| Xinjiang province has become the large cotton production base.This area is arid and seldom rainy all year round,so cotton always suffer from drought stress during the growing season.The cotton aphid,Aphis gossypii Glover,is one of the major pests on cotton.Whether drought stress can indirectly affect the growth and development of A.gossypii by changing the physiological metabolism of cotton,and trigger corresponding population changes as well as physiological responses of A.gossypii populations needs further study.In this study,we use the main cotton variety ’Zhongmian 49’and the cotton aphid population of Korla as research subjects.we set three different drought stress treatments:（1）no drought stress（0%PEG-6000,control）,（2）moderate drought stress（1%PEG-6000）and（3）high drought stress（3%PEG6000）using polyethylene glycol（PEG-6000）,and then determine the growth,development,and the physical metabolites of cotton under three different drought stress treatments to clarify the direct effects of drought stress on cotton.Then,we compared the growth,development,feeding behavior,and physiological metabolism of A.gossypii fed on cotton exposed different drought stress to reveal the indirect effects of drought stress on A.Finally,we compared the growth and physiological responses of six different cotton varieties and population dynamics of A.gossypii under four drought stresses（0%,1%,3%,and 5%PEG6000）to analyze the relationship between drought resistance of different cotton varieties and A.gossypii populations.The main results of this study were as follows:（1）The growth indicators of conventional cotton under different drought stresses were measured,we found that the relative water content of cotton leaves under 3%PEG-6000 treatment was significantly reduced by 10%compared to the control treatments.The biomass of cotton plants under drought treatment was significantly lower than that of the control,which indicated that drought stress had a negative effect on cotton growth.Then the physiological metabolic indexes of cotton under drought stress were assessed,we found that the leaf soluble protein concentration increased significantly with the increase of drought stress,and the soluble protein concentration increased by 84.71%and 85.71%in the 1%and 3%treatment when compared with control treatment,respectively.Besides,the decreased significantly under drought stress compared with control treatment.The soluble sugar content of leaf treated with1%and 3%increased by 24.32%and 48.65%,respectively.The nitrogen content of leaf was significantly reduced under 1%PEG-6000 drought stress treatment compared to control treatment,while leaf nitrogen content was not significantly reduced under 3%PEG-6000 treatment.What’s more,tannin content of leaf showed positive correlation with drought stress concentration,while it increased significantly under 3%PEG-6000 drought stress treatment.In summary,drought stress could obviously affect the physiological metabolism of cotton.（2）We analyzed the growth,development,reproduction,and physiological metabolic enzymes of A.gossypii fed on cotton treated with different drought stresses,and the results showed that drought stress could prolong the developmental duration of A,gossypii nymphs,reduce fecundity and shorten adult lifespan.The intrinsic rate of increase,finite rate of increase,and net reproductive rate of A.gossypii decreased with increased drought stress.The number of A.gossypii on cotton plants was monitored for 40 days,and the number of A.gossypii decreased with the increase of drought stress.The acetylcholinesterase enzyme activity of A.gossypii was highest at 1%PEG-6000 treatment and lowest at 3%PEG-6000 treatment.Multifunctional oxidase enzyme activity increased with increased stress.Glutathione-Stransferase and Carboxylesterase enzyme activity decreased with increased stress.In summary,drought stress had an adverse effect on the growth,development,and reproduction of A.gossypii,and physiological metabolic enzymes of A.gossypii were changes to adapt the stress.The results of feeding behavior of A.gossypii showed that the duration（E2 wave）and number of feedings on the phloem of A.gossypii has decreased with increased drought stress,while the time of secretion of saliva（E1 wave）into phloem sieve elements significantly increased when drought stress increased.These results indicated that drought stress had a negative effect on the feeding efficiency of A.gossypii.The decreased feeding time on xylem（G wave）showed that drought stress had an adverse effect on the effective feeding behavior of A.gossypii.（3）The responses of six cotton varieties differing in drought-resistant under drought stress were tested,we found that the relative leaf water content,the biomass,and concentration of soluble protein of the five drought-resistant varieties of cotton were significantly higher than the drought-sensitive cotton.Thus,the drought-resistant varieties performed better under drought stress.The tannin content of cotton varieties reached the highest value under 1%treatment,and then decreased gradually with the increase of stress concentration,except JM14 and CL55.In addition,the number of A.gossypii on the drought-resistant varieties of cotton was higher than that of the drought-sensitive cotton under drought stress treatment,which indicating that cotton with higher drought resistance is conducive to the occurrence of A.gossypii.In conclusion,the increase of drought stress has significant adverse effects on the population growth and feeding behavior of A.gossypii mainly because of the decrease of relative water content and the increase of tannin in cotton plants with the increase of drought stress.At the same time,under the same drought stress condition,compared with common cotton varieties,drought-resistant cotton plants have stronger physiological regulation and growth maintenance ability,which is more conducive to the occurrence of A.gossypii population.In Xinjiang cotton area,drought stress is one of the most important abiotic factors affecting cotton growth,and breeding drought-resistant cotton varieties is an important direction of cotton industry development in Xinjiang.The results of this study can provide necessary data support for the analysis of the dynamics of A.gossypii population and its mechanism under drought stress in Xinjiang,and also lay an important scientific foundation for the prediction of the evolution trend of A.gossypii population status under the replacement of cotton varieties. |
