Determining of chlorate resistant nit mutant's phenotypes and their frequency in Fusarium oxysporum f. sp. sesami, the causal agent of sesame yellows and wilt oures rotting in sesame, in Fars Province

In order to identification of chlorate resistant Fusarium oxysporum f. sp. sesami nit mutant´s phenotypes and studing their frequency, pathogens were isolated from sesame plants during 2005 and 2006 major sesame growing area in Fars province, such as Darab, Fasa, Noorabad, Kazeroon, Neiriz, Estahbab and Zarghan. In this study, 32 isolates of this pathogen with maximum genetic diversity based on geographic origin were selected for pathogenecity test. Sectors and nitrate non-utilizing (nit) mutants of isolates produced on MMC and PDC media. Frequency of nit mutants on MMC was 264 or 79.5 percent of 356 sectors and on PDC was 330 or 74.16 percent of 415 sectors. Other mutants were Crn mutants that showed minimum wild type growth on Medium containing. Phenotypic classes of chlorate resistante mutants were determined by types of growth on basal medium nitrogen sources such as sodium nitrite, sodium nitrate and hypoxanthine. Mutants were grouped in three phenotypic classes: nit1, nit3 and nitM. The frequency of nit1 in PDC was more than MMC,but frequency of nit3 and vise versa frequency of nitM on MMC was more than PDC. On PDC, 63.94 percent of mutants were nit1 but on MMC, 37.12 and 14.4 percent of mutants were nit3 and nitM, respectively.