Nutrient solution nitrogen form and bird cherry-oat aphid resistance in wheat

The form of nutrient solution nitrogen (NH4-N or NO3-N) provided to plants can have profound influence upon the severity of many crop diseases. It is not known if nutrient solution nitrogen form would affect wheat, (Triticum aestivum L.) resistance to bird cherry-oat aphids (Rhopalosiphum padi L.). The objectives of our growth chamber experiments were to determine if the f arm of nitrogen provided in plant nutrient solutions affected aphid populat ion growth parameters or the ability of wheat to withstand infestation. For aphid population growth experiments, winter wheat plants were watered with a complete nutrient solution containing NO3-N or NH4-N for 13 d prior to i nfestation with nymphs. The time period to adulthood and the number of prog eny produced were recorded. For plant growth experiments, spring wheat plan ts were grown in sand culture using half-strength complete nutrient solutio n containing NO3-N or NH4-N. Approximately 100 apterous aphids were applied to half of the plants 7 d after germination. Plants were harvested for sho ot and root fresh weight measurement 6 days after infestation. Aphid popula tion growth (development time, number of aphids produced, and intrinsic rat e of increase) were not significantly affected by nutrient solution N form treatments. Plants grown with NH4-N nutrient solutions had significantly le ss shoot fresh weight (0.181 g for NH4-N; 0.230 g for NO3-N). Aphid infesta tion also significantly reduced shoot flesh weight (0.149 g in infested; 0. 262 gin control). There were no significant interactions between nutrient s olution N form and aphid treatments for shoot fresh weight. Aphid treatment did not reduce root fresh weight in plants given NO3-N nutrient solution ( aphid infested = 0.15 g; control = 0.15 g), but did in plants given NH4-N n utrient solution (aphid infested = 0.11 g; control = 0.17 g). Thus, while P d form given to wheat plants had no effect on aphid population growth chara cteristics, plants given NH4-N nutrient solution showed less root growth th an plants given the NO3-N nutrient: solutions.