Exploration of microbiome of medicinally important plants as biocontrol agents against Phytophthora parasitica.

In a preliminary plant-based microbiome study, diverse bacterial taxa were identified from different medicinal plants using 16S rRNA gene sequencing. Based on initial antimicrobial screening, eight (8) bacterial endophytes in six (6) different genera, Streptomyces, Pseudomonas, Enterobacter, Bacillus, Arthrobacter, and Delftia, from four important medicinal plants Dodonaea viscosa, Fagonia indica, Caralluma tuberculata, and Calendula arvensis were selected for further analyses. Antimicrobial assays revealed that Pseudomonas taiwanensis MOSEL-RD23 has strong anti-Phytophthora activity. Volatiles produced by P. taiwanensis MOSEL-RD23and Bacillus flexus MOSEL-MIC5 inhibited the growth of Phytophthora parasitica by more than 80%. Ethyl acetate extracts of Streptomyces alboniger MOSEL-RD3, P. taiwanensis MOSEL-RD23, Enterobacter hormaechei MOSEL-FLS1, and Bacillus tequilensis MOSEL-FLS3, and Delftia lacustris MB322 displayed high potency against P. parasitica. All these bacterial extracts showed strong inhibition of more than 80% inhibition in vitro against P. parasitica at different concentrations (4-400 µg/mL). Bacterial extracts showing strong antimicrobial activity were selected for bioactivity-driven fractionation and showed anti-Phytophthoral activity in multiple fractions and different peaks observed in UV-Vis spectroscopy. In the detached-leaf assay against P. parasitica on tobacco, 1% ethyl acetate bacterial extract of S. alboniger MOSEL-RD3, P. taiwanensis MOSEL-RD23, E. hormaechei MOSEL-FLS1, B. tequilensis MOSEL-FLS3, and D. lacustris MB322 reduced lesion sizes and lesion frequencies caused by P. parasitica by 68 to 81%. Overall, P. taiwanensis MOSEL-RD23 showed positive activities for all the assays. Analyzing the potential of bacterial endophytes as biological control agents can potentially lead to the formulation of broad-spectrum biopesticides for the sustainable production of crops.