Isolation and characterisation of bacterial colonies from seeds and in vitro cultures of Fraxinus spp. from Italian sites

Culturable bacteria were isolated from seeds, embryos and contaminated in vitro
cultures of ash (Fraxinus excelsior L., F. ornus L. and F. angustifolia L.) and were
identified using morphological and molecular analyses. Fourteen morphologically
distinct isolates were recovered from seeds of Fraxinus spp. 16S rDNA sequencing
categorised these isolates into ten separate genera. Three strains isolated from contaminated
in vitro cultures, Pantoea agglomerans, Staphylococcus succinus and Aerococcus
viridans, were used for comparative analysis with isolates from seeds.
Antibiotic sensitivity testing of the isolated contaminants, including phytotoxicity
of antibiotics on in vitro cultures of ash, was also investigated. Phytotoxic effects
on explants immersed in ampicillin or cultured on medium containing ampicillin
were negligible, however tetracycline, either alone or in combination with other
antibiotics, had phytotoxic effects. We conclude that ampicillin is a suitable antibiotic
to limit the growth of contaminating bacteria during the in vitro culture of
ash.