Light effects on in vitro adventitious root formation in axillary shoots of mature Prunus serotina

Light effects on in vitro adventitious root formation in axillary shoots of a 95‐year‐old black cherry (Prunus serotina Ehrh.) were examined using microcuttings derived from cultured vegetative buds. Three studies were performed: 1) complete darkness and 4 levels of continuous white light irradiance were tested at 70, 278, 555 and 833 μmol m⁻² s⁻¹; 2) white, red, yellow and blue light were tested to assess the importance of spectral quality; and 3) the effect of blue light at intensities of 7,15, 22 and 30 μmol m⁻² s⁻¹ was also studied, Measurements included rooting percentage, total number of roots per shoot, and shoot and root dry weight. There was a strong negative effect of white light intensity upon root formation. Blue light between 15 and 22 μmol m⁻²: s⁻¹ significantly retarded root formation and completely inhibited it at 36 μmol m⁻² s⁻¹. Shoots treated with yellow light exhibited the highest rooting percentage, mean number of roots per shoot, and root dry weight.