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.

Phosphine resistance in India is characterised by a dihydrolipoamide dehydrogenase variant that is otherwise unobserved in eukaryotes

Phosphine (PH3) fumigation is the primary method worldwide for controlling insect pests of stored commodities. Over-reliance on phosphine, however, has led to the emergence of strong resistance. Detailed genetic studies previously identified two loci, rph1 and rph2, that interact synergistically to create a strong resistance phenotype. We compared the genetics of phosphine resistance in strains of Rhyzopertha dominica and Tribolium castaneum from India and Australia, countries having similar pest species but widely differing in pest management practices. Sequencing analysis of the rph2 locus, dihydrolipoamide dehydrogenase (dld), identified two structurally equivalent variants, Proline49>Serine (P49S) in one R. dominica strain and P45S in three strains of T. castaneum from India. These variants of the DLD protein likely affect FAD cofactor interaction with the enzyme. A survey of insects from storage facilities across southern India revealed that the P45/49S variant is distributed throughout the region at very high frequencies, in up to 94% of R. dominica and 97% of T. castaneum in the state of Tamil Nadu. The abundance of the P45/49S variant in insect populations contrasted sharply with the evolutionary record in which the variant was absent from eukaryotic DLD sequences. This suggests that the variant is unlikely to provide a strong selective advantage in the absence of phosphine fumigation.

Non-target species interaction with sodium fluoroacetate (1080) meat bait for controlling feral pigs (Sus scrofa)

Fresh meat baits containing sodium fluoroacetate (1080) are widely used for controlling feral pigs in Queensland, but there is a potential poisoning risk to non-target species. This study investigated the non-target species interactions with meat bait by comparing the time until first approach, investigation, sample and consumption, and whether dying bait green would reduce interactions. A trial assessing species interactions with undyed bait was completed at Culgoa Floodplain National Park, Queensland. Meat baits were monitored for 79 consecutive days with camera traps. Of 40 baits, 100% were approached, 35% investigated (moved) and 25% sampled, and 25% consumed. Monitors approached (P < 0.05) and investigated (P < 0.05) the bait more rapidly than pigs or birds, but the median time until first sampling was not significantly different (P > 0.05), and did not consume any entire bait. A trial was conducted at Whetstone State Forest, southern Queensland, with green-dyed and undyed baits monitored for eight consecutive days with cameras. Of 60 baits, 92% were approached and also investigated by one or more non-target species. Most (85%) were sampled and 57% were consumed, with monitors having slightly more interaction with undyed baits than with green-dyed baits. Mean time until first approach and sample differed significantly between species groups (P = 0.038 and 0.007 respectively) with birds approaching sooner (P < 0.05) and monitors sampling later (P < 0.05) than other (unknown) species (P > 0.05). Undyed bait was sampled earlier (mean 2.19 days) than green-dyed bait (2.7 days) (P = 0.003). Data from the two trials demonstrate that many non-target species regularly visit and sample baits. The use of green-dyed baits may help reduce non-target uptake, but testing is required to determine the effect on attractiveness to feral pigs. Further research is recommended to quantify the benefits of potential strategies to reduce the non-target uptake of meat baits to help improve the availability of bait to feral pigs.

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.