Use of copper sulphate for controlling systemic contamination in black pepper (Piper nigrum L.) cultures

In vitro propagation is a promising option for the early establishment of the newly evolved varieties. In vitro propagation of black pepper (Piper nigrum L.) is very often limited by systemic presence of bacteria in the explants. Usual sterilization procedures are not effective in overcoming this problem. The endogenous bacteria like Beijerinckia indica exude from the explants into the medium and suppress successful regeneration. Use of antibiotics like streptopenicillin interferes with the growth and proliferation of the cultures. As copper sulphate (CuSO4) has fungicidal, algicidal, molluscicidal, bactericidal and herbicidal properties, the efficacy of copper sulphate to overcome the interference of systemic bacteria in in vitro cultures of black pepper was examined. Culture establishment medium containing CuSO4 100 mg l(-1) supported the maximum growth of explants, with minimum bacterial contamination. There was significant improvement in the growth and proliferation of cultures in multiplication medium supplemented with CuSO4 100 mg l(-1) with an average of 4.2 shoots per culture in eight weeks time, compared to only 2.6 shoots per culture in medium without CuSO4. Sub-culturing the shoots to proliferation medium containing CuSO4 15 mg l(-1) could keep the bacterial growth under check, without causing any copper toxicity, while supporting the maximum number of shoots per culture. Hundred per cent rooting of micro shoots was observed in the rooting medium supplemented with CuSO4 15 mg l(-1). The plantlets could be successfully established ex vitro, without any field mortality. These plants showed superior growth and yield, compared to those raised out of nodal rooted cuttings.