Research Matters - Helping hypocotyls to grow longer

One very efficient way of grafting vegetable seedlings onto disease-resistant rootstocks is to combine grafting and re-rooting into one single operation. Grafting is made easier if the rootstock seedlings have long hypocotyls.

One method for lengthening hypocotyls is to use end-of-day far-red lighting. Light-emitting diodes (LEDs) are particularly well-suited for this because relatively low light intensities are required and, because only brief exposures to light are needed, passing a few LEDs across the crop should prove effective.

In the present experiments, seeds of a squash rootstock 'Tetsukabuto' (Cucurbita maxima x C. moschata) were sown in trays in the dark at 30 degsC. Once their cotyledons were fully expanded, some seedlings were given different end-of-day light intensities from stationery far-red LEDs.

Others were treated by far-red LEDs mounted on a bar set 5cm above the seedlings that moved over them at different speeds. Each of the mobile treatments received four millimoles of far-red light per square metre per day.

Hypocotyls from seedlings given the highest far-red intensity from stationery LEDs were longer than the untreated ones. Hypocotyls under the mobile lights were also longer than untreated ones, while hypocotyl length under end-of-day lighting from either stationary or mobile systems did not differ significantly. Evidently, end-of-day far-red lighting with appropriate LEDs could be a useful technique for increasing hypocotyl length.

Dr Ken Cockshull, Associate Fellow, Warwick Crop Centre, University of Warwick

Effect of End-Of-Day Far-Red Light From a Movable LED Fixture on Squash Rootstock Hypocotyl Elongation by Yang, Kubota, Chia and Kacira (2012). Scientia Horticulturae 136: 81-86. The contents of issues of Scientia Horticulturae and abstracts of papers are provided at

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