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

Abstract

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.

The politics of genetic technoscience for conservation: The case of blight-resistant American chestnut

“…The FHI adopted American chestnut as its “test case” (FHI, 2018) and, in the interest of making rapid progress in the development and field testing of disease-resistant American chestnut trees, enrolled experts already working on American chestnut, including the team at SUNY-ESF and researchers affiliated with TACF. FHI projects have now ended, but they funded a number of developments that have dramatically increased the integration of genetic technologies into chestnut restoration, including assays for earlier detection of blight resistance in transgenic plants (Newhouse et al., 2014), improved somatic embryogenesis techniques for generating whole plants from transformed cells (Holtz et al., 2016), a reference genome for Chinese chestnut (Fang et al., 2013; Kubisiak et al., 2013), and the transformation of American chestnut embryos with candidate blight resistance genes from Chinese chestnut (FHI, 2018). FHI aimed to be ground-breaking in both its commitment to public interests and its “braided process” that considered regulatory, environmental, and social dimensions of the use of genetic technologies for forest health, concurrent with the development of scientific knowledge and protocols (FHI, 2018).…”