Herbicide resistance costs: what are we actually measuring and why?

Despite the considerable research efforts invested over the years to measure the fitness costs of herbicide resistance, these have rarely been used to inform a predictive theory about the fate of resistance once the herbicide is discontinued. One reason for this may be the reductive focus on relative fitness of two genotypes as a single measure of differential performance. Although the extent of variation in relative fitness between resistant and susceptible plants has not been assessed consistently, we know enough about plant physiology and ecology not to reduce it to a single fixed value. Research must therefore consider carefully the relevance of the experimental environment, the life stage and the choice of metric when measuring fitness‐related traits. The reason most often given for measuring the cost of resistance, prediction of the impacts of management options on population dynamics, cannot be addressed using arbitrary components of fitness or a fixed value of relative fitness. To inform management options, the measurement of traits that capture the relevant processes and the main causes of their variation are required. With an emphasis on the benefit of field experiments measured over multiple time points and seasons, we highlight examples of studies that have made significant advances in this direction. © 2017 Society of Chemical Industry     

Genetic variation in Eucalyptus camaldulensis and E. tereticornis for early growth and susceptibility to the gall wasp Leptocybe invasa in China

The gall wasp Leptocybe invasa is a major insect pest on plantation Eucalyptus in many countries. Since appearing in China in 2007 it has had major impacts on commercial plantations—some commonly planted Eucalyptus varieties have proven particularly susceptible, including hybrids involving Eucalyptus camaldulensis and E. tereticornis parent species. Intra-specific variation within each species for L. invasa susceptibility was examined in two seed source and family trials in southwest of Guangdong. The E. camaldulensis trial included 101 seedlots representing five natural stand and six seed orchard sources which also represented three sub-specific taxa. The E. tereticornis trial included 143 seedlots representing 11 natural stand and four seed orchard sources, including breeding seed orchards in China. Both trials were assessed for susceptibility to L. invasa along with height at age 9 months. Sub-specific taxa within E. camaldulensis differed significantly (P < 0.01) in L. invasa susceptibility but not height or survival; subsp. acuta had the lowest average susceptibility and subsp. simulata and obtusa were of intermediate susceptibility whilst material of uncertain sub-specific taxa from India had the highest average susceptibility. In E. tereticornis regions of origin and seed sources within regions differed significantly (P < 0.01) for both L. invasa susceptibility and height; the region China (all somewhat improved sources) had both the best average height growth and lowest susceptibility whilst the region Australia (all natural stand sources) proved inferior to China for both average susceptibility and height. A strong significant correlation was found between seed source average L. invasa susceptibility and annual rainfall at seed source geographic origin in E. tereticornis (r = ?0.873; P < 0.01), implying that seedlots from higher rainfall environments are markedly less susceptible to L. invasa. The equivalent parameter in E. camaldulensis was also strong (r = ?0.730) though not significant, perhaps due to having only five data points available. Differences between families within seed sources for both L. invasa susceptibility and height growth were also highly significant (P < 0.01) with the former trait proving moderately to strongly heritable (h _i ²  = 0.54 ± 0.40 in E. camaldulensis; 0.52 ± 0.50 in E. tereticornis). Height had low to moderate heritability in both species (h _i ²  = 0.11 ± 0.15 and 0.26 ± 0.08 respectively). Tree height and L. invasa susceptibility showed a moderate negative (favourable) genetic correlation in E. camaldulensis (?0.33 ± 0.64) and a moderate to strong negative (favourable) genetic correlation in E. tereticornis (?0.47 ± 0.31). Corresponding phenotypic correlations, though significant, were somewhat weaker (?0.16 and ?0.29 respectively), indicating a trend for taller trees to have lower levels of L. invasa susceptibility.     

An appreciation of the contribution of Frank Stevenson to the advancement of studies of soil organic matter and humic substances

Purpose

The aims of this paper are to outline the state of knowledge with regard to the chemistry of soil organic matter (SOM) prior to 1950; then, to review and evaluate the contributions made by Frank Stevenson during Stevenson’s research period (1950–1994); and subsequently to outline advances that are being made in the modern era.

Progress in the Stevenson period

Frank Stevenson’s research career began in the middle of the twentieth century when a number of techniques of colloid chemistry were available to him, but relatively few of the recently developed instrumental techniques and other procedures of analytical organic chemistry that have enabled significant advances to be made in the chemistry and properties of SOM components.The contributions that Frank Stevenson has made to the chemistry of SOM and of humic substances (HSs) are an integral part of his book (first and second editions) Humus Chemistry: Genesis, Composition, Reactions. The validity of the terms humus and HSs are being questioned as legitimate terms that describe definable components, and SOM is being viewed as a ‘continuum of progressively decomposing organic compounds’. The legitimacy of isolating the organic matter components from their native soil environment is questioned. Those who pose such questions would do well to consider how progress could have been made in the vital life sciences areas of, for example, proteomics and genomics, without the isolation of the relevant cellular components. We recognise the importance of clear and rigorous definitions of HS components and stress the need to isolate these components from the SOM matrix as a prerequisite to the study of the composition, structure and reactivity of these components. We disagree with proposals or suggestions that do not recognise HSs as a scientific entity, and we feel sure that Frank Stevenson would have supported this stance. Various studies of SOM and of HSs have taken place over the centuries, but progress was slow because the tools required to study such complex systems were not available. Frank Stevenson’s research involved many areas of humic chemistry, and his major advances were in aspects of functionality and in the interactions of humic functional groups with metals and to a lesser extent with anthropogenic organic chemicals. His studies of nitrogen and of ammonia in relation to organic matter also had a very great impact.

Progress in the modern era

Frank Stevenson can be said to have provided the stimulation that enabled beginners and established scientists to obtain a good grasp of the fundamentals of SOM and the humic sciences. His scientific contributions have catalysed many of the significant advances that have been made in the field since he retired. In the final section, some of the advances that have been made using modern analytical techniques are addressed and some of the controversial topics that have recently arisen are discussed.

     

Migration strategies of brown trout (Salmo trutta) in a subarctic river system as revealed by stable isotope analysis

We estimated the proportions of anadromous and freshwater‐resident brown trout (Salmo trutta) in different parts of the subarctic River Näätämöjoki/Neidenelva system (Finland and Norway) using carbon, nitrogen and hydrogen stable isotope analyses of archived scales as identifiers of migration strategy. Our results showed that carbon stable isotope values were the best predictor of migration strategy. Most individuals fell into two clearly distinct groups representing anadromous (47%) or freshwater‐resident (42%) individuals, but some fish had intermediate carbon values suggesting repeated movement between freshwater and the sea. The proportion of anadromous individuals decreased steadily with distance from the sea forming a spatial continuum in migration strategies which is probably maintained by the combination of several factors such as divergent availability of food resources, variable migration costs and genetic differences. These within‐catchment differences in migration strategies should be taken into account in fisheries management practices.     

Characterization and selection for phosphorus deficiency tolerance in 99 spring wheat genotypes in Montana

Phosphorus (P) deficiency in soil is a common spring wheat production-limiting factor in Montana. In a pot experiment, three groups of spring wheat genotypes based on source (association mapping, 2016 off-station, and nested association mapping) were grown in 5 (P5) and 30 (P30) mg P kg^?1 potting mix conditions and screened for P deficiency tolerance. Plant height, tiller and head number, grain yields per pot measured were significantly different between P5 and P30 conditions (p?<?.05). Spring wheat genotypes: Unity, Peace, Vida, Reeder, CLTR 15134, ONeal and Fortuna yielded more grains, and equally took up more P in P5 conditions, revealing some degree of P deficiency tolerance. The genetic variability identified in this study for grain yields and P uptake could be used in wheat improvement programs for selecting genotypes with low P tolerance in P deficient soils as well as in organic spring wheat production.     

Eco‐efficiency as a strategy for optimizing the sustainability of pest management

Agricultural industrialization and the subsequent reliance on pesticides has resulted in numerous unintended consequences, such as impacts upon the environment and by extension human health. Eco‐efficiency is a strategy for sustainably increasing production, while simultaneously decreasing these externalities on ecological systems. Eco‐efficiency is defined as the ratio of production to environmental impacts. It has been widely adopted to improve chemical production, but we investigate the challenges of applying eco‐efficiency to pesticide use. Eco‐efficiency strategies include technological innovation, investment in research and development, improvement of business processes, and accounting for market forces. These components are often part of integrated pest management (IPM) systems that include alternatives to pesticides, but its implementation is often thwarted by commercial realities and technical challenges. We propose the creation and adoption of an eco‐efficiency index for pesticide use so that the broad benefits of eco‐efficient strategies such as IPM can be more readily quantified. We propose an index based upon the ratio of crop yield to a risk quotient (RQ) calculated from pesticide toxicity. Eco‐efficiency is an operational basis for optimizing pest management for sustainability. It naturally favors adoption of IPM and should be considered by regulators, researchers, and practitioners involved in pest management. © 2019 Society of Chemical Industry     

Whole farm implications on the application of variable rate technology to every cropped field

In the last 10 years precision agriculture has evolved and it is now possible to manage cropping inputs at the sub field scale. However, the expected return generated by these management practices varies with the amount and predictability of the spatial variation in crop yield across the field and may vary from field to field across the farm. We analysed the spatial variation of crop yield from 20 fields totalling 2832 ha from a 5200 ha farm in Western Australia at the field and the sub field scale to determine the economic value of introducing variable rate management (VRT) strategies to fields across the entire farm. In this case study, 6 out of 20 fields generated an additional economic payoff of AU$15/ha when managed with VRT over uniform management. Sensitivity analysis found that the starting levels of soil fertility were an important driver of the payoff for managing a field with VRT. If starting soil fertility was low and uniform across the field, then no fields generated an economic return of more than AU$7.00/ha when managed with VRT. Other factors, including commodity price, fertiliser price, amount of variation in crop yield within the field moderately increased the value of adopting VRT across fields within farm the value of VRT increased if fertiliser budgets were constrained, particularly if the yield distribution of the field was negatively skewed. While VRT does add value to many fields across the farm, the gains are small and the technology must be implemented cheaply for it to be viable.     

Growth,nutrient utilization,oxidative condition,and element composition of juvenile red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis> fed with fermented soybean meal and scallop by-product blend as fishmeal replacement

A feeding trial was conducted to evaluate the effect of fermented soybean meal and scallop by-product blend (3:2) (FP) on the performance of juvenile red sea bream. Five isocaloric diets were prepared by replacing 0% (FP0), 15% (FP15), 30% (FP30), 45% (FP45), and 60% (FP60) fishmeal (FM) protein with FP, respectively. Triplicate groups of fish (initial mean weight 2.83 g) were fed the test diets for 45 days in a flowthrough seawater system. The results demonstrated that growth rates of fish fed FP0, FP15, and FP30 were similar, and significantly higher (P < 0.05) than those of FP45 and FP60. Nutrient utilization was significantly lower in FP60, with no differences found among the other groups. Dietary heavy-metal contents were affected by inclusion of FP, impacting on whole-body heavy-metal contents. In terms of oxidative stress, fish fed the FP30 diet were in the best condition, since this fish group showed the least oxidative-stressed condition as well as the highest tolerance against oxidation. In conclusion, the approach of utilizing this fermented mixture is promising and it could replace at least 30% FM protein in red sea bream diet without negative effects on performance, body composition or health of fish.