Interaction between water deficit and potato leafhopper (Empoasca fabae) feeding injury on alfalfa (Medicago sativa)

In combination with increasing average temperatures and yield losses from drought events, the frequency of severe droughts is projected to increase in the Midwestern United States. Alfalfa, Medicago sativa, is an important forage and cover crop that experiences stress from water deficit as well as feeding injury by potato leafhopper, Empoasca fabae. Observations suggest that leafhopper injury becomes more significant in times of drought stress. The independent and combined effects of these stressors on alfalfa were assessed by measuring net photosynthesis rate, transpiration rate, stomatal conductance, water use efficiency, plant height, leaflet area, and superoxide dismutase activity in plants grown under greenhouse conditions with one of four soil saturation levels in the presence or absence of the leafhopper. Water treatment and potato leafhopper feeding both significantly affected photosynthesis, transpiration, and stomatal conductance in alfalfa, yet the interaction effects were not significant. Plant height and water use efficiency were significantly affected by water treatment, while leaflet area was not. Photosynthesis, transpiration, stomatal conductance, and plant height increased with decreasing water deficit. Water use efficiency was highest at 50% soil saturation and lowest at 25%. There was no significant effect of soil saturation or leafhopper feeding on superoxide dismutase activity. These results demonstrate that water deficit and leafhopper injury significantly impact the physiological response of alfalfa to stress, yet the two factors may remain independent.