DETECTION AND MECHANISMS OF RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) RESISTANCE IN BARLEY

A collection of 524 barely lines from areas of the world where the Russian wheat aphid, Diuraphis noxia (Mordvilko), and barley, Hordeum vulgare L., have coexisted was evaluated for sympatric resistance to this pest. Mass screening tests were conducted in a growth chamber and greenhouse with seedlings planted in flats. Additional tests to determine the mechanisms of resistance were performed with nine of these lines. The lines and their sources are PI 366444, PI 366447, PI 366449, PI 366450, PI 366453 (Afghanistan); CI 1412, PI 430140, PI 430142 (Iran); and PI 447219 (Spain). Various levels of antibiosis and tolerance were exhibited in most of the lines tested in comparison with 'Wintermalt' (CI 15767), the susceptible control. For example, in the antibiosis test, an average of 27.3 nymphs per adult were produced on PI 366449 compared with 50.0 on 'Wintermalt'. In the tolerance test, plant growth and leaf area of some of the resistant entries were not affected by the Russian wheat aphid, whereas growth and leaf area of infested 'Wintermalt' plants was only 61% of noninfested 'Wintermalt' plants. Plant survivors of these tests have been saved for developing Russian wheat aphid plant-resistant germplasm for the North American barley industry.