بررسي تراكم جمعيت و اثر شته APHIS GOSSYPII )GLOVER( روي گياهچه هاي شش رقم پنبه در شرايط گلخانه اي

Study of Population Density and Effect of Aphis gossypii ( Glover)on Seedlings of Six Cotton Cultivars Under Greenhouse Conditions

In order to assess the reactions of cotton cultivars against the Aphis gossypii, a greenhouse experiment was conducted as a factorial design with six cotton cultivars under infected and non infected conditions by using randomized complete blocks with six replications. This study was conducted at the greenhouses of Plant Protection Department, Faculty of Agriculture, University of Tabriz, Iran, in 2002. The cotton aphid was collected from Moghan cotton fields and reared on cotton cv. Varamin at 27±2°C, 60±5% relative humidity and 16:8 (L:D) photoperiod. The cotton cultivars in each experimental unit were infected at four - leaf stage with two first instar larvae. In this experiment, population density of the aphid, time required for cotton seedlings to reach from 4 to 6 and from 6 to 8 leaf stage and stem growth in infected and non infected plots of six cotton cultivars were assessed. Analysis of data showed that there was a significant difference between the cotton cultivars and also between infected-non infected seedlings for the above mentioned criteria. Interaction between cotton cultivars (4-6 leaf stage) and infection was also significant. The maximum decrease in stem length was observed in Rafsanjan cv. and the minimum decrease was in Zeta-2, Sahel and Mehr, respectively. The maximum and minimum population density of the aphid were observed on Zeta-2 and Sahel, respectively.It was also revealed that cv. Zeta-2 had the shortest larval period (3.83 days), the latest appearance of the winged-adults (29.66 days) and the maximum number of the winged individuals (260.5). Assessment of all the criteria showed that Sahel and Mehr were less sensitive and Zeta-2 was the most sensitive cultivars. So, it is concluded that with further studies, resistance or tolerance can possibly be found in cotton cultivars and avoid the loss caused by aphid.