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Three insect-resistant cotton varieties-Longmian NO.1, Dunmian 9916 and Dunmian V3 in the fields were taken as test materials and the continnous sucking stress of Bemisia tobacci(Gennadius) was taken as test method. The physiological and chemical changes of three cotton varieties were determined under sucking stress of B. tobacci(Gennadius). The comprehensive evalution to the three insect-resisant cotton varieties was conducted using principal compenent analysis. The results were as follows:1 Under sucking stress, significant changes had taken place. With the B. tobacci(Gennadius) sucking time of stress and damage increased, and chlorophyll content and carotenoids the content reduced; MDA content increased; superoxide dismutase, peroxidase and polyphenol oxidase activity increased significantly (P < 0.05). After the end of July, superoxide dismutase and peroxidase activity had a steady decline; soluble protein content increased; ascorbate peroxidase activity was rode and then declined, the changes to significant level (P < 0.05); glutathione reductase activity of different varieties had different changes, glutathione reductase activity of Dunmian V3 increased stress early but fell later, Longmian NO.1 and Dunmian 9916 had a declining trend; gossypol have a significant increase.2 MDA content and cotton insect-resistant were negatively correlated; chlorophyll content, carotenoid content, superoxide dismutase activity, peroxidase activity, polyphenol oxidase activity, soluble protein content, ascorbate peroxidase activity, glutathione reductase activity, gossypol content and cotton insect-resistant were positively correlated.3 In the same variety, the insect population to insect resource at 10 meters was larger than that of 20 meters; reduction of chlorophyll content and carotenoid content was larger; increase the volume of activity of superoxide dismutase, peroxidase, polyphenol oxidase and gossypol, MDA content were larger; increase the volume of soluble protein content was little; ascorbic acid oxidase activity, glutathione reductase activity and distance relationship was not obvious .4 Principal component analysis using 10 physiological indicators obtained the first principal components: superoxide dismutase, peroxidase, catalase, ascorbic acid oxidase, gossypol, soluble protein, carotenoids, glutathione reductase, chlorophyll, the contribution rate was 74.14%; second principal components: MDA, polyphenol oxidase, the contribution rate was 25.86%. The order of insect-resistant strength : Dunmian V3 > Dunmian 9916 > Longmian NO.1.
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