Soil-borne plant pathogens such as Rhizoctonia solani (Kuhn), Pythium ultimum
(Trow) and Sclerotinia trifoliorum (Eriks) can reduce grass and forage legume
establishment. The potential for biocontrol of these pathogens by Trichoderma
fungi was evaluated. Following dual culture assays, nine Trichoderma isolates (five
of Trichoderma atroviride and one each of Trichoderma hamatum, Trichoderma
koningiopsis, Trichoderma viride and Trichoderma virens) were chosen for
assessment in pot experiments. In the presence of R. solani, perennial ryegrass
(Lolium perenne L.) emergence was increased by 60–150% by two isolates of T.
atroviride and by 35–212% by the isolate of T. virens, with the increase depending
on growing medium and amount of pathogen inoculum. Red clover (Trifolium
pratense L.) emergence in the presence of S. trifoliorum was significantly increased
by two T. atroviride isolates and the T. hamatum isolate. In the presence of P.
ultimum, white clover (Trifolium repens L.) emergence was increased by 25–42%
by one isolate of T. atroviride and the T. hamatum isolate. However, for all three
pasture species, some Trichoderma isolates reduced seedling emergence. Seedling
growth (shoot and root fresh weight/plant) of the three pasture species was
significantly increased by one or more T. atroviride isolates. On the basis of these
results for both disease reduction and growth promotion, four T. atroviride
isolates were selected for field assessment as biocontrol agents of soil-borne
pathogens of pasture species.