Chromosomal location of a gene conditioning insensitivity in wheat to a necrosis-inducing culture filtrate from Pyrenophora tritici-repentis

Previous research indicates that infection by the tan spot fungus (Pyrenophora tritici-repentis) produces two genetically distinct symptoms in wheat (Triticum aestivum): tan necrosis and extensive chlorosis. Necrosis-inducing isolates of P. tritici-repentis release a host-selective toxin in culture that produces a reaction highly associated with the induction of tan necrosis in susceptible wheat genotypes. The objectives of this research were to determine the number of genes conditioning insensitivity to a necrosis-inducing culture filtrate in a population of wheat F-3 families, and to map the insensitivity gene(s) using restriction fragment length polymorphisms (RFLPs). The population consisted of 58 F-3 families derived from the cross of a resistant synthetic hexaploid, W-7976, with the susceptible cultivar 'Kulm.' At least 16 individuals from each F-3 family were infiltrated with culture filtrate from the P. tritici-repentis isolate 86-124 and were scored as insensitive or sensitive. Low-copy DNA clones that hybridized to group 5 wheat chromosomes were used to detect RFLPs associated with insensitivity. The families segregated in a ratio of 15:29:14 homozygous insensitive/segregating/homozygous sensitive, suggesting that a single nuclear gene was responsible for conditioning insensitivity to the pathogenic factor(s) in the culture filtrate. RFLPs were detected that flanked the locus conferring insensitivity at distances of 5.7 and 16.5 cM. Aneuploid analysis indicated that this gene resided on the long arm of chromosome 5B. We proposed the symbol tsn1 to designate this gene.