Screening Of Antagonistic Strain Against Phytophthora Nicotianae And Preparation Of Biological Organic Fertilizer

Phytophthora nicotianae is an important soilborne fungal disease occurring on tobacco.It mainly infects the root and stem base of tobacco,forming black indented spots,so it is called"black shank disease".It mainly harms tobacco plants in the field period,causing serious crop loss and tobacco quality decline.Therefore,it is of great practical significance to study the biological control of phytophthora nicotianae.（1）In this paper,we collected 36 soil samples from the root of healthy plants in the tobacco fields with serious tobacco black stem disease in Jingzhou,Chenzhou,Changsha and Liuyang of Hunan Province,and isolated and purified 154 strains of bacteria and 32strains of mycete against phytophthora nicotianae were screened by plate confrontation method.Among them,strain LZW-317 had the best antagonistic effect,and the plate inhibition rate reached 79.32%.After morphological,physiological and biochemical identification,combined with 16S r DNA sequencing,the strain LZW-317 was identified as Pseudomonas koreensis.（2）The single factor experiment and orthogonal experiment showed that strain LZW-317 was cultured in the following media and conditions:bran 22.5 g/L,yeast extract12.5 g/L,magnesium sulfate 0.75 g/L,sodium dihydrogen phosphate 3 g/L,potassium nitrate 3.5 g/L,sodium chloride 1 g/L,initial p H 6.5;The biomass of the strain reached1.12×10¹⁰ CFU/m L after fermentation at 30℃for 50 h at a speed of 240 r/min with inoculation amount of 2.5%.The strain LZW-317 had an antagonistic effect against phytophthora nicotianae.（3）The rapeseed meal and bran were fermented by strain LZW-317 and composted for 37 days to obtain bio-organic fertilizer.The results showed that the organic matter of the fertilizer was 82.96%,the total nutrient was 12.7%,and the effective number of viable bacteria was 12.23×10⁸ CFU/g.The pot experiment of this bio-organic fertilizer showed that the plant height,fresh weight and root fresh weight of tobacco K326 increased by11.46%,12.24%and 26.41%compared with the control,which could effectively promote the growth of tobacco root and plant.