Endophytes represent a ubiquitous and magical world in plants. Almost all plant species studied by different researchers have been found to harbor one or more endophytes, which protect host plants from pathogen invasion and from adverse environmental conditions. They produce various metabolites that can directly inhibit the growth of pathogens and even promote the growth and development of the host plants. In this review, we focus on the biological control of plant diseases, aiming to elucidate the contribution and key roles of endophytes and their metabolites in this field with the latest research information. Metabolites synthesized by endophytes are part of plant disease management, and the application of endophyte metabolites to induce plant resistance is very promising. Furthermore, multi-omics should be more fully utilized in plant–microbe research, especially in mining novel bioactive metabolites. We believe that the utilization of endophytes and their metabolites for plant disease management is a meaningful and promising research direction that can lead to new breakthroughs in the development of more effective and ecosystem-friendly insecticides and fungicides in modern agriculture.

Anthracnose, caused by the fungus Collectotrichum fructicola (C. fructicola), is a major disease affecting the quality and yield of Camellia oleifera (C. oleifera); it reduces C. oleifera yield by 40%–80%. Bacillus subtilis (B. subtilis) YL13 is an antagonistic endophytic bacteria strain isolated from healthy C. oleifera leaves. This study was aimed at investigating the potential of YL13 for the biocontrol of C. oleifera anthracnose and the possible mechanisms involved. In in vitro assays, YL13 demonstrated remarkable antagonistic activity of C. fructicola. Its cell-free filtrates displayed antagonistic activity, which suggested that the metabolites of YL13 might play important roles. In vivo tests showed that the disease index of YL13-treated plants was obviously reduced under greenhouse conditions. YL13 secretes a variety of bioactive metabolites, including protease, cellulase, and siderophore, which might participate in the resistance to C. fructicola. In addition, C. oleifera treated with the fermentation broth of YL13 demonstrated different defense responses, e.g., accumulation of hydrogen peroxide (H₂O₂) and activation of the defense-related enzyme peroxidase (POD), which might contribute directly or indirectly to overcome external stresses. The significant biocontrol effect and host defense-induction activity of YL13 suggested that this B. subtilis strain as well as its metabolites have the potential to be exploited as microbial control agents for the efficient management of C. oleifera anthracnose.

Camellia oleifera (C. oleifera) is one of the four main, woody, edible oil tree species in the world, while C. oleifera anthracnose is mainly caused by the fungus Colletotrichum fructicola (C. fructicola), which severely affects the yield of C. oleifera and the quality of tea oil. Bacillus velezensis (B. velezensis) CSUFT-BV4 is an antagonistic endophytic bacterium isolated from healthy C. oleifera leaves. This study aimed to investigate the biocontrol potential of strain CSUFT-BV4 against C. oleifera anthracnose and its possible functional mechanism, and to determine its growth-promoting characteristics in host plants. In vitro, CSUFT-BV4 was shown to have efficient biofilm formation ability, as well as significant functions in the synthesis of metabolic substances and the secretion of probiotic substances. In addition, the CSUFT-BV4 fermentation broth also presented efficient antagonistic activities against five major C. oleifera anthracnose pathogens, including C. fructicola, C. gloeosporioides, C. siamense, C. camelliae, and C. kahawae, and the inhibition rate was up to 73.2%. In vivo, it demonstrated that the growth of C. oleifera treated with CSUFT-BV4 fermentation broth was increased in terms of stem width, plant height, and maximum leaf area, while the activities of various defense enzymes, e.g., superoxide dismutase (SOD), phenylalanine aminotransferase (PAL), and polyphenol oxidase (PPO), were effectively increased. The remarkable antagonistic activities against C. oleifera anthracnose, the growth-promoting characteristics, and the induction of host defense responses indicate that endophytic bacterium CSUFT-BV4 can be effectively used in the biological control of C. oleifera anthracnose in the future, which will have a positive impact on the development of the C. oleifera industry.