Biological control of Fusarium oxysporum causing damping-off and Pythium myriotylum causing root and crown rot on cannabis (Cannabis sativa L.) plants

Abstract Damping-off, crown rot, and root rot caused by Fusarium oxysporum and Pythium spp. are important diseases that reduce the growth of cannabis plants and cause mortality. There are currently limited management options available to producers in the absence of registered chemical fungicides. The comparative efficacy of five biological-control agents in reducing disease severity was evaluated in this study. Rhapsody® ASO (Bacillus subtilis), Stargus® (Bacillus amyloliquefaciens), Lalstop® (Gliocladium catenulatum, Prestop®), RootShield® Plus WP (Trichoderma harzianum and Trichoderma virens), and Asperello® (Trichoderma asperellum) were applied to cannabis cuttings in rockwool blocks followed 48 hr later by inoculation with a F. oxysporum spore and mycelial suspension. Disease was rated 7, 14 and 21 days post-inoculation. The most effective treatments were Lalstop, Rootshield, Asperello and Stargus, which provided a significant (P < 0.05) reduction (30 to 56.3%) in mean disease severity 14 days post-inoculation compared to the Fusarium inoculated control. Application of Rootshield, Asperello and Lalstop resulted in endophytic colonization of cannabis cuttings when assessed after 2 and 7 days. For Pythium biocontrol, Rootshield Plus WP, Asperello, and Lalstop were applied as a drench to rooted plants 7 days before inoculation with P. myriotylum. Based on disease severity ratings and plant measurements in two experiments, the most effective treatments were Rootshield and Lalstop. Plants receiving Lalstop or Rootshield had significantly (P < 0.05) higher fresh root weights compared to the pathogen only treatment. These results indicate that several biological control agents can protect cannabis plants from infection by Fusarium and Pythium spp. through pre-emptive colonization.