Physiological And Biochemical Responses Of Cucumber Against Infestation By Liriomyza Huidobrensis (Diptera:Agromyzidae)

The physiogical and biochemical responses and mechanism of cucumber after infested by Liriomyza huidobrensis (Blanchard) larvae were studied. The changes of phenylalanine ammonia-lyase(PAL), polyphenol oxidase(PPO), peroxidase(POD), superoxide dismutase(SOD), protease inhibitors(PIs), soluble sugar, soluble protein, chlorophyll, tannin, flavone, cucurbitacin B(CuB), salicylic acid(SA) and jasmonic acid(JA) after Liriomyza huidobrensis larvae feeding continuously in cucumber leaves were tested. The main results showed that:1. The contents of soluble sugar, soluble protein and chlorophyll in cucumber leaves decreased with the increase of damage by the larvae. The minimum contents of soluble sugar, soluble protein and chlorophyll appeared on the7th,5th and7th day, respectively, in the damaged-lightly leaves, and on the5th,5th and7th day, respectively, in the damaged-heavily leaves.2. The contents of tannin, flavone and CuB in cucumber leaves increased with the increase of damage by the larvae. The maximum contents of tannin, flavone and CuB appeared on the7th,5th and3rd day, respectively, in the damaged-lightly leaves, and on the5th,3rd and5th day, respectively, in the damaged-heavily leaves. They were on the5th,3rd and3rd day, respectively, in the lightly-systemic control leaves, and on the3rd,3rd and1st day, respectively, in the heavily-systemic control leaves. The results suggest that the influences of the larval infestation on the contents of tannin and flavone were systemic, and it was systemic on the content of CuB in cucumber leaves in the early stages of the infestion.3. The activities of PAL, PPO, POD and SOD in cucumber leaves which had been feeding by the larvae rose significantly. The magnitude of activity rising of PAL, PPO, POD and SOD increased with the increase of damaged levels, i.e. damaged heavily> lightly> systemically> undamaged. The maximum activities of PAL, PPO, POD and SOD appeared on the5th,7th,5th and7th day, respectively, in the damaged-lightly leaves, and on the3rd,5th,3rd and3rd day, respectively, in the damaged-heavily leaves. They were on the3rd,7th,3rd and5th day, respectively, in the lightly-systemic control leaves, and on the3rd,5th,3rd and3rd day, respectively, in the heavily-systemic control leaves. The results suggest that the influences of the larval infestation on the activities of PAL and PPO in cucumber leaves were systemic.4. The activities of TI and CI in cucumber leaves increased with the increase of damage by the larvae. The magnitude of activity rising of TI increased with the increase of damaged levels is damaged teatments> systemically> undamaged. The maximum activities of damaged-lightly, damaged-heavily, lightly-systemic control and heavily-systemic control appeared on the7th,5th,5th and5th day, respectively; The activity of CI on the four damaged teatments were more than undamaged invariably among the different damaged time, The maximum activities of damaged-lightly, damaged-heavily, lightly-systemic control and heavily-systemic control appeared on the7th,7th,5th and7th day, respectively. The results suggest that the influences of the larval infestation on the activity of CI in cucumber leaves was systemic.5. The content of SA in cucumber leaves increased with the increase of damage by the larvae. The content of SA in four damaged teatments varied with firstly increasing, and then decreasing and finally increasing. The maximum contents of damaged-lightly, damaged-heavily, lightly-systemic control and heavily-systemic control appeared on the3rd,7th,3rd and3rd day, respectively. The results suggest that the influences of the larval heavy infestation on the activity of SA in cucumber leaves was systemic on the damage stage of3rd and9th days.6. The content of JA in cucumber leaves increased with the increase of damage by the larvae. The content of JA varied with firstly increasing, and then decreasing and finally increasing in damaged-lightly, lightly-systemic control and heavily-systemic control, but varied with firstly decreasing, and then increasing and finally decreasing in damaged-heavily. The maximum contents of damaged-lightly, damaged-heavily, lightly-systemic control and heavily-systemic control appeared on the3rd,5th,3rd and7th day, respectively. The results suggest that the influences of the larval heavy infestation on the activity of JA in cucumber leaves was systemic on the damage stage of3rd and7th days.In summary, the contents of chlorophyll, soluble sugar and soluble protein in cucumber leaves decreased significantly, but the contents of2signal substances, such as SA and JA in cucumber leaves, increased significantly after the damage by the Liriomyza huidobrensis larvae. Consequently, it induced the activitives of4defense enzymes and2Pis, and the contents of secondary biochemical chemicals such as tannin, flavone and CuB in cucumber leaves increased significantly. The results suggest that the influence of the larval infestation on the contents of chlorophyll, tannin, flavone, CuB, SA and JA, as well as the activitives of PAL, PPO and CI in cucumber leaves was systemic.