Leaf physiology and morphology of Castanea dentata (Marsh.) Borkh., Castanea mollissima Blume, and three backcross breeding generations planted in the southern Appalachians, USA
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Backcross breeding programs have been used to transfer disease resistance and other traits from one forest tree species to another in order to meet restoration objectives. Evaluating the field performance of such material is critical for determining the success of breeding programs. In eastern North America, The American Chestnut Foundation has a backcross breeding program that uses Chinese chestnut (Castanea mollissima Blume) to introduce resistance of the fungal pathogen chestnut blight [Cryphonectria parasitica (Murr.) Barr.] to the native American chestnut [Castanea dentata (Marsh.) Borkh.]. We compared physiological and morphological characteristics among seedlings of American chestnut, Chinese chestnut, and BC1F3, BC2F3, and BC3F3 hybrid chestnuts during their fourth growing season after field-planting. American chestnut and the BC3F3 breeding generation displayed photosynthetic light-response curves that were similar to each other but different from Chinese chestnut. Rates of photosynthesis were higher for American chestnut and the BC3F3 breeding generation when compared to Chinese chestnut for light levels ≥800 μmol m−2 s−1 photosynthetic photon flux density and for maximum photosynthetic capacity. Leaf morphology variables were not different between American chestnut and any of the breeding generations, but leaf area (on a per leaf basis) of Chinese chestnut was lower than that of any other chestnut type. Our results suggest that backcross breeding can be used to transfer desirable traits for restoration of native species threatened by non-native pathogens.
KeywordsBackcross breeding Castanea dentata Light response curve Species restoration Tree improvement
This research was supported by the USDA Forest Service, Northern Research Station, Southern Research Station, and the National Forest System of the Southern Region. We would like to thank The American Chestnut Foundation and Fred Hebard in particular, as well as David Casey, Jason Rodriguez, and John Blanton (retired) of the National Forests of North Carolina. We would also like to thank Steven Broom and Jeff Humphries for field assistance and Dr. Christina Wells for support with field equipment and for her physiological expertise.
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