Dry Matter Production and Photosynthetic Ability of Oryza officinalis Wall ex Watt under Salinity Stress Condition

This experiment was conducted to evaluate the salt tolerance level of the wild Oryza species, Oryza officinalis Wall ex Watt. Dry matter weight, ion content and photosynthetic rate of O. officinalis were compared with those of two salt-sensitive wild specis, O. rufipogon Griff. and O. australiensis Domin, the salt-tolerant cultivar O. sativa L. cv. Pokkali and the salt-tolerant wild species O. latifolia Desv. under a 12 dS m-1 NaCl-stressed condition. O. officinalis and O. latifolia subjected to salt stress had heavier leaf dry matter than Pokkali, and similar leaf water content (%) to that of Pokkali. O. officinalis and O. latifolia had more accumulated Na+ in the leaves than Pokkali. The photosynthetic rate of O. officinalis and O. latifolia was not decreased by a salt-stressed condition as compared with that of Pokkali. The main factor of the decreased photosynthetic rate was stomatal closure in all species. Furthermore, photosynthetic rate of O. rufipogon was related to non-stomatal limitations. Photosynthetic rate showed a positive correlation with stomatal conductance in O. officinalis, but a clear correlation was not found in O. latifolia. These results indicated that the salt tolerance mechanism of O. officinalis was similar to that of O. latifolia. However, the coefficient of correlation between photosynthetic rate and stomatal conductance showed a difference between O. officinalis and O. latifolia in the response of photosynthetic rate to salinity stress.