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.

Aquilaria sinensis (Lour.) is listed as a nationally endangered plant in China. Heortia vitessoides (Moore) is an important monophagous leaf-eating pest that endangers A. sinensis by seriously affecting its growth. Field studies have found that a small number of plants in the same forest are strongly resistant to insects. In this study, we compared the chemical constituents and volatile components of leaves of the A. sinensis high insect-resistant (A01) and susceptible (S) varieties and analyzed their differential metabolites using non-targeted metabolomics. The results showed that the leaves of A. sinensis that were resistant to insects had lower nutrient contents than those of the susceptible varieties, and the volatile substances contained larger amounts of insect attractants than insect repellants. Insect-resistant A. sinensis leaves were found to be highly enriched in metabolites related to the enhancement of stress resistance, with metabolic pathways mainly focused on flavonoid and flavonol biosynthesis, phenylalanine biosynthesis, phenylalanine metabolism, tyrosine metabolism, and isoquinoline alkaloid biosynthesis. To our knowledge, this is the first study to comprehensively analyze and compare leaf components contributing to the resistance of A. sinensis to H. vitessoides. The results of this study provide a theoretical reference for the future breeding of insect-resistant A. sinensis varieties.