Sifting Of High-efficient Fungicides Against Cucumber Downy Mildew And Control Mechanism

In this study, the cucumber downy mildew was chosen as the object. The floating leafdisc bioassaywas adopted to determine the protective action of11fungicides and the curativeaction of8fungicides. The control effects of fungicides against the cucumber downy mildewwere studied in the field test. These fungicides were applied differently in spraying time andnumber of times includingspraying in flowing period, spraying once disease occurred,spraying repeatedly since the disease occurs, and spraying repeatedly from flowing period.The uptake and translocate behavior of LH-2010A was studied by HPLC. Changes ofprotective enzyme’s activity around the flowering period and after disease were studied toapproach the natural resistance of cucumber against downy mildew..The results are as followed:Chlorothalonil showed the best protective actionthat was47.6times to metalaxyl and it’sEC50was2.69μg/mL. Protective action of LH-2010A was higher than flucopilide, and theEC50were6.70and7.66μg/mL separately. The curative action of flucopilide that is20.9times to metalaxyl was the best in our research, and EC50was9.68μg/mL.EC50ofLH-2010Awas15.1μg/mL that is slightly higher than fluopicolide.The cucumber downy mildew could be controlled partly by spraying protective fungicidein the flowering period. Control effect of25%XMSC was69.39%. The cucumber downymildew could also be controlled after spraying suitable agents once disease occurred, too. Theincrease of disease could be inhibittedby spraying25%LH-2010A SC (375g/ha) and infinito(750mL/ha). The development of disease was inhibited by spraying agents repeatedly sincethe disease occurs. Well protective and curative effect was showed when sprayingLH-2010A(H)3times, and the control effectswere97.74,83.59, and67.19%. The best controleffect was achieved by praying agents repeatedly from flowing period. The disease could behold at a low state even using2kinds of common fungicides.LH-2010A was detected in seedlings after soaking roots in agent solutions. So, it wasabsorbed by cucumber rootsand transported to other sites. LH-2010A was sprayed to theleaves&stems, and it could be detected in leaves&stems and roots after72h. So, LH-2010A isabsorbed by leaves&stems of plants, and transported to roots. It could be concluded that LH-2010A was a novel systemic fungicide with upward and downward conductivities. Theabsorption of cucumber roots would be affected by temperature. Moreover, it would beinhibited by respiratory inhibitors, sucrose and amino acids. So the absorption of cucumberroots to LH-2010A should be an active process.From the nutrition stage to flowering period, the POD activity offered a increasedtrend.PPO activity was fluctuant. POD and PPO activity werenot showed related totheresistance.During the nutrition stage, PAL activity was rise gradually, and reached its peak atthe28th day. Then, PAL activity started to drop. The low activity of PAL may be one of thereasons why cucumber at nutrition stage was susceptible.After infected cucumber downy mildew, POD,PPO and PAL activity of cucumber leaveswere all increased. The polyphenol content of cucumber leaves increased and then declinedafter infection.When disease index was greater than degree2, the polyphenol content was in alow level. So, polyphenol should be one of immune-related factors. The content ofchlorophyll decreased as disease grew.