Categories of resistance at four growth stages in three wheats resistant to the Russian wheat aphid (Homoptera: Aphididae)

Laboratory experiments were conducted to determine categories of resistance to Russian wheat aphid, Diuraphis noxia (Mordvilko), in three wheats, Triticum aestivum L, (PI 372129, PI 243781, and PI 222668) at Zadoks growth stages 10, 20, 30, and 40. 'TAM 107' was used as the susceptible standard. Antixenosis was observed in PI 222668 and PI 372129. Antibiosis was expressed as reduced nymphipositional period, daily nymph production, and fecundity at the jointing (Zadoks 30) and boot (Zadoks 40) stages in PI 243781 and at tillering (Zadoks 20) in TAM 107. Antibiosis, expressed as reduced intrinsic rate of increase, was observed in PI 222668 at tillering (Zadoks 20). Tolerance to chlorosis and leaf rolling was expressed in the three resistant wheats at all growth stages tested. Tiller production, floret formation, spike length and wet weight were affected by Russian wheat aphid feeding after Zadoks 10. Reduction in spike length did not occur in PI 372129 and PI 243781.