| Pepper is a vegetable crop with high economic value,with a planting area of about2 million hectares nationwide,accounting for 40%of the world’s pepper planting area,and is prone to continuous cropping obstacles,resulting in a yield reduction of over 10%after continuous cropping.The occurrence of continuous cropping obstacles is due to the accumulation of allelochemicals,deterioration of soil physical and chemical properties,decreased enzyme activity,and the occurrence of soil borne diseases,among which soil borne diseases caused by fungi such as Fusarium,Phytophthora,and Botrytis are the main reasons for the occurrence of continuous cropping obstacles.Compared to chemical control,biological control has the advantages of being environmentally friendly and not prone to drug resistance,which is an important means to alleviate continuous cropping diseases in pepper.Therefore,this study uses endophytic bacteria isolated from various crops by the research team in the early stage as the test material to screen bacteria that have good antagonistic effects against four types of pepper pathogenic bacteria(Colletotrichum capsici,Fusarium oxysporum,Sclerotinia sclerotiorum and phytophthora capsici),systematically study their disease prevention and growth promotion effects,and clarify their repair effects on continuous cropping obstacles and improvement effects on pepper quality.At the same time,low-cost culture media is used for fermentation and development of bacterial agents,Provide technical support for preventing and controlling continuous cropping obstacles in pepper production,ensuring food safety,and industrial application.The main research results are as follows:(1)The plate confrontation test showed that three of the existing 20 endophytic bacteria(W29,W31,and W48)could effectively inhibit the growth of pathogenic bacteria such as pepper anthracnose,pepper wilt,pepper sclerotium,and phytophthora capsici.Furthermore,10 common plant pathogenic bacteria were further used to evaluate their antimicrobial spectrum.The results showed that all three bacteria had broad-spectrum antimicrobial activity,but the antibacterial ability of W48 strain was significantly higher than that of W29 and W31.The strain W48 was identified as Bacillus amyloliquefaciens by combining physiological and biochemical methods with16S r DNA molecular methods.The strain W48 grows well on LB medium and is in a logarithmic phase during 6-14 hours.It can secrete cellulase,amylase,and protease,and has various characteristics to promote plant growth,such as phosphorus removal,iron carrier production,and IAA production.This indicates that W48 is a plant growth promoting and disease preventing Bacillus amyloliquefaciens with good application potential.(2)Pot experiment showed that the application of strain W48 alone could significantly reduce the incidence rate and disease index of pepper phytophthora blight,which were 50.00%lower than those of the control group.Moreover,the application of strain W48 could significantly increase the biomass of pepper seedlings,with the aboveground weight increased by 45.8%,stem diameter increased by 21.3%,and leaf area increased by 34.8%compared to the control.At the same time,W48 also significantly increased the root activity and chlorophyll content of pepper,strengthening the absorption of photosynthesis by the plant,thereby promoting the growth and development of pepper.(3)The indoor continuous cropping experiment showed that after W48 treatment,the p H value,alkaline available phosphorus,organic carbon content,and EC conductivity of the soil increased by 8.73%,10.9%,35.7%,and 28.6%,respectively,compared to the control group,while the content of alkaline hydrolyzable nitrogen and available potassium did not significantly change;The activities of alkaline phosphatase,sucrase,and urease in the soil were increased by 46.0%,46.4%,and 52.7%compared to the control group,respectively.Through microbiological sequencing technology,it was found that W48 can change the structure of soil microbial communities,significantly increase the relative abundance of beneficial soil microbial genera such as Pseudomonas,Sphingomonas,Bradyrhizobium,Luteimonas,and Myceliophthora,and reduce the relative abundance of pathogenic bacteria such as Botrytis,Cyhalophora,and so on.The correlation analysis results indicate that the composition of microbial communities in pepper rhizosphere soil is closely related to soil physicochemical properties(organic carbon and electrical conductivity).At the same time,W48 has also improved the quality of pepper,significantly increasing the content of vitamin C.(4)Through single factor test,PB test and BB test,the optimal culture medium formula and culture conditions for W48 growth were determined,that is,when corn flour 4.70 g/L,tryptone 6.00 g/L,6.90 g/L Na Cl,inoculation amount 3.50%,rotational speed 220r/min,temperature 32℃,fermentation for 48h,W48 viable bacteria reached the maximum,i.e.7.94×10~8 CFU/m L,which is 1.99 times the number of viable bacteria fermented in basic culture medium,lays the foundation for industrial fermentation.At the same time,using white carbon black as the carrier,a W48effervescent tablet with a bacterial content of 4.10×10~8 CFU/g,was preliminarily prepared,which is convenient for storage,transportation,and use with a viable bacterial count of 3.5×10~8 CFU/g after 90 days. |
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