Validation of the effects of a single one second hypochlorite floral dip on Botrytis cinerea incidence following long-term shipment of cut roses

The effect of a pre-shipment hypochlorite treatment on botrytis incidence was evaluated in a large number of rose cultivars and under different long-term storage conditions. Application parameters, stability and sources of hypochlorite were investigated. Irrespective of the type of packaging and shipment conditions, roses that received a pre-shipment treatment with 100 to 150 mg/L hypochlorite showed a significantly decreased botrytis incidence compared to non-hypochlorite treated roses. The hypochlorite treatment generally was more effective than a comparable treatment with commercial fungicides. Dipping the flower heads for approximately one second in a hypochlorite solution was more effective than spraying the heads. In few cases minor hypochlorite-induced damage on the petal tips was observed at higher concentrations (>200 mg/L). Apart from the effect on botrytis incidence, the treatment resulted in reduced water loss that may have an additional beneficial effect on the eventual flower quality. It is concluded that, apart from other obvious measures to reduce botrytis incidence (prevention of high humidity at the flower heads) a pre-shipment floral dip in 100 to 150 mg/L hypochlorite from commercial household bleach is an easy and cost effective way to reduce botrytis incidence following long term storage/transportation of roses. © 2015, International Society for Horticultural Science. All rights reserved.

Xylem plugging and postharvest longevity of cut Acacia holosericea

An inherently short vase life is a problematic characteristic of cut flowers and foliage for otherwise attractive native Australian Acacia spp. Reasons underlying the poor postharvest water uptake of cut acacia stems have been elusive. A. holosericea was used to investigate possible bacteria-induced and wound-induced xylem occlusion. The effects of bacterial-and wound-induced xylem blockage on water uptake were investigated by light and scanning and transmission electron microscopy. Observations were made on cut stems that stood into either deionised water (DIW; control) or 0.5 mM Cu2+ solution and on stems pulsed with 2.2 mM Cu2+ solution and then stood into DIW. The stem-end region of cut A. holosericea that stood into DIW or Cu2+ solution became covered with bacterial growth after 3 days. Regardless of the bacterial biofilm, the Cu2+ treated stems had improved water relations and vase life. Therefore, the biofilm had little or no effect on cut A. holosericea longevity. Further observations revealed presence of a vessel-occluding substance (gel) originating from axial parenchyma cells in direct physical contact with xylem vessels. The gel exuded into vessel lumens through pit membranes, evidently as a wound-response. Xylem occlusion by gels in A. holosericea may be especially problematic due to an abundance of secretory contact cells relative to xylem elements. Nonetheless, active wound response processes may be the key determinant of short postharvest longevity for this and possibly other cut Acacia spp. Cu2+ treatments, however, disrupted the secretory function of axial parenchyma cells thereby preventing vessel occlusion by the gels.

Nano-silver treatments reduced bacterial colonization and biofilm formation at the stem-ends of cut gladiolus ‘Eerde’ spikes

Postharvest treatments with nano-silver (NS) alleviate bacteria-related stem blockage of some cut flowers to extend their longevity. Gladiolus (Gladiolus hybridus) is a commercially important cut flower species. For the first time, the effects of NS pulses on cut gladiolus ‘Eerde’ spikes were investigated towards reducing bacterial colonization of and biofilm formation on their stems. As compared with a deionized water (DIW) control, pulse treatments with NS at 10, 25 and 50 mg L−1 for 24 h significantly (P ≤ 0.05) prolonged the vase life of cut gladiolus spikes moved into vases containing DIW. The NS treatments enhanced floret ‘opening rate’ and ‘daily ornamental value’. Although there were no significant differences among NS treatments, a 25 mg L−1 NS pulse treatment tended to give the longest vase life and the best ‘display quality’. All NS pulse treatments significantly improved water uptake by and reduced water loss from flowering spikes, thereby delaying the loss of water balance and maintaining relative fresh weight. Fifty (50) mg L−1 NS pulse-treated cut gladiolus spikes tended to exhibit the most water uptake and highest water balance over the vase period. However, there was no significant difference between 25 and 50 mg L−1 NS pulse treatments. Observations of stem-end bacterial proliferation during the vase period on cut gladiolus spikes either with or without NS pulse treatments were performed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). As compared to the control treatment, they revealed that the 25 mg L−1 NS pulse treatment effectively inhibited bacterial colonization and biofilm formation on the stem-end cut surface and in the xylem vessels, respectively. In vitro culture of the bacterial microflora and analysis of biofilm architecture using CLSM revealed that NS treatment restricted bacterial biofilm formation. After static culture for 24 h at 35 °C with 25 mg L−1 NS in the medium, no biofilm form or structure was evident. Rather, only limited bacterial cell number and scanty extracellular polysaccharide (EPS) material were observed. In contrast, mature bacterial biofilm architecture comprised of abundant bacteria interwoven with EPS formed in the absence of NS.