Biocontrol properties of bacillus velezensis SM1 enable field recovery from durian root rot

Abstract

Biocontrol properties of Bacillus spp. are well known due to the antibiotics and bioactive compounds they produce, which promote plant growth and reduce the harm caused by plant pathogens. The role of Bacillus velezensis SM1 as a new biocontrol agent to address durian root rot caused by Phytophthora sp. infection was explored. Chemical, biochemical, and microbiological techniques, including Scanning Electron Microscopy (SEM), were employed to characterize the antagonistic mechanisms of SM1 on Phytophthora palmivora NKST002. Bacterial genomic DNA fragments encoding β-glucanase and cell wall hydrolase enzymes were cloned. The growth inhibitory effect of the expressed clones against the test fungus was evaluated. The bacterium was formulated as dry granules and used after reconstitution in water. The biocontrol property was assessed by applying the reconstituted SM1 on infected durian tissues four times per month and on the soil around the plant base twice per month in durian fields. Increased production of siderophore and superoxide dismutase enzyme was observed when SM1 was grown under stress conditions. Recombinant clones expressing β-glucanase and cell wall hydrolase enzymes were inhibitory to the test fungus. SEM observations showed the entry of SM1 into hyphae, vacuolation, and mycelial cracks in the coculture with NKST002. Diseased durians were cured after exposure to the reconstituted SM1 for one month. Long-term colonization of SM1 in the durian rhizosphere is expected. Overall, Bacillus SM1 demonstrated significant potential for treating durian root rot in crop fields.