Virulence differences of Fusarium roseum isolates in red clover roots not explained by phytotoxins activity

The relationship of toxic fungal metabolites to the virulence of Fusarium roseum 'Acuminatum' and 'Avenaceum' isolates that cause root rot of red clover was investigated. The biological activity of filtrates of root solution cultures was tested, using seed germination, rust spore germination, and root electrolyte and potassium-ion leakage as assays. Although activity was detected for all pathogenic isolates in all assays except the rust spore germination assay, it was not positively correlated with the virulence of the isolates. Histological examinations of infected roots showed a close relationship between hyphal development and visible symptoms. Differences in virulence between isolates of F. roseum could not be obviously related to differential production of phytotoxins.