Study On Physiological Defense Mechanism Of Feeding Pressure Of Therioaphis Trifolii In Alfalfa Seedling

This paper studied the content changes of the chlorophyll and the activities of SOD, POD and PPO of alfalfa seedling leaves damaged by therioaphis trifolii in different pest densities and different days in the flag leaf of three alfalfa varieties (strain) Gannong 3 (R), HA-3(HR), Hunter River(LR), for exploring thephysiological biochemistry dynamic change and the different resistance to aphids characteristic in different alfalfa varieties (strain).In short term of alfalfa seedling leaves damaged by therioaphis trifolii, the chlorophyll content of alfalfa varieties (strain) Gannong 3(R), HA-3(HR), Hunter River(LR)seedling leaves decreased remarkably (P<0.01) by sticking and sucking of therioaphis trifolii in different pest densities and different days.In 0～9 days ,the SOD, POD, PPO activities of 3 alfalfa varieties (strain) increased remarkably in different pest densities and different days. Three kinds of enzyme activities of Gannong 3 increased remarkably compared with control group from third days, stabilized after sixth day and no significant difference compared with ninth day. Three kinds of enzyme activities of HA-3 in artifitial inoculation 15 live larvae per plant increased remarkably compared weth control group from sixth day. Three kinds of enzyme activities of HA-3 in artifitial inoculation 30 live larvae per plant increased notability compared with control group from third day. And three kinds of enzyme activities of HA-3 in two pest densities increased extremely remarkable compared with control group in sixth and ninth day. Three kinds of enzyme activities of Hunter River in two pest densities increased extremely remarkable in third day, and stabilized from third days, no significant difference compared with ninth day. But the PPO activities had notabilith in sixth day compared with ninth day.In damage days, 3 alfalfa varieties (strain) had resistence to therioaphis trifolii, but resistance level was different because of the difference of variety (strain). Although each physiological indexes before treatment had change, no significant different. However, the increase rate of three kinds of enzyme activities of Gannong 3 and Hunter River compared with before treatment increased than HA-3. And there was no significant between Gannong 3 and Hunter River; in sixth day damage by therioaphis trifolii, the increase rate of three kinds of enzyme activities of Gannong 3 and HA-3 compared with the third day significant than Hunter River. In ninth day, the increase rate of three kinds of enzyme activities of HA-3 compared with the sixth day notability increased than Gannong 3 and Hunter River, but there was no significant between Gannong 3 and Hunter River. Therefore, the resistance of HA-3 damaged by therioaphis trifolii reflected slowly but duration is long, the resistance of Hunter River stickded and sucked by therioaphis trifolii reflected fast but duration is short ,and the resistance of gannong 3 is moderate.