Efficacy of biofungicides against root rot and damping-off of microgreens caused by Pythium spp.

Abstract Pythium spp. are the causal agents of Pythium root rot and damping-off on microgreens. The objective of this project was to assess the efficacy of biofungicides on Pythium root rot and damping-off caused by Pythium aphanidermatum and Pythium dissotocum on microgreens in greenhouses. In the first experiment, arugula ( Eruca sativa Mill.), kale ( Brassica oleracea var. sabellica L.), radish ( Raphanus raphanistrum subsp. sativus L.), and mustard ( Brassica juncea L. Czern) microgreens were treated with Companion ® ( Bacillus subtilis GB03), Triathlon BA ® ( Bacillus amyloliquefaciens D747), or RootShield Plus ® ( Trichoderma harzianum KRL-AG2 and Trichoderma virens G-41) in a hydroponic nutrient film technique system. Two days after treatment, the plants were inoculated with 3 × 10 5 zoospores of Pythium spp. After seven days, we measured root necrosis, damping-off incidence and severity, and plant biomass. All plants infected with Pythium spp. were smaller by 28% or more compared with non-inoculated plants. Overall disease was low, but biomass was lower in all treatments inoculated with Pythium spp. Arugula infected with Pythium spp. and treated with Triathlon BA ® resulted in 8% lower disease incidence compared with the positive control, yet Triathlon BA ® resulted in the highest root necrosis. On a separate experiment, arugula and mustard were grown in propagation trays, irrigated manually, and treated with the biofungicides mentioned above or Cease ® ( Bacillus subtilis QST 713). Arugula and mustard plants inoculated with Pythium spp. had 74.4% reduction of shoot dry weight. Arugula and mustard treated with Cease ® , with and without Pythium spp., resulted in ≥59% more biomass compared with the untreated inoculated control. In the tray experiment, all the infected plants treated with biofungicides had more biomass than plants with no biofungicides. Results from this experiment suggest that microbial biofungicides can be introduced in nutrient solutions in nutrient film technique or applied in the irrigation to prevent Pythium root rot and damping-off in brassica microgreens. However, biofungicides can reduce plant biomass and growers may need to extend production time to achieve target yields.