Abstract: 【Objective】 The objective of this study is to optimize the conditions of producing Pythium oligandrum fermentation broth and establish a theoretical foundation for biological control of tobacco black shank. 【Method】 The fermentation parameters were optimized through a single factor and orthogonal experiments, and the biocontrol effects of the fermentation broth were researched by tests on Phytophthora nicotiana, leaves of tobacco in vitro and potted plants in greenhouse. 【Result】 The biomass increased continuously with the culture time, but the inhibition rate increased to the peak then had downward trend. Under the condition of different culture media, temperature, initial pH, illumination time, the more the biomass of mycelia had, the stronger inhibition activity would express, and the correlation coefficients was 0.77**(n=16). Under the condition of culture medium composed of soybean cake powder, initial pH 6.0, 30℃, incubating 6 d and 24 h•d-1 illumination, the biomass of mycelia was the highest and the fermentation broth reached 78.8% for the growth of mycelia and 52.9% for the germination of spore on P. nicotiana. Moreover, the disease incidence and disease index were significantly decreased, the control effect was 69.3%-75.3% in the test on leaves of tobacco in vitro and 55.0%-61.3% in potted plants in greenhouse. 【Conclusion】 In the process of P. oligandrum fermentation, selecting the suitable conditions of the culture medium, pH value, temperature, illumination time and fermentation time, the best inhibition of tobacco black shank can be obtained.

Key words: Pythium oligandrum , fermentation parameter , Phytophthora nicotiana , biocontrol effect