| Cucumber downy mildew caused by Pseudoperonospora cubensis is a global leaf disease, which restricted cucumber production in the practice. Currently, the main prevention measures of cucumber downy mildew are using chemical fungicides and planting resistant varieties. The control effect is not satisfactory, though there are a variety of disease resistant cucumber grown all around the world. To control the cucumber downy mildew still need the use of chemical fungicide. However, extensive use of chemical pesticides would lead to many negative results, such as the enhancement of resistance to fungicides and pesticides residue. In order to find a safe and effective technology to control the spread of cucumber downy mildew, the present research used lentinan as a plant resistance elicitor, and observed the effect on cucumber plant by soaking seed and spraying treatment. We also tested the tynergism to the new fungicide LH-2010A. The results are as followed:1. The seed germination rate, root length, shoot length and fresh weight were increased significantly when the cucumber seeds soaked in62.5,125,250and500mg/L lentinan for8h. The seed soaked in250mg/L lentinan observed the highest germination rate93.0%, which11.3%higher than the control81.7%. The root length and shoot length were also observed the longest growth under this concention, increased1.95cm and0.83cm respectively.500mg/L lentinan treated got the biggest fresh weight,78.52%higher than the control. Those results indicated lentinan can increase the seed germination rate and enhance the growth and root of cucumber seedlings.2. The proline contents of cucumber seedlings were increased when treated by lentinan. This can enhance the ability to bound water and cell membrane structure of cucumber seedlings, so the resistance to adverse environmental was inproved. In addition, lentinan can also increase the chlorophyll content in cucumber seedlings, make the leaves green and strong.3. The sporangium of cucumber downy mildew can germinate normaly in lentinan solution, and the pathogenic capability is not affected. This indicated lentinan can not kill or inhibit the cucumber downy mildew pathogen directly. Spariying150mg/L lentinan on the first true leaves and inoculate downy mildew pathogen3days later, the control effects on the first and the second true leaves were66.13%and56.37%respectively. The control effects reached47.90%when the seeds soaked in250mg/L lentinan for8h.4. In addition, the lentinan can also improved the activity of resistance related enzymes POD, PPO and PAL, the plant can rapidly produce defensive reactions when suffered infection of Pseudoperonospora cubensis.5. Fungicides mixed with lentinan were significantly more effective than either lentinan or fungicides alone in control cucumber downy mildew at florescence. And the dose of fungicides were reduced about30%. At the beginning of cucumber downy mildew spread, the control effect of LH-2010A and lentinan alternated used with7days interval is similar to the control effect of used LH-2010A alone. This indicated both LH-2010A mixed with lentinan and alternated used with7days interval can reduced about25%and50%, without reducing the control effects. This is important to improve the quality of cucumber and delay the development of pathogen-resistant to fungicides. |
