Nursery performance of American and Chinese chestnuts and backcross generations in commercial tree nurseries
The American chestnut [Castanea dentata (Marsh.) Borkh.] was decimated by an exotic fungus [Cryphonectria parasitica (Murr.) Barr] in the early 1900s. Breeding efforts with American and Chinese chestnuts (C. mollissima Blume) produced putatively blight-resistant progeny (BC3F3) in 2007. We compared two nut size classes for differences in seedling quality of bare-root stock grown in commercial nurseries. We compared the BC3F3 generation to parental species and other generations. Nuts in the large size class produced taller trees than nuts in the small size class, but sizing nuts prior to sowing did not reduce variability in nursery seedling size. Results indicate that overall seedling quality could be improved by culling small nuts, but seedling uniformity would only be improved by culling seedlings before planting. We recommend refinement of restoration efforts to match seedling size to site type and planting goals. BC3F3 chestnuts differed from Chinese chestnuts in 67% of tests, and were different than American chestnuts in half the tests, indicating not all American traits were recovered in this early phase of seedling development. Family differences within the BC3F3 generation were most apparent for mean nut weight, and only one BC3F3 family differed from other BC3F3 families in seedling growth characteristics.