First Report of Fusarium solani Canker and Wilt Symptoms on Red Oak (Quercus rubra) in Quebec, Canada.

Fusarium solani (Mart.) Sacc., causing wilt of leaves and twigs in the crown and annual cankers on trunks and branches of red oak (Quercus rubra L.) in the field, was found for the first time in Canada. F. solani is known to occur on red or black oaks of sect. LOBATAE: nuttall oak (Q. nuttallii E. J. Palmer), red oak, willow oak (Q. phellos L.), and water oak (Q. nigra L.) throughout the eastern half of the United States (1,2). In autumn 1997 and summer 1998, the disease was observed in 10-year-old trees at an experimental plantation near Cazaville (45°03', 74°22') located 5 km north of New York State in the St. Lawrence Valley of Québec, where 224 of 350 (64%) of the trees were symptomatic. The fungus was isolated on 2% potato dextrose agar from the necrotic bark around the active cankers (0.5 to 32 cm long) or it was obtained as erumpent sporodochia at green bark lenticels initiated from subcortical streaks in a moist chamber (relative humidity >90%). Previously, no fungus had been isolated from brown streaks found in vascular tissues with the use of two trapping techniques, either in a moist chamber or in water. From detached dead bark, other opportunistic fungi such as an Alternaria sp., Cytospora intermedia, a Phoma sp., and a Teichospora sp. were also isolated. Koch's postulates was completed for F. solani by dipping the roots of five 2-year-old Q. rubra seedlings that had their stem collar wounded by removal of a 5 mm area of bark, in a conidial suspension (4 × 10 conidia per ml) for 30 min. Five control seedlings were dipped in sterile, distilled water. Plants were potted in a soil mix and incubated in a growth chamber at 22°C. Within 3 weeks, inoculated plants exhibited wilted leaves and necrotic bark symptoms similar to those originally observed. The fungus was reisolated from the leaf petioles and bark tissues of symptomatic plants, but never from the controls. After 1 month all inoculated seedlings were dead. The pathogen could have a significant impact on commercial oak production in Québec. References: (1) W. A. Sinclair et al. 1993. Diseases of Trees and Shrubs. 3th ed. Cornell University Press, Ithaca, NY. (2) E. R. Toole. Plant Dis. Rep. 50:160, 1966.