Dynamics of plant populations in Heteropogon contortus (black speargrass) pastures on a granite landscape in southern Queensland. 3. Dynamics of Aristida spp. populations

The dynamics of the unpalatable Aristida spp. (wiregrasses) were measured in a subset of treatments contained within an extensive grazing study conducted between 1990 and 1996 in H. contortus pasture in southern Queensland. This paper reports the results from these treatments which included 2 land classes (silver-leaved and narrowleaved ironbark), 3 stocking rates (0.3, 0.6 and 0.9 beasts/ha) in both native pasture and legumeoversown native pasture, all in the absence of fire. Changes in plant density and basal area of Aristida spp. reflected differences in both the survival and size of existing plants together with a large seedling recruitment in 1991. Two different taxa of Aristida spp. were distinguished; however, there were no clear differences in the response of these 2 taxa to the treatments. Grazing had the greatest impact on population dynamics through reducing basal area as stocking rate increased. Neither landscape position nor legume oversowing had a major impact on Aristida spp. The results suggest that populations of Aristida spp. will be highest under light grazing and that seedling recruitment may be episodic

Dynamics of plant populations in Heteropogon contortus (black speargrass) pastures on a granite landscape in southern Queensland. 4. The effects of burning on H.contortus and Aristida spp. populations

This paper reports an experiment undertaken to examine the impact of burning in spring together with reduced grazing pressure on the dynamics of H. contortus and Aristida spp. In H. contortus pasture in south-eastern Queensland. The overall results indicate that spring burning in combination with reduced grazing pressure had no marked effect on the density of either grass species. This was attributed to 2 factors. Firstly, extreme drought conditions restricted any increase in H. contortus seedling establishment despite the presence of an adequate soil seed bank prior to summer; and secondly, some differences occurred in the response to fire of the diverse taxonomic groupings in the species of Aristida spp. present at the study site. This study concluded that it is necessary to identify appropriate taxonomic units within the Aristida genus and that, where appropriate, burning in spring to manage pasture composition should be conducted under favorable rainfall conditions using seasonal forecasting indicators such as the Southern Oscillation Index

Optically active gossypol as a circular dichroism probe of interactions with serum albumins

The (+)-enantiomer of the polyphenolic binaphthyl gossypol, has been shown to be a useful CD probe of interactions with human and bovine serum albumin. (+)-Gossypol binds to albumin with same affinity as recemic (±)-gossypol, as shown by fluorescence quenching, and also displaces bilirubin from its albumin binding site. The CD characteristics of bound gossypol are different in the case of the two proteins.

Field evaluation of a plant activator, captan, chlorothalonil, copper hydroxide, iprodione, mancozeb and strobilurins for the control of citrus brown spot of mandarin

Brown spot (caused by Alternaria alternata) is a major disease of citrus in subtropical areas of Australia. A number of chemicals, the strobilurins azoxystrobin, trifloxystrobin, pyraclostrobin and methoxycrylate, a plant activator (acibenzolar), copper hydroxide, mancozeb, captan, iprodione and chlorothalonil/pyrimthanil were tested in the field for its control. Over three seasons, trees in a commercial orchard received 16, 14 and 7 fungicide sprays, respectively, commencing at flowering in the first season, and petal fall in the later seasons. In all experiments, the strobilurins used alone, or incorporated with copper and mancozeb, were as effective as, or better than the industry standard of copper and mancozeb alone. The only exception was trifloxystrobin, which when used alone was less effective than the industry standard. Acibenzolar used alone was ineffective. Applying a mixture of azoxystrobin and acibenzolar was found to reduce the incidence of brown spot compared with applying azoxystrobin alone but, in either case, disease levels were not found to be significantly different to the industry standard. Captan, iprodione and chlorothalonil/pyrimthanil were as effective as the industry standard. The incidence and severity of rind damage were significantly lowest in the azoxystrobin, methoxycrylate, iprodione and chlorothalonil/pyrimthanil treatments. Medium and high rates of trifloxystrobin (0.07 g/L, 0 .15 g/L) and pyraclostrobin (0.8 g/L, 1.2 g/L) applied alone were the only treatments found to be IPM-incompatible as shown by the elevated level of scale infection on fruit.

Breastmilk-saliva interactions boost innate immunity by regulating the oral microbiome in early infancy

Introduction Xanthine oxidase (XO) is distributed in mammals largely in the liver and small intestine, but also is highly active in milk where it generates hydrogen peroxide (H2O2). Adult human saliva is low in hypoxanthine and xanthine, the substrates of XO, and high in the lactoperoxidase substrate thiocyanate, but saliva of neonates has not been examined. Results Median concentrations of hypoxanthine and xanthine in neonatal saliva (27 and 19 μM respectively) were ten-fold higher than in adult saliva (2.1 and 1.7 μM). Fresh breastmilk contained 27.3±12.2 μM H2O2 but mixing baby saliva with breastmilk additionally generated >40 μM H2O2, sufficient to inhibit growth of the opportunistic pathogens Staphylococcus aureus and Salmonella spp. Oral peroxidase activity in neonatal saliva was variable but low (median 7 U/L, range 2–449) compared to adults (620 U/L, 48–1348), while peroxidase substrate thiocyanate in neonatal saliva was surprisingly high. Baby but not adult saliva also contained nucleosides and nucleobases that encouraged growth of the commensal bacteria Lactobacillus, but inhibited opportunistic pathogens; these nucleosides/bases may also promote growth of immature gut cells. Transition from neonatal to adult saliva pattern occurred during the weaning period. A survey of saliva from domesticated mammals revealed wide variation in nucleoside/base patterns. Discussion and Conclusion During breast-feeding, baby saliva reacts with breastmilk to produce reactive oxygen species, while simultaneously providing growth-promoting nucleotide precursors. Milk thus plays more than a simply nutritional role in mammals, interacting with infant saliva to produce a potent combination of stimulatory and inhibitory metabolites that regulate early oral–and hence gut–microbiota. Consequently, milk-saliva mixing appears to represent unique biochemical synergism which boosts early innate immunity.

Spectral and thermal sensing for nitrogen and water status in rainfed and irrigated wheat environments

Variable-rate technologies and site-specific crop nutrient management require real-time spatial information about the potential for response to in-season crop management interventions. Thermal and spectral properties of canopies can provide relevant information for non-destructive measurement of crop water and nitrogen stresses. In previous studies, foliage temperature was successfully estimated from canopy-scale (mixed foliage and soil) temperatures and the multispectral Canopy Chlorophyll Content Index (CCCI) was effective in measuring canopy-scale N status in rainfed wheat (Triticum aestivum L.) systems in Horsham, Victoria, Australia. In the present study, results showed that under irrigated wheat systems in Maricopa, Arizona, USA, the theoretical derivation of foliage temperature unmixing produced relationships similar to those in Horsham. Derivation of the CCCI led to an r2 relationship with chlorophyll a of 0.53 after Zadoks stage 43. This was later than the relationship (r2 = 0.68) developed for Horsham after Zadoks stage 33 but early enough to be used for potential mid-season N fertilizer recommendations. Additionally, ground-based hyperspectral data estimated plant N (g kg)1) in Horsham with an r2 = 0.86 but was confounded by water supply and N interactions. By combining canopy thermal and spectral properties, varying water and N status can potentially be identified eventually permitting targeted N applications to those parts of a field where N can be used most efficiently by the crop.

Stabilization of the Alleged 'Bishomoaromatic' Bicyclo[3.2.l]octa-2,6-dienyl Anion by Counterion Interactions and by Hyperconjugation

Hyperconjugation and inductive effects, rather than homoaromaticity, are responsible for the stabilization of the title anion in the gas phase; interaction of the double bond with the Li+ gegenion in the endo geometry contributes additionally in solution.

Effect of inter-edge Coulomb interactions on transport through a point contact in nu=5/2 quantum Hall state

We study transport across a point contact separating two line junctions in a nu = 5/2 quantum Hall system. We analyze the effect of inter-edge Coulomb interactions between the chiral bosonic edge modes of the half-filled Landau level (assuming a Pfaffian wave function for the half-filled state) and of the two fully filled Landau levels. In the presence of inter-edge Coulomb interactions between all the six edges participating in the line junction, we show that the stable fixed point corresponds to a point contact that is neither fully opaque nor fully transparent. Remarkably, this fixed point represents a situation where the half-filled level is fully transmitting, while the two filled levels are completely backscattered; hence the fixed point Hall conductance is given by G(H) = 1/2e(2)/h. We predict the non-universal temperature power laws by which the system approaches the stable fixed point from the two unstable fixed points corresponding to the fully connected case (G(H) = 5/2e(2)/h) and the fully disconnected case (G(H) = 0).

Comparative growth and pathogenicity of geographical isolates of Sclerotinia sclerotiorum on lentil genotypes

Isolates of Sclerotinia sclerotiorum were collected from infected lentil plants from 2 agro-ecological zones of Syria and used to study their comparative growth on culture media and pathogenicity on different lentil genotypes. The growth studies were carried out on Potato Dextrose Agar (PDA) growth media under laboratory conditions. Mycelial radial growth and sclerotial production were the parameters used to compare the isolates. Pathogenicity studies were carried out with selected isolates on 10 lentil genotypes, infected as detached shoots and as whole potted-plants in the plastic house. The isolates showed considerable variation in cultural characteristics through mycelial growth, mycelial pigmentation and sclerotial production in the media plates. There were significant differences in the growth and sclerotial production of most of the isolates, but no apparent correlation between mycelial growth and sclerotial production among the isolates. Genotype by isolate interactions was significant for the isolates tested for pathogenicity. These interactions, however, appeared to be caused by differences in virulence of the isolates and did not suggest the occurrence of distinct pathogenic races of the pathogen isolates.

Host-delivered RNAi: An effective strategy to silence genes in plant parasitic nematodes

Root-knot nematodes (Meloidogyne spp.) are obligate, sedentary endoparasites that infect many plant species causing large economic losses worldwide. Available nematicides are being banned due to their toxicity or ozone-depleting properties and alternative control strategies are urgently required. We have produced transgenic tobacco (Nicotiana tabacum) plants expressing different dsRNA hairpin structures targeting a root-knot nematode (Meloidogyne javanica) putative transcription factor, MjTis11. We provide evidence that MjTis11 was consistently silenced in nematodes feeding on the roots of transgenic plants. The observed silencing was specific for MjTis11, with other sequence-unrelated genes being unaffected in the nematodes. Those transgenic plants able to induce silencing of MjTis11, also showed the presence of small interfering RNAs. Even though down-regulation of MjTis11 did not result in a lethal phenotype, this study demonstrates the feasibility of silencing root-knot nematode genes by expressing dsRNA in the host plant. Host-delivered RNA interference-triggered (HD-RNAi) silencing of parasite genes provides a novel disease resistance strategy with wide biotechnological applications. The potential of HD-RNAi is not restricted to parasitic nematodes but could be adapted to control other plant-feeding pests.

Effect of microwave radiation on seed mortality of rubber vine (Cryptostegia grandiflora R.Br.), parthenium (Parthenium hysterophorous L.) and bellyache bush (Jatropha gossypiifolia L.)

A trial was undertaken to evaluate the effect of microwaves on seed mortality of three weed species. Seeds of rubber vine (Cryptostegia grandiflora R.Br.), parthenium (Parthenium hysterophorous L.) and bellyache bush (Jatropha gossypiifolia L.) were buried at six depths (0, 2.5, 5, 10, 20 and 40 cm) in coarse sand maintained at one of two moisture levels, oven dry or wet (field capacity), and then subjected to one of five microwave radiation durations of (0, 2, 4, 8 and 16 min). Significant interactions between soil moisture level, microwave radiation duration, seed burial depth and species were detected for mortality of seeds of all three species. Maximum seed mortality of rubber vine (88%), parthenium (67%) and bellyache bush (94%) occurred in wet soil irradiated for 16 min. Maximum seed mortality of rubber vine and bellyache bush seeds occurred in seeds buried at 2.5 cm depth whereas that of parthenium occurred in seeds buried at 10 cm depth. Maximum soil temperatures of 114.1 and 87.5°C in dry and wet soil respectively occurred at 2.5 cm depth following 16 min irradiation. Irrespective of the greater soil temperatures recorded in dry soil, irradiating seeds in wet soil generally increased seed mortality 2.9-fold compared with dry soil. Moisture content of wet soil averaged 5.7% compared with 0.1% for dry soil. Results suggest that microwave radiation has the potential to kill seeds located in the soil seed bank. However, many factors, including weed species susceptibility, determine the effectiveness of microwave radiation on buried seeds. Microwave radiation may be an alternative to conventional methods at rapidly depleting soil seed banks in the field, particularly in relatively wet soils that contain long lived weed seeds.

Growth and species interactions of Eucalyptus pellita in a mixed and monoculture plantation in the humid tropics of north Queensland

This study investigated whether mixed-species designs can increase the growth of a tropical eucalypt when compared to monocultures. Monocultures of Eucalyptus pellita (E) and Acacia peregrina (A) and mixtures in various proportions (75E:25A, 50E:50A, 25E:75A) were planted in a replacement series design on the Atherton Tablelands of north Queensland, Australia. High mortality in the establishment phase due to repeated damage by tropical cyclones altered the trial design. Effects of experimental designs on tree growth were estimated using a linear mixed-effects model with restricted maximum likelihood analysis (REML). Volume growth of individual eucalypt trees were positively affected by the presence of acacia trees at age 5 years and this effect generally increased with time up to age 10 years. However, the stand volume and basal area increased with increasing proportions of E. pellita, due to its larger individual tree size. Conventional analysis did not offer convincing support for mixed-species designs. Preliminary individual-based modelling using a modified Hegyi competition index offered a solution and an equation that indicates acacias have positive ecological interactions (facilitation or competitive reduction) and definitely do not cause competition like a eucalypt. These results suggest that significantly increased in growth rates could be achieved with mixed-species designs. This statistical methodology could enable a better understanding of species interactions in similarly altered experiments, or undesigned mixed-species plantations.

Selecting for increased barley grain size

In this study, 120–144 commercial varieties and breeding lines were assessed for grain size attributes including plump grain (>2.8 mm) and retention (>2.5 mm+>2.8 mm). Grain samples were produced from replicated trials at 25 sites across four years. Climatic conditions varied between years as well as between sites. Several of the trial sites were irrigated while the remaining were produced under dryland conditions. A number of the dryland sites suffered severe drought stress. The grain size data was analysed for genetic (G), environmental (E) and genotype by environment (G×E) interactions. All analyses included maturity as a covariate. The genetic effect on grain size was greater than environmental or maturity effects despite some sites suffering terminal moisture stress. The model was used to calculate heritability values for each site used in the study. These values ranged from 89 to 98% for plump grain and 88 to 96% for retention. The results demonstrated that removing the sources of non-heritable variation, such as maturity and field effects, can improve genetic estimates of the retention and plump grain fractions. By partitioning all variance components, and thereby having more robust estimates of genetic differences, plant breeders can have greater confidence in selecting barley genotypes which maintain large, stable grain size across a range of environments.

Short-term responses of leaf growth rate to water deficit scale up to whole-plant and crop levels: An integrated modelling approach in maize.

Physiological and genetic studies of leaf growth often focus on short-term responses, leaving a gap to whole-plant models that predict biomass accumulation, transpiration and yield at crop scale. To bridge this gap, we developed a model that combines an existing model of leaf 6 expansion in response to short-term environmental variations with a model coordinating the development of all leaves of a plant. The latter was based on: (1) rates of leaf initiation, appearance and end of elongation measured in field experiments; and (2) the hypothesis of an independence of the growth between leaves. The resulting whole-plant leaf model was integrated into the generic crop model APSIM which provided dynamic feedback of environmental conditions to the leaf model and allowed simulation of crop growth at canopy level. The model was tested in 12 field situations with contrasting temperature, evaporative demand and soil water status. In observed and simulated data, high evaporative demand reduced leaf area at the whole-plant level, and short water deficits affected only leaves developing during the stress, either visible or still hidden in the whorl. The model adequately simulated whole-plant profiles of leaf area with a single set of parameters that applied to the same hybrid in all experiments. It was also suitable to predict biomass accumulation and yield of a similar hybrid grown in different conditions. This model extends to field conditions existing knowledge of the environmental controls of leaf elongation, and can be used to simulate how their genetic controls flow through to yield.

Phylogenetic considerations for predicting the host range of Ustilago sporoboli-indici, a potential biological control agent for Sporobolus species in Australia

The ribosomal DNA internal transcribed spacer region was amplified and sequenced from a selection of specimens of the Sporobolus smut Ustilago sporoboli-indici. Phylogenetic comparison with other Ustilago and Sporisorium species revealed strong support for an evolutionary radiation of Ustilago species infecting the Chloridoideae and Pooideae, of which U. sporoboli-indici forms a major lineage. Comparisons are made with other groups of plant pathogenic fungi, and it is concluded that phylogenetic analyses of potential biocontrol agents are useful for identifying pathogens that are derived from evolutionary lineages that parasitize a wide range of unrelated plants. Such pathogens are less desirable as biocontrol agents as they may have a greater likelihood of infecting plants outside their normal host ranges.