THE INFLUENCE OF COBALT CHLORIDE ON IN-VITRO SHOOT PROLIFERATION IN CUCUMBER (CUCUMIS-SATIVUS L.)

The improvement of in vitro shoot regeneration using cobalt chloride was studied on two cucumber varieties, namely Spring Swallow (SS) and Tasty green (TG). Explants used were the proximal and distal cotyledon and hypocotyl explants. Proximal cotyledon and hypocotyl explants of the two varieties displayed poor regeneration under in vitro shoot regeneration medium (MS basal nutrients containing different concentrations of BAP) without the addition of cobalt chloride to both seed germination medium (MS medium without agar) and shoot regeneration medium(SRM). A slight improvement in the shoot regeneration response was observed when cobalt chloride (CoCl2) was added to seed the germination medium (SGM) at concentrations 10,30 up to 50 mu M(-1). Further improvements were observed in both varieties when CoCl2 concentration up to 50 mu M(-1) was added to the SRM. However, shoot regeneration as well as number of shoots per explant were effectively increased in proximal cotyledon and hypocotyl as well as distal cotyledon of both varieties when cobalt chloride was added in both SGM and SRM. Distal hypocotyl of both varieties was unresponsive even when CoCl2 was added in the germination as well as the regeneration media, whereas, distal cotyledon was unresponsive only with the SRM (without the addition of cobalt chloride). Shoot primordia were observed 10 to 16 days after explants were cultured on SRM.