Population Race Structure of Pyrenophora tritici-repentis Prevalent on Wheat and Noncereal Grasses in the Great Plains

Abstract

The fungus Pyrenophora tritici-repentis, cause of tan spot of wheat, is an important foliar pathogen worldwide. Genetic variation in the fungal population prevalent in the Great Plains was studied by analysis of 270 single-spore isolates of P. tritici-repentis recovered from wheat, durum, and 10 noncereal grasses: Alti wild rye, barnyard grass, crested wheatgrass, intermediate wheatgrass, needle and thread grass, quackgrass, smooth bromegrass, sand reedgrass, slender wheatgrass, and wild barley. The isolates were grouped into five known races based on necrosis and/or chlorosis induction on standard differentials with two additional wheat genotypes ND495 and M-3. The isolates recovered from wheat were races 1, 2, and 4, while those from durum were races 1 and 5. Isolates from noncereal grasses were all race 4, except for the recovery of two isolates of race 1 from smooth bromegrass. Race 3 was not found in this study. This is the first record of barnyard grass and slender wheatgrass as alternative hosts for P. tritici-repentis. The recovery from noncereal grasses suggests that the fungus has a fairly wide host range; however, predominance of a race that is avirulent on wheat on these grasses tends to eliminate their significance in the disease epidemiology of wheat. The results indicate that P. tritici-repentis has a diverse population on wheat and noncereal grasses. For durable resistance, wheat lines should be tested against all virulent races found in the field.

Proteinaceous necrotrophic effectors in fungal virulence

“…Like PtrToxA, PtrToxB is also a small secreted protein (6.6 kDa) which causes chlorosis on sensitive wheat genotypes and is encoded by a multicopy gene, PtrToxB (Orolaza et al 1995;Strelkov et al 1999;Martinez et al 2001). Although not as prevalent as PtrToxA, PtrToxB has been found to be produced by several isolates around the world (Ali and Francl 2003;Friesen et al 2005;Lamari et al 2005). Wheat sensitivity is conditioned by the dominant Tsc2 gene, which has been mapped to the short arm of chromosome 2B (Strelkov et al 1999;Friesen and Faris 2004).…”

Race Diversity of Pyrenophora tritici-repentis in South Dakota and Response of Predominant Wheat Cultivars to Tan Spot

“…is an important foliar disease of wheat in the US Northern Great Plains (NGP) [1]. In addition to wheat, a primary and economical host, the fungus has a wide host range that includes cereals such as barley, oat, rye and many non-cereal grasses [2][3][4]. The fungus produces ovalshaped tan necrotic spots with a chlorotic halo and a small black spot in the center of the leaves of susceptible cultivars.…”

“…Virulence variation in P. tritici-repentis has been observed based on an isolate's ability to produce necrosis and/ or chlorosis symptoms on appropriate wheat differential genotype. So far, the isolates from wheat and alternative host plants have been grouped into eight races [ 2,[9][10][11] and race 1 was the most prevalent race observed in Africa, Asia, Europe, North and South America [2,9,[11][12][13][14][15]. Further, P. tritici-repentis produces three host-selective toxins, Ptr ToxA, Ptr ToxB, and Ptr ToxC, which are associated with necrosis and chlorosis symptoms in toxins sensitive wheat genotypes [11,[16][17][18].…”

Mapping QTL for resistance againstPyrenophora tritici-repentisin wheat

“…Glenlea, Katepwa, 6B365, 6B662, Salamouni were selected based on Andrie et al (2007). M3 (Synthetic wheat, also designated as W7976) was added to the standard set of differentials to increase the chance of finding more variants in the fungal population as suggested by Ali and Francl 2003. The seeds were proportionated by Dr. Shaukat of Dep.…”