Seed and seedling characteristics of hybrid chestnuts (Castanea spp.) derived from a backcross blight-resistance breeding program

Abstract

Abstract American chestnut (Castanea dentata) was a foundation species in the eastern United States until chestnut blight (Cryphonectria parasitica) infestation resulted in range-wide catastrophic reduction. Since 1983, The American Chestnut Foundation (TACF) has engaged in a breeding program aimed at restoring C. dentata to the wild. The primary goal has been to introduce blight resistance from Castanea mollissima while recovering a C. dentata phenotype via successive backcrosses. To diversify the genetic base, state chapters of TACF have been producing BC3 and BC4 (third and fourth backcross) lines using C. dentata from across its native range. This study focuses on morphology and chemistry of seeds, and morphology and early growth of seedlings derived from BC3 and BC4 trees selected for blight resistance in state chapters. Our primary comparisons were among backcross, pure C. mollissima, and pure C. dentata lines. Seed traits included a suite of morphological characters known to differ between C. dentata and C. mollissima, as well as dry matter, total carbohydrate, sugar, protein, lipid, and phenolic content. Seedling traits included variables such as stem basal diameter and height, leaf variables such as number and area, and relative growth in key parameters such as stem volume. C. mollissima lines tended to differ significantly from C. dentata and backcross lines in most parameters, while C. dentata and backcross types tended to overlap broadly in traits. These results suggest that seed and seedling characteristics of backcross hybrids studied here are likely to be sufficiently similar to C. dentata for use in restoration programs.