Spectral Distribution of Light in a Tobacco Canopy and Effects of End-of-Day Light Quality on Growth and Development.

Shifts in spectral distribution of light were determined within and below a canopy of field-grown burley tobacco (Nicotiana tabacum L. cv. Burley 21). The leaves transmitted much far red light relative to red and blue light. Thus, shaded leaves received more far red light, relative to red and blue, than was received by unshaded leaves. Under field conditions, tobacco plants within rows grew taller than did those at the west end of rows.Developmental effects of end-of-day red and far red light were studied in the controlled environment laboratory. Plants that received far red light last, each day, resembled plants shaded by other plants. The far red-irradiated plants developed longer internodes, were lighter green in color, and had thinner leaves than the red-irradiated ones. Plants of both treatments had the same number of leaves on the main axis. However, the red-irradiated plants developed branches from axils of lower leaves, while no branching occurred on plants that received far red radiation last each day.