Interaction Between Moisture Stress and Potato Leafhopper (Homoptera: Cicadellidae) Damage in Alfalfa

Abstract

The combined and independent consequences of moisture stress and potato leafhopper (PH), Empoasca Fabe Harris, injury on alfalfa, Medic ago saliva L., quality were investigated under controlled conditions. Plant water potentials, percentage of crude protein, and free amino acid profiles were determined in PLH-infested and non infested alfalfa exposed to three soil moisture deficit levels. Results suggest an interaction between moisture stress and PH injury. PH feeding had no effect on water potentials of either severely water-stressed or amply watered plants. However, PLH-infested alfalfa under mild soil moisture deficits (-0.07 omega pascals [MPa] soil moisture tension) showed a reduced ability to imbibe water compared with non infested plants. Although PH feeding and soil moisture deficit independently decreased crude protein levels in alfalfa, PH feeding and moderate moisture stress (-0.5 to -1.2 ma soil water tension), when combined, reduced crude protein levels further than moderate moisture stress alone. Individual free amino acid concentrations, in general, were reduced, but praline concentrations showed marked increases caused by both types of stress. In one trial, total amino acid concentrations were significantly reduced by PH feeding alone. Soil water deficits and PH feeding, individually or combined, reduced total amino acid concentrations when praline was subtracted from the total. Plant water potential, percentage crude protein, and free amino acid concentration are indirect measures of alfalfa growth. Because these parameters apparently are influenced by PH feeding and water stress, independently and by interaction, these factors should be considered when determining economic injury levels and thresholds for PH in alfalfa.