Canker formation and decay in sugar maple and paper birch infected by Cerrenaunicolor

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Abstract
Cerrenaunicolor (Bull.: Fr.) Murr. (= Daedaleaunicolor) (Aphyllophorales, Polyporaceae) was found to cause a canker rot on two northern hardwood tree species, sugar maple (Acersaccharum Marsh.) and paper birch (Betulapapyrifera Marsh.). Pathogenicity of the fungus was determined by inoculation and examination of cankers 6 months, 1.5 years, and 2.5 years later. The two isolates used were found to differ in pathogenicity. Chemical and morphological barriers formed to compartmentalize the fungus. A zone of enhanced cell wall lignification and the formation of suberized impervious cells which composed the necrophylactic periderm in the host were observed. Xylem discoloration, callus formation, and periderm layers were more pronounced in maple than in birch. Cerrenaunicolor moved past host barriers via a mass of hyphae which annually penetrated weak points in the necrophylactic periderm and subsequently killed the adjacent cambium. Once past the necrophylactic periderm and into the xylem, C. unicolor was an aggressive decay organism which caused an extensive white rot. In naturally infected trees, columns of decay were two or three times longer than the cankers. Multiple zones of decayed and discolored wood were present in the xylem as a result of repeated attacks by the fungus.