Screening of Bacillus thuringiensis strains to identify new potential biocontrol agents against Sclerotinia sclerotiorum and Plutella xylostella in Brassica campestris L.

Abstract Sclerotiniose, caused by Sclerotinia sclerotiorum (Lib.) deBary, is a destructive disease of Brassica campestris L. Injuries caused by insect pests, such as Plutella xylostella (L.), increase the occurrence of this disease. One hundred and sixty-one Bacillus thuringiensis strains from the Bacillus Genetic Stock Center were screened to identify strains that might protect B. campestris from both plant diseases and insect pests in this study. Challenge-inoculation assays showed seventeen B. thuringiensis strains effectively suppressed S. sclerotiorum growth by inducing systemic resistance in B. campestris, and six of these strains exhibited high insecticidal activity against P. xylostella. In addition, B. thuringiensis elicited a strong hypersensitive response in B. campestris leaves and triggered systemic signals that were transferred from treated roots and leaves to untreated leaves. Quantitative real-time PCR and transcriptome sequencing showed genes involved in salicylic acid, ethylene, and jasmonic acid signaling and in brassinosteroid synthesis pathways were upregulated. The phenotypic and genotypic diversity of B. thuringiensis makes it an effective biocontrol agent for simultaneously protecting B. campestris from sclerotiniose and P. xylostella.