sr26, Sr27, Sr28, Sr32, Sr33, Sr35, Sr36, Sr37, Sr39, Sr40, Sr42, Sr44, Sr45, Sr46, Sr47, Sr51, Sr52, Sr53, Sr55 (Lr67/Yr46/ Pm46), Sr57 (Lr34/Yr18/Pm38), and Sr58 (Lr46/Yr29/Pm39), are effective or partially effective against the Ug99 race group [91][92][93][94][95][96][97][98][99][100]. Among these 27 genes, Sr2, Sr13, Sr22, Sr25, Sr26, Sr35, Sr39 and Sr40 were reported to be the most effective against Ug99 [87,[101][102][103].…”

“…More than 20% of the germplasms and elite lines of South African wheat carry Sr24 as a major resistance gene [198]. The stem rust resistance genes Sr25 and Sr26 are effective against variants of Ug99, TTKST and TTTSK [87,95], The stem rust resistance gene Sr31 is very common in world wheat varieties. Before the emergence of Ug99, stem rust resistance was maintained mainly by Sr31 in most countries around the world, except for Australia [101].…”