Study On Chitin-induced Resistance Of Cucumber To Downy Mildew

Downy mildew was caused by Pseudoperonospora cubensis ?Berk.&Curt.? Rostov, and wasa major foliar disease of cucumber in the world. At present,the control of downy mildew mainlyrelied on selection of resistant varieties and fungicides. Because control by fungicides had toomuch negative impact and selection of resistant varieties had much difficulty, so only relying onthese two pathways to control this disease had several limitations. Therefore, how to developnew bio-pesticides had been one of the directions of the world's agricultural scientists to workhard. Resent years, plant induced resistance was a new idea of the plant disease control, somebiological preparation could make use of the plant's own defense system to stimulate the level ofplant resistance and improve the ability to resist disease. As a result, a new situation for theprevention and control of cucumber downy mildew was born. According to the principle of plantinduced resistance, basied on outdoor biological control test, indoor toxicity determination testand exploration of its mechanism of action, biological agents-chitin as the inducer wasresearched in this experiment, in order to offer theoretical basis to the control of downy mildew.The main results were as follows:1. The tested cucumber varieties was “Jinyou No.35” and pathogens was collected in JiyangCounty, Shandong Province. Using the method of condition index survey,we tested the controleffect after induced by the chitin and commonly used chemical fungicide. The results showedthat: chitin did can control this disease, the control efficiency up to59.2%, and even better thansome chemical fungicides, and the degree of polymerization and concentration of the chitin wereidentified as low molecular weightchitin800times.2. According to indoor pot method, we surveyed cucumber downy mildew virulencedetermination induced by chitin, result showed that among the three molecular weight of chitin,the low molecular weight chitin was best and the EC50was0.7992?g?mL^-1; We could alsoobserve the inhibitory effect after induced by chitin, such as pathogen sporangium germination,release, swimming, and germ tube elongation under the microscope.3. The physiological and biochemical mechanisms of cucumber downy mildew induced bychitin were researched according to several antioxidant enzyme activity indicators.The resultswere as follows: Chitin could induce SOD,CAT,POD,PPO,PAL activity were higher than thecontrol group throughout the sampling period. These activities all showed decreased afterincreasing trend and activity was increased by1.5-2times. We concluded increasing of theseactivities was the internal factors.4. The change of protein content or types in cucumber was researched by SDS-PAGE andMALDI-TOF technology, so that to explore the resistant mechanism. The results showed: Afterinduced seven days, there were two protein bands obviously thicker, and one band was12Kb, the other one was55Kb. According to test, the differentially expressed protein was Ribulose1,5-bisphosphate carboxylase/oxygenase. This enzymes could accelerate the photosynthetic rateof plants,so to resistance against downy mildew.