SCREENING FOR GREENBUG RESISTANCE IN HORDEUM-CHILENSE ROEM-ET-SCHULT

Schizaphis graminum (Rondani) is a serious pest of cultivated wheat (T riticum aestivum L.) and resistance is only available in other related species such as Hordeum chilense. Amphiploids between H. chilense and Triticum spp. have been obtained, and addition lines of H. chilense i n wheat have been developed. Thirty-five accessions of H. chilense wer e screened to identify greenbug antixenosis, antibiosis and tolerance. Antixenosis was determined in a conventional host free choice test; a ntibiosis was measured by aphid life cycle and fecundity rate, and tol erance was tested in a conventional infestation test of 4 weeks. Two c ommercial barley cultivars were used as susceptible and resistant cont rols. Eight H. chilense accessions showed higher degrees of antixenosi s than the resistant check, 19 were similar and the rest were lower. A ll accessions were more resistant than the susceptible check. Measured by aphid life cycle, 22 H. chilense accessions showed higher antibios is than the resistant cv., and all exhibited a higher antibiotic effec t on fecundity rates than the control. A similar degree of tolerance t o that of the resistant control was observed in six accessions, the re maining entries ranged between the controls. The presence of one mecha nism did not exclude the existence of other mechanisms in the same ent ry 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 wit hin entries for the three mechanisms.