Genetics of wheat–Pyrenophora tritici-repentis interactions

Abstract

Tan spot, caused by an ascomycete fungus Pyrenophora tritici-repentis, is one of the most devastating foliar diseases of wheat. This fungus induces two distinct symptoms, tan necrosis and extensive chlorosis, on susceptible wheat cultivars. Besides causing average yield losses of 5-10%, tan spot also causes significant losses in grain quality by grain shriveling, red smudge, and black point. Conservation agriculture in combination with wheat monoculture involving cultivation of susceptible cultivars has resulted in frequent onset of tan spot epidemics worldwide. Development of new resistant wheat cultivars, in conjunction with crop rotation, will provide an effective, economical, and environmentally safe means of controlling tan spot. Presently, eight races of P. tritici-repentis have been identified worldwide based on the ability to induce necrosis and chlorosis symptoms on a set of differential wheat cultivars. P. tritici-repentis is a homothallic fungus having both sexual and asexual reproduction resulting in high genetic diversity worldwide. Both quantitative and qualitative mode of inheritance for resistance to tan spot of wheat has been reported. The tan spot fungus produces multiple host-specific toxins and host resistance is highly correlated to insensitivity to toxins. Genetic studies have further confirmed that wheat-P. tritici-repentis follows the toxin model of gene-for-gene hypothesis although other mechanism of host-pathogen interaction may exist and exploitation of all resistance phenomenon is to be adopted to develop durable resistant cultivars.

Evaluation of CIMMYT germplasm for resistance to leaf spotting diseases of wheat

“…development, yield losses of up to 50% have been reported (Shabeer & Bockus 1988;Singh et al 2010). Tan spot also causes significant loss in grain quality by red smudge, dark smudge and black point (De Wolf et al 1998;Fernandez et al 1998).…”

“…Although, the application of fungicides and disease management strategies are effective in controlling tan spot, their use may leave undesirable affects causing environmental concerns and higher cost of production. Therefore, resistant cultivars are the most effective, economical, and environmentally friendly means of controlling tan spot of wheat (De Wolf et al 1998;Singh et al 2010).…”

“…Presently isolates of the tan spot fungus are classified into 8 races (Lamari et al 2003). Three races 2, 3, and 5 can be designated as basic races while other races based on the reaction on the standard differential set are different combinations of the basic races with the exception of race 4 which is avirulent (Singh et al 2010).…”

“…Toxin Ptr ToxA, a wellcharacterized host-selective proteinaceous toxin, is produced by races 1, 2, 7, and 8 (Singh et al 2010), is the main factor causing the necrotic symptom in susceptible wheat cultivars. Chlorosis inducing toxins Ptr ToxB, produced by races 5, 6, 7, and 8 and Ptr ToxC produced by race 1, and hypothesized to be produced by races 3, 7, and 8, have been identified and well characterized.…”

“…Chlorosis inducing toxins Ptr ToxB, produced by races 5, 6, 7, and 8 and Ptr ToxC produced by race 1, and hypothesized to be produced by races 3, 7, and 8, have been identified and well characterized. Studies have established that sensitivity to toxins Ptr ToxA, Ptr ToxB, and Ptr ToxC and susceptibility to their producer races are each controlled by the same gene (De Wolf et al 1998;Singh et al 2010).…”