Potato Leafhopper Injury and Fusarium Crown Rot Effects on Three Alfalfa Populations

Evidence suggests that homopterous insects and crown-rotting Fusarium species interact to impose stresses affecting alfalfa (Medicago sativa L.) persistence; however, few experiments quantify the combined effects of those two stressors on alfalfa. Our objective was to investigate the effects of Fusarium crown rot and potato leafhopper (Empoasca fabae Harris), alone and in combination, on three alfalfa populations differing in resistance to potato leafhopper and Fusarium crown rot. Treatments were Fusarium-inoculated plus leafhopper-infested, only leafhopper-infested, only Fusarium-inoculated, and uninoculated-uninfested in 35-wk experiments. Potato leafhoppers were introduced onto plants in greenhouse cages either before or after inoculation with a known crown-rotting isolate of Fusarium oxysporum Schlect. There were few Fusarium x potato leafhopper or Fusarium x potato leafhopper x population interactions, indicating that overall, the effects of Fusarium and potato leafhopper were additive. Both Fusarium and potato leafhopper injury caused stand losses, and the combined effects of Fusarium and potato leafhopper, under two different inoculation plus infestation sequences, were essentially the same. In the presence of both Fusarium and potato leafhopper, the population having resistance to both organisms had a three- to sevenfold increase in plant survival and a three- to 4.6-fold increase in yield compared with the population lacking resistance to either organism.

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