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

Abstract

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 (δ 13C) analysis offers potential for screening simultaneously for both high g s and high WUE. Ten cultivars of strawberry ( Fragaria × 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. δ 13C 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’. δ 13C of all plant material was higher in water limited than well watered plants and showed significant differences between cultivars. In one experiment leaf δ 13C indicated lowest WUE in ‘Elvira’ and highest WUE in ‘Totem’. δ 13C 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.