Decay of date palm wood by white-rot and brown-rot fungi

Abstract

Wood from trunks of Canary Island date palm (Phoenix canariensis) was decayed for 12 weeks with white-rot fungi (Ganoderma colossum, G. zonatum, Phanerochaete chrysosporium, Scytinostroma galactinum, or Trametes versicolor) or brown-rot fungi (Wolfiporia cocos, Gloeophyllum trabeum, or Fomitopsis pinicola). Using the vermiculite-block assay, white-rot fungi caused significantly more weight loss (63%) than brown-rot fungi (32%). Of the white-rot fungi, G. colossum caused the greatest weight loss (81%), while S. galactinum caused the least (36%). In contrast, weight loss caused by the brown-rot fungi was similar. Chemical analyses indicated that both white-rot and brown-rot fungi caused losses of starch, holocellulose, and lignin. White-rot fungi, however, removed greater amounts of lignin than the brown-rot fungi with three species, S. galactinum, P. chrysosporium, and G. zonatum, causing selective delignification. Scanning and transmission electron microscopy showed that phloem and parenchyma cells were more susceptible to decay than xylem and fiber cells. Starch grains were degraded by all fungi and were nearly removed in wood decayed by G. colossum. In wood decayed by white-rot fungi, cell walls were eroded and middle lamellae were degraded. Selective delignification was observed in fibers adjacent to vascular tissue in wood decayed by the three white-rot fungi. In wood decayed by brown-rot fungi, walls of ground parenchyma and vascular bundle cells were swollen and fragmented when physically disrupted. In wood decayed by F. pinicola, some cell walls were nearly disintegrated. Key words: selective delignification, simultaneous decay, ultrastructure.