Evaluation of Antixenosis and Tolerance of Different Wheat Varieties to Schizaphis graminum

Greenbug، Schizaphis graminum (Rondani)، is a major pest of small grains، particularly wheat in Iran. The most effective method to control this insect pest is the use of resistant varieties and lines. In this research، 57 wheat varieties were screened at either two or three leaf stage، as based upon the mean number of aphids on plants. Antixenosis experiment was conducted through counting the number of aphids attracted to each plant variety. In the antixenosis tests after 24، 48 and 72 hr past from the experiments. the highest number of aphids were observed to be attracted to Sepahan variety while the lowest numbers attracted to Omid and Aadl varieties. Tolerance mechanism was assessed as based upon the height of the plant where the aphids were feeding on، and as well upon the decrease in the plant''s percentage of dry and wet weight. Aadl and Omid varieties were found out as the most tolerant varieties to S. graminum. The two varieties exhibited the highest tolerance and were the least preferred hosts as regards S. graminum.