Identification and elimination of bacterial contaminants from yam tissue cultures

Abstract

Yam tissue cultures grown on yam multiplication medium are often contaminated with endogenous bacteria. These contaminants affect multiplication rates of plant cultures and may provide a source of inoculum in the progeny of microplants. The aim of this study was to detect and control bacterial contamination in yam tissue cultures using antibiotics. The bacterial isolates were identified using standard microbiological methods. Antibiotic sensitivity test was carried out on the bacterial isolates to know their sensitivity or resistance to some common antibiotics used in plant tissue culture. Streptomycin, Rifampicin and Gentamicin chosen for further investigation were screened for bactericidal activity and phytotoxic effects on yam plantlets in liquid yam multiplication (YM) medium. Single nodes from infected plants were treated by inoculating into liquid YM medium containing antibiotics either singly or in combination. The effect of pH on bactericidal activity of the antibiotic was also determined. The antibiotics were added to yam multiplication medium in the following dosages: Streptomycin-500μg, 750μg, 1000μg and 1250μg/ml, Rifampicin-40μg, 80μg, l60μg, and 320μg/ml and gentamicin- 20μg, 40μg, 80μg and 160μg/ml. Antibiotic sensitivity test was also performed on the bacterial isolates and three antibiotics were identified as being potentially useful in eliminating the bacterial contaminants. Five bacterial isolates were obtained from contaminated yam cultures and these were classified as Corynebacterium fascians, Corynebacterium michiiganese, Paracoccus denitrificans, Erwinia stewartii and one unidentified species. The best results were obtained with the addition of 320μg/ml of Rifampicin. Combination of Rifampicin (80 μ/ml) and Streptomycin (250 μ/ml) were effective in treatment. Inhibition of growth by antibiotics was best at pH 6.9.