VIEW ARTICLE

Cytology and Histology

Cytochemical Aspects of Cellulose Breakdown During the Infection Process of Rubber Tree Roots by Rigidoporus lignosus. Michel R. Nicole, Orstom-Forêts Canada, 1055 Rue du Peps, G1V 4C7 Sainte-Foy, Québec, Canada; Nicole Benhamou, Département de Phytologie, Faculté des Sciences de l’Agriculture et de l’Alimentation, Université Laval, C1K 7P4 Sainte-Foy, Québec. Phytopathology 81:1412-1420. Accepted for publication 26 June 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1412.

An exoglucanase purified from a cellulase produced by the fungus Trichoderma harzianum was bound to colloidal gold and used for ultra-structural detection of cellulosic ?-(1-4)-D-glucans in root tissues of rubber trees (Hevea brasiliensis) infected by the white rot root pathogen, Rigidoporus lignosus. Large amounts of ?-1,4-glucans were found in cell walls of healthy roots, except in suberized walls that were not labeled. Gold particles were absent in the fungal wall inside rhizomorphs and in infected host cells. In infected roots, cell wall degradation occurred both close to and at a distance from hyphae, causing variable decaying patterns. Few gold particles or absence of labeling were observed in degraded phellem and phloem cell walls. In xylem vessel elements, labeling did not occur over incompletely digested areas of the S₂ layer of secondary walls. During pit penetration by hyphae, degraded primary walls and the S₁ layer of secondary walls were devoid of gold particles. The present cytochemical data provide evidence for cellulose degradation in roots of rubber trees infected by R. lignosus. They demonstrate indirectly the implication of cellulases in the decay process and give more insight into the role cellulose degradation plays in white rot pathogenesis by R. lignosus.