Isolation of Endophytic Bacteria from Woad and Screening of the Strains to Lyse Plasmodiophora brassicae Spores

Purpose To effectively prevent and control the clubroot disease of woad.

Methods Endophytic bacteria from roots, stems, leaves and seeds of woad were obtained by tissue isolation method. The spore lytic ability and clubroot disease control efficacy in pot test were evaluated to assess the biocontrol potential. The potential strains were identified by morphological characteristics and molecular biology.

Results A total of 72 endophytic bacterial strains were isolated from woad, including 2, 9, 10, 15, and 36 strains isolated from roots, stems, leaves, seeds and peels, respectively. There were 20 endophytic bacteria capable of lysing resting spores, and the lytic ability of strain PP4, KZ7, J5, and KZ5 were higher. Among them, strain PP4 caused 34.75% and 58.43% mortality rates of Plasmodiophora brassicae spores after 24 h and 48 h treatments, respectively. After treating the diseased potted plants with the above four strains of bacteria at a dose of 1×10⁷ CFU/mL, strain PP4 had a disease control efficacy of 65.29% on the clubroot disease at 60 days, which was higher than that of 75% chlorothalonil wettable powder diluted 2000 times (chemical agent control) (52.59%), and the control efficacy of the other three strains bacteria was lower than that of the chemical agent control. Strains PP4, J5 and KZ5 were identified as Bacillus velezensis, and strain KZ7 identified as B. subtilis.

Conclusion Among the four strains of biocontrol bacteria screened, the effect of PP4 is better than that of chemical agent control. Since the amount of pathogen inoculated in the pot experiment was higher than that in the field, it is expected that the bacteria can be applied to prevent and control clubroot disease in the field.