WILD AND CULTIVATED BARLEY GENOTYPES DEMONSTRATE VARYING ABILITY TO ACCLIMATE TO PLANT WATER DEFICITS

Wild barley (Hordeum spontaneum Koech.) crosses easily with cultivated barley (Hordeum vulgare L.) and so can be used as novel germplasm in breeding programs. In order to examine the potential usefulness of wil d barley as a source of germplasm with characteristics beneficial to c rop plants exposed to plant water deficits, wild barley accessions wer e collected from a range of habitats in Israel. Photosynthetic capacit y at low leaf water potential (Psi(w),), and cellular-level stress acc limation capability were evaluated in these lines. Genotypes identifie d as having the capacity to maintain higher photosynthesis at low leaf Psi(w), (i.e.'high acclimation lines'), as a group, demonstrated seve ral related cellular-level physiological acclimation mechanisms when e xposed to water deficits. These genotypes underwent relatively greater osmotic adjustment under stress. Osmotic adjustment in these lines wa s associated with the capacity to shift the protoplast volume/leaf Psi (w), relationship upon exposure to stress such that greater cell volum e was maintained at low Psi(w). Wild barley accessions which showed lo w photosynthesis under stress did not demonstrate this acclimation mec hanism. Some of the wild barley accessions demonstrated greater osmoti c adjustment in response to plant water deficits than the two varietie s of cultivated barley which were also evaluated in this study. It is concluded that wild barley may be a good source of germplasm which sho ws resistance to water stress, specifically regarding the capacity to acclimate to plant water deficits such that photosynthesis is not as s ensitive to low leaf Psi(w)..