INDUCTION AND GENETIC-CHARACTERIZATION OF ULTRAVIOLET-SENSITIVE MUTANTS IN THE ELM TREE PATHOGEN OPHIOSTOMA-ULMI (SENSU-LATO)

The lethal and mutagenic effects of ultraviolet (uv) irradiation on Ophiostoma ulmi sensu lato were tested. Exposure to uv rays increased the frequency at which benomyl-resistant mutants were recovered in five wild-type strains representing the non-aggressive species 0. ulmi and both Eurasian and North American races of the aggressive 0. novo-ulmi. Treatment of yeast-like cells from wild-type strain MH 75 and laboratory strain LB 44-R-2 with the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine allowed the recovery of four uv-sensitive mutants. All mutants were photoreactivable, whereas one strain was resistant to caffeine. Meiotic analysis provided evidence that the four strains carried non-allelic mutations. The uvs1 and uvs3 loci were linked and found to occur on linkage group I. The uvs2 and uvs4 loci were assigned to linkage groups III and IV, respectively. Two of the uv-sensitive strains also appeared to be hypermutable and might therefore be useful for the induction of additional types of mutants in 0. ulmi sensu lato.