Abstract
Blight-resistant American chestnut (Castanea dentata) may soon be commercially available, but few studies have tested methods to produce high quality seedlings that will be competitive after planting. This study evaluated the performance of one American, one Chinese (C. mollissima), one second-generation backcross (BC3F2), and 10 third-generation backcross chestnut families (BC3F3). We examine growth over one year in a commercial tree nursery in east Tennessee. We examined relationships among nut size and weight and seedling growth, between germination timing and seedling survival, and between germination percentage and growth. Across the population tested, a 1 g increase in nut weight corresponded to a 6 cm increase in seedling height, a 0.5 mm increase in root collar diameter and one additional first order lateral root, but models had low predictive power. BC3F3 chestnuts grew similarly to American chestnuts, with substantial differences in growth among chestnut families within generation. Nuts that germinated by 23 April had greater than 1955 odds of surviving the first growing season than nuts that germinated in late May. American and backcross chestnut growth slowed in late June, presumably due to exhaustion of their cotyledons before leaf expansion. These results will help nursery managers refine cultural practices to maximize growth of backcross chestnuts.
Highlights
The American chestnut (Castanea dentata (Marsh.) Borkh) was a dominant forest tree in the easternUnited States until two nonnative pathogens virtually eliminated it as a canopy species
This study extends the study of Clark et al [11] by testing additional families and using individual nut weight, in addition to the mean nut weight of the treatments, to predict seedling quality, and by comparing early growth of chestnut to that of northern red oak
Chestnuts sown came from one American family, one Chinese family, one BC3F2 hybrid family and ten BC3F3 hybrid families [7] (Table 1), all derived from open-pollinated crosses
Summary
The American chestnut (Castanea dentata (Marsh.) Borkh) was a dominant forest tree in the easternUnited States until two nonnative pathogens virtually eliminated it as a canopy species. & Zucc.) chestnuts in a backcross breeding approach [6,7,8]. This approach incorporates an initial cross between a Chinese or Japanese chestnut and an American chestnut (F1), followed by a series of backcrosses to American chestnuts (BC1F1, BC2F1, and BC3F1) and an intercrossing generation (BC3F2). The final cross in the breeding scheme is among third generation backcross trees (BC3F2) to reach the BC3F3 generation. In theory, this final generation will have the growth habit of American chestnut and blight resistance of an
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