It is beneficial if the hypocotyl is reasonably long because the graft union can then be made well above the surface of the rooting material. In the present experiments, fiveto seven-day-old seedlings of the tomato rootstocks 'Aloha' and 'Maxifort' were given various lighting treatments at the end of each day.
The light source was small incandescent lamps that emit a high proportion of their output in the "far-red" waveband. This proportion could be further enhanced by passing the light through blue, transparent acrylic sheets that absorbed most of the accompanying "red" light.
Seedlings that received light from the incandescent lamps for 12 minutes at the end of each day had hypocotyls that were significantly longer than those of the controls and hypocotyl length was further increased if the light was passed through the blue, acrylic sheets. Far-red end-of-day lighting treatments such as these are preferable to the use of chemicals for controlling hypocotyl length.
Dr Ken Cockshull, Associate Fellow, Warwick Crop Centre, University of Warwick
End-of-Day Far-Red Light Quality and Dose Requirements for Tomato Rootstock Hypocotyl Elongation by Chia and Kubota (2010). HortScience 45 (10): 1501-1506. ISHS members can view HortScience from the website www.ishs.org.