Study On The Pathogenesis Of Soil-Borne Fusarium Wilt Of Cucumber And Biological Control

There are two approaches to control cucumber fusarium wilt:chemical control and biological control. The chemical control could easily cause environmental pollution and pesticide residue, the use of antagonistic bacteria against the cucumber fusarium wilt is drawing more and more attention. Therefore, it is important to study the pathogenesis of soil-borne fusarium wilt of cucumber and the biological control in fusarium-infested soil, which is of theoretical and practical significance to the development of cucumber production, reducing environmental pollution and maintaining sustainable agricultural development.In present study, pot experiments were conducted to study the mechanism of cucumber wilt in fusarium-infested soil, and whether application of microbial organic fertilizers could reduce the incidence of wilt. In order to study the physiological mechanism of soil-borne fusarium wilt of cucumber and to clarify the reasons cucumber wilt, water absorption and transportation, assimilation metabolize, and protective enzyme system were investigated before and after pathogen infection and the application of microbial organic fertilizers.The main results obtained were listed as followes:1. Pot experiments were conducted to study the water relations of cucumber leaves in different pathological grade plants, and to study the effects of organic and microbial organic fertilizers on water relations. (1) When the cucumber was infected soil-borne fusarium, leaf specific weight, leaf chlorophyll content, photosynthesis, stomatal conductance and transpiration rate were significantly decreased. Photosynthesis and stomatal conductance were decreased by 80% and 60%, respectively. (2) There were significantly negative relationships between leaf hydraulic conductance, leaf water content and callose content in petioles. In addition, callose content in roots and petioles increased with increasing pathological grade, which resulted in a decrease in leaf water content, root and leaf hydraulic conductance. (3) Application of microbial organic fertilizer could suppress callose formation, and maintain root and leaf hydraulic conductance, leaf water content and photosynthesis. (4) Relative electrical conductivity was 3 times higher in infected leaves, which indicated that the plasma membrane was destroyed. Therefore, the formation of callose in infected plants restrained water transport, and decreased leaf water content and photosynthesis. The application of microbial organic fertilizers in continuous cropping soil could alleviate the effects of pathogeny on plant water absorption and transportation.2. The yield and plant height were higher in healthy soil than in continuous cropping soil. During the process of disease, the transportation of assimilates, carbon and nitrogen metabolism was influent. When the plants were infected soil-borne fusarium, soluble sugar was increased in leaves, while decreased in basal stem. Total nitrogen, phosphorus, potassium, and nitrate reductive activity was decreased. Proline content was increased in the process of disease, but there were no effects on soluble proteins. Nitrate nitrogen content was decreased and ammonium nitrogen increased in the process of disease. Application of microbial organic fertilizers could alleviate the negative effects of plants to stress.3. Defense enzyme activity was different in resistant and sensitive cultivar before and after pathogen infection and the application of microbial organic fertilizers. (1) When plants were infected soil-borne fusarium, SOD and POD activity could immediately increase, and the increase in resistant cultivar was higher than in sensitive cultivar. After application of microbial organic fertilizers, SOD and POD activity was low. (2) CAT activity was higher in resistant cultivar, and application of microbial organic fertilizers could increase CAT activity in leaves. After the application of microbial organic fertilizers, PPO and PAL activity were increased and the increase in resistant cultivar was higher. When plants were infected soil-borne fusarium, PAL and PPO activity was decreased. (3) MDA content was higher in resistant cultivar than in sensitive cultivar. In continuous cropping soil, the increase in MDA was higher in resistant cultivar when infected soil-borne fusarium. Application of microbial organic fertilizers can efficiently decrease leaf MDA content. (4) The activity of glucanaseand and chitinasewas was low in healthy plants no matter in healthy soil or continuous cropping soil. With increasing pathological grade, the activity of glucanaseand and chitinasewas first increased, and then decreased.4. There was significant difference in soil microbial flora in continuous cropping rhizosphere. In continuous cropping soil, bacteria amount was decreased, and soil fungi quantity was increased. After the application of microbial organic fertilizers, bacteria and actinomycetes quantity were increased, while fungi and fusarium quantity was decreased.