It then becomes reasonable to consider whether the development of the trees could be modified by modifying the spectral properties of the covering film.
In the experiments reported below, one-year-old peach and cherry trees were grown in plastic pots both in the field and under film plastics in greenhouses. Two films contained additives that absorbed red light with the outcome that less red light relative to far-red light passed through them.
Three further films contained additives that absorbed ultraviolet radiation and then re-emitted it as blue, red, or red and blue light. The control film contained no additives but reduced light transmission by much the same amount as the other films.
The film with the smallest proportion of red to far-red light produced the longest shoots and the thickest trunks both on cherry and peach trees. The effects of the three luminescent films were smaller, although shifting light from ultraviolet to red did increase shoot length.
Evidently, the development of fruit trees can be modified by covering them with film plastics having specific spectral properties, although more work is needed to refine this approach.
Dr Ken Cockshull, Associate Fellow, Warwick Crop Centre, University of Warwick
Radiometric Properties of Photoselective and Photoluminescent Greenhouse Plastic Films and Their Effects on Peach and Cherry Tree Growth by Schettini, De Salvador, Scarascia-Mugnozza and Vox (2011). Journal of Horticultural Science & Biotechnology 86 (1): 79-83. The authors' abstract of their manuscript can be seen in full at www.jhortscib.com