Studies On Preventive And Mechanism By Several Inductors To Downy Mildew On Muskmelon

Downy mildew is one of the major diseases of melons. Whether be grown on the open field or on the protected horticulture systems, melons are therefore often subject to severe loss. There are insufficiencies in all the traditional disease-prevention methods. Disease-resistance induced by phytoextraction is very secure and able to greatly reduce the pressure of chemical prevention, increase the stability and sustainability of the agricultural production system. Besides, it is environment-friendly. Natural virus-resistant substances from plants are hot spots of researches on bio-prevention in recent years, Chinese medicinal herb have conspicuous curative effect. Researches on extracting active substances that are of relatively fine curative effect from Chinese medicinal herb are becoming the front edge of researching and developing non-polluted bio-revulsant. Therefore, it is of vital importance to research on the preventative effect of plant revulsant on melon downy mildew, the formation process of melon disease-resistance induced by phytoextraction.This thesis proposes disease-resistant cultivar---Yindi and susceptible variety---Kalakesai as Test material, BTH, arborvitae, Chinese medicinal herb II that are sifted from preparatory experiments as revulsants, studies the preventative effect of revulsants on downy mildew and the changes of relevant disease-resistant substances, enzymatic activity, and photosynthetic characteristics in the process of induced resistance, and understands the curative effect of on a couple of revulsants on diseases of several lamellar parts of melons, and the influence on fruit quality. The results shows that:(1) BTH, arborvitae, Chinese medicinal herb II are of fine preventative effect on melon downy mildew, and there is no obvious difference between that of arborvitae and BTH.(2) After handling the melon at the periods of vine extend,Period of early florescence,period of young fruit,BTH, arborvitae, Chinese medicinal herb II can all conspicuously induce the resistance of melon against downy mildew, white powder, anthrax, and stem blight, greatly reducing the index of diseases. The effect of BTH is relatively stable; spraying at the later stage is better than that of the previous stage, and it makes no difference whether spraying for once or twice. The effect of resistance against downy mildew is relatively better by using BTH at the period of young fruit of melons. All treatments have greatly reduced the disease index of white powder, but there is no conspicuous difference among these treatments. The preventative effect is the best when taking arborvitae to deal with anthrax. BTH is best for curing stem blight at the periods of Period of early florescence and young fruit. There is no difference between the curative effect of Oriental arborvitae and BTH, but there is difference between that of Chinese medicinal herb II on different diseases. All treatments are different while dealing with different varieties. The preventative effect on disease-resistant cultivar---Yindi is better than that of susceptible variety---Kalakesai. And it reduces with the elongation of the disease spell and the severity of the disease extent.(3) Inoculated with downy mildew after treatments of three revulsants, contents of MDA, lignine and HRGP, and different kinds of enzymatic activity in melon seedlings all change greatly. The contents of MDA increases slowly while elongates in time, the contents of lignin and HRGP and the activity of PPO, POD, PAL, CHI, GLU all increase conspicuously, being in accordance with the preventative effect. To compare among varieties, the enzymatic activity of disease-resistant cultivar---Yindi is higher than that of susceptible variety---Kalakesai, but compared with the increase-extent of only inoculated with downy mildew, after the treatment of revulsants, enzymatic activity of Kalakesai is relatively higher than that of Yindi.(4) After the treatments of BTH, arborvitae, Chinese medicinal herb II, the total contents of chlorophyll, net photosynthetic rate, and stomatal conductance of a melon leaf increased at the same period will slow the decrease-extent of net photosynthetic rate, total contents of chlorophyll, and stomatal conductance of a melon leaf induced by inoculated with downy mildew,inhibit the retrogradation of virus on chloroplast, reduce the interference of virus on chlorophyll synthesis, reduce the symptoms, slow the aging of lamina, and increase the lamina photosynthesis and plant disease-resistance.(5) Treating melons with revulsants before harvesting can conspicuously increase the yield per unit of fruit, dissoluble solid substance, and fruit hardness. Different curative effect on the yield per unit of Yindi is more obvious than that of Kalakesai, however, the effect on the content of dissoluble solid substance of Kalakesai is more obvious than that of Yindi.