EFFECT OF WATER-STRESS ON THE GUAR - BRADYRHIZOBIUM SYSTEM USING PEG-6000

Cyamopsis tetragonoloba (guar) is an annual drought-tolerant legume gr owing in areas with a rainfall of 400 to 600 mm per year. Its native s ymbiont, Bradyrhizobium sp GB2 is affected by osmotic potentials highe r than -0.4 MPa in liquid medium supplemented with PEG 6000 as an osmo tic agent. Development and tolerance of the legume, survival of the mi croorganism and effect of water stress on the symbiosis establishment were determined. Less development and growth of plants subjected to st ress were observed; nodulation was present only in treatments with wat er deficit of up to -0.08 MPa, where the observed effects could be due to PEG rather than to water deficit. Total peroxidase activity decrea sed in root and increased in leaves under stress conditions. A signifi cant increase of soluble isoforms was observed in nodules. Nodulation (up to -1.24 MPa) was obtained using water stress-tolerant strains of Bradyrhizobium sp.