Identification, fermentation condition optimization and control effect of an antagonistic strain MC4-2 against Phytophthora parasitica var. nicotianae

Abstract:

[Background] Tobacco black shank is a fungal disease caused by Phytophthora parasitica var. nicotianae, which has brought great losses to tobacco production in China. [Objective] In this study, a strain MC4-2 was isolated from Periplaneta americana intestinal tract, which had antagonistic effect on P. parasitica var. nicotianae. [Methods] The strain MC4-2 was identified by morphological characteristics, physiological and biochemical methods and 16S rRNA gene sequencing. The fermentation medium and fermentation conditions of strain MC4-2 were optimized by single factor and orthogonal experiment using the OD value of bacterial fermentation broth at the wavelength of 600 nm as the index. The control effect of this strain on tobacco black shank was confirmed by potted experiment in greenhouse. [Results] Through the plate confrontation test, it was found that strain MC4-2 had a good inhibitory effect on P. parasitica var. nicotianae, and the inhibition rate could reach 64.04%; 16S rRNA gene sequence analysis showed that the similarity between strain MC4-2 and Bacillus subtilis reached 99%, and the morphological and physiological and biochemical characteristics were basically consistent with that of strain MC4-2; The optimal medium formula was peptone 1.0 g, yeast extract 1.0 g, sucrose 1.5 g, distilled water 100 mL. The results showed that the optimal fermentation conditions were inoculation amount of 8%, liquid volume of 30 mL, initial pH of 6.0, rotation speed of 210 r/min, temperature of 32 ℃, culture time of 60 h and light time of 12 h/d. The results of indoor pot experiment showed that the average control effect of strain MC4-2 on tobacco black shank could reach 63.86%. [Conclusion] This study provides an important reference for the biological control of B. subtilis MC4-2.

Key words:intestinal bacteria of Periplaneta americana;Bacillus subtilis;Phytophthora parasitica var. nicotianae;fermentation conditions;control effect