Haibin Cai

Fungal leaf anthracnose, caused by Colletotrichum species, is a major leaf disease of rubber trees, significantly reducing global natural rubber yields. To explore sustainable and safe biological control strategies, eight bacterial strains were isolated from rubber tree tissues, demonstrating antagonistic activity against Colletotrichum pathogens (C. siamense and C. australisinense). Among these, WSR1 exhibited the most pronounced antifungal effect, with inhibition rates of 87.64% and 89.03% against C. siamense and C. australisinense, respectively. Genomic analysis identified WSR1 as Bacillus velezensis. In pot experiments, WSR1 exhibited preventive efficacy of 77.24% and 73.42% for C. siamense and C. australisinense induced anthracnose, respectively, with therapeutic efficacy of 42.28% and 45.57%. WSR1 compromised the integrity of the cell walls and membranes of both C. siamense and C. australisinense, while inducing reactive oxygen species (ROS) accumulation within the hyphae. Additionally, WSR1 enhanced rubber tree resistance to anthracnose by activating defense-related enzymes, including phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD). Plate assays and genomic analysis revealed that WSR1 secretes fungal cell wall-degrading enzymes (cellulases, pectinase, and protease) and siderophores. Furthermore, LC-MS and gene cluster analysis confirmed the synthesis of antagonistic secondary metabolites, such as surfactin, macrolactin H, and fengycin. This study represents the first identification of Bacillus velezensis as a potential biocontrol agent against rubber tree anthracnose, offering a promising candidate for the eco-friendly management of rubber tree diseases.

Anthracnose, caused by Colletotrichum siamense, is a major limiting factor for global natural rubber production. To develop sustainable control strategies, seven bacterial strains with antagonistic activity against C. siamense were isolated from healthy rubber tree leaves, with strain WR7 demonstrating the most significant antifungal effect, exhibiting an inhibition rate of 82.36%. Pot experiments revealed that WR7 achieved a disease control efficacy of 71.65% against C. siamense-induced anthracnose. Genomic analysis identified WR7 as Bacillus altitudinis. This strain inhibits pathogen growth through multiple mechanisms, including disruption of the pathogen’s cell wall and membrane integrity, induction of reactive oxygen species accumulation in hyphae, and secretion of cellulase, glucanase, protease, and siderophores. Gene cluster analysis further confirmed the potential of WR7 to synthesize antagonistic secondary metabolites such as lichenysin, fengycin, and bacilysin, while its sterile filtrate and volatile compounds also exhibited significant antifungal activity. Moreover, treatment with WR7 activated defense-related enzymes, including catalase and superoxide dismutase in rubber tree leaves, thereby enhancing the plant’s defense responses. This study is the first to report that Bacillus altitudinis WR7 has potential as a biocontrol agent for managing rubber tree anthracnose, offering a novel resource for sustainable disease management in rubber production.

Background and aims Red root rot disease, caused by the soil-borne pathogen Ganoderma pseudoferreum, is a severe threat to the natural rubber industry. However, disparities in microbial composition and metabolic profiles between healthy and diseased rubber trees (Hevea brasiliensis) in rhizosphere and near-rhizosphere soils remain unclear. Thus, this study aimed to investigate the disease-induced changes in microbial community structure and function and elucidate the underlying mechanisms. Methods The microbial composition and metabolite profiles of healthy and diseased rubber trees in rhizosphere and near-rhizosphere soils were compared using metagenomic sequencing and ultra-performance liquid chromatography-tandem mass spectrometry. Results In diseased rhizosphere soils, bacterial abundance significantly increased, but bacterial diversity decreased; fungal abundance and diversity both decreased. In diseased near-rhizosphere soils, bacterial richness markedly increased, but bacterial diversity decreased; fungal richness remained statistically unchanged, and diversity was unaffected. Co-occurrence network analysis showed that microbial interaction density increased in diseased soil. Ganoderma positively correlated with several functional microbial groups but strongly negatively correlated with biocontrol agents. Lignin-degrading fungi Trametes and Dichomitus, which are significantly enriched in the diseased rhizosphere, significantly positively correlated with Ganoderma. Metabolomic analysis revealed the upregulation of defense-related metabolites (e.g., 3-methylsalicylic acid, 5'-glucosyloxy-oxojasmonate, and abscisic acid) and plant cell wall-associated components (e.g., ferulic acid) in the diseased rhizosphere. Conclusion This study offers scientific evidence elucidating the microecological mechanisms behind red root rot disease and lays the groundwork for developing microbiome-based ecological control strategies.

To obtain an effective bacterial biocontrol strain against the fungal pathogen Ganoderma pseudoferreum, causing rubber tree red root rot disease, healthy rubber tree tissue from Baisha County, Hainan Province, was selected as the isolation source, and bacterial strains with strong antifungal effects against G. pseudoferreum were screened. The strain was identified by molecular biology, in vitro root segment tests, pot growth promotion tests, and genome detection. The strain was further evaluated by biological function tests, genome annotation analysis, and plant defense-related enzyme activity detection. The results show that strain LSR7 had good antagonistic effects against G. pseudoferreum, and the inhibition rate reached 88.49%. The strain LSR7 was identified as Bacillus velezensis by genome sequencing. In a greenhouse environment, LSR7 prevents and treats red root rot disease in rubber trees and promotes the growth of rubber tree seedlings. LSR7 secreted cell wall hydrolases (protease, glucanase, and cellulase), amylases, and siderophores. LSR7 also formed biofilms, facilitating plant colonization. Genome prediction showed that LSR7 secreted multiple antifungal lipopeptides. LSR7 enhanced rubber tree resistance to G. pseudoferreum by increasing the activity of defense enzymes. Bacillus velezensis LSR7 has biocontrol potential and is a candidate strain for controlling red root rot disease in rubber trees.

Red root rot disease is a devastating fungal disease of rubber trees caused by Ganoderma pseudoferreum (Wakef). Biocontrols using beneficial microorganisms are safe and sustainable. We isolated a DHR18 endophytic bacterium from a healthy rubber tree to obtain a new efficient antagonistic bacterium for red root rot disease affecting rubber trees and evaluated the mechanism of action involved using a double culture assay, genome annotation analysis, and the ethyl acetate extraction method. The results revealed that the DHR18 strain inhibits G. pseudoferreum growth and has broad-spectrum antifungal activity by secreting cell wall hydrolases (proteases and chitinases), indole-3-acetic acid, and siderophores. Furthermore, it fixes nitrogen and is involved in biofilm formation and phosphate solubilisation, improving disease resistance and tree growth. The results showed that the antifungal substances secreted by DHR18 are mainly lipopeptides. Simultaneously, DHR18 enhanced the rubber tree resistance to G. pseudoferreum by increasing the activities of defence enzymes superoxide dismutase, phenylalanine ammonia lyase, peroxidase, catalase, and polyphenol oxidase. The results indicate that B. arboris DHR18 has biocontrol potential and could be used as a candidate strain for the control of red root rot disease in rubber trees.

Natural rubber is an important national strategic and industrial raw material. The leaf anthracnose of rubber trees caused by the Colletotrichum species is one of the important factors restricting the yields of natural rubber. In this study, we isolated and identified strain Bacillus velezensis SF334, which exhibited significant antagonistic activity against both C. australisinense and C. siamense, the dominant species of Colletotrichum causing rubber tree leaf anthracnose in the Hainan province of China, from a pool of 223 bacterial strains. The cell suspensions of SF334 had a significant prevention effect for the leaf anthracnose of rubber trees, with an efficacy of 79.67% against C. siamense and 71.8% against C. australisinense. We demonstrated that SF334 can lead to the lysis of C. australisinense and C. siamense mycelia by causing mycelial expansion, resulting in mycelial rupture and subsequent death. B. velezensis SF334 also harbors some plant probiotic traits, such as secreting siderophore, protease, cellulase, pectinase, and the auxin of indole-3-acetic acid (IAA), and it has broad-spectrum antifungal activity against some important plant pathogenic fungi. The genome combined with comparative genomic analyses indicated that SF334 possesses most genes of the central metabolic and gene clusters of secondary metabolites in B. velezensis strains. To our knowledge, this is the first time a Bacillus velezensis strain has been reported as a promising biocontrol agent against the leaf anthracnose of rubber trees caused by C. siamense and C. australisinense. The results suggest that B. velezensis could be a potential candidate agent for the leaf anthracnose of rubber trees.

Natural rubber is an important national strategic and industrial raw material. Leaf anthracnose of rubber tree caused by the Colletotrichum species is one of the important factors restricting the yield of natural rubber. In this study, we isolated and identified strain Bacillus velezensis SF334 that exhibited significant antagonistic activity against both of C. australisinense and C. siamense, the dominant species of Colletotrichum causing leaf anthracnose of rubber trees in Hainan province of China, from a pool of 223 bacterial strains. The cell supernatants of SF334 had a significant prevention effect for leaf anthracnose of rubber tree with an efficacy of 79.67% against C. siamense and 71.8% against C. australisinense, respectively. We demonstrated that SF334 can lead to the lysis of C. australisinense and C. siamense mycelium by causing mycelial expansion, resulting in mycelial rupture and subsequent death. B. velezensis SF334 also harbors some traits of plant growth-promoting rhizobacterium such as secreting siderophore, protease, cellulose, pectinase and auxin of indole-3-acetic acid (IAA), as well as has broad-spectrum antifungal activity against some important plant pathogenic fungi. The genome combined with comparative genomic analyses indicated that SF334 possesses most genes of the central metabolic and secondary metabolites of B. velezensis strains. To our knowledge, this is the first time to report a Bacillus velezensis strain as a promising biocontrol agent against leaf anthracnose of rubber tree caused by C. siamense and C. australisinense. The results suggest that B. velezensis could be a potential candidate agent for leaf anthracnose of rubber tree.