Evaluation of Elite Wheat Germ Plasm for Resistance to Tan Spot

Abstract

Tan spot, caused by Pyrenophora tritici-repentis, is a serious foliar disease of wheat (Triticum aestivum) in North America. Control of tan spot through management practices and fungicide application is possible; however, the use of resistant varieties is the most effective and economical means of controlling tan spot. This study was conducted to determine the disease reaction of 126 elite hard red spring, white, and durum wheat varieties and advanced breeding lines collected from the northern Great Plains of the United States and Canada to individual races/toxins of P. tritici-repentis. Seedling evaluation of the 126 genotypes was done under controlled environmental conditions with virulent races 2, 3, and 5 of P. tritici-repentis and toxins Ptr ToxA and Ptr ToxB. Based on disease reactions, two resistant varieties and two advanced breeding lines adapted to the northern Great Plains were found to be resistant to all the races and insensitive to the toxins tested. Additionally, six genetically diverse lines/varieties were identified to be resistant to tan spot; however, these sources may not be well adapted to the northern Great Plains. These results suggest that the wheat germ plasm contains a broad genetic base for resistance to the most prevalent races of P. tritici-repentis in North America, and the resistant sources identified in this study may be utilized in wheat breeding programs to develop tan spot resistant varieties.

Evaluation and Association Mapping of Resistance to Tan Spot and Stagonospora Nodorum Blotch in Adapted Winter Wheat Germplasm

“…A large portion of the HRWW lines evaluated were susceptible to individual isolates, which is similar to the findings from most of the previous studies using other wheat germplasm Chu et al 2008a,c;Mergoum et al 2007;Singh et al 2006;Xu et al 2004b). Noriel et al (2011) conducted the first tan spot resistance screening in a collection of winter wheat germplasm including cultivars, breeding lines, and landraces mainly from the United States and China.…”

“…Previous studies for identifying sources of resistance were done for one (Mergoum et al 2007;Noriel et al 2011;Rees and Platz 1990;Singh et al 2006) or both of these diseases but only with one or two races or isolates Chu et al 2008a,c;Xu et al 2004b). Because we evaluated these lines with multiple races or isolates of the two pathogens, it was possible to provide a comprehensive and robust data set to wheat breeders.…”

“…ToxA-insensitive and tan spot-susceptible lines have also been identified in the previous screening studies Noriel et al 2011;Singh et al 2006). This could be explained by the presence of Ptr ToxC or other unknown NE-sensitivity gene interactions (Faris et al 2013;Noriel et al 2011).…”

“…in the northern Great Plains of the United States (De Wolf et al 1998;McMullen and Adhikari 2009;Singh et al 2006). The two diseases often occur simultaneously and are major components of the leaf spotting complex (McMullen and Adhikari 2009).…”

“…Screening for resistance to tan spot or SNB has been conducted on various wheat germplasms, including bread wheat from Brazil (Rees and Platz 1990); synthetic hexaploid wheat (Xu et al 2004b); tetraploid wheat, including Triticum turgidum, T. carthlicum, T. dicoccum, T. polonicum, and T. dicoccoides (Chu et al 2008a,c); hard red spring wheat cultivars or elite breeding lines from the Northern Great Plains (Mergoum et al 2007;Singh et al 2006); and wild grass-wheat derivatives (Alam and Gustapson 1988;Oliver et al 2008). This has led to the identification of some sources of resistance to each disease or both.…”