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Summary
The physiological responses of wild Oryza species (Oryza latifolia Desv., a salt-tolerant species and O. rufipogon Griff., a salt-susceptible species) to salinity stress were investigated by comparing with check varieties of cultivated rice (O. sativa L.), SR26B (salt-tolerant) and IR28 (salt-susceptible). As the NaCl concentration of water culture solution was raised to 12 dS m–1 (about 113mM), leaf Na+ content per dry matter in wild Oryza species increased from 4 to 17 times as compared with the control (no NaCl treatment), whereas the accumulation was lower in cultivated rice varieties. The increased concentration of leaf Na+ resulted in the decrease in leaf water potential (Ψw) in all rice species, although the degree of decline in photosynthetic rate was different among the varieties. It was notable that the photosynthetic rate was cdmost constant in O. latifolia though Ψw decreased to – 2.0 MPa with the increased NaCl concentration in the water culture solution. A significant negative correlation between free-proline content and osmotic potential (Ψs) of leaf blade was found in both salt tolerant entries, SR26B and O. latifolia. In spite of higher leaf Na+ storage, the survival rate of O. latifolia was higher than that of SR26B, indicating that the mechanism of salt tolerance in O. latifolia may be different from that in SR26B.
