Screening and identification of endophytic antagonistic bacteria from tobacco and their control effect and growth-promoting effect on black shank disease

To screen endophytic bacteria from tobacco plants (Nicotiana tabacum) that have both antagonistic and growth-promoting effects against Phytophthora nicotianae, endophytic bacteria were isolated from healthy tobacco plants in Luoyang. Through the plate confrontation method, mycelial growth rate method and Salkowski colorimetric method, strains with mycelial inhibition rates of P. nicotianae greater than 50% and high indole-3-acetic acid (IAA) production were selected. The selected strains were identified based on morphological, physiological and biochemical characteristics and phylogenetic analysis of 16S rDNA and gyrB genes. The control efficacy and growth-promoting effects of the target strains on tobacco black shank disease were evaluated through pot and field experiments. The results showed that seven strains were identified from 1,217 endophytic bacteria, including Bacillus velezensis (strains 8XY2, 5ZJ1-10 and 7XY25), Bacillus subtilis (strains 5ZJ23 and 8ZJ7), Bacillus pumilis (strain 6SJ11) and Microbacterium foliorum (strain 5SY32). Among them, the mycelial inhibition rates of the fermentation filtrates of strains 6SJ11 and 7XY25 against P. nicotianae were 70.56% and 68.39%, respectively, and the IAA production was 10.48 mg·L^–1 and 11.12 mg·L^–1, respectively. The pot experiment showed that the preventive effects of strains 6SJ11 and 7XY25 on tobacco black shank disease were 42.09% and 40.52%, respectively, and the control effects were 40.39% and 46.46%, respectively. In the field experiment, the control effects of strains 6SJ11 and 7XY25 in the vigorous growth stage reached 67.48% and 63.24%, respectively. In conclusion, strains 6SJ11 and 7XY25 can effectively control tobacco black shank disease and promote the growth of tobacco plants at different growth stages.