BIOCONTROL OF PHYTOPHTHORA DISEASE IN CITRUS USING BACILLUS PUMILUS ISOLATED FROM DISEASE-SUPPRESSIVE CITRUS RHIZOSPHERE
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Abstract
Phytophthora spp. is a notorious pathogen causing detrimental effects on citrus crops, including root rot, leaf chlorosis, and gummosis, ultimately resulting in diminished yields and tree mortality. Effective control methods for this disease are currently lacking. This study aimed to isolate a biological control agent (BCA) capable of antagonistic activity against Phytophthora disease. A total of 143 bacterial strains were isolated from the rhizosphere of healthy citrus trees. Among them, four Bacillus strains exhibited robust antagonistic activity against multiple Phytophthora species, including Phytophthora nicotianae, Phytophthora parvispora, Phytophthora palmivopa, Phytophthora citrophthora, and Phytophthora mekongensis, known pathogens affecting citrus trees. Both bacterial exudates and volatile compounds produced by these strains demonstrated potent inhibitory effects on Phytophthora growth, with inhibition rates ranging from 30.28% to 99.98% across all tested Phytophthora species. The isolated bacterial strains were denoted as VN-H5, VN-H8, VN-F8, and VN-K13 through 16S RNA - GyrB - PyrE concatenated sequence analysis, all belonging to the species Bacillus pumilus with 100% similarity. In summary, this study underscores the isolation and screening of bacteria with antagonistic activity against various Phytophthora strains, highlighting the potential of four biocontrol candidate strains, VN-H5, VN-H8, VN-F8, and VN-K13, in managing Phytophthora disease in citrus. Additionally, it marks the pioneering use of B. pumilus in Phytophthora control experiments for citrus trees in Vietnam and globally.
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