Microbial contamination in tissue culture of Chlorophytum borivilianum, a rare medicinal herb: identification and prevention

Abstract

When inflorescence axis was used as the explant for micropropagation of Chlorophytum borivilianum, 50% of tubes became contaminated at Stage-I of in vitro culture. Bacteria (Bacillus licheniformis, Micrococcus sp. and Panibacillus sp.) and fungi (Alternaria sp., Aspergillus sp., Cladosporium sphaerospermum and Fusarium sp.) were the most common contaminants.The effectiveness of synthetic antimicrobial compounds in inhibiting the growth of contaminants was compared. Five antibiotics, penicillin (PE), norfloxacin (NF), tobramycin (TB), gatifloxacin (GT) and ofloxacin (OF), at 1%–15%, and four fungicides, Bavastin (BV), Captan (CA), Fluconazole (FL) and Trichoderma biofungicide (TV), at 0.5–2%, were tested on the bacterial and fungal isolates respectively. GT (5%) and OF (8%) inhibited 100% growth of bacteria, but the former was more efficient. BV and CA at 1–2% appeared to be the most effective fungicides. MIC of antibiotics was higher (8–10%) than MIC of fungicides (1–2%). The two most effective antibiotics (GT, OF) and fungicides (BV, CA) were also evaluated in vitro for phytotoxicity. The observed MPCs for GT, OF, BV and CA were 4%, 9%, 1% and 1.5% respectively. They were then tested in combination at their respective MICs in amended MS media and culture survival was recorded at Stage-I. Ninety per cent of cultures survived with GT (4%) + BV(1%) combination, while the combination of GT and CA was highly toxic. Enhancement in culture survival by 40% resulted from synergistic or additive effects of GT and BV.