Influence of species and hybrid status on induction of somatic embryogenesis in Castanea

The American chestnut (AC; Castanea dentata (Marsh.) Borkh.) once dominated the forests of eastern North America prior to the introduction of chestnut blight in the late 19th century. A somatic embryogenesis (SE) system developed for American chestnut is potentially applicable for clonally propagating blight-resistant trees produced by The American Chestnut Foundation's hybrid backcross breeding program. In this program, AC trees are hybridized with blight-resistant Chinese chestnut (CC; Castanea mollissima Blume) trees, followed by multiple generations of backcrossing to AC trees. It is possible, however, that the proportion of CC parental contribution in the hybrid backcross material could affect the success of SE using the AC protocol. Over three years of culture initiations, we tested the effects of the relative parental contributions of AC and CC on the success of SE induction using our standard AC culture initiation protocol and, subsequently, a published protocol for SE in European chestnut (Castanea sativa Mill.). With our standard AC protocol, open-pollinated AC and open-and control-pollinated hybrid backcross BC3F3 seed explants, as well as open-pollinated BC2 seed explants, successfully produced embryogenic tissue, while CC, F1, and BC1 explants did not. The European chestnut protocol produced Chinese chestnut embryogenic tissue and, subsequently, somatic embryos. The first BC3F3 somatic seedlings are currently growing in field tests.