2018 ASHS Annual Conference

Pythium root rot and damping-off is a common disease in greenhouse crops including lettuce grown in hydroponic systems. Synthetic chemical products registered for specific use in hydroponic production systems in greenhouses are limited. The objective of this project was to assess the efficacy of microbial biofungicides for control of root rot caused by Pythium spp. in lettuce (Lactuca sativa cv. Rex and Spretnak) seedlings. Seven day old lettuce seedlings were treated with Companion (Bacillus subtilis GB03), RootShield Plus (Trichoderma harzianum T-22 and Trichoderma virens G-41), Triathlon BA (Bacillus amyloliquefaciens D747), and Cease (Bacillus subtilis QST 713) following specimen label instructions. 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. Lettuce plants infected with Pythium spp. had between 73.9% and 86.5% lower shoot and root dry weight than non-inoculated plants, respectively. All plants inoculated with Pythium and treated with microbial biofungicides were bigger than plants inoculated with Pythium and no microbial biofungicides. Root necrosis was observed in all plants treated with Pythium. However, differences in plant wilting and mortality were not observed between treatments. We did not see any damping-off. Results from this experiment suggest that beneficial microbes can reduce the negative effects of Pythium spp. infection at the seedling stage. However, in the absence of disease, biomass was reduced by the microbial biofungicides.