Effects Of Two Allelochemicals From Welsh Onion Root Exudates On Cucumber Seedling And Rhizopheric Microbes

Cucumber(Cucumis sativus L.) is one of the main vegetables for protected cultivation, and continuous cropping obstacle has become an important factor restricting high yield and sustainable development of protected cucumber.Reasonable rotation cropping can prevent and control continuous cropping obstacles effectively, welsh onion crop rotation can effectively reduce the impact of cucumber continuous cropping, but its internal mechanism is not fully understood. In this study, on the basis of kowning main allelochemicals in the welsh onion root exudates, using exogenous substances substituting welsh onion root exudates treated the cucumber seedlings of continuous cropping soil potting and quartz sand cultivation in greenhouse, and explored the effects on the cucumber seedlings and rhizospheric microbes, in order to illuminate the effects or mechanisms of welsh onion-cucumber rotation from the allelopathic angle of root exudates, and provid the theory basis for setting a reasonabale cropping systems. The main results were as follows:1. After 3 times of root irrigation, 0.6 mmol·L-1 benzothiazole treatment promoted the growth of cucumber seedlings, improved photosynthetic pigment content and net photosynthetic rate, reduced rhizospheric EC, but improved pH. When the concentration reached 0.6 mmol·L-1 or more, the activities of urease, phosphatase, catalase and polyphenol oxidase in rhizosphere soil increased. 0.3 mmol·L-1, 0.6 mmol·L-1 could increased the number of bacteria, actinomycetes and fungi in rhizosphere soil, and improved the proportion of bacteria to fungi.2. After 3 times of root irrigation, low concentrations of diethyl phthalate had no significant effect on growth and physiological properties of cucumber seedlings, but 1.2 mmol·L-1 inhibited the growth and metabolism. When the concentration reached 0.9 mmol·L-1 or or more, the activities of urease, phosphatase, catalase enzymes and polyphenol oxidase in rhizosphere soil increased, and the number of bacteria, actinomycetes and fungi in cucumber rhizosphere soil increased. However, 0.3 mmol·L-1 and 0.6 mmol·L-1 diethyl phthalate decreased the number of fungi, but increased the proportion of bacteria to fungi.3. Suitable concentrations of benzothiazole had obvious promoting effect on cucumber seedlings. 0.6 mmol·L-1 benzothiazole promoted the growth of cucumber seedling, increased root vigor, photosynthetic pigment content and net photosynthetic rate, enhanced the activities of SOD, POD and CAT, reduced the electrolyte leakage, superoxide anion radicals and MDA content, and alleviated membrane lipid oxidation.4. 0.3 mmol·L-1 diethyl phthalate increased stem diameter, and the content of chlorophyll a, but had no effect on other growth and physiological indicators of seedling. However 1.2 mmol·L-1 diethyl phthalate inhibited the growth of cucumber seedlings, reducing root vigor, photosynthetic pigment content and net photosynthetic rate, and decreased the activities of SOD, POD and CAT, but increased electrolyte leakage, superoxide anion radicals and MDA content.5. 0.3 mmol·L-1 benzothiazole or diethyl phthalate reduced the disease incidence and disease index of Fusarium wilt in cucumber seedlings, improved their resistance to the disease, but when the concentration reached 1.2 mmol·L-1, both benzothiazole and diethyl phthalate could reduce the resistance of seedlings to Fusarium wilt.