Clubroot (Plasmodiophora brassicae) Suppression Under Biocontrol Agents in Pak choi with Variations in Physiological, Biochemical, and Bacterial Diversity

Plasmodiophora brassicae Woronin is responsible for an infectious disease called clubroot, which poses a significant threat to cruciferous vegetables. This study aimed to determine the efficacy of biological agents including Trichoderma harzianum and Sophora flavescens in reducing clubroot severity in Pak choi. For this purpose, an in vitro pot experiment was conducted. For the application of T. harzianum (MD), 10 g powder was mixed in each pot with the substrate , while 5 mL (from the diluted solution 5 mL/L) of S. flavescens (RD), and 20 mL (from the diluted solution 500 µL/L) of fluazinam (ZD) was applied around the root of every plant along with clubroot pathogen P. brassicae . The results revealed that the clubroot disease index (DI) efficiently reduced by the application of T. harzianum and S. flavescens up to 36.02%, 45.43%, as compared to positive control fluazinam 49.05%, respectively. Moreover, under clubroot stress T. harzianum increased total chlorophyll contents, total carotenoid contents, shoot diameter, leaf number, fresh weight of shoot by 15.33%, 21.21%, 21.83%, 25%, 14.24%, and enzymatic activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD) increased by 14.85%, 21.76% and 19.22%, respectively, as compared to fluazinam. Additionally, the 16S rRNA gene sequence of endophytic bacterial communities under clubroot stress revealed that plants treated with P. brassicae only (D) increased the relative abundance of phylum Proteobacteria by 82% as compared to fluazinam (67%). Beta diversity distance matrix analysis based on the principal coordinate algorithm (PCoA) and Non-metric multidimensional scaling method showed a significant distance between T. harzianum and other applied treatments. Overall, T. harzianum and S. flavescens affected and structured the bacterial community in Pak choi and efficiently reduced the clubroot disease. This study will facilitate researchers to biologically control cruciferous clubroot and their ecological functions with endophytic bacteria in brassica species.