Study On The Interaction Among Liriomyza Huidobrensis-Cucumber Downy Mildew-Cucumber

Liriomyza huidobrensis (Blanchard) is a wide-spread agricultural pest in the world, which has caused huge loss in many crops including cucumber, bean, rape and etc. The fly usually occurs together with the downy mildew on greenhouse cucumber, which indicates the potential interactions between L. huidobrensis. Downy mildew and cucumber. In this study, the interactions between L. huidobrensis, Downy Mildew (Pseudoperonospora cubensis) and cucumber were studied. The effects of the plant defensive system on the fly and Downy Mildew were also investigated from the perspective of the host plant defense.The results were as follows:1. The severity and duration of the miner infestation had significant effects on the infection of the downy mildew on cucumbers. The disease indices of downy mildew varied mostly6days after inoculation compared with the healthy leaves. The disease indices were reduced by5.18and16.29, respectively, at the levels of light and high severity. Downy mildew was inoculated with different intervals after the eggs laid on cucumber. The disease index reached to the peak of9.26on6days after P. cubensis inoculation while the egg was laid on leaves6days before inoculation.2. We investigated the effects of host plant volatiles induced by the miner infestation, P. cubensis infection or both on the fly’s host selection behavior using Y-tube olfactory. The behavioral response experiments showed that the repllent effects of P. cubensis-induced cucumber volatiles on the L. huidobrensis adults.3. The variations of soluble protein, soluble sugar, tannic, flavonoids and chlorophyll contents were monitored after P. cubensis infection by Bradford (coomassie blue staining) method, Anthrone colorimetry, Phosphomolybdic-Phosphotungstic acid phenol clorimetry, Soxhlet extraction and acetone extraction method, respectively. The results showed that the contents of soluble sugar, soluble protein, tannin and flavone in cucumber leaves increased with the increase of severity of infection by P. cubensis. while the content of chlorophyll decreased.4. After P. cubensis infection, the activities of4enzymes, including phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO). peroxidase (POD) and Superoxide dismutase (SOD), were increased with the severity of damage in cucumber.5. The volatiles of healthy plants and infected plants by P. cubensis were extracted by solid phase microextraction technique (SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS).21volatile compounds were trapped from the healthy plant with15of them identified by analysis.25kinds of volatile compounds were trapped from the infected with6compounds unidentified, while19kinds in them were identified by qualitative analysis, including4terpenoids,6hydrocarbons,2olefins,4aromatic hydrocarbons, and each of alcohol, aldehyde, and esters. Compared with the healthy control, the treatments emitted extra4compounds, such as bicyclo [2.2.1] hepta-2,5-diene-7-ol,1,3,5,5-tetramethyl-1,3-cyclohexadiene,4-methyl-l-pentene,(trans)-3,7-dimethyl-1.3,6-octatrienyl.