Competition in artifical plant growth media by Trichoderma spp.

The key to achieve successful, reproducible biological control is the gradual appreciation that knowledge of the ecological interactions taking place in soil and root environments is required to predict the condition under which biological control can be achieved and, indeed, it may be part of the reason why more biocontrol agents are reaching the market place. A comparative evaluation of life strategies of both the pathogen and its antagonists is required to predict the fate of a biopesticide in agricultural systems.The objectives of this work have been: 1) to screen a collection of Trichoderma isolates in a natural pot mix in order to select potential fungal antagonists to be employed in the biocontrol of Rhizoctonia solani damping-off of radish, and 2) to verify the hypothesis that competition for a food base plays a role in reducing pathogen activity. Fifteen Trichoderma spp., selected among 150 isolates according to their growth rate, were evaluated as potential biocontrol agents against the soil-borne plant pathogen Rhizoctonia solani on radish in vivo in a natural peat based growth medium usually employed in commercial production. Two different temporal antagonist-pathogen soil inoculation procedures were employed. Four potential biocontrol agents, all identified as T. harzianum according to the ITS sequences, were selected according to their ability of reducing radish damping off, and were employed in a Competitive Saprophytic Ability (CSA) test, in order to investigate the role of competition for a food base as a possible mechanism of biocontrol. Three of these T. harzianum isolates were able to both significantly reduce haulm fragments possession by the pathogen and damping off of radish. Reduction of possession spans for a limited period of time, varying according to the antagonists, but even after R. solani was able to re-colonize haulm fragments, the positive effects on damping off were still evident, demonstrating a “residual” effect of antagonists. On the whole, competition for the food base explains a large part of the recorded effects.