2018 ASHS Annual Conference

Pythium spp. are the causal agents of Pythium root rot and damping-off in arugula (Eruca sativa) in hydroponic systems. Synthetic chemical fungicides are not registered for application in hydroponic solutions and few are registered for application on edibles in greenhouses. The objective of this project was to assess the efficacy of microbial biofungicides on Pythium root rot caused by Pythium spp. on arugula in hydroponic systems. Companion (Bacillus subtilis GB03), Triathlon BA (Bacillus amyloliquefaciens D747), or RootShield Plus (Trichoderma harzianum T-22 and Trichoderma virens G-41) were applied at label rate to germinated sprouts. One day after treatment, the plants were inoculated with Pythium spp. at 1 x 10⁵ zoospores per mL. After seven days, we measured root necrosis, disease incidence and severity, fresh and dry shoot, and root weight. All plants inoculated with Pythium spp. were smaller by 40.1% or more compared with non-inoculated plants. All plants treated with microbial biofungicides with or without Pythium spp. were smaller than the untreated control. Plants inoculated with Pythium spp. and treated with microbial biofungicides had lower disease incidence compared with the control. Root necrosis was lower in plants treated with Companion and RootShield Plus. Results from this experiment suggest that beneficial microbes can be introduced in nutrient solutions and reduce the negative effects of Pythium infection. Disease incidence and severity were reduced in most cases. However, plant growth was also reduced when microbial biofungicides were applied. Further research will be conducted to identify if lower microbial biofungicides rates or combined applications can reduce the negative effects of microbial biofungicides in plant growth.