Fengycin produced by Bacillus subtilis NCD-2 is involved in suppression of clubroot on Chinese cabbage

Abstract

Clubroot, caused by the obligate parasite Plasmodiophora brassicae, is one of the most important diseases of Brassicaceae family. Bacillus spp. that produce lipopeptide antibiotics are often used as biocontrol agents to suppress soilborne diseases. B. subtilis NCD-2 isolated from the cotton rhizosphere has been found to inhibit pathogenic fungi through the production of fengycin-type cyclopeptides. In this study, the biocontrol efficacy of B. subtilis NCD-2 against P. brassicae and the role of fengycin in disease suppression were evaluated on Chinese cabbage in glasshouse. B. subtilis NCD-2 reduced clubroot disease incidence and severity up to 47.7% and 51.6%, respectively, while the fengycin defective mutant ΔfenC and a PhoP/PhoR two-component regulatory system mutant, ΔphoP, were unable to prevent this disease. In vitro, P. brassicae resting spore cells were lysed when treated with standard fengycin and crude fengycin extracts of the wild type B. subtilis NCD-2, but not of its mutant ΔfenC. Moreover, the population dynamics of B. subtilis and P. brassicae was determined using quantitative real-time PCR (qPCR). The results were surprising that the wild type B. subtilis NCD-2 and its mutant ΔfenC colonized at similar rates in the rhizosphere, while levels of P. brassicae DNA in the rhizosphere and root tissue were reduced following B. subtilis NCD-2 treatment, but there was no effect of the mutant ΔfenC. Thus, the production of fengycins in B. subtilis NCD-2 may play a promising role in the suppression of P. brassicae in the rhizosphere and reduction of incidence of clubroot disease in Chinese cabbage.