| The biochemical characteristic is a kind of important foundation to resist insects. Not only affects food nutrition, the digest ability, the food directing property, dwelling and spawning of insects, but also affects other characteristics indirectly. All kinds of biochemical material in wheat are primary factor of anti-aphis breed. Therefore during studying on wheat's anti-aphis process, each biochemical substance which affects in different anti-aphis varieties should be study intensively. It is no doubt those can give anti-aphis breeding on wheat a broader prospect.This research uses the different resistant rank the material as the experimental object, takes Therioaphis trifolii as the biological stimulation factor, establishes the small ecosystem among the wheat– aphis by manual work, analysis several biochemical indexes (soluble sugar, starch, soluble protein, three kind of enzymes and total phenol) in wheat's different varieties before and after piercing by aphis respectively, inquires into the change rule of biochemical activities in the initial period plant, discusses the biochemical resistance response of wheat to aphis furthermore.1. The relationship between different anti-aphis wheat varieties'the nutrients and anti-aphis machanismDuring 5 days'damaging, the content of soluble sugar and soluble protein in seedling leaves of five wheat varieties was determined. The results showed that: soluble sugar content in the five different wheat varieties have decreased compared with non-damaged ones and the lower the resistance of varieties, soluble sugar content decrease greater; after inoculation, the content of soluble sugar in five wheat varieties was lower than non-damaged ones and the decreasing change in the five wheat varieties had no apparent regularity. The correlation analysis indicated that there was negative correlation between the soluble sugar content and aphid Ratio of five wheat varieties, but there was no correlation between soluble protein content and aphid Ratio of five wheat varieties.2. The relationship between different anti-aphis wheat varieties'enzymes and anti-aphis machanismThe enzyme activities of the superoxide dismutase (Superoxide dismutase, SOD), the peroxide enzyme (Peroxidase isozyme, POD) and the polyphenoloxidase (Polyhenoloxidase, PPO) had been determined in the five different anti-aphis wheat varieties before and after inoculation. It showed that,during the trial period, the activities of SOD,POD and PPO in leaves of all varieties increased remarkably with the days after inoculating. Correlation analysis showed that there was negative correlation between wheat aphid Ratio and the activies of SOD, POD, PPO.3. The relationship between different anti-aphis wheat varieties'total phenols and anti-aphis machanismThe total phenol content in five different wheat varieties was determined by using Folin method before and after inoculation. The results show that on the first day of inoculation, the total phenol content has risen, but the total phenol content in the next twice experiment followed a downward trend. The correlation analysis between total phenol content of different wheat varieties and aphid Ratio showed that total phenol content has no correlation with wheat varieties resistance to Rhopalosiphum padi.In the five days after Rhopalosiphum padi L. damaged, nutrients, the key enzyme, toal phenols content in five kinds of wheat varieties'leaves all had changed in varying degree but different varieties has showed different resistance levels. Particularly the high resistant variety XM800 and high susceptible variety has displayed extremely prominent.The purpose in this study is to definite the possibility of resistance mechanisms and to identify the anti-aphid related physiological and biochemical indexes in the five differently resistant wheat varieties in order to provide test data for research of wheat's anti—aphid mechanism , to offer reference of breeding insect-resistant alfalfa and the achievement of sustained Rhopalosiphum padi L. control.
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