Identification, biocontrol and growth-promoting effects of an antagonistic strain CZ-56 against tobacco target spot

To screen rhizosphere growth-promoting bacteria with good control effect on tobacco target spot, antagonistic bacteria against pathogen of tobacco target spot were obtained from rhizosphere soil of healthy tobacco plants by plate isolation culture and confrontation culture. The strain with the best antagonistic effects was then identified by morphological, biochemical and physiological characteristics and 16S rDNA phylogenetic analysis. The growth-promoting and resistance induction effects of the antagonistic strain on tobacco plants and its control efficiency on tobacco target spot were studied. The results showed that an antagonistic strain CZ-56 was identified as Pseudomonas mosselii. Strain CZ-56 demonstrated an inhibition rate of 83.33% against Rhizoctonia solani, and its fermentation filtrate could cause mycelia malformation of R. solani. In vitro test confirmed that strain CZ-56 could effectively prevent the expansion of tobacco target spot. The preventive and therapeutic efficiencies in pot experiments were 72.58% and 83.06%, respectively. The fermentation filtrate of CZ-56 also promoted the growth of tobacco seedlings and increased the activity of defense enzymes, including polyphenol oxidase (PPO), superoxide dismutase (SOD), peroxidase (POD) and phenylalanine ammonlyase (PAL) in tobacco leaves. Therefore, strain CZ-56 has good control effects on tobacco target spot.