Genetic analysis of sensitivity to a Pyrenophora tritici-repentis necrosis-inducing toxin in durum and common wheat

The fungus Pyrenophora tritici-repentis produces a toxin (Ptr ToxA) that ca uses rapid cell necrosis in sensitive wheat genotypes. A single recessive g ene (tsnl) on chromosome 5BL in common wheat confers insensitivity to this toxin. Our objectives were to analyze the allelic relationships of genotype s that have shown insensitivity to a P. tritici-repentis necrosis-inducing toxin, map the gene for insensitivity to the necrosis-inducing factor produ ced by P. tritici-repentis in a durum wheat population, and determine the r eaction to P. tritici-repentis of aneuploid genotypes that do not contain t he gene. Greenhouse-grown plants of seven populations from crosses of insen sitive genotypes; an F-2 population of durum wheat; and 'Chinese Spring' an euploid, substitution, and deletion lines were infiltrated with Ptr ToxA. A ll crosses involving insensitive genotypes failed to produce sensitive prog eny, indicating that the same gene is present in these genotypes. The gene for insensitivity in the durum population was mapped to the same region on 5BL as in common wheat using restriction fragment length polymorphism marke rs. 'Chinese Spring', its homoeologous group 5 nullisomic-tetrasomic stocks , and 5BL deletion lines were insensitive to the toxin. Substitution of a 5 B chromosome from sensitive genotypes into 'Chinese Spring' resulted in sen sitivity. Therefore, insensitivity is not conferred by a gene product per s e, but rather conferred by absence of a gene for sensitivity.