Controlling microbial contamination and browning of coconut (Cocos nucifera L.) inflorescence culture

Abstract

Surface contamination of explants and culture browning are major problems associated with in vitro culture procedures. The study was aimed at investigating the effect of different sterilizing agents in controlling microbial contamination and browning in coconut (Cocos nucifera L) inflorescence culture. Eeuwens medium, supplemented with 2,4-Dichlorophenoxyacetic acid (2,4-D) at concentration 40 mg/l and 6-Benzyl amino purine (BAP) at concentration 1 mg/l was used for the experiment. Immature coconut inflorescences with intact inner spathes were used as explants. The explants were sterilized with different sterilizing agents: mercuric chloride (HgCl₂), sodium hypochlorite (NaClO), silver nitrate (AgNO₃) and calcium hypochlorite (Ca(ClO)₂), each at concentrations 0.1, 0.2, 0.3 and 0.4 % for 5 min sterilization time. This was followed by rinsing the explants with distilled water four successive times and were inoculated on Eeuwens medium. Percentage culture contamination and level of browning were recorded on weekly basis for four weeks. The results obtained showed that contamination was less in the cultures, whose explants were sterilized with HgCl₂ and AgNO₃, but the level of culture browning was higher, four weeks after culture initiation when HgCl₂ was used for sterilization. By a way of comparison, AgNO₃ at concentrations between 0.1 - 0.3 % were most effective and to be preferred for sterilizing coconut inflorescence in controlling culture contamination and browning. It is therefore recommended that contamination and browning in coconut inflorescence cultures can be controlled by the use of AgNO₃ at concentrations between 0.1 – 0.3.

Keywords:  Cocos nucifera, Immature inflorescence, Sterilizing agents, Contamination and Browning