INCREASE OF EMBRYOGENIC CALLUS FORMATION IN CUCUMBER BY INITIAL CULTURE ON HIGH-CONCENTRATION OF 2,4-DICHLOROPHENOXYACETIC ACID

Cucumber (Cucumis sativus L.) leaf explants were cultured either conti nuously on standard medium containing 4.5 mu M 2,4- dichlorophenoxyace tic acid (2,4-D) and 4.4 mu M benzylaminopurine, or first cultured for various periods at different levels of 2,4-D, picloram or naphthalene acetic acid (NAA), and then transferred to standard medium. When cultu red continuously on standard medium, less than 10% of the explants for med embryogenic callus. Initial culture on picloram or NAA, or on 2,4- D at a low concentration (1.4 mu M) did not result in any embryogenic callus formation. Embryogenic callus formation increased to 40% if dur ing the initial phase of the culture (10 days), the 2,4-D concentratio n was raised to 14 mu M. Prolonged culture on 14 mu M 2,4-D resulted i n less embryogenic callus formation.