COLONIZATION OF CROP RESIDUES BY WHITE-ROT FUNGI - CELL-WALL MONOSACCHARIDES, PHENOLIC-ACIDS, RUMINAL FERMENTATION CHARACTERISTICS AND DIGESTIBILITY OF CELL-WALL FIBER COMPONENTS IN-VITRO

Objectives were to evaluate the effect of fungal treatment on monomers of structural carbohydrates, major cell wall phenolic acids and rumin al fermentability in vitro during small and large scale treatment proc ess. Samples from two previously conducted experiments were used in th e present study as follows: Samples from botanical fractions (leaf and stem) of rice straw colonized by Cyathus stercoreus (Cs), Phanerochae te chrysosporium (Pc) and Pleurotus sajorcaju (Ps) were evaluated for in vitro fermentation characteristics, in vitro digestibility (IVD) of cell wall fiber constituents and changes in cell wall phenolic acids (PA) and monosaccharides. The same analyses were repeated for the seco nd set of samples obtained from a large scale trial where rice straw w as decayed with Cs in 5 kg batches. The effect of processing of straw, straw pre-soaked in water to achieve 80% moisture, also compared with unprocessed rice straw which served as a positive control. Xylose:ara binose ratio was higher for control rice stem than for leaf which sugg ests that arabinose substitution with xylose may differ between leaf a nd stem. Stem contained more p-coumaric acid (p-CA) and less ferulic a cid (FA) than leaf, but total PA was higher for stem. Hemicellulose (H C) in rice leaf, calculated as the sum of monomers, was selectively an d extensively consumed by Ps and Cs while Pc selectively consumed only glucose derived from cellulose. Arabinose and xylose were solubilized during Pc growth on leaf, but not metabolized. Consequently, less tot al PA degraded by Pc was found in leaf than with the other two fungi. IVDMD and p-CA were highly correlated (r = -0.73) yet other factors su ch as the cellulose: p-CA ratio also contributed to the variation in I VDMD. Uronic acids were only partially degraded by fungal treatment. O f all fungi, Cs and Ps improved IVDMD of rice leaf; primarily because of increased digestion of cellulose. Increased IVDMD was further evide nt by a 1.7 fold increase in the total volatile fatty acid production. Processing of straw prior to fungal treatment decreased IVDMD by more than three-fold, but no apparent mechanism was found. Results of thes e experiments indicate that improvement of rice straw quality was depe ndent on fungal species, botanical fractions, and preparation of subst rate prior to fungal decay.