ADAPTATIONS TO HERBIVORY IN ALFALFA (MEDICAGO SATIVA)

Alfalfa (Medicago sativa L.) possesses numerous adaptations to herbivores. As with other wild plants, general chemical defences (notably medicagenic acid in alfalfa) and general anti-insect structures (notably trichomes) provide some protection against a wide spectrum of polyphagous insects. Several morphological adaptations protect alfalfa against specialized insect feeders, especially those that consume the seeds. Alfalfa has been disruptively selected by man to possess morphological adaptations and tolerance for two contrasting classes of herbivory: continuous grazing by livestock and intermittent harvesting for hay. Domestication of alfalfa has lowered the effectiveness of several natural adaptations against insects. Occasionally, however, artificial selection for resistance against certain insect species has, often unintentionally, resulted in selection for structural features discouraging these insects. Preadaptations of wild alfalfa for the horse facilitated this plant's domestication as a speciali...