Alfalfa Stem Anatomy and Potato Leafhopper (Homoptera: Cicadellidae) Resistance

Medicago clones with different levels of resistance were examined histologically and by in vitro digestion in rumen fluid to determine if anatomical features of the stem contribute to resistance to the potato leafhopper, Empoasca fabae (Harris). Glandular hairs, stems with small cross-sectional areas, and highly lignified tissues were associated with potato leafhopper resistance. A cylinder of hard tissues, composed of lignified xylem elements, phloem fibers, and interfascicular areas, surrounded the pith and was linked to reduced oviposition. The hard cylinder was present in the first internode (from apex) of two of the resistant clones and in older, more distal internodes of other clones. Early lignification of tissues forming the cylinder appeared to contribute to potato leafhopper resistance either by mechanically or by chemically deterring or preventing feeding and oviposition.