EFFECTS OF GROWTH STAGE OF RESISTANT AND SUSCEPTIBLE BARLEY ON THE RUSSIAN WHEAT APHID, DIURAPHIS-NOXIA (HOMOPTERA, APHIDIDAE)

The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a serious pes t of barley in western North America. To help manage this pest, a Russ ian wheat aphid-resistant germplasm line STARS-9301B was recently rele ased to barley breeders for incorporation into their cultivars. Inform ation about the antixenosis and antibiosis mechanisms of resistance in the 1st-leaf stage was previously reported, but information about the se mechanisms of resistance in later plant growth stages has not been available. This study reports on antixenosis and antibiosis tests cond ucted under controlled conditions on three growth stages of STARS-9301 B and 'Morex', a Russian wheat aphid-susceptible malting barley cultiv ar. In general, aphid reactions in the later growth stages were simila r to those on 1st-leaf stage plants except that antixenosis was demons trated in STARS-9301B when data from all growth stages were combined. Antibiosis continues to contribute to resistance in more mature plants of STARS-9301B. Previous work showed that tolerance is the most impor tant resistance mechanism of STARS-9301B seedlings. Tolerance data for comparing barley entries beyond the seedling stage are not available because a practical, uniform test to determine tolerance levels at the se older plant growth stages has not been developed. The results of th is study show that spring barley entries can be reliably tested in ear ly growth stages for antixenosis and antibiosis to the Russian wheat a phid.