Trifolirhizin and maackiain in red clover: changes in Fusarium roseum “Avenaceum”-infected roots and in vitro effects on the pathogen

Levels of trifolirhizin, a pterocarpanoid glycoside found in aseptically grown roots of red clover (Trifolium pratense) at concentrations as high as 1·6 mg g⁻¹ dry weight, decreased as symptom severity increased in roots inoculated with Fusarium roseum “Avenaceum” and harvested 6 days after inoculation. The aglycone maackiain, not detected in uninfected roots, was present in all but the least severely infected roots; however, trifolirhizin loss was evident even in these lightly damaged roots.

Radial mycelial growth of F. roseum was not inhibited by trifolirhizin and, although maackiain inhibited growth, the percentage inhibition decreased over the 4 day incubation period. Germ tube growth of F. roseum was more markedly inhibited by maackiain than was mycelial growth. In liquid culture, F. roseum hydrolysed trifolirhizin to maackiain and, under similar conditions, this pathogen caused a relatively rapid loss of maackiain from the medium.