Biotypic differences in Russian wheat aphid (Diuraphis noxia) between South African and Hungarian agro-ecosystems

The effect of Russian wheat aphid Diuraphis noxia (Mordvilko) from South Africa and Hungary was measured on susceptible and resistant South African wheat cultivars and a susceptible Hungarian barley cultivar. For the three cultivars (‘SST 333’, ‘Betta’, and ‘Isis’) tested in both countries, Hungarian D. noxia reduced plant weight and leaf area more than South African D. noxia and this difference increased over time. Hungarian D. noxia reduced plant weight and leaf area of the resistant wheat SST 333 more than the susceptible wheat Betta. Hungarian D. noxia also reduced plant weight of the resistant wheat ‘PI 262660’ more than the susceptible wheat Betta (although the opposite was true for leaf area). In Hungary the resistant SST 333 and PI 262660 showed similar severe symptoms of yellowing and leaf rolling as susceptible Betta. In addition, Hungarian D. noxia caused visible water imbalance in resistant wheats SST 333 and PI 262660. The differences in damage did not result from higher growth rate of Hungarian D. noxia colonies because aphid numbers did not differ consistently between countries or match the differences in damage. Differences between Hungarian and South African D. noxia suggest genetic differences between these populations. These results support the idea that resistant plant germplasm has geographical limits because of variation in agro-ecosystems.