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Schizaphis graminum (Rondani) is a serious pest of cultivated wheat {Triticum aestivum L.) and resistance is only available in other related species such as Hordeum cbilense. Amphiploids between H. chilense and Triticum spp. have been obtained, and addition lines of H. chilense in wheat have been developed.Thirty-five accessions of H. chilense were screened to identify greenbug antixenosis, antibiosis and tolerance. Antixenosis was determined in a conventional host free choice test; antibiosis was measured by aphid life cycle and fecundity rate, and tolerance was tested in a conventional infestation test of 4 weeks. Two commercial barley cultivars were used as susceptible and resistant controls.Eight H. chilense accessions showed higher degrees of antixenosis than the resistant check, 19 were similar and the rest were lower. All accessions were more resistant than the susceptible check. Measured by aphid life cycle, 22 H. chilense accessions showed higher antibiosis than the resistant cv., and all exhibited a higher antibiotic effect on fecundity rates than the control. A similar degree of tolerance to that of the resistant control was observed in six accessions, the remaining entries ranged between the controls. The presence of one mechanism did not exclude the existence of other mechanisms in the same entry and therefore, independence of the different mechanisms is proposed.Most of the accessions showed higher variability than both controls for the three mechanisms, and it appears to be genetic variability within entries for the three mechanisms.

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