Photoperiod effects on growth rate of in vitro cultured soybean embryos.

The growth rate of excised soybean (Glycine max [L.] Merrill) embryos grown in liquid culture increased linearly as photoperiod was increased from 0 to 20 h at an irradiance of 9 W m-2 measured between wavelengths of 700-850 nm from clear incandescent lamps. When irradiance levels were varied between 0.1 and 1.7 W m-2, the maximum growth rates of embryos occurred at ca. 0.5 W m-2 at both 10- and 16-h photoperiods. When the light source was changed from clear incandescent lamps, with a red (600-700 nm) to far-red (700-770 nm) ratio of ca. 1.07, to a BCJ incandescent lamp (Corning Glass dark red, transparent envelope and a red to far-red ratio of ca. 0.19), the growth rate of embryos slowed. These results are consistent with a high irradiance response for growth of soybean embryos.