Identification and management of microbial contaminants of banana in vitro cultures

Abstract

Microbial contamination is one of the major challenges hampering the application of in vitro micropropagation technique for mass production of pest-free banana planting materials at the Sokoine University of Agriculture in Tanzania. Objectives: The objectives of this study were to identify bacterial and fungal contaminants of banana in vitro cultures and to test the efficacy of selected antibiotics and antifungal agents in the elimination of such contaminants. Methodology and results: Purified bacterial isolates were identified based on vegetative cell shape, gram reaction, fluorescent pigment and standard biochemical tests. On the other hand, pure fungal isolates were microscopically identified based on structural and morphological characters. Four antibiotics, namely rifampicin, gentamicin, chloramphenicol and vancomycin each at 100, 150 and 200mg /litre and three antifungal agents, namely ketoconazole, fluconazole and nystatin each at 100, 150 and 200 mg/litre were used in the culture susceptibility tests of the identified bacteria and fungi, respectively. The bacterial contaminants of banana in vitro cultures were Proteus spp., Erwinia spp., Klebsiella spp. and Staphylococcus spp. while the fungal contaminants were Aspergillus spp., Fusarium spp,. Penicillium spp. and Candida spp. Culture susceptibility tests revealed that gentamicin, rifampicin and chloramphenicol each at 150mg/litre effectively suppressed the growth of all the identified bacteria while only ketoconazole at 200mg/litre inhibited the growth of all the identified fungal contaminants. Conclusion and application of results: Proteus, Erwinia, Klebsiella and Staphylococcus are the major bacterial contaminants while Aspergillus, Fusarium, Penicillium and Candida are the main fungal contaminants of banana in vitro cultures. These contaminants can effectively be eliminated by incorporation in the growth media of gentamicin, rifampicin and chloramphenicol each at 150mg/litre and ketoconazole at 200mg/litre. Further studies are required to investigate the negative side-effects of these antibiotics and antifungal agents on the growth and genetic stability of banana in vitro cultures.