Selection of White-Rot Fungi for Bioprocessing of Wheat Straw into Ruminant Feed

White-rot fungi are effective at delignification of agricultural residues, which increase the accessibility to structural carbohydrates and enhance its degradability in the rumen. Fungal pretreatment of lignocellulosic biomass is influenced by various factors including types and conditions of the substrates used, as well as fungal strains/species. Hence, the selection of the best performing fungal strains/species is fundamental for an optimal pretreatment and for future breeding activities to expand the potential in the bioprocessing of agricultural residues. Three white-rot fungi species have been used in this study: Ceriporiopsis subvermispora (CS), Pleurotus eryngii (PE) and Lentinula edodes (LE). Ten to twelve strains from each species were evaluated and selected for their capabilities in improving the in vitro degradability of wheat straw. Wheat straw was inoculated with the spawn of each fungal strains/species under solid state fermentation for 7 weeks. Untreated samples (control) were also run along the treated samples. Weekly samples were analyzed for the total in vitro gas production (IVGP). Data were analyzed as a function of fungal strains (within species), incubation period and their interactions. Out of 32 fungal strains from different species tested, 18 strains showed a significantly higher (p < 0.05) IVGP compared to control after 7 weeks of treatment. Three best strains within each species with highest IVGP were selected for further analyses, assessment and comparison across species. Three best CS strains had a mean IVGP of 297 ml/g OM, while PE and LE had mean IVGP of 257.8 and 291.8 ml/g OM, respectively. The total carbohydrate to lignin (C/L) ratio was calculated to exhibit the selectivity of fungi in degrading lignin. There was a good correlation between IVGP and C/L ratio (r = 0.67; p < 0.001) indicating that a fungus which resulted in a high in vitro degradability, was more selective in degrading lignin. In conclusion, there were considerable variations in the IVGP of the treated wheat straw, not only between species, but also among different strains within each species. Three best performing strains from each species have been selected for further investigation of their benefit in ruminants, and can also be used for future breeding activities.