Feeding behavior of biotypes E and H greenbug (Homoptera : Aphididae) on previously infested near-isolines of barley

The feeding behavior of virulent and avirulent greenbug biotypes after prec onditioning of the plant with virulent and avirulent greenbug biotypes was examined. A pair of near-isolines of barley, Hordeum vulgare L., differing by the antibiosis greenbug-resistance gene Rsg1a were used. Rsg1a confers r esistance to all greenbug biotypes except biotypes H and J. When data from a 420-min feeding monitor period were divided into 2 periods (0-210 min and 210-420 min), differences in feeding behavior were noted during the later period. Biotype E probed 3.5-fold more frequently and fed in the phloem for 5- to 8-fold less total time when feeding on Rsg1a+ plants than on Rsg1a- plants or when biotype H fed on either the resistant or susceptible isoline . The feeding behavior of biotype E was not altered by preconditioning Rsg1 a+ plants with biotype H. However, when biotype H was monitored on Rsg1a+ p lants that were preconditioned for 24 h with biotype E, biotype H probed e- fold more often and spent 4-fold less time feeding in the phloem when compa red with biotype H feeding on Rsg1a+ plants that were not preconditioned. T his reduction did not occur for biotype H when monitored on Rsg1a- plants t hat had been preconditioned with biotype E or on Rsg1a+ that had been preco nditioned with biotype H. These results suggest that the Rsg1a gene confers an inducible form of resistance that can be triggered by plant recognition of an avirulent greenbug biotype.