The rhizosphere competence of the biological control agent Trichoderma atroviride isolate C52 was studied on onion roots both in the glasshouse and in the field when introduced into soil in a range of formulations. Proliferation of T. atroviride in the rhizosphere was formulation-dependent. A pellet formulation maintained the fungal concentration at 10 5 cfu per g soil, whereas solid-substrate and seed-coating formulations gave concentrations of 10 4 and 10 1 cfu per g soil, respectively.To facilitate rhizosphere-competence studies, a UP-PCR band profile generated with primer L45 for isolate C52 was used to enable conclusive identification of T. atroviride C52 when recovered from soil. When isolate C52 was introduced into Sclerotium cepivorum -infested soil as both pellet and solid-substrate formulations, there was no statistically significant difference in the disease control between these treatments, but the pellet treatment doubled the percentage of healthy plants compared with the control treatment.

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 T. atroviride and one each of T. hamatum, T. koningiopsis, T. viride and T. 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 soilborne pathogens of pasture species.

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Trichoderma harzianum C52 is an effective biocontrol agent of the onion white rot pathogen Sclerotium cepivorum For this biocontrol agent to be integrated into an existing disease management programme it must be compatible with the fungicides commonly used on onions The sensitivity of T harzianum spores to the field rate of eight fungicides commonly applied to onions was determined in an in vitro assay Results indicate that T harzianum was least sensitive to procymidone and captan and most sensitive to mancozeb tebuconazole and thiram A glasshouse pot trial confirmed that T harzianum was sensitive to mancozeb but tolerant of captan This research indicates that in furrow applications of T harzianum would be compatible with a captan and/or benomyl seed treatment for control of other seedling diseases

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