MODES OF RESISTANCE IN BARLEY SEEDLINGS TO 6 APHID (HOMOPTERA, APHIDIDAE) SPECIES

Resistance to the six most important cereal aphid species in Mexico (Rhopalosiphum maidis [Fitch], R. padi [L.], Metopolophium dirhodum [Walker], Sitobion avenae [F.], Schizaphis graminum [Rondani], and Diuraphis noxia [Mordvilko]) was assessed in seedlings of 'Gloria/Come' barley that had previously been shown to be resistant to D. noxia and 'Esperanza' that had proven to be susceptible. The resistance of 'Gloria/Come' to D. noxia, and the susceptibility of 'Esperanza', in terms of antibiosis on seedlings, was confirmed. The antibiosis of 'Gloria/Come' seedlings was confined to D. noxia, but an effect on other aphids was recorded on excised leaves. The antibiotic effect of 'Gloria/Come' on D. noxia was evident as decreased nymph production in comparison with that on 'Esperanza' and significantly more nymphs were produced on excised leaves than on seedlings by the six aphid species. Daily nymph production was correspondingly reduced on seedlings in comparison with on excised leaves, although aphid longevity was greater on seedlings than on excised leaves. Reproductive period was significantly reduced on 'Gloria/Come' compared with 'Esperanza' and was longer on seedlings than on excised leaves. 'Gloria/Come' was less preferred by D. noxia than 'Esperanza', but the other five aphid species showed no preference for the two barleys.