Study On Biological Control Of Endophytic Bacteria Isolated From Kochia Scoparia On Brown Rot Of Nectarines

Comparing with chemical pesticide control, biological control is more efficient for plant diseases and harmless for organisms. Biocontrol also has good compatibility with environment. In addition, it doesn't make pathogen acquire resistance easily. Biocontrol has become a significant area of research for domestic and foreign scholars. The results of preliminary study showed that D-1, D-23 and D-25 isolated from Kochia scoparia had better inhibitory effect on various plant pathogenic fungi. Three endophytic bacteria were classified and identified. A series of researches of D-1 on the controlling effect on postharvest brown rot of nectarines, biocontrol mechanism, safety determination and enhancing the bioefficacy of microbial antagonist were conducted in the project, which laid a solid foundation for the application and production of D-1 in the biological control of postharvest diseases.1. By evaluating on morphology, measuring the physiological and biochemical features, analyzing of 16s rDNA sequences and gyrB sequences, D-1, D-23, D-25 were characterized as Bacillus thuringiensis, Bacillus amyloliquefaciens and Bacillus thuringiensis, respectively.2. The biocontrol effect of Bacillus thuringiensis D-1 on postharvest brown rot of nectarines indicated that the control effect of 106,107,108CFU·mL-1 of D-1 was 81.64%, 95.85% and 97.67%, respectively. The disease rate of nectarines was 27.78%,13.33%,8.89% respectively after being soaked in three different concentration (106,107, 108CFU·mL-1) of D-1 for 10 min and stored for 15d, CK group was 56.67%, and 1-MCP group was 47.78%. Similarly, the loss weight rate of nectarines was 5.24%,4.33% and 2.64% respectively, CK group was 6.92%, and 1-MCP group was 2.56%. The result of acute oral toxicity test showed that male and female mice to the powder of D-1 is more than 20000 mg·kg-1 which belonged to the non-toxicity.3. The study showed that control effect of bacteria suspension and fermented liquid were the best, sterile supernatant that followed, and sterilant solution was the least. At those treatments of inoculating antagonist before pathogen, the control effect was the best. And when the time interval between antagonist and pathogen was 8h or longer, brown rot could be suppressed completely. Wherever pathogen was exist or not, D-1 could reproduced rapidly in fruit wound. In order to clear the interaction of antagonist and pathogen on wound of nectarine fruit, images of scanning electron microscopy (SEM) after inoculation for 24h following treatments were observed. D-1 could inhibit spores germination, make extracellular matrix leak out, and hypha was distorted and digested. As a result, Bacillus thuringiensis D-1 could secrete antifungal substance and make colonization on wound rapidly. Combing D-1 with 1%CaCl2,2%CaCl2,1% NaHCO3 or 2% NaHCO3, the control effect enhanced 23.97%, 27.83%,22.32% and 25.8% respectively than D-1 alone.