Physiological characterisation of salt-resistant rice (Oryza sativa) somaclones

The progenies of 90 R-0 plants regenerated from mature embryo-derived rice (Oryza sativa L.) calli obtained from two cultivars (I Kong Pao, salt-sensi tive and Aiwu, moderately resistant) exposed to NaCl stress at various step s of in vitro culture, were screened for their salinity resistance in nutri tive solution. Sixteen R-1 families presented a higher survival rate in str ess conditions than their corresponding initial cultivar and several of the m exhibited an improvement in the mean number of spikelets per panicle and total grain weight produced per stressed plant. In four cases, the better b ehaviour of the somaclonal family could be related to physiological modific ations such as a higher K+:Na+ discrimination, preferential Na+ accumulatio n in the oldest leaves, lower decrease in cell membrane stability or higher tissue tolerance to internal Na+ accumulation. In some cases, these physio logical properties were transmitted to R-2 progenies. Heritabilities of yie ld-related parameters were quantified in control and stress conditions. The relationships between these parameters and the physiological behaviour of stressed material are discussed in relation to the effectiveness of in vitr o culture techniques for the selection of salt-resistant plants in rice com pared with a simple mass selection.