SELECTION FOR SALT TOLERANCE IN-VITRO USING MICROSPORE-DERIVED EMBRYOS OF BRASSICA-NAPUS CV TOPAS, AND THE CHARACTERIZATION OF PUTATIVE TOLERANT PLANTS

Microspore-derived embryos of Brassica napus cv. Topas that survived s alt stress, were obtained after selection against otherwise lethal dos es (0.6 and 0.7%?%) of NaCl after mutagen treatment. A total of 10 sal t-surviving embryos were obtained out of a possible 834 000 embryos th at were mutagenized. One embryo out of a possible 845 000 obtained fro m non-mutagenized controls survived but failed to develop into a plant . Visual assessment after salt stress indicated that both the putative salt-tolerant plants and plants from control seeds behaved similarly. However, based on individual characteristics related to salt toleranc e, one of the lines (PST-2) accumulated less sodium and retained more potassium, and hence was able to maintain a more favorable Na:K ratio as compared to the controls under salt stress. Also chlorophyll a fluo rescence induction and quenching signals indicated a high energetic st ate of the thylakoid membranes in PST-2 under salt stress. The other p utative salt-tolerant line (PST-1) had a higher background level of pr oline that may have enabled it to survive salt stress during initial s creening, although its later performance was no better than the contro l plants.