Abstract
Microbial contamination is a common problem that causes significant losses in plant micropropagation systems. The present study reports on the identification and control of bacterial contaminants in banana in vitro cultures. Twelve isolates belonging to Bacillus pumilus (S2), Bacillus subtilis (R2 and M4), Geobacillus stearothermophilus (S1, S3, S4, P2, M3 and R3) and Paenibacillus spp. (P1, R1 and M2) were identified by sequencing of 16S rRNA, gyrA or gyrB genes. Antibiotic susceptibility testing was performed with the disk diffusion method on bacterial isolates using 36 antimicrobial agents. Some antibiotics, notably Ticarcillin, Penicillin, Ampicillin, Cefazolin and Imipenem, had a broader range of bactericidal activity than others did. When contaminated axillary shoot cultures of banana were treated with 100 or 200 mg·L−1 of ticarcillin, ampicillin or penicillin the bacteria were eliminated, but a reduction in shoot multiplication and growth was observed. These findings contribute to minimizing the losses in the commercial micropropagation of banana.
Highlights
Tissue culture is one of the key tools of plant biotechnology and has been extensively exploited to meet the growing demands for elite planting material to produce healthy and pathogen-free plants at any time of the year in reduced time and physical space
Plant tissue cultures can be contaminated by endophytes or rhizosphere microorganisms that colonize plants in their growth habitat
The microbial contaminants that appeared around the base of the in vitro grown banana shoots (Figure 1A) were streaked onto four different media, i.e., trypticase soy agar (TSA), potato dextrose agar (PDA), Middelbrook and R2A to permit the growth of different bacterial species
Summary
Tissue culture is one of the key tools of plant biotechnology and has been extensively exploited to meet the growing demands for elite planting material to produce healthy and pathogen-free plants at any time of the year in reduced time and physical space. Microbial contamination is one of the major restrictions in commercial micropropagation systems. It causes difficulties in culture initiation, reduction of multiplication and rooting efficiency, tissue necrosis, and culture mortality [1,2]. Internal bacterial contamination (intra- or inter-cellular) can survive surface disinfection. These bacteria are not necessarily pathogenic or harmful to plants in the natural system, they can induce serious problems during in vitro culture. Endophytic bacteria are beneficial to host plants as they enhance the plants’ defense against diseases [3], but they cause serious problems in tissue culture systems.
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