Selecting for nutritive value in Digitaria milanjiana. 3. Relation of chemical composition and morphological and anatomical characteristics to the difference in digestibility of divergently selected full sibs, and comparison with D. eriantha ssp. pentzii

Abstract

Comparisons were made of the dry matter digestibility (DMD) and yield of plant fractions harvested from long-established swards of 6 genotypes of Digitaria milanjiana selected from 3 F1 families for high and low leaf digestibility, and D. eriantha ssp. pentzii (pangola grass). Defined leaf blade, sheath and stem internode fractions were collected at different sward development stages and analysed for DMD, chemical composition, and tissue morphological and anatomical characteristics. The leaf blade of each high-digestibility genotype was consistently superior (1.9-4.5 percentage units) in DMD to that of its low digestibility counterpart, and to pangola grass, at both vegetative and reproductive -- stages. For leaf sheath and stem, the superiority in DMD of the high digestibility group was not evident or was less pronounced. The high DMD selections had green leaf dry matter yields comparable to those of the low DMD group but higher than those of pangola grass. The gain in DMD for leaf blade of the high over the low digestibility selection was consistently correlated with a decrease in cell wall content, acid detergent fibre or lignin, and poorly correlated with other chemical and leaf morphological characteristics. High and low DMD genotypes did not differ in the proportion of cell types in leaf or stem, or in other measured anatomical characteristics.