Research matters ... paclobutrazol influences water loss

Dr Ken Cockshull, Emeritus Fellow at Warwick HRI, highlights the latest findings from horticultural research.

Paclobutrazol is a plant-growth regulator that shows promise as a growth retardant on ornamental crops. The chemical may also improve the ability of plants to cope with water stress.

The strawberry tree (Arbutus unedo Award of Garden Merit) was selected for these investigations because it conserves water by closing the stomata in its leaves during the hottest daylight hours. Uniform seedlings were selected and grown in pots of compost in a greenhouse.

The treatments were three different doses of paclobutrazol (0, 60 or 100mg per litre) applied to the compost as single, 45ml drenches. The compost was irrigated via drippers and the volume of water supplied was calculated by multiplying the duration of dripping by the nominal volume dripped per hour.

Any water that leached from the pots was collected and its volume recorded. The difference between what was supplied and what was collected was assumed to have been transpired.

Paclobutrazol markedly reduced shoot fresh weight, plant height and the number of leaves produced. It also reduced daily water consumption, especially in the 100mg treatment, but by more than was anticipated from the reduction in leaf area. The results showed that this occurred because paclobutrasol also reduced water loss through the stomata.

Influence of Paclobutrazol on Water Consumption and Plant Performance of Arbutus unedo Seedlings by Navarro, Sanchez-Blanco and Banon (2007). Scientia Horticulturae 111: 133-139. The contents of issues of Scientia Horticulturae and abstracts of papers are provided at

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