Detection of hybridization between Castanea dentata (Marsh.) Boorkh. and non-native congeners in Ontario

The fungal pathogen, Cryphonectria parasitica, introduced to North America in the early 20th century, has reduced natural populations of Castanea dentata (American chestnut) by 99 percent. The remaining individuals are often interspersed with non-native Castanea species; however, the existence of hybrids has not been tested. My research characterizes four putative parental species morphologically and genetically (randomly amplified polymorphic DNA), and examines the remnant Castanea populations of southern Ontario for hybrids. Both methods were able to distinguish between C. dentata and three non-native Castanea species, but only the molecular techniques could clearly identify nonnative and hybrid Castanea trees in Ontario forests. One hybrid of American and Japanese chestnut species was detected in an Ontario woodlot, showing for the first time that non-native genetic material is entering the Canadian C. dentata population. Canadian chestnut is also somewhat distinct from American chestnut in morphology and genetics.