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 continuously on standard medium containing 4.5 µM 2,4- dichlorophenoxyacetic acid (2,4-d) and 4.4 µM benzylaminopurine, or first cultured for various periods at different levels of 2,4-d, picloram or naphthaleneacetic acid (NAA), and then transferred to standard medium. When cultured continuously on standard medium, less than 10% of the explants formed embryogenic callus. Initial culture on picloram or NAA, or on 2,4-d at a low concentration (1.4 µM) did not result in any embryogenic callus formation. Embryogenic callus formation increased to 40% if during the initial phase of the culture (10 days), the 2,4-d concentration was raised to 14 µM. Prolonged culture on 14 µM 2,4-d resulted in less embryogenic callus formation.Abbreviations BA benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - NAA naphthaleneacetic acid