Selection for salt tolerance in lucerne (Medicago sativa L.) using tissue culture

Studies were made of the influence of four different levels of NaCl (0, 75, 150, 250, mM) on the growth of callus of five lines of lucerne (Medicago sativa L.). These lines were based on the U.S.A. cultivar CUF 101 and comprised an unselected population and two populations selected for NaCI tolerance through one (line T-1) and two (line T-2) cycles of recurrent selection and two populations similarly selected for NaCI sensitivity through one line (line S-1) and two (line S-2) cycles of recurrent selection. Calli of the five lines, derived from the hypocotyl tissue, were exposed to NaCl by transferring them to various concentrations of NaCl. While it appeared that callus of salt-tolerant lines under certain levels of NaCl were somewhat less affected by NaCl than the "non-tolerant" lines, there was no marked general relationship of the reputed differences in whole plant tolerance the lines and the callus tolerance to NaCl. An experiment was conducted to further examine the relationship between whole plant salt-tolerance of unselected CUF 101, and its salt-tolerant (T-1) and the salt-sensitive (S-1) lines and callus derived from their plants. It revealed moderately high positive correlations between a number of measures of seedling growth and callus fresh weight when both were exposed to similar ranges of NaCI concentration. This thesis study gave no strong evidence that salt tolerance in lucerne is consistently expressed in the callus and that tolerance to NaCl concentration at the cellular level, which is likely to be the main basis of callus tolerance, is a very significant component of whole plant tolerance to NaCl. Regeneration of plants was induced in callus that had been exposed to NaCl on a solid (agar) Boi2Y medium. Regeneration was obtained from callus of unselected CUF 101 after exposure to 75 mM NaCI and the salt-sensitive line (S-1) after exposure to 150 mM NaCl. Regenerated plants were grown to maturity. Plants regenerated from the same callus were artificially intercrossed to provide seed of regenerated populations which were grown to examine them for the presence of somaclonal variation, both for salt tolerance and plant morphological characters. No significant change was detected in variation for salt tolerance in the progenies of regenerated plants compared with respective normal "parent" populations. However, increased variation was observed in regenerated populations for a number of plant morphological characters such as leaflet number, size and shape