Screening Trichoderma spp. as a Biocontrol Agent of Impatiens Downy Mildew (Plasmopara obducens)

Abstract

A relatively recent epidemic of Plasmopara obducens, the oomycete responsible for Impatiens downy mildew, has spread throughout several countries including the United States. If P. obducens oospore behavior is similar to other, better studied downy mildews, oospores may be able to remain in the soil for long periods of time, making it extremely difficult to eliminate the disease. The objective of this experiment was to determine if Trichoderma asperellum isolate 04-22 and a second unidentified Trichoderma species (isolate Tri-4) has the potential to remediate soils infested with P. obducens oospores. The experiment showed the effects of T. asperellum 04-22 and Trichoderma sp. isolate Tri-4 on P. obducens oospores was negligible, and no mycoparasitism was observed. Only one replicate showed a lower number of oospore plasmolysis in the treatment plate compared to the control. The Trichoderma spp. treatment plates showed greater than 50% plasmolysis in all cases. The experiment demonstrated that the two Trichoderma spp. are unlikely to be an effective biological control agent of P. obducens oospores, particularly for soil sanitation purposes.