Print PageThe American chestnut (Castanea dentata (Marshall) Borkh.) was a significant species throughout the eastern United States before its functional removal by chestnut blight (Cryphonectria parasitica (Murr.) Barr). Hybrid-backcross breeding that adds the blight resistance of Chinese chestnut (Castanea mollissima Blume) to American chestnut stock is being used to support species restoration. However, preliminary evidence suggests that backcross material may not have the full cold tolerance needed for restoration in the north. The cold tolerance of nuts is of particular concern because reproductive tissues are particularly sensitive to freezing damage, yet nut viability is essential for wide-spread restoration. The common use of Chinese and American chestnut from southern locations in breeding efforts may suppress cold tolerance levels. We measured nut cold tolerance for a range of pure American and Chinese chestnut seed sources using controlled freezing trails and assessing injury by measuring relative electrolyte leakage. We examined American chestnut sources by region - north, central and southern portions of the species’ range, and by temperature zone (warm, moderate or cold) that differentiated sources based on winter low temperatures in the areas where they originated. The cold tolerances of northern red oak (Quercus rubra L.) acorns were also assessed for comparison.
Results/Conclusions
Nuts of Chinese chestnut were significantly less cold tolerant than American chestnut nuts and red oak acorns, which had similar mean cold hardiness levels. Among American chestnut sources, nuts from the southern region were significantly less cold tolerant than nuts from the northern region, with nuts from the central region being intermediate in hardiness. Significant differences among sources were also identified within each region. Nuts from warm and moderate temperature zones exhibited similar levels of cold tolerance, but were significantly less cold tolerant than nuts from the cold temperature zone. There were significant differences among sources within the warm and moderate temperature zones, but not within the cold temperature zone. The consistently high cold tolerance of nuts from the cold temperature zone may reflect more uniform selection for greater hardiness in this region. Significant differences in cold tolerance among Chinese chestnut and red oak sources were also detected. Preferential use of Chinese and American chestnut sources with elevated nut cold tolerance may help assure that resulting backcrossed stock not only has the needed blight resistance, but also has the cold hardiness necessary for species restoration in the north.
