Pectin degradation during root decay of rubber trees by Rigidoporus lignosus

Aplysia gonad lectin, which binds polygalacturonic acid, was complexed to colloidal gold and used for localizing molecules that contain polygalacturonic acid in rubber tree roots infected with the white-rot root fungus Rigidoporus lignosus. Colonization of root tissues was associated with strong wall alteration of phloem cells and with degradation of the compound middle lamella in both the phloem (10 weeks after inoculation) and the xylem (15 weeks after inoculation). Our data suggest that pectin breakdown during root decay likely occurs after cellulose and lignin breakdown and may result from the fungal pectinase activities that were detected in vitro. Released pectin oligomers may act as inducers of both fungal laccase and of the tree defense system during root invasion.