Isolation and characterization of non cerato-ulmin producing laboratory induced mutants of Ophiostoma novo-ulmi.

Five laboratory mutants of Ophiostoma novo-ulmi EAN isolate H328 were obtained from uv-irradiated and unirradiated blastoconidia. Although the mutants were initially selected on the basis of various characteristics, including failure to produce cerato-ulmin (CU) in the culture filtrate, growth-temperature responses and colony morphology, they all were eventually also found unable to produce CU when grown in liquid shake culture at 23 °C and 33°, or they produced CU only in negligible amounts. This association suggests possible linkages between CU production and other fungal metabolic pathways. Genetic analysis of crosses between the mutants and a wild type isolate of EAN 0. novo-ulmi suggested that each mutant involved a change at a single-locus, at least as far as segregations for colony morphology were concerned. Pathogenicity trials using the five mutants were carried out on four-year old Ulmus carpinifola and U. procera. Two out of the five mutants showed a significant reduction in pathogenicity in comparison to the 0. novo-ulmi wild type isolate H328.