Interactions between Sudangrass Lines Selected for Differing Nitrate Expression and Sorghum Aphid

Abstract

Sudangrass (Sorghum sudanense Stapf) is widely cultivated as a summer annual forage across the southern Great Plains because of its robust forage yield potential. However, the accumulation of nitrates and the potential harm to livestock have restricted the use of Sudangrass for feeding ruminants. Since 2013, the sorghum aphid (SA), Melanaphis sorghi (Theobald) (Hemiptera: Aphididae), has been damaging sorghum and Sudangrass production. However, the interaction between SA feeding and nitrate accumulation in Sudangrass has not been determined. In this study, we evaluated the effect of SA feeding on different Sudangrass lines, comparing them to a susceptible and a resistant sorghum variety and measuring the physiological responses and nitrate concentration after aphid feeding. Additionally, we evaluated the use of these grass lines on SA demographics. Initial infestations of 100 SA per plant that were allowed to feed and proliferate for 20 days increased nitrate concentrations in Sudangrass by more than 60% compared to controls. Concurrently, the Sudangrass lines selected for high nitrate levels drastically reduced SA demographic parameters, comparable to those of the resistant sorghum control. Although the adoption of resistant cultivars is recommended for aphid management, the Sudangrass lines selected may not be the best option for SA management because their accumulation of nitrates in response to herbivory can cause ruminant poisoning.