Stereological analysis of Medicago truncatula Gaertn. stem as a pre-breeding technique to improve digestibility

Abstract

Structural characteristics of stem, especially the proportion of lignified tissues, have a strong impact on digestibility in many legume species. Anatomical analysis of stem of M. truncatula cultivars was performed using stereological method in order to examine genotypic variability in histological parameters that affect digestibility and assess tissue proportions along the stem maturity gradient. Lignification was first recorded in primary xylem walls. Volume densities (Vv) of phloem and xylem increased linearly from the top to the bottom of the stems. Lignification of parenchyma pith cells occurred simultaneously with intensive xylem development. On the contrary, the proportions of epidermis, mechanical and parenchyma tissue significantly decreased along the stem. Lignified secondary xylem was the tissue with the highest Vv and estimated as the one with the highest potential impact on digestibility. Therefore, the improvement of digestibility could be achieved through the reduction of its proportion.