Population Dynamics of Three Commercial Biocontrol Organisms on Strawberry Plants Grown in Coir Substrate Under Protection

ABSTRACT Understanding the ecology of biocontrol agents (BCAs) is needed for their effective deployment. We used a propidium monoazide (PMA)‐based quantitative PCR method to study the dynamics of viable populations of (1) Gliocladium catenulatum and Trichoderma asperellum on root surfaces following drenching and (2) G . catenulatum and Bacillus subtilis on leaves and flowers via spraying. Experiments were conducted on table‐top strawberry grown in coir substrate under protection. The viable population size of both G . catenulatum and T . asperellum on roots did not decrease or increase for at least 2 weeks after application. Both G . catenulatum and B. subtilis survived on strawberry flowers, with the mortality rate varying greatly among individual applications. There was an overall decrease in the viable population size for both BCAs, but only a small proportion of variability in the BCA mortality rate was attributable to weather conditions. The daily mortality rate linearly decreased with the increasing daily variability in vapour pressure deficit. Neither G . catenulatum nor B. subtilis led to a statistically significant reduction in Botrytis infection of flowers when applied at a concentration of 10 8 spores/mL ( G . catenulatum ) or 10 9 CFU/mL ( B. subtilis ) before or after inoculation of flowers with 10 5 spores/mL Botrytis cinerea . This failure in controlling B. cinerea may partially be due to the possibility that some flowers were infected by naturally occurring B. cinerea before BCAs were applied. The present research suggests that biocontrol of root pathogens in strawberry grown in coir substrate may hold a greater promise than the control of flower/fruit diseases.