Investigation of potential antibacterial action for postharvest copper treatments of cut Acacia holosericea

The mechanisms of action of Cu2+ in improving the longevity of cut flowers and foliage have not been elucidated. Possible antimicrobial action of Cu2+ against stem end and vase solution colonising bacteria was investigated using Cu2+ treatments optimised for cut Acacia holosericea A. Cunn. ex G. Don foliage stems. These treatments were a 5 h pulse with 2.2 mM Cu2+ or a 0.5 mM Cu2+ vase solution versus a deionised water (no Cu2+)control. Bacterial growth over time was assessed by a standard plate count agar technique and with scanning electron microscopy. Cu2+ treatments significantly extended the cut foliage vase life. However, they did not have sustained antibacterial activity against stem end or vase solution colonising bacteria. Also, regular recutting of 1-2 cm from the stem ends did not substantially improve either cut stem water relations or longevity. The positive effects of Cu2+ treatments were unaffected by the repeated stem end recutting. It was concluded that the primary mechanism of Cu2+ was not antibacterial. Moreover, naturally growing vase solution and stem end microbial populations had relatively insignificant effects on cut A. holosericea vase life. Research into alternative mechanisms of Cu2+ is required. (C) 2012 Elsevier B.V. All rights reserved.