EFFECTS OF THE RUSSIAN WHEAT APHID ON OSMOTIC POTENTIAL AND FRUCTAN CONTENT OF WINTER-WHEAT SEEDLINGS

The effect of an autumn Russian wheat aphid, Diuraphis noxia (Mordvilko), infestation on winter wheat, Triticum aestivum L., was investigated using osmotic potential, fructan content and field survival measurements to estimate coldhardiness. An average infestation of 147 aphids per plant, under simulated hardening conditions, increased the osmotic potential of 'Froid' and 'Brawny' (more or less coldhardy varieties, respectively) seedlings by 0.236 and 0.345 MPa, respectively. A natural field infestation averaging 9.7 aphids per plant reduced fructan contents of Froid and Brawny seedlings by 22.60 and 59.10 g kg-1 dry wt., respectively. Similar trends occurred after a natural freeze period. Field survival and yield results indicate that the autumn infestation reduced the winter survivability of Brawny by 54% and reduced grain yields by 1217 kg ha-1; survival and yield of infested Froid were not significantly affected. PI 372129, a D. noxia resistant winter wheat genotype was not affected by an infestation in regard to these parameters. These studies suggest that coldhardiness in Froid and Brawny was reduced by D. noxia though only the less hardy Brawny had a significantly reduced winter survivability and grain yield. Therefore, the effects of an autumn D. noxia infestation on some winter wheat genotypes may interact with a winter climate and increase the potential for winterkill.