Thermal imaging and carbon isotope composition indicate variation amongst strawberry (Fragaria x ananassa) cultivars in stomatal conductance and water use efficiency

Cultivars with low stomatal conductance (g(s)) may show high water use efficiency (WUE) under drought conditions, but under optimal conditions low g(s) may result in low vigour. A combination of thermal imaging and carbon isotope composition (delta C-13) analysis offers potential for screening simultaneously for both high g(s) and high WUE. Ten cultivars of strawberry (Fragaria X ananassa Duch.) were grown in well watered or water limited conditions. Thermal images were taken of the plants, with various approaches to determine the optimal protocol for detecting variation in g(s), including use of reference leaves, grids to maintain leaves horizontal, and collection of meteorological data in synchrony with thermal images. delta C-13 of leaves, fruit, and crowns was determined. An index of g(s) derived from the temperature of horizontal leaves and the temperature of wet and dry references showed significant differences between cultivars and between well watered and water limited plants, as did g(s) estimated from leaf temperature, the temperature of a dry reference, and humidity. Thermal imaging indicated low g(s) in 'Elsanta' and 'Totem' and relatively high g(s) in well watered 'Elvira', 'Florence' and 'Cambridge Favourite'. delta C-13 of all plant material was higher in water limited than well watered plants and showed significant differences between cultivars. In one experiment leaf delta C-13 indicated lowest WUE in 'Elvira' and highest WUE in 'Totem'. delta C-13 was inversely correlated with an index of g(s) derived from thermal imaging. Although the results indicate substantial variation in g(s) and WUE between cultivars, generally all cultivars responded to water deficit by lowering g(s) and hence increasing WUE. (C) 2011 Elsevier B.V. All rights reserved.