| The cotton aphid, Aphis gossypii (Glover) (Homoptera:Aphididae), is a cosmopolitan, and is one of the major destructive pests on cotton in Xinjiang, located in all cotton-growing areas. This research evaluated the resistance of main cotton varieties to A. gossypii in budding stage, and explore mechanisms of the morphological, biochemical and induced resistance of some of main cotton varieties to A. gossypii, the main results as follows:(1)Resistance of twenty-two cotton varieties (lines) to A. gossypii in budding stage were identified preliminarily in Xinjiang. The results showed that three varieties are highly resistant to A. gossypii, with Xinhai21 as the most resistant, Xinluzao26 and Xinzamian2 as middle resistant, and Zhongmiansuo35 and 81-3 as most susceptible ones. Xinluzao22, Xinluzaol2, Xinpaotail, BiaozaAl, Xinluzaol3, Xinluzaol9 and Xinluzaol6 damaged were relatively light.(2)This research deals with the relationship between wax content and hair density with the resistance to the cotton aphis in nine main cotton varieties (lines), the results showed that there were significant differences in wax content among different varieties (F=5.134, Fo.o5(8.18)=2.51), with Xinhai21 as the most content, and Zhongmiansuo35,81-3, Xinluzao24, Xinluzaol2 as were lower. The regression equation was: y=160.82-78.868x, R=0.706, P=0.034<0.05. The wax content of different varieties was in negative correlation with the resistance, the result showed that the high content of wax was an indicator of high resistance to A. gossypii. There was significant difference in the hair density of different varieties (F=59.065, Fo.o5(8.81)=2.06), with Xinhai21 and Xinzamian2 as the most hairiness. The hair density were positively correlated with the cotton resistance to A. gossypii, by influencing aphis feeding behavior. The hair density of different varieties was in negative correlation with the damage index.(3)The principal component analysis of nine cotton varieties (lines) showed that the eight amino acids makes great contribution to the first three pieces of principal component, and as principal components of amino acids. The linear correlations between the principal components of amino acids and the damage index were calculated by stepwise regression. The best multiple linear regression equation of nine cotton varieties damage index(Y) to eight kinds of free amino acids content such as aspartic acid(x1), serine(x2), glutamic acid(x3), glycin(x4), arginine(x5), proline(x6), tyrosine(x7) and methionine(x8) was: y=134.701-68.238x3+15.939x6+48.749x5, R=0.884, F=5.967, F0.05(3,5)=5.41. Correlation analysis showed that the effect of regression was obvious, the damage index has obviously negative correlation with the content of free glutamic acid, and has obviously positive correlation with free proline and arginine. In other words, more content of free glutamic acid, better was resistance to A. gossypii, more content of free proline and arginine, better is susceptible A. gossypii.(4) The resistance to aphid of cotton varieties (lines) with soluble sugar content(x1), tannin content(x2), free gossypol content(x3), amino acids(x4), and total nitrogen content(x5) are closely related. Damage index(y) with the five kinds of biochemical substances stepwise regression analysis: y=109.886-545.048x3+41.788x2-99.373x1, R=0.984, F=51.536, F0.01(3.5)=12.06, correlation analysis showed that the effect of regression was obvious. Regression equation showed that the content of tannin was in negative correlation with resistance to A. gossypu, while both free gossypol and soluble sugar were also in positive correlation with the resistance, and more content of free gossypol, better was resistance to A. gossypu.(5)Both normal and damaged cotton varieties (lines) proline content there were significant differences in cotton budding stage, highly resistant varieties Xinhai 21 and the Xinzamian2 of higher proline content, while cotton individual were damaged by aphids, proline content was substantial increase, and resistance more than susceptible. Proline content has very significant negative correlation with the damage index, r=-0.852, P=0.004<0.01. The proline was an important resistance to A. gossypii substances, and its was obvious effects with inherent and inducible resistance in cotton varieties.(6)The activity of Phenylalanine ammonia (PAL), Peroxidase (POD), Polyphenol oxidase (PPO) results showed that three enzymes have definite differences, resistance higher than susceptible ones. When cotton individual were damaged, all the three kinds of activity have different levels of increase, Xinhai 21, Xinzamian2, Xinluzaol3 activity increased rate than Zhongmiansuo35 and 81-3, analysis of variance showed that among the three activity have very significant differences.(7) The Xinluzaol3 were damaged by Aphis atrata (Zhang) in seedling stage, and again damaged by A. gossypii in budding stage, the physiological state and nutrient component were changed. The result showed that the Xinluzaol3 both the first were damaged by A. atrata (Zhang) and were damaged only by A. gossypii with the proline content, PAL, POD, PPO activity differences have reached very significant. In the seedling cotton individual were damaged by A. atrata (Zhang), the cotton individual were synthesized and accumulated secondary substances of resistance to aphid, then were damaged by A. gossypii, these resistance substances were effective mobilized with the relevant defense system to damage index expand. Both proline content and activity of enzyme more than only one damaged by A. gossypii. The cotton individual were damaged by A. atrata (Zhang) in seedling stage after, amino acids and nitrogen content were droped, the nutrient began to deteriorate, and maked against growth and development of A. gossypii. |
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