Characterization of rice (Oryza sativa L.) F-3 populations selected for salt resistance. I. Physiological behaviour during vegetative growth

Plants belonging to a somaclonal family (R-3-1-23, obtained from a salt- re sistant callus of the salt-sensitive cultivar I Kong Pao (IKP, salt-sensiti ve)) were crossed with this intital cultivar IKP or with plants of the elit e breeding line IR31785 (IR31, extremely salt-sensitive). Two other crosses were also performed: IR31 x IKP and IKP x Aiwu, where Aiwu is a moderatly salt-resistant cultivar. The physiological behaviour of F-3 populations was analysed after 21 and 42 days of exposure to 0 or 30 mM NaCl and compared to the behaviour of plants selected within parental populations. A clear im provement in terms of survival percentages was demonstrated for plants issu ed from IR31 x 1-23 and IR31 x IKP. These F-3 populations exhibited lower N a accumulation in shoots, higher Ca accumulation in roots, higher ratios of shoot P/root P than the parents after 42 days of salt exposure. Salt stres s induced a decrease of shoot K, an increase of shoot Cl and proline and a decrease of osmotic potential in all populations. Correlation analysis indi cated that no physiological parameter recorded in the absence of salt stres s may be used as a reliable selection marker to predict the plant behaviour in salt stress conditions. K/Na ratio recorded in the stressed plants was significantly correlated with surviving percentages recorded after 90 days of salt stress, suggesting that this physiological parameter in stress cond itions appears to be the most reliable selection criterion for salt resista nce in rice.