Yield retention of resistant wheat cultivars, severely infested with Russian wheat aphid, Diuraphis noxia (Kurdjumov), in South Africa

Abstract

Russian wheat aphid, Diuraphis noxia (Kurdjumov), has been a serious pest of wheat in South Africa since 1978. Wheat producers observed that resistant cultivars, developed for control of this aphid, differed in resistance and questioned whether insecticide treatment would be economically justifiable. This study was undertaken to confirm and quantify the observed differences in sixteen resistant cultivars under field conditions. A split-plot field trial with four replicates was planted near Bethlehem, South Africa. The yield of each aphid- infested plot was expressed as a percentage of the yield of the corresponding aphid-free plot giving percentage yield retained after infestation for each cultivar. The percentage yield retained varied in 2000 from 33.0% to 119%; in 2001 from 28.3% to 150.0% and in 2003 from 28.4% to 109.2 %. Cultivars were ranked and classified into more resistant and less resistant groups for each year and an AMMI analysis was conducted. Some cultivars compensated for D. noxia infestation with infested plots giving higher yield than aphid-free plots. It was shown that the level of resistance was not the same in all resistant cultivars and varied dramatically between cultivars and years when measured under severe D. noxia infestation.