Combined effects of inundative biocontrol and anaerobic soil disinfestation (ASD) using non-host cover crops as carbon sources for clubroot management in mustard greens

Experiments were designed to evaluate the combination of commercially available biocontrol agents and cover crops that could be used as carbon source amendments in anaerobic soil disinfestation (ASD) for clubroot disease management utilizing a factorial randomized complete block design with three replications. The first factor was ASD amendment (winter rye, ryegrass, sudangrass or leek cover crop, wheat bran (standard)), and non-amended controls - covered (anaerobic control) and uncovered (aerobic control). The second factor was biocontrol treatment (Prestop (Gliocladium catenulatum); Actinovate (Streptomyces lydicus), Serenade (Bacillus subtilis) or no biocontrol product). Cover crops were grown in 350-ml pots containing muck soil inoculated with the clubroot pathogen (Plasmodiophora brassicae) for 45 days in growth chambers. Then cover crops were uprooted, chopped into small pieces, and mixed with soil in the same pot. Each pot was saturated with tap water before inoculation of biocontrol products and then enclosed in two Ziploc® bags. After three weeks, bags were removed, soil aired for one week, and mustard greens 'Green Wave' seeded. Prestop and Serenade consistently reduced the clubroot index alone and in combination with wheat bran- and sudangrass-amended ASD treatment. Furthermore, ASD with winter rye consistently showed synergy with Serenade and Actinovate, and ASD with sudangrass showed synergy with Actinovate, Prestop and Serenade in reducing clubroot indices. Combining ASD amended with selected cover crops with Serenade, Actinovate or Prestop may enhance ASD efficacy for clubroot management in organic and conventional farming systems.