Breeding for Resistance

In 2001, the Canadian Chestnut Council embarked on a program to breed blight resistant American chestnuts adapted to Ontario containing at least 90% American chestnut of Canadian origin within 20 years. With support from the Ontario Trillium Foundation, first phase (2001-2004) of the Canadian Chestnut Council program 1) obtained plants, seeds and pollen of American hybrids that are known to be moderately resistant to chestnut blight, 2) identified Canadian parents at diverse locations throughout the province, and 3) hybridized the selected Canadian parents with the American hybrids and started to plant trees from these hybridizations at two sites. Pollen of the three American trees used was given to us by Dr. Sandra Angnostakis of the Connecticut Experiment Station, and Mike Nemoroski and Dragan Galic travelled the Province to pollinate the Canadian trees in situ. In the second phase (2004-2007) the hybrid chestnuts developed in the first phase were planted and maintained at two sites Also, within this program the Canadian Chestnut Council, hybridized existing Canadian parents to obtain trees that are Canadian in origin. By 2007, the Canadian Chestnut Council had 767 trees originating from hybrids between Canadian trees and trees, partially resistant to chestnut blight, supplied by the Connecticut Agricultural Experiment Station. It also had 681 trees originating from hybrids of Canadian trees of unknown resistance/susceptibility to chestnut blight. These trees are housed at the Tim Horton Onondaga Farm, St George, Ontario and Riverbend Farms, Aylmer, Ontario. From 2007 through 2013, we have been inoculating these trees with two strains of Cryphonectria parasitica (UG1128, less virulent, and UG546V, virulent) to estimate their resistance to the disease. Results have indicated that our two populations, one derived from pollen of resistant Connecticut trees and one derived from pollen of Canadian trees have reacted similarly, as have the trees from the two sites. This has been supported by grants from the Species at Risk Stewardship Fund. (Ontario Ministry of Natural Resources). From the inoculations, we have been able to identify trees which would be suitable as parents. These were trees that had smaller lesions in both of two years, based on inoculations on branches over 15mm diam. Parents were selected at both Riverbend and Onondaga Farms (Dale and Galic, 2013). The trees selected originated from eleven Ontario mother-trees, and three of non-Ontario origin. Each year from 2009 we have been hybridizing selected parents to produce seed for the second generation. These included crosses where both parents were of Canadian origin and others where both parents were hybrid trees. These trees are housed at the Tim Horton Onondaga Farm, St George, Ontario, Riverbend Farms, Aylmer, and Casier Farm, St. Thomas, Ontario and we have planted over 10,000 trees in the second generation. In 2016, marked the first time we successfully inoculated the trunks of about 250 trees. The initial results show that, as expected, there is a large range of resistance-susceptibility in the population. In 2012, we surveyed our surviving trees for the weight of the nuts. We found nuts varied from 1.5-7 grams, a five-fold range with 1-6 nuts per burr. Again, the two populations were similar This was supported by the Canadian Agricultural Adaptation Program of the Agricultural Adaptation Council. In the past few years, we have completed the crosses of the selected first generation trees and inoculated many of the second-generation trees.

In 2021, we have found some American chestnut trees with sufficient resistance to be able to move to the third generation. These third generation (F3) trees are now in the field.

Then the challenge will be to repopulate the forests in Ontario.