Calcium Cyanamide Against Cucumber Root Rot Disease Caused By Fusarium Solani And Its Effect On Soil Microbial Community

With the rapid development of protected vegetable, soil-borne disease in production prevention is becoming a major problem. Calcium cyanamide (CaCN2) is a kind of effective and environment-friendly soil fumigant and has been used for more than100years. In recent years, researchers have been focus on the control effect of soil-borne diseases. However, there was little study about the optimal application conditions of CaCN2and its effect on soil microbial community. Fusarium solani f. sp. cucurbitae (F. solani) caused cucumber root rot disease, was researched in this study using a variety of methods, including microbial phospholipid fatty acid technology (PLFA), real-time PCR and conventional bioassay and so on. This study explored the inhibitory effect of CaCN2on F. solani, cucumber root rot control effect and optimal conditions of CaCN2, and revealed the mechanism of CaCN2on soil oil microbial community. The main results were summarized as follows:1. This study showed the antimicrobial effect of CaCN2on F. solani. This study established Hoechest33342-PI double staining technique, which could effectively identify F. solani spore viability. Combined with laboratory bioassay, it showed the significant antimicrobial effect of CaCN2on the activity of F. solani spore, spore germination and mycelial growth. The inhibitory effect increased with the concentration (0-3000mg/L) enhanced, and the longer the treatment, the more significant inhibitory effect. Spores mortality rate was close to100%and germination rate was zero when treated with CaCN2at the concentration of1000-2000mg/L for48h. In addition, the inactivation spores after treated by CaCN2could be stained with PI, which could be further inferred that CaCN2had damaged the cell membrane of F. solani.2. The results showed that CaCN2reached its optimum inhibitory effect on F. solani at the temperature above35℃and the soil absolute water content of60%. When CaCN2was at the rate of100g/m2, no pathogen was detectable by heated above35℃for9days, and the control efficiency reached75.67%by disinfection for15days under greenhouse condition. The control effect was better when the temperature was higher and the disinfection time was longer. It could reach the optimum inhibitory effect at the soil absolute water content of60%, and the inhibitory effect increased nearly80%for15days treated by CaCN2indoor at the60%soil absolute water content than10%soil absolute water content. The average control efficiency of CaCN2against F. solani was98.15%. 3. Real-time fluorescent quantitative PCR and microbial phospholipid fatty acid (PLFA) methods were used to detect the influence of soil disinfection treated by CaCN2on the population of F. solani and soil microbial community. The results showed that after treated by CaCN2at the rate of120g/m, the soil microorganisms quickly restored after a transient inhibition, and the population of F. solani was weakened, which effectively control the cucumber root rot caused by F. solani. When treated by CaCN2with the rate of60g/m2, the soil microbial community could fully recovered, while the inhibition effect of F. solani was poor, resulting in serious cucumber root rot caused by F. solani. When treated with CaCN2at the rate of225g/m2, the pathogen was killed, and soil microbial community has also been weakened, which destroyed the original balance of micro-ecological system in soil and resulted in recovering population of F. solani causing cucumber root rot disease.4. After soil disinfection with CaCN2and uncovered the plastic film, planting crops as early as possible could improve the recovery of soil microbial communities. The soil microbial biomass carbon and the total microbial PLFAs of planting growth for60days were significantly more than planting growth for23days; however, there was no difference with the soil microbial biomass of unplanting growth for23days and60days. This suggested that after soil treated by CaCN2, planting soil could quicken the recovery of soil microbial, which provided a healthy soil ecological environment for plant growth.5. Long-term CaCN2disinfection could significantly increase soil microbial activity and soil microbial diversity. In the soil treated with CaCN2for four times within8years, the bacteria and actinomycetes were significantly higher than the soil treated with one time and never using CaCN2, especially the content of soil microbial PLFA a15:0, i16:0,16:1∞7c, cyl7:0and17:0. However, the number of fungi of soil treated with CaCN2for four times was significantly lower than the other two treatments. It indicated that after long-term soil disinfection with CaCN2, the soil microflora changed from fungi type to bacterial type, which provided a normal, healthy soil ecological environment for plant growth and reduced the possibility of disease outbreaks.The control effect against cucumber root rot and the influence on soil microbial community of soil disinfection with CaCN2was researched in this study. This study manifested that the optimal application conditions of CaCN2was at higher temperatures in summer with soil absolute water content at around60%, and the optimal rate of120g/m2(plow layer25cm). This study also revealed the soil micro-ecological mechanism of soil treated by CaCN2and solarization. Long-term application of CaCN2could improve soil microbial community diversity, increase the activities of soil microbial and promote plant growth. This study provided a theoretical basis for CaCN2to overcome succession cropping obstacle and sustainable use of soil disinfection with CaCN2.