Abstract: Walnut anthracnose, caused by several Colletotrichum genus species, is recognized as one of the most destructive and economically important diseases, resulting in considerable losses. The implementation of biological control is expected to provide a favorable alternative to chemical methods for disease management, as it is environmentally friendly, less prone to resistance development, and offers high safety levels. In the present study, an endophytic bacteria strain GYX7, isolated from healthy walnut leaves, exhibited the most potent inhibitory activity against the pathogens of walnut anthracnose, including C. gloeosporioides, C. fructicola, C. siamense, C. fioriniae and C. aenigma, with inhibition rates ranging from 70.56% to 80.78%. Microscopic examination indicated that strain GYX7 induced morphological distortions and lysis of the mycelium during confrontation culture. Furthermore, strain GYX7 demonstrated a broad-spectrum antifungal, inhibiting 13 phytopathogens except Pythium aphanidermatum. Based on morphological, physiological, and biochemical characteristics and a phylogenetic tree constructed using 16S rDNA and gyrB gene sequences, strain GYX7 was identified as Bacillus velezensis. The volatile compounds produced by strain GYX7 were found to contribute to its biocontrol capabilities. The aseptic filtrate of strain GYX7 at a 20% concentration significantly inhibited the growth and spore germination of C. fructicola, with inhibition rates of 82.24% and 98.17%, respectively. Enzyme activity assays indicated that strain GYX7 produced various hydrolytic enzymes, including protease, cellulase, pectinase, and β-1,3-glucanase. Additionally, the strain was found to possess genes that encode antimicrobial substances, including surfactin, bacillomycin, fengycin, iturin, bacillaene, bacillibactin, bacilysin, macrolactin and difficidin, as identified through polymerase chain reaction (PCR). In vitro inoculation experiments showed that strain GYX7 effectively reduced the incidence and severity of walnut anthracnose. These findings suggest that strain GYX7 has the potential to be a biocontrol agent for managing walnut anthracnose.

Key words: walnut anthracnose, Bacillus velezensis, biological control, antagonism