Potential of combined biological control agents to cope with Phytophthora parasitica, a major pathogen of Choisya ternata

Phytophthora parasitica infection of Choisya ternata can cause important economical loses due to root rot disease. This research focused on testing the potential benefit of chemical treatment (Mefenoxam) and Biological Control Agents (Glomus intraradices, Gliocladium catenulatum, Trichoderma atroviridae and Bacillus amyloliquefaciens) in protecting C. ternata against P. parasitica. BCAs were applied as individual and/or combined treatments. The effect of the treatment was observed by monitoring C. ternata symptoms. A real-time PCR targeting the ypt1 gene was also adapted to evaluate P. parasitica development in the substrate. The use of Mefenoxam provided the higher level of plant protection. However, a significant reduction in plant symptoms and P. parasitica development was also observed with the combined treatment of G. intraradices with G. catenulatum and G. intraradices with T. atroviridae. Another combined treatment with G. catenulatum and B. amyloliquefaciens increased the pathogen density and severity. No individual treatment had a significant effect on the pathogen. Our results highlight the potential of biological control in protecting C. ternata against P. parasitica and the advantage of combined strategies.