PHOTOSYNTHESIS OF 6 BARLEY GENOTYPES AS AFFECTED BY WATER-STRESS

The effect of water stress on plant water status and net photosyntheti c gas exchange (P-N) in Six barley genotypes (Hordeum vulgare L.) diff ering in productivity and drought tolerance was studied in a controlle d growth chamber. Osmotic adjustment (OA), P-N, Stomatal conductance ( g(s)), and the ratio intercellular/ambient CO2 concentration (C-i/C-a) were evaluated at four different levels of soil water availability, c orresponding to 75, 35, 25 and 15 % of total available water, Variabil ity in OA capacity was observed between genotypes: the drought toleran t genotypes Albacete and Alpha showed higher OA than drought susceptib le genotypes Express and Mogador. The genotype Albacete exhibited also higher P-N than the others at low water potential (Psi). The ratios o f P-N/g(s) and C-i/C-a showed that differences in photosynthetic inhib ition betweeen genotypes at low Psi were probably due to nonstomatal e ffects. In Tichedrett, a landrace genotype with a very extensive root development, OA was not observed, however, it exhibited a capacity to maintain its photosynthetic activity under water stress.