Anatomical Characteristics of Smooth Bromegrass Clones Selected for In Vitro Dry Matter Digestibility1

Abstract

Digestibility plays an important role in forage nutritive value. Anatomical components have repeatedly been demonstrated to influence digestibility of forage crops. Eighteen clones of smooth bromegrass (Bromus inermis Leyss.) selected for either high or low in vitro dry matter digestibility (IVDMD) were evaluated determine if adequate genotypic variation existed for anatomical and chemical components and their relationship with IVDMD. Clones were planted in five randomized complete blocks at Arlington, WI (Piano silt loam—fine‐silty, mixed, mesic Typic Argiudoil) in August 1981. In June 1982, when the clones were just 100% headed, whole‐plant, leaf and stem material were collected for evaluation of IVDMD, neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent linguine, insoluble ash, and anatomical components of stems and leaves. A cryostat was used to cut 12 μm sections of leaf and stem material for estimation of percentage tissue types. High IVDMD clones had significantly greater percentages of the most readily digestible tissue types (stem chlorenchyma and leaf mesophyll), a significantly lower percentage of lignified leaf vascular tissue, and thicker stems than the low IVDMD clones. Reduced genotypic variation within the high IVDMD group of clones was observed for IVDMD and most anatomical components compared to variation among the low IVDMD clones. Significant variation for NDF, ADF and cellulose was detected among the high IVDMD clones. Continued gains from selection for improve digestibility within the population derived from the nine high IVDMD clones may be difficult due to the narrowed genetic base for IVDMD and stem and leaf anatomy, but selection for improved dry matter intake potential appears to have some merit.