Of Lime Nitrogen On The Microbial Population And Cucumber Fusarium Wilt Pathogen Affect Study

It has been reported that calcium cyanamide, as a fungicide to control soil borne disease, has an efficiency on suppressing clubroot disease in cabbage, fusarium wilt in cucumber and melon etc.. But few studies focused on the ecological environment for soil microbial organisms. Soil microbial organisms which form a large population comprised of numerous and diverse components play key roles in energy and nutrient cycle, organic substance decomposition, soil fertility maintenance, plant growth and disease protection. Therefore, it is of important meanings to study the mechanisms of control of soil borne disease by calcium cyanamide with respect to the effects on changes in microbial community.In this study, three concentrations of calcium cyanamide (21.5g/m~2, 85g/m~2 and 212.5g/m~2) were applied to select the most effective dosage to control fusarium wilt disease in cucumber. Medium culture, BIOLOG and DGGE (denaturing gradient gel electrophoresis) methods were used to examine the microbial diversity in the soil ecosystems. The results are as follows:1. The number of microbial organisms did not change significantly for 21.5g/m~2 dosage treatment. Moderate concentration had influences on both bacteria and fungi whereas had little effects on actinomyces. High concentration had dramatic influences on all of the three microbial organism communities. For 85g/m~2 dosage treatment, the number of bacteria reduced to 67%, and the number of fungi reduced to 70% of the control level after 1 day treatment. However, the number of bacteria returned back when the number of fungi decreased further to 40% after 3 days treatment. The number of fungi began to rise after 7 days treatment. For 212.5g/m~2 dosage treatment, the number of bacteria reduced to 16%, the number of fungi reduced to 32% and the number of actinomyces reduced to 10% of the control level after 1 day treatment. However, the number of bacteria returned to 20% when the number of fungi and actinomyces reduced further to 8% and 3% respectively after 3 days treatment. All of these returned to control level after 15 days.2. According to the results of Biolog, both moderate and high dosages reduced the activity of microbial organisms, although the effect of 85g/m~2 dosage treatment was less remarkable. The AWCD number of 168h was 0.97 for 85g/m~2 dosage treatment, and it decreased to 0.26 under high concentration when the control number is 1.14. The low concentration treatment excited activity of microbial organisms. However, this effect wastransient and vanished rapidly. After 7 days, the AWCD numbers of all treatment were similar, suggesting that the activity of microbial organisms was resumed.3. The microbial communities were similar to control under low and moderate dosages from the analysis of DGGE. Most dominant microbial communities were similar, despite minor variations for some specific microbial communities. Oppositely, the microbialecology was changed drastically under high dosage treatment.4. The low dosage was not sufficient to reduce the pathogeny efficiently, for over 70% Fusarium oxysporum, f. sp. Cucumerinum was still alive after this treatment. The results of another two dosages were efficacious. The 85g/m2 dosage treatment could reduce the number of pathogeny by over 93% and the 212.5g/m2 dosage treatment showed the greatest reduction of the pathogeny by over 95%. But cucumber seedlings were not able to survive under such high concentration.