MEMBRANE COMPETENCE AMONG AND WITHIN FRAGARIA SPECIES VARIES IN RESPONSE TO DEHYDRATION STRESS

The effect of dehydration stress on membrane competence among and with in Fragaria species was evaluated using index of injury, I-d, and tiss ue ionic conductance, g(Ti). Single accessions of F. chiloensis ssp. l ucida Duch., F. virginiana ssp. glauca (S. Watson) Staudt, F. virginia na ssp. virginiana Duch., F. xananassa Duch., and F. vesca L. were use d to study interspecific variation. Leaf thickness and total electroly te content were greatest for the F. chiloensis ssp. lucida accession a nd least for the F. virginiana ssp. glauca accession, but foliar elect rolyte concentration did not vary across accessions. The g(Ti) values were >5-fold higher from 0 to 2 hours than for other intervals, declin ing over time. Significant differences in g(Ti) and I-d values were on ly evident at 2 and 4 hours within stress levels, and increased as str ess level increased. While the F. chiloensis ssp. lucida accession exh ibited low g(Ti) values at 70 % relative water content (RWC), it showe d 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 dehydrat ion 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 examine d using four accessions each of F. chiloensis and of F. virginiana whi ch 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 lo wer than those for the F. virginiana accessions, but significant intra specific variation was also observed. In spite of the differences betw een species means, the evidence of intraspecific variation indicates t hat 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 c haracterization of membrane competence, g(Ti) and I-d were comparable techniques for identification of potential drought tolerance in Fragar ia.