INVOLVEMENT OF ETHYLENE IN APHID INFESTATION OF BARLEY

The recently arrived Russian wheat aphid (RWA) is a major pest of whea t and barley in the United States. RWA induced ethylene production in Morex, a barley variety susceptible to RWA, but induced little ethylen e production in PI 366450, a barley resistant to RWA. Greenbugs, anoth er aphid pest, induced ethylene production in PI 366450 and Morex, bot h of which are susceptible to greenbugs. RWA infestation results in pr onounced symptoms on barley including leaf streaking, stunting of grow th, and rolled leaves. Incubation of barley in ethylene (5 and 50 mul/ l) or other plant hormones (auxin, gibberellic acid, zeatin, kinetin, and abscisic acid at 10(-4) M) failed to produce streaking or rolling in uninfested plants or to alter the production of these symptoms in i nfested plants. Incubation of Morex and PI 366450 in ethylene caused s ome stunting of the leaves and internodes that emerged during or soon after ethylene incubation. However, the leaf and internode that emerge d 9 days after incubation showed some compensatory, or increaed, growt h.