Plant diseases and insect pest damage cause tremendous losses in forestry and fruit tree production. Even though chemical pesticides have been effective in the control of plant diseases and insect pests for several decades, they are increasingly becoming undesirable due to their toxic residues that affect human life, animals, and the environment, as well as the growing challenge of pesticide resistance. In this study, we review the potential of hydrolytic enzymes from Bacillus species such as chitinases, β-1,3-glucanases, proteases, lipases, amylases, and cellulases in the biological control of phytopathogens and insect pests, which could be a more sustainable alternative to chemical pesticides. This study highlights the application potential of the hydrolytic enzymes from different Bacillus sp. as effective biocontrol alternatives against phytopathogens/insect pests through the degradation of cell wall/insect cuticles, which are mainly composed of structural polysaccharides like chitins, β-glucans, glycoproteins, and lipids. This study demonstrates the prospects for applying hydrolytic enzymes from Bacillus sp. as effective biopesticides in forest and fruit tree production, their mode of biocidal activity and dual antimicrobial/insecticidal potential, which indicates a great prospect for the simultaneous biocontrol of pests/diseases. Further research should focus on optimizing the production of hydrolytic enzymes, and the antimicrobial/insecticidal synergism of different Bacillus sp. which could facilitate the simultaneous biocontrol of pests and diseases in forest and fruit tree production.

Walnut anthracnose caused by Colletotrichum gloeosporioides is a deleterious disease that severely affects the production of walnut (Juglans regia L.). The aim of this study was to assess the antifungal and growth promotion activities of Bacillus velezensis CE 100 as an alternative to chemical use in walnut production. The crude enzyme from B. velezensis CE 100 exhibited chitinase, protease, and β-l,3-glucanase activity and degraded the cell wall of C. gloeosporioides, causing the inhibition of spore germination and mycelial growth by 99.3% and 33.6% at 100 µL/mL, respectively. The field application of B. velezensis CE 100 culture broth resulted in a 1.3-fold and 6.9-fold decrease in anthracnose disease severity compared to the conventional and control groups, respectively. Moreover, B. velezensis CE 100 produced indole-3-acetic acid (up to 1.4 µg/mL) and exhibited the potential for ammonium production and phosphate solubilization to enhance the availability of essential nutrients. Thus, field inoculation of B. velezensis CE 100 improved walnut root development, increased nutrient uptake, enhanced chlorophyll content, and consequently improved total biomass by 1.5-fold and 2.0-fold compared to the conventional and control groups, respectively. These results demonstrate that B. velezensis CE 100 is an effective biocontrol agent against anthracnose disease and a potential plant growth-promoting bacteria in walnut tree production.

Due to the increasing health and environmental risks associated with the use of fungicides in agriculture, alternatives—such as using plant growth-promoting bacteria (PGPB) to suppress phytopathogens—that simultaneously improve plant yield, are important. This study evaluated the biocontrol efficiency of Bacillus velezensis CE100 against Macrophomina phaseolina and Fusarium oxysporum f. sp. fragariae, the respective causal agents for charcoal rot and fusarium wilt diseases in strawberry, and its potential to enhance strawberry growth and fruit production. B. velezensis CE 100 produced fungal cell wall-degrading enzymes, chitinases, and β-1,3-glucanases; and inhibited the mycelial growth of M. phaseolina and F. oxysporum f. sp. fragariae by 64.7% and 55.2%, respectively. The mycelia of both phytopathogenic fungi showed severe swelling and rupturing of the hyphae compared to the smooth, normal growth in the control group. Moreover, B. velezensis CE100 produced up to 2.8 units/mL of indole-3-acetic acid (IAA) during incubation and enhanced root biomass in strawberries. Consequently, B. velezensis CE 100 not only increased the fruit yield of strawberries by controlling the fungal diseases but also through enhancing plant growth. The findings of this study indicate that B. velezensis CE100 could be a safe, ecofriendly biocontrol alternative to chemical fungicides in strawberry production.

Root rot diseases, caused by phytopathogenic oomycetes, Phytophthora spp. cause devastating losses involving forest seedlings, such as Japanese cypress (Chamaecyparis obtusa Endlicher) in Korea. Plant growth-promoting rhizobacteria (PGPR) are a promising strategy to control root rot diseases and promote growth in seedlings. In this study, the potential of Bacillus velezensis CE 100 in controlling Phytophthora root rot diseases and promoting the growth of C. obtusa seedlings was investigated. B. velezensis CE 100 produced β-1,3-glucanase and protease enzymes, which degrade the β-glucan and protein components of phytopathogenic oomycetes cell-wall, causing mycelial growth inhibition of P. boehmeriae, P. cinnamomi, P. drechsleri and P. erythoroseptica by 54.6%, 62.6%, 74.3%, and 73.7%, respectively. The inhibited phytopathogens showed abnormal growth characterized by swelling and deformation of hyphae. B. velezensis CE 100 increased the survival rate of C. obtusa seedlings 2.0-fold and 1.7-fold compared to control, and fertilizer treatment, respectively. Moreover, B. velezensis CE 100 produced indole-3-acetic acid (IAA) up to 183.7 mg/L, resulting in a significant increase in the growth of C. obtusa seedlings compared to control, or chemical fertilizer treatment, respectively. Therefore, this study demonstrates that B. velezensis CE 100 could simultaneously control Phytophthora root rot diseases and enhance growth of C. obtusa seedlings.

In this study, the biocontrol ability of bacterial antagonists of fungal pathogens, B. thuringiensis KYC and B. velezensis CE 100 was investigated for the inhibition of root-knot nematode, Meloidogyne incognita, and subsequent growth promotion of tomato. Based on the results of dual-culture assay, both Bacillus strains showed antagonistic activities against six different phytopathogenic fungi. The bacterial culture filtrates (BCF) of two Bacillus strains had a strong toxic effect on egg hatching and second-stage juvenile (J2) survival of M. incognita. With increasing concentration of BCF and incubation period, the hatching rate of the nematode egg was significantly inhibited and J2 mortality was remarkably increased. Moreover, the crude enzymes which were extracted from culture supernatants of two Bacillus strains caused structural damage to nematode eggs and J2 at 1, 3 and 5 days after inoculation. The pot experiment revealed that B. thuringiensis KYC and B. velezensis CE 100 significantly promoted tomato shoot growth compared to fertiliser treatment. However, root fresh weight was significantly increased in fertiliser treatment due to numerous masses in roots. The number of egg masses and root gall index in the treatment group with both Bacillus strains were significantly decreased compared to those in fertiliser treatment. Higher populations of B. thuringiensis KYC and B. velezensis CE 100 (4.12 and 6.52 × 10⁶ CFU g⁻¹of soil) were detected in the tomato rhizosphere. These results demonstrated the potential of B. thuringiensis KYC and B. velezensis CE 100 as biocontrol agents to control plant-pathogenic fungi and root-knot nematode and as biofertilisers to promote plant growth.

Colletotrichum gloeosporioides is the most prevalent phytopathogen, causing anthracnose disease that severely affects the production of various fruit trees, including walnut and jujube. In this study, the volatile organic compounds (VOCs) from Bacillus velezensis CE 100 disrupted the cell membrane integrity of C. gloeosporioides and reduced the spore germination by 36.4% and mycelial growth by 20.0% at a bacterial broth concentration of 10%, while the control group showed no antifungal effect. Based on the headspace solid-phase microextraction/gas chromatography-mass spectrometry (HS-SPME/GC-MS) analysis, seven VOCs were identified from the headspace of B. velezensis CE 100. Out of the seven VOCs, 5-nonylamine and 3-methylbutanoic acid were only detected in the headspace of B. velezensis CE 100 but not in the control group. Both 5-nonylamine and 3-methylbutanoic acid showed significant antifungal activity against the spore germination and mycelial growth of C. gloeosporioides. Treatment with 100 µL/mL of 5-nonylamine and 3-methylbutanoic acid suppressed the spore germination of C. gloeosporioides by 10.9% and 30.4% and reduced mycelial growth by 14.0% and 22.6%, respectively. Therefore, 5-nonylamine and 3-methylbutanoic acid are the potential antifungal VOCs emitted by B. velezensis CE 100, and this is the first report about the antifungal activity of 5-nonylamine against C. gloeosporioides.