Antimicrobial activity and field control effect of an antagonistic bacterial strain kc-16 against tea gray blight

Abstract:

[Background] Tea gray blight is a major disease attacking tea plants. Chemical methods are mainly used to control this disease, and the chemical residues and pathogen resistance caused by chemical control need to be solved urgently. Exploring biocontrol microorganisms is an important measure to ensure the safety and increase the yield of tea production. [Objective] To screen the Bacillus strains with inhibitory effects on tea gray blight and clarify the inhibitory activity and field control effect of the strain screened out, providing support for the development of biocontrol methods for tea gray blight. [Methods] A plate confrontation experiment was conducted to screen out the strain with antagonistic effect on Pseudopestalotiopsis theae, the pathogen causing tea gray blight. The strain was identified based on morphological, physiological, and biochemical characteristics and sequence analysis of the 16S rRNA. Various plates were utilized to examine the production of enzymes lysing fungal cell walls by the strain. Plate confrontation tests were conducted to determine the inhibitory activities of different metabolites produced by the strain on Ps. theae. The inhibition rates against nine common species of plant pathogenic fungi were measured to assess the antifungal spectrum of the strain. Finally, field experiments were conducted to evaluate the effects of the strain on tea gray blight and yield of tea plants. [Results] A strain kc-16 with antagonistic effect on Ps. theae was screened out, with the inhibition rate of (79.62±0.82)%, and it was identified as Bacillus subtilis subsp. inaquosorum by morphological, physiological, and biochemical characteristics and 16S rRNA gene sequence analysis. Strain kc-16 demonstrated nitrogen-fixing, iron carriers producing and phosphorus-solubilizing abilities but lacked the potassium-solubilizing ability, and it could secrete protease, cellulase, β-1,3-glucanase, and chitinase. In addition, strain kc-16 inhibited nine species of pathogenic fungi, with inhibition rates ranging from 46.67% to 81.00%. The extracellular substances of strain kc-16 exhibited inhibitory effects on the pathogen of tea gray blight. Specifically, the cell-free filtrate, crude protein extract, volatile substances, and non-volatile substances of this strain showcased the inhibition rates of 69.00%, 58.00%, 47.50%, and 78.71%, respectively. In field experiments, B. subtilis subsp. inaquosorum showed tea gray blight-preventing and growth-promoting effects on tea plants. It reduced the incidence of tea gray blight while increasing the fresh weight of tea leaves (one bud and one leaf) by 25.0% compared with the blank control. [Conclusion] B. subtilis subsp. inaquosorum inhibits tea gray blight and promotes the growth of tea plants, demonstrating the application potential. The results of this study provide theoretical support for the future research and application of this strain in the control of plant diseases.