Nutrient Solution Nitrogen Form and Bird Cherry-Oat Aphid Resistance in Wheat

Abstract

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 form of nitrogen provided in plant nutrient solutions affected aphid population 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 infestation with nymphs. The time period to adulthood and the number of progeny produced were recorded. For plant growth experiments, spring wheat plants were grown in sand culture using half-strength complete nutrient solution 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 shoot and root fresh weight measurement 6 days after infestation. Aphid population growth (development time, number of aphids produced, and intrinsic rate of increase) were not significantly affected by nutrient solution N form treatments. Plants grown with NH4-N nutrient solutions had significantly less shoot fresh weight (0.181 g for NH4-N; 0.230 g for NO3-N). Aphid infestation also significantly reduced shoot fresh weight (0.149 g in infested; 0.262 g in control). There were no significant interactions between nutrient solution 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 nutrient solution (aphid infested = 0.11 g; control = 0.17 g). Thus, while N form given to wheat plants had no effect on aphid population growth characteristics, plants given NH4-N nutrient solution showed less root growth than plants given the NO3-N nutrient solutions.