Glandular Morphology from a Perennial Alfalfa Clone Resistant to the Potato Leafhopper

Abstract

The commercial release of several cultivars of perennial, glandular‐haired alfalfa (Medicago sativa L.) for control of the potato leafhopper, Empoasca fabae (Harris), has increased the need to identify the causal mechanism of resistance. The objectives of this experiment were to examine the morphology and exudate of the glandular trichomes found on the perennial alfalfa clone FGplh13, in addition to comparing their density and distribution. Light, scanning, and transmission electron microscopy were utilized to characterize the morphology of the glandular trichomes and their associated exudate. Two distinct trichome morphologies, erect and procumbent glandular trichomes, occurred. The erect glandular trichomes consisted of multicellular stalks (5–11 cells) and gland heads, with the cells being arranged in distinct tiers. The procumbent glandular trichomes were composed of a stalk (1–2 cells) bent almost parallel to the plant surface. The procumbent gland head contained 8 to 12 cells, which were distinctly arranged in two to three tiers. Both types of trichomes released exudates that appeared to accumulate in a subcuticular space within a distal extrusion. Exudate from the procumbent glandular trichome became attached to the tibia of a potato leafhopper nymph. Entrapment of first instar potato leafhoppers by the glandular trichomes was also observed for the first time on a perennial glandular‐haired alfalfa clone. The erect glandular trichome was the most dense morphology on the stem, petiole, and leaf midvein.