Combinations of plant-derived compounds against Campylobacter in vitro

Campylobacter occur in fresh retail poultry products as a result of their colonization of the gastro-intestinal tract of chickens during growth. Feed additives could be used for suppression of Campylobacter levels in the chickens prior to slaughter. To address this opportunity, feed manufacturers are targeting natural antimicrobials from plant material as new forms of consumer-accepted feed additives. However, to be practical, these natural antimicrobials must be effective at low concentrations. The current study has validated an improved laboratory method to study minimal inhibitory concentrations of plant compounds and their combinations against Campylobacter. The assay was shown to be valid for testing lipid-soluble and water-soluble plant extracts and byproducts from the food industry. The study screened 29 extracts or plant-derived compounds and their mixtures for anti-Campylobacter activity using a laboratory assay. Combinations of oregano, lactic acid, and sorghum byproduct showed effective synergy in anti-Campylobacter activity. The synergies allowed a large reduction in the concentration of the individual compounds needed to kill the bacteria with an 80% reduction in concentration being achieved for oregano essential oil. The assay gives rise to further opportunities for the testing of a greater range of combinations of plant-derived compounds and other natural antimicrobials. The method is robust, simple, and easily automated, and it could be used to adjust the cost of feed formulations by reducing costs associated with antimicrobial feed additives.

The combined effect of biological control with plant competition on the management of parthenium weed (Parthenium hysterophorus l.)

Parthenium hysterophorus L., (Asteraceae) commonly known as parthenium weed, is a highly invasive plant that has become a problematic weed of pasture lands in Australia and many other countries around the world. For the management of this weed, an integrated approach comprising biological control and plant competition strategies was tested in southern central Queensland. Two competitive pasture plant species (butterfly pea and buffel grass), selected for their high competitive ability, worked successfully with the biological control agent (Epiblema strenuana Walker) to synergistically reduce the biomass of parthenium weed, by between 62 and 69%. In the presence of biological control agent, the corresponding biomass of competitive plants, butterfly pea and buffel grass increased in comparison to when the biological control agent had been excluded, by 15 and 35%, respectively. This suggests that biological control and competitive plants can complement one another to bring about improved management of parthenium weed in Australia. Further, this approach may be adopted in countries where some of the biological control agents are already present including South Africa, Ethiopia, India, Pakistan and Nepal.

Effect of added nitrogen on plant litter decomposition depends on initial soil carbon and nitrogen stoichiometry

Increasing organic carbon inputs to agricultural soils through the use of pastures or crop residues has been suggested as a means of restoring soil organic carbon lost via anthropogenic activities, such as land use change. However, the decomposition and retention of different plant residues in soil, and how these processes are affected by soil properties and nitrogen fertiliser application, is not fully understood. We evaluated the rate and extent of decomposition of 13C-pulse labelled plant material in response to nitrogen addition in four pasture soils of varying physico-chemical characteristics. Microbial respiration of buffel grass (Cenchrus ciliaris L.), wheat (Triticum aestivum L.) and lucerne (Medicago sativa L.) residues was monitored over 365-days. A double exponential model fitted to the data suggested that microbial respiration occurred as an early rapid and a late slow stage. A weighted three-compartment mixing model estimated the decomposition of both soluble and insoluble plant 13C (mg C kg−1 soil). Total plant material decomposition followed the alkyl C: O-alkyl C ratio of plant material, as determined by solid-state 13C nuclear magnetic resonance spectroscopy. Urea-N addition increased the decomposition of insoluble plant 13C in some soils (≤0.1% total nitrogen) but not others (0.3% total nitrogen). Principal components regression analysis indicated that 26% of the variability of plant material decomposition was explained by soil physico-chemical characteristics (P = 0.001), which was primarily described by the C:N ratio. We conclude that plant species with increasing alkyl C: O-alkyl C ratio are better retained as soil organic matter, and that the C:N stoichiometry of soils determines whether N addition leads to increases in soil organic carbon stocks.

Exotic plant pests–a threat to the sustainability of Australia’s grains industry

Exotic plant pests (EPPs) threaten production, market access and sustainability of Australian plant production systems. For the grains industry there are over 600 identified EPPs of which 54 are considered high priority, posing a significant threat. Despite Australia’s geographical isolation and strong quarantine systems, the threat from EPPs has never been higher with the increasing levels of travel and trade, emphasising the need for improving our efforts in prevention, preparedness and surveillance for EPPs.

Constrained linear minimax filter for systems with large plant uncertainties

This paper presents a method of designing a minimax filter in the presence of large plant uncertainties and constraints on the mean squared values of the estimates. The minimax filtering problem is reformulated in the framework of a deterministic optimal control problem and the method of solution employed, invokes the matrix Minimum Principle. The constrained linear filter and its relation to singular control problems has been illustrated. For the class of problems considered here it is shown that the filter can he constrained separately after carrying out the mini maximization. Numorieal examples are presented to illustrate the results.

Precise determination of aquatic plant wet mass using a salad spinner

The reliable assessment of macrophyte biomass is fundamental for ecological research and management of freshwater ecosystems. While dry mass is routinely used to determine aquatic plant biomass, wet (fresh) mass can be more practical. We tested the accuracy and precision of wet mass measurements by using a salad spinner to remove surface water from four macrophyte species differing in growth form and architectural complexity. The salad spinner aided in making precise and accurate wet mass with less than 3% error. There was also little difference between operators, with a user bias estimated to be below 5%. To achieve this level of precision, only 10–20 turns of the salad spinner are needed. Therefore, wet mass of a sample can be determined in less than 1 min. We demonstrated that a salad spinner is a rapid and economical technique to enable precise and accurate macrophyte wet mass measurements and is particularly suitable for experimental work. The method will also be useful for fieldwork in situations when sample sizes are not overly large.

Management of mango decline using thiophanate methyl and plant activators through a macro infusion system

Mango decline disease has become a major cause of tree losses of about 7-10% in all mango growing areas of Pakistan. This study evaluated the effectiveness of plant activators used in conjunction with the fungicide thiophanate methyl in managing mango decline disease. The study was conducted in the Multan district using trees rated as 1-2 on a decline severity scale and displaying symptoms of gummosis, bark splitting, canker formation, and leaf drooping. Experimental treatments included three plant activators viz. Bion, Planofix, and Root king in conjunction with or without thiophanate methyl, delivered through a macro infusion system. This was the first time a macro infusion system had been used in Pakistan. The injection system delivered the fungicide/activator mixture into the tree trunk under pressure through a series of holes bored into the xylem tissue. Tree disease symptoms were recorded fortnightly to assess the treatment efficacy. After three months, thiophanate methyl, in combination with Bion, was found to be the most effective treatment with trees displaying no apparent disease symptoms. When thiophanate methyl was used alone, or in combination with Root king and Planofix, the symptoms of bark splitting and gummosis persisted.

The mating system of the true fruit fly Bactrocera tryoniand its sister-species,Bactrocera neohumeralis

The frugivorous ‘true’ fruit fly, Bactrocera tryoni (Queensland fruit fly), is presumed to have a non-resourced-based lek mating system. This is largely untested, and contrary data exists to suggest Bactrocera tryoni may have a resource-based mating system focused on fruiting host plants. We tested the mating system of Bactrocera tryoni, and its close sibling Bactrocera neohumeralis, in large field cages using laboratory reared flies. We used observational experiments that allowed us to determine if: (i) mating pairs were aggregated or non-aggregated; (ii) mating system was resource or non-resource based; (iii) flies utilised possible landmarks (tall trees over short) as mate-rendezvous sites; and (iv) males called females from male-dominated leks. We recorded nearly 250 Bactrocera tryoni mating pairs across all experiments, revealing that: (i) mating pairs were aggregated; (ii) mating nearly always occurred in tall trees over short; (iii) mating was non-resource based; and (iv) that males and females arrived at the mate-rendezvous site together with no evidence that males preceded females. Bactrocera neohumeralis copulations were much more infrequent (only 30 mating pairs in total), but for those pairs there was a similar preference for tall trees and no evidence of a resource-based mating system. Some aspects of Bactrocera tryoni mating behaviour align with theoretical expectations of a lekking system, but others do not. Until evidence for unequivocal female choice can be provided (as predicted under a true lek), the mating system of Bactrocera tryoni is best described as a non-resource based, aggregation system for which we also have evidence that land-marking may be involved. This article is protected by copyright. All rights reserved

Studies on Plant Demography: Ranunculus Repens L., R. Bulbosus L. and R. Acris L.: III. A Mathematical Model Incorporating Multiple Modes of Reproduction

This paper presents a comparative population dynamics study of three closely related species of buttercups (Ranunculus repens, R. acris, and R. bulbosus). The study is based on an investigation of the behaviour of the seeds in soil under field conditions and a continuous monitoring of survival and reproduction of some 9000 individual plants over a period of 21/2 years in a coastal grassland in North Wales. The data were analysed with the help of an extension of Leslie's matrix method which makes possible an simultaneous treatment of vegetative and sexual reproduction. It was found that R. repens (a) depends more heavily on vegetative as compared with sexual reproduction, (b) shows indications of negatively density-dependent population regulation, and (c) exhibits little variation in population growth rates from site to site and from one year to the next. In contrast, R. bulbosus (a) depends exclusively on sexual reproduction, (b) shows indications of a positively density-dependent population behaviour, and (c) exhibits great variation in population growth rates from site to site and from one year to the next. R. acris exhibits an intermediate behaviour in all these respects. It is suggested that the attributes of R. repens are those expected of a species inhabiting a stable environment, while R. bulbosus exhibits some of the characteristics of a fugitive species.

Context-dependent mate choice in the sand goby, Pomatoschistus minutus

The results presented in this thesis show that all females of a given population do not necessarily choose similar mating partners. Specifically, partner preferences of a fish, the sand goby (Pomatoschistus minutus), varied among individual females and depended on the social context at the time of choice. I also show that females assess multiple mate choice cues simultaneously; partner preferences were based more strongly on an interaction effect between different choice cues than on any individual cue. Furthermore, I found that preferred matings involved fitness benefits in the form of increased offspring success, but these benefits were not significantly affected by mate compatibility. Hence, mate choice for partner compatibility does not appear to be an important determinant of the observed variation in female mate preferences in this species. The context-dependency of female mating preferences revealed is relevant to how genetic variation in sexually selected traits might be maintained: as the mating success of a certain male type varies according to the choice context, directional sexual selection on male traits is shown to be less intense than generally thought making for a slower loss of genetic variation in these traits. Mating preferences of sand gobies were assessed by giving females a binary choice between males that differed in body size and/or other focus traits. These association preferences were found to be sexually motivated, repeatable and to correspond to actual mating decisions.

Quarantine and surveillance strategies for plant pathogen detection and control

Incursions of plant pests and diseases pose serious threats to food security, agricultural productivity and the natural environment. One of the challenges in confidently delimiting and eradicating incursions is how to choose from an arsenal of surveillance and quarantine approaches in order to best control multiple dispersal pathways. Anthropogenic spread (propagules carried on humans or transported on produce or equipment) can be controlled with quarantine measures, which in turn can vary in intensity. In contrast, environmental spread processes are more difficult to control, but often have a temporal signal (e.g. seasonality) which can introduce both challenges and opportunities for surveillance and control. This leads to complex decisions regarding when, where and how to search. Recent modelling investigations of surveillance performance have optimised the output of simulation models, and found that a risk-weighted randomised search can perform close to optimally. However, exactly how quarantine and surveillance strategies should change to reflect different dispersal modes remains largely unaddressed. Here we develop a spatial simulation model of a plant fungal-pathogen incursion into an agricultural region, and its subsequent surveillance and control. We include structural differences in dispersal via the interplay of biological, environmental and anthropogenic connectivity between host sites (farms). Our objective was to gain broad insights into the relative roles played by different spread modes in propagating an invasion, and how incorporating knowledge of these spread risks may improve approaches to quarantine restrictions and surveillance. We find that broad heuristic rules for quarantine restrictions fail to contain the pathogen due to residual connectivity between sites, but surveillance measures enable early detection and successfully lead to suppression of the pathogen in all farms. Alternative surveillance strategies attain similar levels of performance by incorporating environmental or anthropogenic dispersal risk in the prioritisation of sites. Our model provides the basis to develop essential insights into the effectiveness of different surveillance and quarantine decisions for fungal pathogen control. Parameterised for authentic settings it will aid our understanding of how the extent and resolution of interventions should suitably reflect the spatial structure of dispersal processes.