Mendelian inheritance of resistance to tan spot [Pyrenophora tritici-repentis] in selected genotypes of durum wheat (Triticum turgidum)

Isolates of Pyrenophora tritici-repentis induce necrosis and chlorosis in susceptible wheats. The inheritance of the chlorosis response induced by race 1 and the necrosis reaction induced by races 1, 3, 5, and the toxin Ptr ToxA was investigated in the durum wheat Lines 4B160, 4B242, 4B1149, and cv. Coulter. F-1, F-2, and F-2-derived F-3 progenies (F-2:3) from resistant/resistant, susceptible/resistant, and susceptible/susceptible crosses were evaluated under growth room conditions. No segregation was observed in F-2 and F-2:3 progenies from the cross 4B1149/4B242 (resistant/resistant). Reaction to necrosis and chlorosis induced by race 1 in the F-2 and F-2:3 progenies from cross 4B160/Coulter (chlorotic/necrotic) was found to be controlled by two independently inherited loci. Reaction to necrosis induced by race 1 in crosses involving cv. Coulter (susceptible necrotic) was found to be controlled by a single locus; this locus also controls reaction to the toxin Ptr ToxA produced by races 1 and 2. Two additional and independently inherited loci controlling reactions to races 3 and 5 were identified in crosses involving line 4B160 (necrotic to races 3 and 5); one locus controls reaction to race 3, the second controls reaction to race 5. Susceptibility to necrosis and chlorosis was found to be a dominant trait throughout this study. Overall, four dominant and independently inherited genes, conferring susceptibility to the presently known races of P. tritici-repentis, were identified.