Interactions of Phytophthora cinnamomi and Trichoderma spp. in relation to propagule production in soil cultures at 26 °C

Effects of Trichoderma harzianum and T. polysporum on chlamydospore production by two isolates of Phytophthora cinamomi were determined over a 21-day period in nonsterile, sterilized, and sterilized amended soil. Trichoderma was either coinoculated with P. cinnamomi or added to the cultures on day 3 of the incubation period. In nonsterile soil, conversion of mycelial fragments in the P. cinnamomi inoculum to chlamydospores resulted in an initial slight increase in chlamydospore numbers. In cultures where either of the Trichoderma isolates was added on day 3, a significiant reduction in chlamydospore numbers was observed on day 4; however, neither of the Trichoderma isolates at either inoculation time significantly affected clamydospore numbers by day 21. Results from studies with sterilized amended soil indicated that a reduction in P. cinnamomi chlamydospore numbers by either of the Trichoderma isolates was dependent upon availability of simple carbohydrates. In sterilized nonamended soil, the number of chlamydospores was increased in cultures containing either Trichoderma isolate; in sterilized amended soil chlamydospore numbers were initially reduced, followed by a general increase as the nutrients were depleted. Neither of the Trichoderma isolates exhibited significant antagonistic qualities toward P. cinnamomi.