Use of image analysis to quantify histological structure along the stems of alfalfa (Medicago sativaL.)

Alfalfa is a forage legume for which vegetative biomass (stems and leaves) is harvested. Lignification of the oldest internodes of the stems contributes to reduced stem digestion by ruminants, but also glucose recovery in bio—fuel production. We described and quantified morphological and histological structure of the stem of two genotypes. At the top of the stems, four to six internodes had increasing length and diameter, non—lignified tissues and separated vascular bundles. The following internodes had a constant or decreasing length, but an increasing diameter from the top to the bottom of the stems. In parallel, xylem thickness and pith parenchyma area increased, but the cortex thickness remained almost constant. The cell walls of the xylem were progressively thicker. These results can be used in other studies aiming at describing genetic or environmental variation for stem histological traits.