Membrane competence among and within Fragaria species varies in response to dehydration stress

The effect of dehydration stress on membrane competence among and within Fragaria species was evaluated using index of injury, I(d), and tissue ionic conductance, g(Ti). Single accessions of F. chiloensis ssp. lucida Duch., F. virginiana ssp. glauca (S. Watson) Staudt, F. virginiana ssp. virginiana Duch., F. xananassa Duch., and F. vesca L. were used to study interspecific variation. Leaf thickness and total electrolyte content were greatest for the F. chiloensis ssp. lucida accession and least for the F. virginiana ssp. glauca accession, but foliar electrolyte concentration did not vary across accessions. The g(Ti) values were >5fold higher from 0 to 2 hours than for other intervals, declining over time. Significant differences in g(Ti) and I(d) values were only evident at 2 and 4 hours within stress levels, and increased as stress level increased. While the F. chiloensis ssp. lucida accession exhibited low g(Ti) values at 70% relative water content (RWC), it showed greater relative membrane injury than the other species expressed as g(Ti), I(d), or the ratio of stress g(Ti) to control g(Ti) as dehydration level increased. Although the F. virginiana ssp. glauca accession had the highest g(Ti) values, even at 100% RWC, its relative injury as stress level increased was not as great as that of the F. chiloensis accession. In a second experiment, intraspecific variation was examined using four accessions each of F. chiloensis and of F. virginiana which were dehydrated to 50% RWC. The species mean g(Ti), I(d), and g(Ti) ratio values at 2 and 4 hours for the F. chiloensis accessions were lower than those for the F. virginiana accessions, but significant intraspecific variation was also observed. In spite of the differences between species means, the evidence of intraspecific variation indicates that not all accessions of a species exhibit similar drought responses (i.e., membrane competence). Due to the consistent conclusions derived from using either g(Ti) or I(d) after 2 or 4 hours of incubation for characterization of membrane competence, g(Ti) and I(d) were comparable techniques for identification of potential drought tolerance in Fragaria.