| Cucumber is one of the vegetable crops on largest consumptions in daily life of our country. In recent years, the planting area of cucumber in our country has been more than million hectares, of which the planting area of cucumber of protected field occupies a considerable proportion. The cucumber powdery mildew caused by Sphaerotheca fuliginea, because the incubation period is short, and its secondary infection is strong. At the same time, cucumber powdery mildew is an air-borne disease, it’s even widely spread when cucumber planted in a relatively closed greenhouse. It can damage the quality and its production while the disease is serious. At present, the main approaches to control of cucumber powdery mildew is based on themical control, supplemented by disease resistance breeding and biological control. In recent years, with the enhancement of people’s environmental awareness, the demand quantity for green food is increasing. Development of a non-toxic, high efficiency and low residue fungicides to control powdery mildew appeared in the eyes of researcher at home and abroad. Based on the soybean oil and lecithin(SOL) developed by our research group, the following points are further studied, and screen the optimal dilutional concentrations of SOL, and clarify the disease prevention mechanism.(1) Through research of the biological characteristics of asexual conidia of Sphaerotheca fuliginea, we clear and definited the effect of germination of various environment factors to conidia. The result showed that the optimum germination humidity of conidia of S. fuliginea was 95%, the optimum germination temperature was 25℃,and germination rate of conidia treted by light dark alternation is significantly higher than the single light and dark treatment groups. The optimal germination p H of conidia is 7.the optimum carbon source is glucose. The optimum nitrogen source is KNO3.(2) The stability of the SOL has been tested under the different temperature, p H and storage stability.SOL can be saved 1~3 days under the condition of 4 ℃ and p H 7 after being prepared. The results of indoor pot experiment and greenhouse experiment showed that 300 times diluent of SOL has the best preventive efficacy and therapeutic efficacy. The results showed that preventive efficacy and therapeutic efficacy of indoor pot experiment were 100% and 97.54%, respectively. The results of greenhouse experiment showed that therapeutic efficacy of SOL in the early and middle period were 86.09% and 60.84%, respectively. Chlorophyll content of cucumber leaf was positively correlated with preventive efficacy after applying SOL which provides a meaningful guideline for biological prevention and control of cucumber powdery mildew.(3) We conducted the preliminary study of microscopic level through the preventive effect of SOL by using the method of alcoholic lactophenol trypan blue, and preliminary observed that the protective efficiency of SOL are more significant than thiophanate-methyl of positive control and CK. The conidia of S. fuliginea treated with SOL only produced a small number of germ tubes after inoculation of 48 h. But conidia of S. fuliginea of thiophanate methy and CK group produced germ tubes after inoculation of 12 h. We further clear and revealed the mechanism of control of SOL to S. fuliginea by using scanning microscope technique. The results showed that the conidia of S. fuliginea appeared dry, shrinkage, the growth of germ tube was restrained, and could not continue to form the infection peg and ultimately inhibit the infection of host plant when SOL agent as a protective agent. When SOL agents as a therapeutic agent, we found that already formed germ tube is difficult to continue to grow, and was obviously inhibited. The conidia of S. fuliginea appeared dry and collapse, the generated germ tube appeared fracture and the out releasing of inclusions. The above results suggested 300 times diluent of SOL had very good control effect on cucumber powdery mildew, and we preliminarily clear and definited the control mechanism of SOL. |
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