Classical Biological Control for the Protection of Natural Ecosystems.

Of the 70 cases of classical biological control for the protection of nature found in our review, there were fewer projects against insect targets (21) than against invasive plants (49), in part, because many insect biological control projects were carried out against agricultural pests, while nearly all projects against plants targeted invasive plants in natural ecosystems. Of 21 insect projects, 81% (17) provided benefits to protection of biodiversity, while 48% (10) protected products harvested from natural systems, and 5% (1) preserved ecosystem services, with many projects contributing to more than one goal. In contrast, of the 49 projects against invasive plants, 98% (48) provided benefits to protection of biodiversity, while 47% (23) protected products, and 25% (12) preserved ecosystem services, again with many projects contributing to several goals. We classified projects into complete control (pest generally no longer important), partial control (control in some areas but not others), and "in progress," for projects in development for which outcomes do not yet exist. For insects, of the 21 projects discussed, 59% (13) achieved complete control of the target pest, 18% (4) provided partial control, and 41% (9) are still in progress. By comparison, of the 49 invasive plant projects considered, 27% (13) achieved complete control, while 33% (16) provided partial control, and 47% (24) are still in progress. For both categories of pests, some projects' success ratings were scored twice when results varied by region. We found approximately twice as many projects directed against invasive plants than insects and that protection of biodiversity was the most frequent benefit of both insect and plant projects. Ecosystem service protection was provided in the fewest cases by either insect or plant biological control agents, but was more likely to be provided by projects directed against invasive plants, likely because of the strong effects plants exert on landscapes. Rates of complete success appeared to be higher for insect than plant targets (59% vs 27%), perhaps because most often herbivores gradually weaken, rather than outright kill, their hosts, which is not the case for natural enemies directed against pest insects. For both insect and plant biological control, nearly half of all projects reviewed were listed as currently in progress, suggesting that the use of biological control for the protection of wildlands is currently very active.

Assessing for genetic and environmental effects on ruminant feed quality in barley ( Hordeum vulgare )

Grain samples from a combined intermediate and advanced stage barley breeding trial series, grown at two sites in two consecutive years were assessed for detailed grain quality and ruminant feed quality. The results indicated that there were significant genetic and environmental effects for “feed” traits as measured using grain hardness, acid detergent fibre (ADF), starch and in-sacco dry matter digestibility (ISDMD) assays. In addition, there was strong genotypic discrimination for the regressed feed performance traits, namely Net Energy (NE) and Average Daily Gain (ADG). There was considerable variation in genetic correlations for all traits based on variance from the cultivars used, sites or laboratory processing effects. There was a high level of heritability ranging from 89% to 88% for retention, 60% to 80% for protein and 56% to 68% for ADF. However, there were only low to moderate levels of heritability for the feed traits, with starch 30–39%, ISDMD 55–63%, ADF 56–68%, particle size 47–73%, 31–48% NE and ADG 44–51%. These results suggest that there were real differences in the feed performance of barleys and that selection for cattle feed quality is potentially a viable option for breeding programs.

Simulating the effects of saline and sodic subsoils on wheat crops growing on Vertosols

Soils with high levels of chloride and/or sodium in their subsurface layers are often referred to as having subsoil constraints (SSCs). There is growing evidence that SSCs affect wheat yields by increasing the lower limit of a crop's available soil water (CLL) and thus reducing the soil's plant-available water capacity (PAWC). This proposal was tested by simulation of 33 farmers' paddocks in south-western Queensland and north-western New South Wales. The simulated results accounted for 79% of observed variation in grain yield, with a root mean squared deviation (RMSD) of 0.50 t/ha. This result was as close as any achieved from sites without SSCs, thus providing strong support for the proposed mechanism that SSCs affect wheat yields by increasing the CLL and thus reducing the soil's PAWC. In order to reduce the need to measure CLL of every paddock or management zone, two additional approaches to simulating the effects of SSCs were tested. In the first approach the CLL of soils was predicted from the 0.3-0.5 m soil layer, which was taken as the reference CLL of a soil regardless of its level of SSCs, while the CLL values of soil layers below 0.5 m depth were calculated as a function of these soils' 0.3-0.5 m CLL values as well as of soil depth plus one of the SSC indices EC, Cl, ESP, or Na. The best estimates of subsoil CLL values were obtained when the effects of SSCs were described by an ESP-dependent function. In the second approach, depth-dependent CLL values were also derived from the CLL values of the 0.3-0.5 m soil layer. However, instead of using SSC indices to further modify CLL, the default values of the water-extraction coefficient (kl) of each depth layer were modified as a function of the SSC indices. The strength of this approach was evaluated on the basis of correlation of observed and simulated grain yields. In this approach the best estimates were obtained when the default kl values were multiplied by a Cl-determined function. The kl approach was also evaluated with respect to simulated soil moisture at anthesis and at grain maturity. Results using this approach were highly correlated with soil moisture results obtained from simulations based on the measured CLL values. This research provides strong evidence that the effects of SSCs on wheat yields are accounted for by the effects of these constraints on wheat CLL values. The study also produced two satisfactory methods for simulating the effects of SSCs on CLL and on grain yield. While Cl and ESP proved to be effective indices of SSCs, EC was not effective due to the confounding effect of the presence of gypsum in some of these soils. This study provides the tools necessary for investigating the effects of SSCs on wheat crop yields and natural resource management (NRM) issues such as runoff, recharge, and nutrient loss through simulation studies. It also facilitates investigation of suggested agronomic adaptations to SSCs.

Timing of infection of macadamia fruit by Pseudocercospora macadamiae and climatic effects on growth and spore germination.

Pseudocercospora macadamiae causes husk spot of macadamia. Husk spot control would be improved by verifying the stages in fruit development susceptible to infection, and determine some of the climatic conditions likely to lead to high disease pressure periods in the field. Our results showed that the percent conidia germination and growth of germ tubes and mycelia of P. macadamiae were greatest at 26 degrees C, with better conidia germination associated with high relative humidity and free water. The exposure of match-head-sized and pea-sized fruit stages to natural P. macadamiae inoculum in the field led to 2 5-fold increases in husk spot incidence, and up to 8.5-fold increases in premature abscission, compared with unexposed fruit. Exposure of fruit stages later than match-head-sized and pea-sized fruit generally caused no further increases in disease incidence or premature abscission. Climatic conditions were found to have a strong influence on the behaviour of P. macadamiae, the host, oil accumulation, and the subsequent impact of husk spot on premature abscission. Our findings suggest that fungicide application should target fruit at the match-head-sized stage of development in order to best reduce yield losses, particularly in seasons where oil accumulation in fruit is prolonged and climatic conditions are optimal for P. macadamiae.

Gene expression evidence for off-target effects caused by RNA interference-mediated gene silencing of Ubiquitin-63E in the cattle tick Rhipicephalus microplus.

Knowledge of cattle tick (Rhipicephalus (Boophilus) microplus; Acari: Ixodidae) molecular and cellular pathways has been hampered by the lack of an annotated genome. In addition, most of the tick expressed sequence tags (ESTs) available to date consist of similar to 50% unassigned sequences without predicted functions. The most common approach to address this has been the application of RNA interference (RNAi) methods to investigate genes and their pathways. This approach has been widely adopted in tick research despite minimal knowledge of the tick RNAi pathway and double-stranded RNA (dsRNA) uptake mechanisms. A strong knockdown phenotype of adult female ticks had previously been observed using a 594 bp dsRNA targeting the cattle tick homologue for the Drosophila Ubiquitin-63E gene leading to nil or deformed eggs. A NimbleGen cattle tick custom microarray based on the BmiGI.V2 database of R. microplus ESTs was used to evaluate the expression of mRNAs harvested from ticks treated with the tick Ubiquitin-63E 594 bp dsRNA compared with controls. A total of 144 ESTs including TC6372 (Ubiquitin-63E) were down-regulated with 136 ESTs up-regulated following treatment. The results obtained substantiated the knockdown phenotype with ESTs identified as being associated with ubiquitin proteolysis as well as oogenesis, embryogenesis, fatty acid synthesis and stress responses. A bioinformatics analysis was undertaken to predict off-target effects (OTE) resulting from the in silico dicing of the 594 bp Ubiquitin-63E dsRNA which identified 10 down-regulated ESTs (including TC6372) within the list of differentially expressed probes on the microarrays. Subsequent knockdown experiments utilising 196 and 109 bp dsRNAs, and a cocktail of short hairpin RNAs (shRNA) targeting Ubiquitin-63E, demonstrated similar phenotypes for the dsRNAs but nil effect following shRNA treatment. Quantitative reverse transcriptase PCR analysis confirmed differential expression of TC6372 and selected ESTs. Our study demonstrated the minimisation of predicted OTEs in the shorter dsRNA treatments (similar to 100-200 bp) and the usefulness of microarrays to study knockdown phenotypes.

Soil carbon stock in the tropical rangelands of Australia: Effects of soil type and grazing pressure, and determination of sampling requirement.

On-going, high-profile public debate about climate change has focussed attention on how to monitor the soil organic carbon stock (C(s)) of rangelands (savannas). Unfortunately, optimal sampling of the rangelands for baseline C(s) - the critical first step towards efficient monitoring - has received relatively little attention to date. Moreover, in the rangelands of tropical Australia relatively little is known about how C(s) is influenced by the practice of cattle grazing. To address these issues we used linear mixed models to: (i) unravel how grazing pressure (over a 12-year period) and soil type have affected C(s) and the stable carbon isotope ratio of soil organic carbon (delta(13)C) (a measure of the relative contributions of C(3) and C(4) vegetation to C(s)); (ii) examine the spatial covariation of C(s) and delta(13)C; and, (iii) explore the amount of soil sampling required to adequately determine baseline C(s). Modelling was done in the context of the material coordinate system for the soil profile, therefore the depths reported, while conventional, are only nominal. Linear mixed models revealed that soil type and grazing pressure interacted to influence C(s) to a depth of 0.3 m in the profile. At a depth of 0.5 m there was no effect of grazing on C(s), but the soil type effect on C(s) was significant. Soil type influenced delta(13)C to a soil depth of 0.5 m but there was no effect of grazing at any depth examined. The linear mixed model also revealed the strong negative correlation of C(s) with delta(13)C, particularly to a depth of 0.1 m in the soil profile. This suggested that increased C(s) at the study site was associated with increased input of C from C(3) trees and shrubs relative to the C(4) perennial grasses; as the latter form the bulk of the cattle diet, we contend that C sequestration may be negatively correlated with forage production. Our baseline C(s) sampling recommendation for cattle-grazing properties of the tropical rangelands of Australia is to: (i) divide the property into units of apparently uniform soil type and grazing management; (ii) use stratified simple random sampling to spread at least 25 soil sampling locations about each unit, with at least two samples collected per stratum. This will be adequate to accurately estimate baseline mean C(s) to within 20% of the true mean, to a nominal depth of 0.3 m in the profile.

Genetic effects and genetic relationships among shrunken (sh2) sweet corn lines and F1 hybrids

The objectives of this study were to quantify the components of genetic variance and the genetic effects, and to examine the genetic relationship of inbred lines extracted from various shrunken2(sh2) breeding populations. Ten diverse inbred lines developed from genetic background, were crossed in half diallel. Parents and their F1 hybrids were evaluated at three environments. The parents were genotyped using 20 polymorphic simple sequence repeats (SSR). Agronomic and quality traits were analysed by a mixed linear model according to additive-dominance genetic model. Genetic effects were estimated using an adjusted unbiased prediction method. Additive variance was more important than dominance variance in the expression of traits related to ear aspects (husk ratio and percentage of ear filled) and eating quality (flavour and total soluble solids). For agronomic traits, however, dominance variance was more important than additive variance. The additive genetic correlation between flavour and tenderness was strong (r = 0.84, P <0.01). Flavour, tenderness and kernel colour additive genetic effects were not correlated with yield related traits. Genetic distance (GD), estimated from SSR profiles on the basis of Jaccard's similarity coefficient varied from 0.10 to 0.77 with an average of 0.56. Cluster analysis classified parents according to their pedigree relationships. In most studied traits, F1 performance was not associated with GD.

Screening bacterial metabolites for inhibitory effects against Batrachochytrium dendrobatidis using a spectrophotometric assay

Certain bacteria present on frog skin can prevent infection by the pathogenic fungus Batrachochytrium dendrobatidis (Bd), conferring disease resistance. Previous studies have used agar-based in vitro challenge assays to screen bacteria for Bd-inhibitory activity and to identify candidates for bacterial supplementation trials. However, agar-based assays can be difficult to set up and to replicate reliably. To overcome these difficulties, we developed a semi-quantitative spectrophotometric challenge assay technique. Cell-free supernatants were prepared from filtered bacterial cultures and added to 96-well plates in replicated wells containing Bd zoospores suspended in tryptone-gelatin hydrolysate-lactose (TGhL) broth medium. Plates were then read daily on a spectrophotometer until positive controls reached maximum growth in order to determine growth curves for Bd. We tested the technique by screening skin bacteria from the Australian green-eyed tree frog Litoria serrata. Of bacteria tested, 31% showed some degree of Bd inhibition, while some may have promoted Bd growth, a previously unknown effect. Our cell-free supernatant challenge assay technique is an effective in vitro method for screening bacterial isolates for strong Bd-inhibitory activity. It contributes to the expanding field of bioaugmentation research, which could play a significant role in mitigating the effects of chytridiomycosis on amphibians around the world.

Spatial and temporal effects of grazing management and rainfall on the vertebrate fauna of a tropical savanna

Grazing by domestic livestock is one of the most widespread uses of the rangelands of Australia. There is limited information on the effects of grazing by domestic livestock on the vertebrate fauna of Australia and the establishment of a long-term grazing experiment in north-eastern Queensland at Wambiana provided an opportunity to attempt an examination of the changes in vertebrate fauna as a consequence of the manipulation of stocking rates. The aim was to identify what the relative effects of vegetation type, stocking rate and other landscape-scale environmental factors were on the patterns recorded. Sixteen 1-ha sites were established within three replicated treatments (moderate, heavy and variable stocking rates). The sites were sampled in the wet and dry seasons in 1999-2000 (T-0) and again in 2003-04 (T-1). All paddocks of the treatments were burnt in 1999. Average annual rainfall declined markedly between the two sampling periods, which made interpretation of the data difficult. A total of 127 species of vertebrate fauna comprising five amphibian, 83 bird, 27 reptile and 12 mammal species were recorded. There was strong separation in faunal composition from T-0 to T-1 although changes in mean compositional dissimilarity between the grazing stocking rate treatments were less well defined. There was a relative change in abundance of 24 bird, four mammal and five reptile species from T-0 to T-1. The generalised linear modelling identified that, in the T-1 data, there was significant variation in the abundance of 16 species explained by the grazing and vegetation factors. This study demonstrated that vertebrate fauna assemblage did change and that these changes were attributable to the interplay between the stocking rates, the vegetation types on the sites surveyed, the burning of the experimental paddocks and the decrease in rainfall over the course of the two surveys. It is recommended that the experiment is sampled again but that the focus should be on a rapid survey of abundant taxa (i.e. birds and reptiles) to allow an increase in the frequency of sampling and replication of the data. This would help to articulate more clearly the trajectory of vertebrate change due to the relative effects of stocking rates compared with wider landscape environmental changes. Given the increasing focus on pastoral development in northern Australia, any opportunity to incorporate the collection of data on biodiversity into grazing manipulation experiments should be taken for the assessment of the effects of land management on faunal species.

Grazing impacts on the susceptibility of rangelands to wind erosion: The effects of stocking rate, stocking strategy and land condition

An estimated 110 Mt of dust is eroded by wind from the Australian land surface each year, most of which originates from the arid and semi-arid rangelands. Livestock production is thought to increase the susceptibility of the rangelands to wind erosion by reducing vegetation cover and modifying surface soil stability. However, research is yet to quantify the impacts of grazing land management on the erodibility of the Australian rangelands, or determine how these impacts vary among land types and over time. We present a simulation analysis that links a pasture growth and animal production model (GRASP) to the Australian Land Erodibility Model (AUSLEM) to evaluate the impacts of stocking rate, stocking strategy and land condition on the erodibility of four land types in western Queensland, Australia. Our results show that declining land condition, over stocking, and using inflexible stocking strategies have potential to increase land erodibility and amplify accelerated soil erosion. However, land erodibility responses to grazing are complex and influenced by land type sensitivities to different grazing strategies and local climate characteristics. Our simulations show that land types which are more resilient to livestock grazing tend to be least susceptible to accelerated wind erosion. Increases in land erodibility are found to occur most often during climatic transitions when vegetation cover is most sensitive to grazing pressure. However, grazing effects are limited during extreme wet and dry periods when the influence of climate on vegetation cover is strongest. Our research provides the opportunity to estimate the effects of different land management practices across a range of land types, and provides a better understanding of the mechanisms of accelerated erosion resulting from pastoral activities. The approach could help further assessment of land erodibility at a broader scale notably if combined with wind erosion models.