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 Op hiostoma ulmi sensu lato were tested. Exposure to uv rays increased th e 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 laborat ory strain LB 44-R-2 with the alkylating agent N-methyl-N'-nitro-N-nit rosoguanidine allowed the recovery of four uv-sensitive mutants. All m utants were photoreactivable, whereas one strain was resistant to caff eine. Meiotic analysis provided evidence that the four strains carried non-allelic mutations. The uvs1 and uvs3 loci were linked and found t o occur on linkage group I. The uvs2 and uvs4 loci were assigned to li nkage groups III and IV, respectively. Two of the uv-sensitive strains also appeared to be hypermutable and might therefore be useful for th e induction of additional types of mutants in 0. ulmi sensu lato.