Nineteen genotypes of Hordeum vulgare were characterized as partially resistant or susceptible regarding growth of the bird cherry - oat aphid (Rhopalosiphum padi L.). These genotypes were treated with volatiles from undamaged plants of barley cultivar Alva. Aphid host acceptance (AHA) was significantly affected in seven genotypes, and the magnitude of the effect was positively correlated with aphid growth (AG) in a resistance screening test. Changes in AHA induced by volatiles from the same genotype were also positively correlated with AG. All genotypes were tested as inducers with cultivar Kara as the receiver of volatiles. Five genotypes induced significant reductions in AHA of Kara. The results show that aphids are able to detect changes in responding plants induced by volatiles from another cultivar. Plant volatile interactions may thus be a component of induced resistance to aphids. These interactions could influence the results of experiments used to select for insect-resistant plants in plant breeding programmes
