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.

Photosynthetic responses of subtidal seagrasses to a daily light cycle in Torres Strait: A comparative study

In this study, we examined the photosynthetic responses of five common seagrass species from a typical mixed meadow in Torres Strait at a depth of 5–7 m using pulse amplitude modulated (PAM) fluorometry. The photosynthetic response of each species was measured every 2 h throughout a single daily light cycle from dawn (6 am) to dusk (6 pm). PAM fluorometry was used to generate rapid light curves from which measures of electron transport rate (ETRmax), photosynthetic efficiency (α), saturating irradiance (Ek) and light-adapted quantum yield (ΔF/F′m) were derived for each species. The amount of light absorbed by leaves (absorption factor) was also determined for each species. Similar diurnal patterns were recorded among species with 3–4 fold increases in maximal electron rate from dawn to midday and a maintenance of ETRmax in the afternoon that would allow an optimal use of low light by all species. Differences in photosynthetic responses to changes in the daily light regime were also evident with Syringodium isoetifolium showing the highest photosynthetic rates and saturating irradiances suggesting a competitive advantage over other species under conditions of high light. In contrast Halophila ovalis, Halophila decipiens and Halophila spinulosa were characterised by comparatively low photosynthetic rates and minimum light requirements (i.e. low Ek) typical of shade adaptation. The structural makeup of each species may explain the observed differences with large, structurally complex species such as Syringodium isoetifolium and Cymodocea serrulata showing high photosynthetic effciciencies (α) and therefore high-light-adapted traits (e.g. high ETRmax and Ek) compared with the smaller Halophila species positioned lower in the canopy. For the smaller Halophila species these shade-adapted traits are features that optimise their survival during low-light conditions. Knowledge of these characteristics and responses improves our understanding of the underlying causes of changes in seagrass biomass, growth and survival that occur when modifications in light quantity and quality arise from anthropogenic and climatic disturbances that commonly occur in Torres Strait.

Patterns in tropical seagrass photosynthesis in relation to light, depth and habitat

Seagrass meadows across north-eastern Australia, survive a range of environmental conditions in coastal bays, reefs, estuarine and deepwater habitats through adaptation of a range of structural, morphological and physiological features. The aim of this study was to investigate the influence of spatial features (habitat type, site and depth) and photon flux on the photosynthetic performance of 11 tropical seagrass species. Pulse amplitude modulated (PAM) fluorometry was used to generate rapid light curves from which measures of maximal electron transport rate (ETRmax), photosynthetic efficiency (?), saturating irradiance (Ek) and effective quantum yield (?F/Fm?) were derived. The amount of light absorbed by leaves (absorption factor) was also determined for each population. In intertidal habitats many seagrass species exhibited typical sun-type responses with a close coupling of both ETRmax and Ek with photon flux. Photosynthetic performance ranged from minima in Thalassodendron ciliatum to maxima in Syringodium isoetifolium. The absence of a coupling between photosynthetic performance and photon flux in subtidal populations was most likely due to highly variable light climates and possible light attenuation, and hence the photo-biology of estuarine and deepwater seagrasses exhibited photosynthetic responses indicative of light limitation. In contrast seagrass species from shallow reef and coastal habitats for the most part exhibited light saturation characteristics. Of all the variables examined ETRmax, Ek and ?F/Fm? were most responsive to changing light climates and provide reliable physiological indicators of real-time photosynthetic performance of tropical seagrasses under different light conditions.

Weed species richness, density and relative abundance on farms in the subtropical grain region of Australia

Weed management is one of the most important economic and agronomic issues facing farmers in Australia's grain regions. Weed species occurrence and abundance was monitored between 1997 and 2000 on 46 paddocks (sites) across 18 commercial farms located in the Northern Grain Region. The sites generally fell within 4 disjunct regions, from south to north: Liverpool Plains, Moree, Goondiwindi and Kingaroy. While high species richness was found (139 species or species groups), only 8 species occurred in all 4 regions and many (56 species) only occurred at 1 site or region. No species were observed at every site but 7 species (Sonchus spp., Avena spp., Conyza spp., Echinochloa spp., Convolvulus erubescens, Phalaris spp. and Lactuca serriola) were recorded on more than 70% of sites. The average number of species observed within crops after treatment and before harvest was less than 13. Species richness tended to be higher in winter pulse crops, cotton and in fallows, but overall was similar at the different sampling seasons (summer v. winter). Separate species assemblages associated with the Goondiwindi and Kingaroy regions were identified by correspondence analysis but these appeared to form no logical functional group. The species richness and density was generally low, demonstrating that farmers are managing weed populations effectively in both summer and winter cropping phases. Despite the apparent adoption of conservation tillage, an increase in opportunity cropping and the diversity of crops grown (13) there was no obvious effect of management practices on weed species richness or relative abundance. Avena spp. and Sonchus spp. were 2 of the most dominant weeds, particularly in central and southern latitudes of the region; Amaranthus spp. and Raphanus raphanistrum were the most abundant species in the northern part of the region. The ubiquity of these and other species shows that continued vigilance is required to suppress weeds as a management issue.

Management of Tobacco streak virus in sunflower and pulse crops

Management of Tobacco streak virus in sunflower and pulse crops.

Reducing the impact of pulse diseases in the northern region

Diseases remain a significant impediment to the achievement of maximum yield potential of pulses (chickpea, peanut and mungbean) and sunflowers in the GRDC northern region. This project worked closely with public and private breeding programs to identify sources of resistance to the major diseases of pulses and sunflower that dominate in the region. Through varied surveillance activities, a watching brief on pulse and sunflower diseases was maintained and a timely and appropriate response was made to several significant disease outbreaks. Information on the biology and management of diseases was extended to clients in a wide variety of ways.

Epidemiology and management of tobacco streak virus in sunflower and pulse crops

Epidemiology and management of tobacco streak virus in sunflower and pulse crops.

Food-borne pathogens - a key issue for all food animal industries

The modern consumer has an attitude that food safety is non-negotiable issue – the consumer simply demands food to be safe. Yet, at the same time, the modern consumer has an expectation that the food safety is the responsibility of others – the primary producer, the processing company, the supermarket, commercial food handlers and so on. Given this environment, all food animal industries have little choice but to regard food safety as a key issue. As an example, the chicken meat industry, via the two main industry funding bodies – the Rural Industries Research and Development Corporation (Chicken Meat) and the Poultry CRC – has a comprehensive research program that seeks to focus on reducing the risks of food-borne diseases at all points of the food processing chain – from the farm to the processing plant. The scale of the issue for all industries can be illustrated by an analysis of the problem of campylobacterosis – a major food-borne disease. It has been estimated that there are around 230,000 cases of campylobacterosis per year. In 1995, it was estimated that each case of food-borne campylobacterosis in the USA was costing between $(US) 350-580. Hence, a reasonable conservative estimate is that each Australian case in 2010 would result in a cost of around $500 (this includes hospital, medication and lost productivity costs). Hence, this single food-borne agent could be costing Australian society around $115 million annually. In the light of these types of estimated costs for just one food-borne pathogen, it is easy to understand the importance that all food animal industries place on food safety.

Effects of three different nano-silver formulations on cut Acacia holosericea vase life

The relative efficacies of three chemically different nano-silver (NS) formulations were evaluated for their potential to extend the vase life of short-lived cut Acacia holosericea foliage. The novel proprietary formulations were neutral NS, acidic NS and ionic NS. They were characterised in terms of particle size, pH value, colour and odour. The NS treatments were applied as vase (lower concentrations) or pulse (higher concentrations) solutions. Among the treatments compared, neutral NS as a 4 mg L-1 vase solution or as a 40 mg L-1 24 h pulse treatment and acidic NS as a 0.5 mg L-1 vase solution or as a 5 mg L-1 24 h pulse treatment significantly (P <= 0.05) extended the vase life of A. holosericea. Vase life extensions over the deionised water (DI) controls were associated with better maintenance of relative fresh weight and vase water uptake, suppression of bacterial growth in the vase water and stem-end, and delaying stem blockage. In contrast, ionic-NS applied as a 0.5 or 1 mg L-1 vase solution treatment or as a 5 or 10 mg L-1 pulse treatment caused severe phytotoxicity to cut A. holosericea stems. The results suggest that NS treatments, especially neutral NS and acidic NS pulse treatments, could be a potential postharvest technology for commercial application to cut A. holosericea. (C) 2011 Elsevier B.V. All rights reserved.