Influence of the biocides PPM™ and Vitrofural on bacteria isolated from contaminated plant tissue cultures and on plant microshoots grown on various media

Bacterial contamination is often a serious problem during plant micropropagation. When disinfection of the initial explants fails, and bacteria are not detected at the initial stage of propagation, they can survive unobserved as a contamination in the plant explants and only appear when the population of microshoots is large. Biocides added to the culture media can be used to help reduce bacterial multiplication. This research was aimed at determining whether the use of PPM (TM) and Vitrofural could restrict the growth of various bacteria (Methylobacterium lusitanum, Paenibacillus spp., Pseudomonas putida, Serratia marcescens, and Staphylococcus pasteuri) isolated from plant cultures, and whether these biocides were detrimental to shoot multiplication and rooting in anthurium, blackberry, chrysanthemum, hosta, raspberry, and strawberry microshoots. PPM (TM) and Vitrofural restricted the growth of bacteria in agar-diffusion assays for periods of 1 d to 21 d, depending on the bacterial genotype, the type and concentration of biocide, and the number of days from the start of the assay. PPM (TM) inhibited the growth of M. lusitanum for 21 d, P putida for 14 d, S. pasteuri for 3 d, and Paenibacillus spp. and S. marcescens for 2 d. Vitrofural limited the growth of M. lusitanum for 21 d, P putida for 14 d, Paenibacillus spp. for 7 d, and S. marcescens for 1 d. PPM (TM) at 3 ml l(-1), 5 ml l(-1), or 10 ml l(-1), and Vitrofural at 25 mg l(-1), 35 mg l(-1), or 45 mg l(-1) significantly. affected the multiplication and rooting characteristics of microshoots. The influence of each biocide depended on its concentration, the plant genotype, and the type of medium used. In most cases, both biocides decreased shoot and root lengths and shoot and root numbers, compared to the untreated controls. Both biocides also showed some positive effects on selected plant genotypes. At all concentrations, PPM (TM) increased the number of axillary shoots in anthurium, while all concentrations of Vitrofural increased the number of axillary shoots in blackberry. Although PPM (TM) and Vitrofural decreased shoot multiplication and some rooting characteristics, if necessary they may be added to plant tissue culture media. However, their toxicity towards explants of a given plant genotype should first be tested.