Abstract
A study of the effects of agricultural biocides on T-2 toxin production by Fusarium sporotrichioides was broadened to include other lipid products of this fungus. A detailed study of the impact of physical conditions and other aspects of the cultivation of the toxigenic mould in liquid shaken culture led to the development of an assay protocol appropriate for the assay of biocide activity. The protocol, which had been optimised with respect to reproducibility, incorporated a time-course and two biocide treatments one of which is calculated to produce little or no inhibition, the other to approximate 50% inhibition. Fungicides which act against growth and growth related activity tend to produce little change in the biomass specific yield (BSY) of lipid products. In contrast, biocides which inhibit growth through inhibition at specific sites in lipid biosynthesis produce patterns of differential BSYs, including enhancement, which vary according to dose, fungal development and the agent applied. Of particular note is the response elicited by tridemorph which at the ED dose causes a reduction in total lipid and a large enhancement in T-2 toxin production. The low dose rate produces enhanced growth and strongly inhibits the production of toxin. A more detailed investigation of this compound led to a testable, if speculative, model of interdependant regulation in primary and secondary lipid biosynthesis. The activities of five ergosterol biosynthesis inhibitors (EBIs), of which tridemorph is one, are documented and it is suggested that the EBIs, as a group, might prove to be useful tools in future studies of regulation in lipid bioynthesis. Three herbicides tested showed limited inhibition of growth but a marked influence on lipid biosynthesis. Data from a study of toxin production in field barley showed the results from liquid culture to be broadly predictive.