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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. [ABSTRACT FROM AUTHOR]

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Main conclusion: The presence of Bacillus cereus plays a key role in clubroot suppression and improves plant biomass in pak choi. B. cereus is reported for the first time as a novel biocontrol agent against clubroot. Plasmodiophora brassicae Woronin causes a devastating infectious disease known as clubroot that is damaging to cruciferous vegetables. This study aimed to isolate beneficial bacteria from the rhizosphere soil of pak choi (Brassica campestris sp. chinensis) and to evaluate the ability of the isolate to reduce the severity of clubroot. Strains obtained from the rhizosphere of symptomless pak choi were first selected on the basis of their germination inhibition rate and effects on the viability of P. brassicae resting spores. Eight bacterial isolates had inhibitory effects against the resting spores of clubroot causing pathogen. However, MZ-12 showed the highest inhibitory effect at 73.4%. Inoculation with MZ-12 enhanced the plant biomass relative to plants grown without MZ-12 as well as P. brassicae infected plants. Furthermore, enhanced antioxidant enzymatic activities were observed in clubroot-infected plants during bacterial association. Co-inoculation of the plant with both P. brassicae and MZ-12 resulted in a 64% reduction of gall formation in comparison to plants inoculated with P. brassicae only. Three applications of MZ-12 to plants infected with P. brassicae at 7, 14 and 21 days after seeding (DAS) were more effective than one application and repressed root hair infection. According to 16S rDNA sequence analysis, strain MZ-12 was identified as had a 100% sequence similarity with type strain Bacillus cereus. The findings of the present study will facilitate further investigation into biological mechanisms of cruciferous clubroot control. [ABSTRACT FROM AUTHOR]

Pak choy (Brassica campestris ssp. chinensis L.) is the major vegetable crop cultivated in China. During December 2017, leaf rot was frequently observed on leaves of pak choy in greenhouses of Shanghai, China. Diseased leaf samples were plated onto acidified potato dextrose agar and fungal cultures were isolated and identified as Rhizopus oryzae, based on morphological features and molecular identification. Definitive identification as R. oryzae was based on the comparative molecular analysis of rRNA gene sequences. Blast analysis revealed 99% similarity with R. oryzae. Pathogenicity was determined by inoculating healthy pak choy leaves and plants with hyphal suspensions of R. oryzae. The fungus was re-isolated from developing similar lesions on the inoculated plants and identified as similar to the inoculated fungus, thus fulfilling Koch's postulates. This is the first report of fungal leaf rot caused by R. oryzae on pak choy in China. [ABSTRACT FROM AUTHOR]

• Plasmodiophora brassicae Wor., is an obligate biotrophic protest. • P. brassicae infects the roots of cruciferous crops, inducing galls or clubs that lead to wilting, loss of productivity, and ultimately plant death. • The pathogenic effect of clubroot disease is controlled by single and combined exogenous application of melatonin and trichoderma. • The combined inoculation enhanced plant vegetative growth and antioxidant enzyme activities in the infected roots of pak choi plant. Clubroot disease causes significant damage to cruciferous crops worldwide, resulting in severe decrease in plant yield. Plants tolerate biotic stresses through various mechanisms, including pathogen-associated molecular patterns (PAMPs) that activate immunity and plant resistance proteins. However, humans often resort to non-ecofriendly methods such as chemical applications to control biotic stresses. Melatonin (N-acetyl-5-methoxytryptamine) and Trichoderma are environmentally friendly and cost-effective alternative strategies to protect plants from pathogen attacks. Additionally, they have favorable effects on horticultural crop growth, fruit ripening, flowering, and provide stress resistance to abiotic and biotic diseases. In the present study, we aimed to control clubroot disease in Pak choi through single and combined exogenous application of melatonin and Trichoderma. We analyzed their effects on plant biomass, chlorophyll contents and observed alterations in their antioxidant system. Our results demonstrated that the combined application of 50 µM melatonin and 100 g Trichoderma efficiently control clubroot disease up to 74.85% compared to plants only supplemented with Plasmodiophora brassicae , as indicated by the disease index. Furthermore, we observed increased plant growth and antioxidant enzyme activities, including Ascorbic acid peroxidase (APX), superoxide dismutase (SOD); catalase (CAT), glutathione reductase (GR), and peroxidase (POD). Additionally, malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2) levels were reduced. Moreover, increased levels of chlorophyll, carotenoids and plant biomass have been observed in plants co-inoculated with melatonin and Trichoderma application. These findings provide valuable insights that can be utilized to enhance crop stress tolerance in challenging environments and increase plant yield. The use of environmentally friendly and cost-effective alternatives to chemical control can help mitigate the damage caused by clubroot disease to cruciferous crops. [ABSTRACT FROM AUTHOR]