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Cell lines were established from the seed of two elite US rice lines (L-202 and M-202) as well as Indica rice varieties Pokkali, IR 28 and IR 42. Salt-tolerant cell lines were selected from these callus cultures by a single step selection process on tissue culture medium containing 1% (0.171 M) NaCl. Plants were regenerated from the salt-tolerant lines. The salt selection process and regeneration of the embryogenic callus had minimal adverse effect on subsequent plant growth, since the regenerated plants were vigorous, have flowered and in most cases were fertile. Seed was collected from the regenerated plants and the germinated seedlings were tested for salt tolerance. The R2 seedling salt tolerance was compared for plants regenerated from salt selected cell lines of L-202 that had been maintained on 1% NaCl for 1, 4 and 5 months. Heritable improvement in salt tolerance was obtained in R2 seedlings from one plant that had been regenerated after 5 months of selection on salt-containing medium. These results indicate that short-term salt selected rice callus contains many embryogenic calli that do not carry heritable changes in the salt tolerance phenotype and therefore necessitates screening for the tolerance phenotype in the progeny of the regenerated plants. Thus, as shown in the case of L-202 (R4), prolonging the selection process in vitro for rice improves the likelihood of regenerating plants with improved salt tolerance. |
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