Rex Stanton

Confirmation of Fasciola hepatica resistant to triclabendazole in naturally infected Australian beef and dairy cattle

Graphical abstract

Factors Affecting Silverleaf Nightshade (Solanum elaeagnifolium) Germination

Abstract Silverleaf nightshade is a widespread, deep-rooted, summer-growing perennial that significantly reduces production in Australian crop and pasture systems. It has an extensive root system, which competes both directly and indirectly with summer and winter pastures and crops through depletion of soil moisture and nutrients. Long-distance dispersal of seeds is an important mechanism for its spread and management. A range of experiments was conducted to determine the factors influencing seed production and seedbank dynamics. Seed production ranged from 1,814 to 2,945 m−2. Diurnally fluctuating temperatures of 25/15 C provided the optimal thermal conditions for germination, with germination not affected by light. Osmotic stress reduced germination, with no germination occurring at −1MPa. Germination was reduced to 5% at 160 mM NaCl, suggesting some salt sensitivity. Germination occurred over a pH range of 4 to 10, but declined with increasing acidity. Viability of buried seed declined to around 20% after 3 yr, with seed buried at 10 cm remaining the most viable. The prolonged seed persistence in the soil indicates a long-term control program is necessary for depleting the soil seedbank. Nomenclature: Silverleaf nightshade, Solanum elaeagnifolium Cav. SOLEL.

Sheep are potential vectors for the spread of canola (Brassica napus) seed

Sheep and other livestock are capable of ingesting seeds from weeds and desirable pasture species and excreting a percentage of viable seeds. As livestock are used to graze stubble paddocks after harvest, any crop seed shed before harvest or spilt during the harvesting process could also be ingested and subsequently excreted as viable seed. Knowledge of the rate of passage and viability of crop seed ingested by livestock is critical for good farm hygiene so that seeds are not inadvertently spread from the source paddock. Merino wethers were placed on a diet containing whole canola seed (10% total dry matter), and faeces were collected while canola was in the diet and for a further 6 days after canola was removed from the diet. Seed was found to pass through the wethers in less than 1 day, and reached a constant level after 2 days. When canola seed was removed from the diet, the majority of seed was passed during the first 2 days, but seed was excreted for up to 5 days. Seed germinability was reduced after 1 day, and further still after 2 days, but did not significantly decrease after this. While sheep are capable of excreting germinable canola seeds for up to 5 days after they were last included in the diet, use of a 7-10-day holding period will ensure that canola is not inadvertently spread beyond the grazed stubble paddock.

Phytotoxic Activity and Chemical Composition of Aqueous Volatile Fractions from Eucalyptus Species

The essential oils from four Eucalyptus species (E. spathulata, E. salubris, E. brockwayii and E. dundasii) have been previously confirmed to have stronger inhibitory effects on germination and seedling growth of silverleaf nightshade (Solanum elaeagnifolium Cav.). The aqueous volatile fractions (AVFs) were the water soluble volatile fractions produced together with the essential oils (water insoluble fractions) during the steam distillation process. The aim of this study was to further assess the phytotoxicity of AVFs from the four Eucalyptus species and their chemical composition. The fresh leaves of the four Eucalyptus species were used for the extraction of AVFs. The AVFs were tested for their phytotoxic effects on the perennial weed, silverleaf nightshade under laboratory conditions. The chemical compositions of the AVFs were determined by gas chromatograph–mass spectrometry (GC-MS). Our results showed that the AVFs had strong inhibition on the germination and seedling growth of silverleaf nightshade. The inhibition index increased with the increasing concentrations of AVFs. The inhibitory effects of the AVFs varied between different Eucalyptus species. The AVF from E. salubris demonstrated the highest inhibitory activity on the weed tested, with complete inhibition on germination and seedling growth at a concentration of 75%. The GC-MS analysis revealed that 1,8-cineole, isopentyl isovalerate, isomenthol, pinocarvone, trans-pinocarveol, alpha-terpineol and globulol were the main compounds in the AVFs. These results indicated that all AVFs tested had differential inhibition on the germination and seedling growth of silverleaf nightshade, which could be due to the joint effects of compounds present in the AVFs as these compounds were present in different quantities and ratio between Eucalyptus species.

Intrusive trichome bases in the leaves of silverleaf nightshade (Solanum elaeagnifolium; Solanaceae) do not facilitate fluorescent tracer uptake.

PREMISE OF THE STUDY Solanum elaeagnifolium (silverleaf nightshade), having originated in the Americas, is now a serious summer-growing, perennial weed in many countries, including Australia. Most surfaces of the plants have a dense covering of trichomes, giving them a silvery-white appearance, hence the common name. We aimed to identify structural and functional properties of its leaves, especially the trichomes, that may affect the uptake of foliar-applied tracer dyes. METHODS The structure of leaves of Solanum elaeagnifolium was examined by light and scanning electron microscopy. The potential for transport of materials between trichomes and veins was studied with symplastic (carboxyfluorescein diacetate) and apoplastic (lucifer yellow) tracer dyes. KEY RESULTS Mature leaves had a dense covering of complex, stellate trichomes on both surfaces, particularly the abaxial. The basal cells of Solanum elaeagnifolium trichomes penetrated into the underlying palisade mesophyll layers. The innermost lobes of these basal cells sometimes contacted the bundle sheath of the veins, but were not observed to directly contact the xylem or phloem. We found that neither symplastic nor apoplastic dyes were transferred between the basal cells of the trichomes and the vascular tissues. The trichome layer repelled water-based tracer dyes, while one of four adjuvants tested facilitated entry of both symplastic and apoplastic dyes. CONCLUSIONS Our results did not support a transport function for the trichomes. The trichomes may protect the mesophytic leaves from invertebrate herbivory, while also probably decreasing radiation absorbed resulting in cooler leaves in this summer-growing species.

Development of SSR Markers for Genetic Analysis of Silverleaf Nightshade (Solanum elaeagnifolium) and Related Species

Silverleaf nightshade (2n = 2x = 24) is a serious weed in the Solanaceae, for which no specific molecular markers are currently available. In order to investigate the extent and distribution of genetic diversity among accessions of silverleaf nightshade, we developed 23 simple sequence repeat (SSR) markers from publicly available nucleotide and EST databases for silverleaf nightshade. Eleven of them were single-locus polymorphic markers. The number of alleles among these loci ranged from 2 to 4. The observed and expected heterozygosity ranged from 0 to 0.97 and 0.07 to 0.64, respectively. Fourteen SSR markers enabled to amplify alleles in morphologically similar species quena. These results proved that the SSR markers that we developed could be useful for (1) determining genetic diversity and structure among natural populations of silverleaf nightshade and (2) identifying silverleaf nightshade and quena ecotypes. This is the first set of species-specific SSR markers identified in silverleaf nightshade, which could contribute to the better understanding of genetic diversity of silverleaf nightshade and related species.

Annual ryegrass (Lolium rigidum) seed survival and digestibility in cattle and sheep

A trial was conducted to investigate the survival and digestibility of annual ryegrass (ARG) seed (Lolium rigidum L.) eaten by sheep and cattle. Sheep (n= 8) and cattle (n = 8) were fed a basal diet containing 1:1 lucerne chaff:oaten chaff with (ARG) or without (control) the inclusion of 20% total dry matter of annual ryegrass seed in a changeover design. Intake was restricted to 17 g/kg liveweight. Digestibility of the control diet was lower (P<0.01) for sheep than cattle. Annual ryegrass seed was present (P<0.01) in the faeces of both sheep and cattle within 24 h of first ingestion. Some 10.8 and 32.8% of seed ingested was excreted by sheep and cattle respectively, with 3.9% (sheep) and 11.9% (cattle) remaining germinable. Annual ryegrass seed continued to be excreted by both sheep and cattle up to 5 days after removal from the diet. Dry matter digestibility of the annual ryegrass diet was 53% in cattle.