Abstract: A strain D5-8 with strong inhibitory effect on tobacco black shank was isolated and purified from the intestinal tract of Periplaneta americana. The strain D5-8 was identified as Bacillus tequilensis by morphological characteristics, physiological and biochemical characteristics and 16S rRNA gene sequence analysis. The fermentation conditions of strain D5-8 were optimized and its control effect on tobacco black shank disease was also determined. Single factor test and orthogonal test were carried out on the fermentation medium and fermentation conditions with the OD₆₀₀ value of bacterial fermentation broth and the inhibition rate against pathogenic bacteria as indexes, and control effect of strain D5-8 on tobacco black shank was determined by pot experiment. The results showed that the inhibition rate of strain D5-8 against Phytophthora nicotiana reached 66.80%. The optimal medium was beef extract 8 g, yeast extract 5 g and maltose 10 g in distilled water 1000 mL. The optimal fermentation conditions were as follows: temperature 28 ℃, initial pH 6, rotational speed 210 r/min, liquid volume 30 mL, inoculation volume 2%, culture time 60 h and light time 4 h. Pot experiment showed that the control efficacy of D5-8 fermentation broth (10⁸cfu/mL) on tobacco black shank disease was 66.89% and 53.72%, which were higher than that of original fermentation broth (61.84% and 51.83%).

Key words: Periplaneta americana, tobacco black shank, Bacillus tequilensis, identification, optimization of fermentation conditions