RELATIONSHIP BETWEEN STALK CELL-WALL DIGESTIBILITY AND FIBER COMPOSITION IN MAIZE

The stalk fraction of recombinant inbred lines of maize (RILs), harves ted shortly before silage stage, was used to determine genetic variati on for organic matter digestibility (OMD) and cell wall digestibility (CWD) as well as variation for fibre content leg neutral (NDF) and aci d detergent fibre (ADF)) and chemical composition leg hemicellulose, c ellulose, lignin, total phenolics and the phenolic acid esters: p-coum aric, ferulic and vanillic acid). OMD and CWD, as monitored in an in v itro incubation using rumen fluid, ranged between 64.6 and 80.7% and 4 4.9 and 63.0%, respectively. The fibre content varied from 460 to 675 g kg(-1) dry matter (NDF) and from 258 to 405 g kg(-1) dry matter (ADF ). Generally, hemicellulose (HEM) was present in lower amounts in the cell wall than cellulose (CEL). Comparison of two subsets of the RILs with either a low or a high CWD demonstrated that the RILs with the lo w CWD contained higher concentrations of fibre and enhanced amounts of all cell wall constituents measured except for HEM and ferulic acid ( Fa). The Fa content of the low CWD subset was lower and no significant subset difference was present for HEM. The correlations between two b locks in a field trial (repeatability) was high for all forage quality traits, except HEM, total phenolics (tPHEN), p-coumaric acid and vani llic acid. A close negative relationship existed between OMD and NDF, ADF, CEL and permanganate lignin (pLIG) showing absolute correlation c oefficients above r = 0.80. The association of CWD to these cell wall properties was either weak or moderate. In contrast to all other cell wall constituents, tPHEN correlated better to CWD than to OMD (r = -0. 82 and -0.62, respectively). By means of multiple regression, a regres sion equation was generated for CWD and OMD using ASH, pLIG and tPHEN or ASH, NDF, pLIG and tPHEN, respectively, as explanatory variables. A bout 92% of the variation of OMD and 80% of the variation of CWD could be explained by these regression models with residual standard deviat ions of 1.37% and 2.19%, respectively.