Influence of High Concentrations of Copper Sulfate on In Vitro Adventitious Organogenesis of Cucumis sativus L.

Copper (Cu) is an essential plant micronutrient. This report is the first to assess the effects of high copper sulfate (CuSO4) levels on in vitro callus and shoot formation of cucumber. Four-day-old cotyledon explants from the inbred line Wisconsin 2843 and the commercial cultivars Marketer and Negrito were used. Murashige and Skoog (MS)-derived callus and shoot induction medium containing 0.5 mg L−1 indole-3-acetic acid (IAA) and 2.5 mg L−1 6-benzylaminopurine (BAP) was supplemented with CuSO4 (0.2–5 mg L−1). The response on callus-derived shoots showed that the optimal concentration of CuSO4 was 8- to 200-fold greater than in standard MS medium. Shoot frequency (SF) and shoot number (SN) were assessed, and Marketer > Negrito > Wisconsin 2843, where 1, 0.2 and 5 mg L−1 CuSO4 produced the highest results, respectively. SF and SN increased 6- and 10-fold in Wisconsin 2843 and twice in the other cultivars. All explants formed calluses, and in two of the three cultivars, callus extension was significantly affected by CuSO4 application. SN showed a strong relationship with CuSO4 levels and no association with callus extension. The results show that specific CuSO4 concentrations higher than in standard MS medium increase adventitious cucumber shoot organogenesis.