Population dynamics of Trichoderma in fumigated and compost-amended soil and on strawberry roots

Effectiveness of Trichoderma strains for biocontrol of soilborne pathogens requires an improved understanding of soil and root ecology of this fungus. We compared the population dynamics of Trichoderma hamatum strain T382 (T382) and indigenous Trichoderma spp. in soil and on roots in different strawberry production systems. Strawberry transplants, either amended or not-amended with Trichoderma biocontrol strains, were planted in field soil left untreated or treated with soil fumigant, compost, and compost-amended with T382. Soil and root samples were taken between October and June of two production seasons (2002-03 and 2003-04), and Trichoderma populations were assessed by plating soil dilutions and root pieces onto selective medium. Identity of T382 was confirmed using strain-specific primers. T382 became established and maintained a stable population of 103 cfu/g soil throughout the growing season when added to field soil in amended compost, but T382 was rarely isolated from strawberry roots. Populations of indigenous Trichoderma spp. were up to 60-fold greater in fumigated soil than in any other soil treatment. Indigenous Trichoderma spp. were isolated from a greater proportion (20-50%) of roots in fumigated soil than from roots in the other treatments (0-20%). Transplant treatments did not significantly affect Trichoderma populations on roots or in soil during field production. This study showed that compost may be used as a substrate to establish and promote survival of Trichoderma in field soil, and illustrates how soil manipulation can affect population dynamics of indigenous Trichoderma spp. on roots and in soil.