Incubation temperature affects growth and efficacy of white-rot fungi to improve the nutritive value of rice straw

Abstract

Context: A great body of evidence is available on the in vitro efficacy of white-rot fungi (WRF) to degrade lignin in fibre-rich biomass (e.g. wheat straw, wood chips and rice straw (RS)) and improve the biomass' nutritive value for ruminants. Aims: Determining the impact of incubation temperature of three WRF to improve the nutritional value of rice straw. Methods: Growth of Ceriporiopsis subvermispora, Lentinula edodes and Pleurotus eryngii on RS for 26 days at the following six temperature regimes: continuous at 24°C, 30°C, 35°C and 40°C, and 3 days at 35°C and 40°C, with subsequent days at 24°C. In a follow-up experiment, improvement in fermentability in buffered rumen fluid of RS treated by the three WRF at 24°C and 30°C for up to 8 weeks was investigated. Key results: All three fungi grew at temperatures up to 35°C, with no growth observed at 40°C, with C. subvermispora being more temperature sensitive. There were significant differences in cellulose, hemicellulose and lignin degradation of RS at 24°C and 30°C, with C. subvermispora degrading 69% and 90% of the hemicellulose and lignin respectively at 30°C, greater than at 24°C (55% and 80% respectively). For L. edodes, there were significant differences in cellulose degradation between 24°C and 30°C, with 12% more degradation at 30°C, but not for hemicellulose and lignin. In vitro gas production showed no significant differences between the two incubation temperatures for either of the two fungi. Pleurotus eryngii treatment did not show any improvement in terms of in vitro gas production. Conclusions: Treatment of RS with L. edodes and C. subvermispora, but not P. eryngii, is robust and temperature changes will not have a major impact on their efficacy as long as the temperature remains below 30°C. Implications: Temperature during the incubation of WRF with rice straw needs to be below 30°C for this biotechnology to be applied in practice.