Abstract
The frequency of spontaneous mutants resistant to both chlorate and selenite was compared with the frequency of mutations induced by ultraviolet rays. The results showed that, the frequencies of chlorate resistance strains which isolated from two different parenting strains, AA1 and SW1, were higher than 27 and 23 times from spontaneous frequencies respectively, so as for selenite resistant results, the induced and isolating mutants of two different parenting strains, AA1 and SW3, were about 5 and 8 times higher than their spontaneous frequency, respectively. The mutant strains (Chl5-Chl9) and (Chl13-Chl27) were all resistant to chlorate-nitrate auxotrophic but they were distributed between spontaneous and induced as well as white or black conidia, while the mutants sel1-sel5 resistance to the selenite are color mutants (white conidia) and sulfates auxotrophic at the same time. Heterokaryon was also formed in Alternaria alternata between the two black Chl10 strains, nitrate auxotrophic, have the genotype (nit10, w2 +, s2 +) and the white Sel2 strain, have the genotype (nit10 +, w2s2) which represent important Preliminary event at the beginning of a para-sexual analysis in this plant pathogen fungus