FORAGE QUALITY VARIATION AMONG MAIZE INBREDS - RELATIONSHIPS OF CELL-WALL COMPOSITION AND IN-VITRO DEGRADABILITY FOR STEM INTERNODES

Forty-five inbred maize (Zea mays L) lines were evaluated for genetic variation in stem cell-wall concentration, composition and degradabili ty, and for relationships among cell-wall components and polysaccharid e degradability. Cell-wall neutral sugars, uronic acids, Klason lignin , and ester- and ether-linked phenolic acids were measured on lower st em internode samples collected at the time of silking in 2 years. Twen ty-four and 96 h in-vitro ruminal fermentations were used to determine the rapidly and potentially degradable cell-wall polysaccharide fract ions, respectively. Genetic variation (P < 0.05) was found for all mea sures of cell-wall composition and many estimates of rapidly and poten tially degradable cell-wall polysaccharide components. Inbred line mea ns varied by 50-300% for most traits. Three brown midrib mutant inbred lines included in the study were not the lowest in lignin content nor did they exhibit the greatest cell-wail degradabilities in this popul ation of inbred maize. Year of growth (environment) influenced (P < 0. 05) cell-wall traits even though reproductive physiological maturity a t sampling was similar in both years. Degradability of the cell-wall p olysaccharide components were intercorrelated (P < 0.05) within the ra pidly and potentially degradable fractions, but rate and extent of deg radation of the cell-wall components were not correlated (P > 0.05), e xcept for uronic acids. A multiple regression model of principal compo nents (R(2) = 0.41, P < 0.05) indicated that cell-wall lignification a nd substitution of wall polymers with phenolic and uronic acids were n egatively associated, and pectic substances were positively related wi th rapid polysaccharide degradation. Very little of the variation (R(2 ) = 0.15, P < 0.05) in potential cell-wall polysaccharide degradation could be explained by this multiple regression analysis. There is a la rge degree of genetic variation among current inbred maize lines for s tem cell-wall quality traits, which should allow improvement of maize as a forage crop. Because of the complex matrix interactions in cell-w all organization, however, no single cell-wall component, or simple co mbination, can accurately predict degradability of maize cell walls.