Discussion
Biodelignification of paddy straw seems to be a promising approach to overcome the problem of its lesser digestibility and thus lower nutritive value (Taniguchi et al. 2005). Selective ligninolysis results into more lignin loss when compared to other components, which enhances the in vitro digestibility as well as minimizes the TOM loss. Different fungi have been reported for their selective ligninolytic ability (Adaskaveg et al. 1995; Arora et al. 2002) and enhancement in in vitro digestibility of lemon grass, citronella bagasse and wheat straw (Rolz et al. 1986; Arora and Sharma 2009b). Degradation of lignin and enhancement in digestibility can be positively correlated from the current experimental data also (r = 0·856).
Phanerochaete chrysosporium and P. brevispora enhanced the maximum in vitro digestibility up to 250 g kg−1 with a respective loss of about 394 and 200 g kg−1 in lignin. Phanerochaete chrysosporium was nonselective in lignin degradation and degraded all the fibres simultaneously which resulted in more holocellulose loss and thus degraded a large amount (464 g kg−1) of TOM. On the other hand, P. brevispora degraded only 98 g kg−1 TOM during the fermentation process, which accounts for its more selective ligninolysis leaving behind a sufficient amount of TOM available to the animal as feed (Fig. 4). For the practical purpose, higher TOM loss severely limits the use of P. chrysosporium, which is in the consonance with earlier observations (Jung et al. 1992). The degradation profile of P. chrysosporium indicates that the higher holocellulose degradation may be because of the higher production of xylanase and CMCase-like enzymes. Similar remarks were also made during an earlier observation while working with P. chrysosporium (Kerem et al. 1992).