Evaluation, Selection and In vitro Propagation of Sugar Maple (Acer saccharum Marsh.)

Sugar maple (Acer saccharum Marshall) tree is an important part of North American forest ecosystems as well as a source of sap for maple syrup production. The quality, yield, and productivity of syrup can be considerably improved while also reducing production costs and the carbon footprint of the process by developing elite germplasm with high sap sugar content. The current work aims to provide a basis to identify and propagate elite sugar maple trees. A 22-year old seed based population of trees of uniform age, planted in uniform spacing was evaluated for sap sugar content and tree morphology (height and trunk circumference) over a period of three years and statistical measures to correct spatial trends in productivity were assessed. Furthermore, clonal propagation of sugar maple through conventional and micropropagation techniques has been largely unsuccessful and the basis of this recalcitrance has remained unknown. Optimization of light intensity to improve in vitro multiplication was attempted by culturing plantlets under three intensities (4, 16 and 40 μmol m−2 s−1) of two spectra of light (red-blue and full-spectrum white) and quantifying stress using chlorophyll fluorometry. The salient findings of this research are: 1) The nutritionally important properties of maple syrup vary across its grades and light transmittance, indicating the advantages of selecting and propagating elite trees to produce specific grades of syrup, 2) nearest neighbour based spatial correction method was superior over thin plate spline in eliminating the spatial trends in the field, 3) the critical factor limiting sugar maple’s response to in vitro propagation was light intensity and a unique low light intensity is required to overcome its recalcitrance. Since several limitations of conventional in vitro lighting systems viz., non-uniform intensity, inability to modulate intensity and spectra, and tedious procedures for randomization and replication of light quality treatments were faced, 3D printing was employed to develop a novel culture vessel with independently controlled LED lighting. Overall, the present studies not only provide a basis to identify, and propagate elite sugar maple trees but also provide novel tools to evaluate the influence of light quality in in vitro studies.