GENERATION AND UTILIZATION OF CHEMICAL-RESISTANT MUTANTS IN PYRENOPHORA-TRITICI-REPENTIS, THE CAUSAL AGENT OF TAN SPOT OF WHEAT

Tan spot, caused by the fungal pathogen Pyrenophora tritici-repentis, is a major leaf spot disease of wheat worldwide. To facilitate genetic analysis of this homothallic fungus, mutants resistant to the fungici de iprodione or hygromycin B were created through ultraviolet light mu tagenesis and used in sexual crosses. Conidia from two isolates of P. tritici-repentis, sensitive to both chemicals (iprodione-S hygromycin- S), were exposed to ultraviolet light to obtain four mutants resistant to iprodione but sensitive to hygromycin B (iprodione-R hygromycin-S) and three mutants resistant to hygromycin B but sensitive to iprodion e (iprodione-S hygromycin-R). The mutants were paired in all combinati ons, and the markers allowed crossed progeny to be distinguished from selfed progeny. Crossed ascospore progeny from pairings between iprodi one-R hygromycin-S isolates and iprodione-S hygromycin-R isolates and between iprodione-R hygromycin-a isolates and iprodione-S hygromycin-S segregated 1:1 for resistance-sensitivity to both iprodione and hygro mycin B. These results indicate that one locus controls iprodione resi stance and a second independent locus controls hygromycin B resistance . This study should facilitate further genetic research on the tan spo t fungus by providing a simple marker system.