| ABSTRACT With the extensive planting of transgenic Bt cotton, the main insect pest, Helicoverpa armigera Hubner in cotton field, has been effectively controlled, but this resulted in the outbreak of Aphis gossypii Golver and other non-target insect pests. At present, many researchers pay more attention to studying on transgenic cotton with resistant genes to piercing sucking insects, especially the cotton aphid. However, there is not a set of evaluation system to decide whether the transgenic cotton has resistance to Aphis gossypii Golver or other piercing sucking insects until now. In present paper, we chose12cotton varieties (transgenic Bt gene cotton H2and its parental cotton zhongmian12; transgenic Bt+CpT1gene cotton zhong41and its parental cotton zhong23; transgenic insect resistant lectin gene cotton8008and its parental cotton su006; transgenic insect resistant lectin gene cotton8009and its parental cotton su011, transgenic insect resistant hybrid cotton jinmian34and conventional cotton tai8; transgenic cotton18and its parental cotton18qin) as host plants for cotton aphid Aphis gossypii Golver. We mainly researched on the fitness of the cotton aphid, Aphis gossypii Glover (Homoptera:Aphididae) on different cotton varieties, effects of trans-exogenous insect resistant genes on cotton lectin, determinations of honeydew excretion by Aphis gossypii as indexes of aphid resistance of transgenic insect resistant cottons, effects of trans-exogenous insect resistant genes on cotton nutrition and secondary metabolites. All results were as follows.1. Fitness of the cotton aphid, Aphis gossypii Glover (Hemiptera:Aphididae) on different cotton varietiesUsing three methods to evaluate the fitnesss of cotton aphid after feeding on different cotton varietyes, but the conclusions obtained from population life table, inhibition rate of cotton aphid’s density and aphid damage index were not same. We found that the intrinsic rate of natural increase of transgenic cottons were greater than their parental cottons except the transgenic cotton18by the method of population life table, the level of aphid resistance of transgenic Bt cotton H2was higher than its parental cotton zhongmianl2, and the transgenic insect resistant lectin gene cotton8008didn’t have aphid resistance compared with its parental cotton su006by the method of inhibition rate of cotton aphid’s density. However, the results from aphid damage index showed that the level of aphid resistance of H2and zhongmianl2was same, also8008and su006. The result of inhibition rate of cotton aphid’s density showed that transgenic Bt+CpTI cotton didn’t have aphid resistance compared with its parental cotton zhong23, but the result of aphid index was completely different. So, we could conclude that the fitness of the cotton aphid on different cotton varieties by these three methos was not good enough due to their accurcy, we must make use of other methods to determine the resistance of cotton varieties to cotton aphid.2.Effects of trans-exogenous insect resistant genes on cotton lectinDuring the vegetative growth period of cotton, the hemagglutination activity (HA) of cotton lectin changed. The HA increased or decreased after the introduction of some exogenous insect resistant genes including Bt, CpTI or agglutinin genes with different insect resistant mechanisms on target insect pests into cotton genome. The HA detected with chicken red cell treated by trypsinase was64times that of controlled processing. The cotton lectin was a kind of lectin stable to heat treatment, it was stable at below45℃, but its activity decreased as a result of long treatment time or high temperature. Using the methods of hemagglutinin reaction and colorimetry, we can detect the contents of cotton lectin easily, they can be used as the important methods to evaluate the HA in cotton, especially when trans-exogenous agglutinin genes express in cotton.3.Determinations of honeydew excretion by Aphis gossypii as indexes of aphid resistance of transgenic insect resistant cottonsThe resistance of cottons to the cotton aphid Aphis gossypii can be obtained via aphid honeydew production. In present paper the effects of different transgenic insect resistant cottons on the amount of honeydew excreted by Aphis gossypii were detected by the methods of semi-quantity, quantity and colorimetry. The relationship between honeydew excretion and the number of aphid was obtained, a regression equation is y=0.0135x-0.5323, with a correlation coefficient r=0.9988. By contrast, the colorimetry was very accurate, stable and convenient, it can be used as an important method in analysis the aphid resistance of cottons.4.Effects of trans-exogenous insect resistant genes on cotton nutrition and secondary metabolitesThe presence of exogenous genes in transgenic cotton causes changes in its parental cotton including changes of its own physicochemical properties and gene sequence, and these changes could lead to effects on the cotton aphid Aphis gossypii. Based on the analysis of related aphid resistant materials in six cotton varieties, such as secondary metabolites including tannic, free gossypol, free amino acids, soluble sugars and protein. The results showed that the cottents of free amino acids of transgenic insect resistant Bt gene cotton H2and transgenic insect resistant lectin gene cotton8008were lower than their parents, the contents of tannic decreased in the transgenic cottons, but the content of free gossypol was higher than that in their parents, meanwhile, there were significant differences in the contents of soluble sugars and protein between these transgenic cottons and their parents except the transgenic insect resistant lectin gene cotton8008and its parental cotton su006. Furthermore, there were differences among all test varieties, and there were significant differences among some varieties (P<0.05or P<0.01). These results suggested that the presence of foreign genes in transgenic cottons have already produced big impact on the biosynthesis of aphid resistant materials, for example, tannic, free gossypol, free amino acids, soluble sugars, protein and so on. From these results, we could speculate that the level of aphid resistance of these cotton varieties are absolutely different. |
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