Are Pesticides Suitable Model Substances for the Evaluation of Industrial Chemicals in the Environment?

Definitions are given for the terms «environmental chemical>> and «undue persistence>>. A suggested model for the general evaluation of environmental chemicals is a balanced combination of the evaluations of environmental radioactivity and of pesticides. The classification of environmental chemicals should be based on chemical structures only, independent of use patterns. For the evaluation of any chemical, the knowledge of its total production and of the quantitative use pattern is indispensable.     

The dynamics of Phytophthora infestans populations in the major potato-growing regions of Asia – A review

Asia is now the largest potato-producing region of the world and late blight, caused by Phytophthora infestans, is the most important pathogen limiting production. This review documents, in both the historical and the current context, the population structure of P. infestans in the major areas of potato production in Asia. Information from diverse sources regarding the stated or inferred clonal pathogen lineages present, population changes, and possible migration routes of the pathogen into the countries of this region have been reviewed to aid researchers and those involved in managing late blight in Asia. The single most important factor for population change and resultant epidemics in this region has been found to be migration of pathogen genotypes from Europe and the Americas. Reducing the impact of such migration in the future will necessitate putting in place improved phytosanitary measures. To achieve this, data sharing using global networks such as AsiaBlight and EuroBlight is imperative.     

Quality assurance in plant health diagnostics – the experience of the Danish Plant Directorate

Worldwide, there is increasing focus on implementation of Quality Assurance systems (QA-systems) in plant health diagnostic laboratories. Several laboratories are in the development or implementation phase and some laboratories have gained accreditation through approval by national accreditation boards. To initiate the process of developing and implementing QA-systems, management and staff need a strong motivation factor. First, because it is a time-consuming and demanding process to go through. Second, because plant health testing does not fit very well into the QA-systems that traditionally were developed for chemical or physical testing laboratories. External pressure is often the only way to generate this motivation factor amongst staff and management to initiate the development of QA-systems. The principal motivation factor in our laboratory was a national requirement that official testing laboratories should implement QA-systems. At the Danish Plant Directorate (PD) we have gained experiences with accreditation of plant health diagnostic methods during the past 5 years. The focus of this paper is a presentation of the consequences and the practical approach to comply with the requirements of ISO 17025 in our plant health diagnostic laboratory. This includes the themes: staff competence and responsibilities, documentation and traceability, and continuous assessment and improvement of the QA-system.     

Life at the edge – the cytology and physiology of the biotroph to necrotroph transition in Hymenoscyphus fraxineus during lesion formation in ash

The progress of colonization of ash stems from ascospore inocula of Hymenoscyphus fraxineus was examined by light and electron microscopy. The main aim of the study was to characterize the cytology of the biotroph to necrotroph transition during lesion formation. Following direct penetration into epidermal cells, the fungus produced intracellular hyphae that invaded up to five cells before plant cells died. A lack of close attachment between the hyphal cell wall and plant cell membrane was revealed by plasmolysis of epidermal cells. Plant cells died at the centre of the infection but hyphae at the edge were typically found in living plant cells even around large lesions. During biotrophic invasion, the cytoplasm of penetrated plant cells showed very little response despite the plant cell membrane being in direct contact with the fungal cell wall. Before plant cell death, dark staining of the cytoplasm and proliferation of small vesicles was noted, but organelles retained normal ultrastructure. Dead plant cells contained dark brown, osmiophilic droplets. Penetration between epidermal or collenchyma cells was usually targeted to shared pits and involved constriction of hyphae. The transition to necrotrophy was not associated with a clear change in hyphal morphology. Biotrophic intracellular hyphae contained dense cytoplasm but hyphae in dead plant cells were more vacuolated. Remarkably little plant cell wall degradation was observed despite the fungus penetrating up to 18 cells deep into stem tissue. Features of the development of the ash dieback fungus are compared with other hemibiotrophic pathogens.     

Virulence variation of cucurbit powdery mildews in the Czech Republic – population approach

Kosman diversity models were applied to analyses of virulence (disease reaction patterns) variation of 115 isolates of two cucurbit powdery mildew (CPM) species, Golovinomyces orontii (Go) and Podosphaera xanthii (Px), collected in the Czech Republic from 2010 through 2012. Diversity within and distances between Go and Px populations and each other in a spatio-temporal context and with regard to original host plant species were analyzed based on virulence patterns of individual isolates on a set of 21 melon (Cucumis melo L.) race differential genotypes. Significant differentiation among the Go and Px pathogen populations was revealed, and the results clearly demonstrate and confirm that the set of differential C. melo genotypes is well composed because of high differentiation capacity. Differentiation of pathogens among years was significant for both species. No significant difference between Go isolates from different host plant species was established due to high variability among Go isolates, but there was significant host-specific differentiation among Px isolates. Differentiation of pathogens among regions was not detected. These results revealed high virulence variation in isolates of Go and Px, and their spatio-temporal fluctuations. High diversity in virulence of Go isolates supports the treatment of Go as a complex of different (sub)species with distinct virulence factors. Similar relationships of selected Go isolates in a UPGMA dendrogram in a previously reported multigene phylogenetic tree support the logic and suitability of the Kosman assignment based approach to population studies of organisms with asexual or mixed modes of reproduction. The approach applied in this study provides a complex view of virulence structures of powdery mildew populations, and when combined with race determination and denomination on melon, it may serve as a base to understandvirulence variation of these CPM species from a spatio-temporal viewpoint.     

A new haplotype of “Candidatus Liberibacter solanacearum” identified in the Mediterranean region

“Candidatus Liberibacter solanacearum”, a phloem-limited and Gram-negative bacterium that is spread from infected to healthy plants by psyllid insect vectors, is an economically important pathogen of solanaceous and carrot crops in the Americas, New Zealand and Europe. Three haplotypes of “Ca. L. solanacearum” have previously been described, two (LsoA and LsoB) in relation to solanaceous crops in the Americas and New Zealand and the third (LsoC) to carrots in Finland. Herein, we describe a fourth haplotype of this ‘Candidatus Liberibacter’ species (LsoD), also associated with carrots, but from Spain and the Canary Islands and vectored by the psyllid Bactericera trigonica. In addition, LsoC was confirmed in carrot and psyllid samples recently collected from Sweden and Norway. Phylogenetic analysis of the 16S rRNA gene suggests that two of the haplotypes, one in the Americas and the other in northern Europe are closer to each other in spite of a large geographic separation and host differences. Furthermore, during this study, potatoes with symptoms of zebra chip disease recently observed in potato crops in Idaho, Oregon and Washington states were analyzed for haplotype and were found to be positive for LsoA. This liberibacter haplotype was found in psyllids associated with the diseased potato crops as well. This finding contrasts with an earlier report of LsoB from psyllids in Washington which came from a laboratory colony originally collected in Texas.     

Components of maritime pine susceptibility to twisting rust – A path coefficient analysis

Data collected in a three-year field experiment on infection and damage by Melampsora pinitorqua on maritime pines showing contrasting growth were analysed by means of path analysis. The severity of infection in 2 year-old pines could be mainly explained by the amount of susceptible tissues (elongating shoots). In contrast, two years later, intrinsic susceptibility, i.e. expressed after inoculation, was shown to have the most important direct effect on the amount of infection. Intrinsic susceptibility could be satisfactorily assessed by artificial inoculations on excised shoots under controlled conditions. Shoot potassium and phosphorous contents were shown to have marked positive effects on susceptibility. The hypothesis of an age effect on the relative importance of different resistance mechanisms, i.e. avoidance and active resistance, in maritime pine interaction with twisting rust is discussed.     

Do we have the tools to manage resistance in the future?

Pesticide resistance is a major factor affecting world food and fibre production, but that has been contained so far by the availability of diverse modes of action. Overcoming resistance by switching to a new mode of action is a concept easily grasped by growers but threatened by losses through resistance and new registration requirements. Opportunities for innovation and development of a diversity of novel modes of action exist through harnessing recent advances, fundamental to all eukaryotes and largely funded for medical rather than agricultural objectives, in understanding cell biology and development. The cystoskeleton, cell wall synthesis, signal transduction and RNAi are discussed as examples where new targets are now exposed. However, new modes of action will be delivered not only by sprayer or seed treatment but also through transgenic crops, although these still need to be transferred from experiment to practice. Improvements in modelling protein structures and target-site changes, supplemented by rapid diagnostics to detect resistance early, will improve resistance risk management and integrate chemical, biopesticide, transgenic and conventional breeding around the concept of diversity in modes of action. However, before agronomy can translate this into practical antiresistance strategies, there is a need to direct more resources to the biochemistry and cell biology of pests, diseases and weeds to translate these new discoveries into key tools needed to manage resistance in the future.     

Mucor Species in Orchard Soil – Population Dynamics and Pathogenicity on Pear Fruit

Strains of Mucor piriformis were isolated from orchard soils and from packinghouse dump-tank waters. Pathogen propagules were not found in fruit sample washings. M. piriformis was the most prevalent of the Mucor isolates, only one of 67 isolates was a different Mucor sp., possibly M. racemosus. The population of the pathogen propagules fluctuated in an annual cyclic pattern, declining in warm months and increasing after harvest. The viability of sporangiospores was markedly affected by rain. There was a good correlation (r=0.88) between the number of recovered propagules in the soil and the amount of rainfall. M. piriformis isolates caused decay on pear at 0°C after 14 days.     

Andropogon annulatus and Ischaemum rugosom – Two New Weeds of Sugarcane in Trinidad

Abstract

Potato cyst-nematode species are believed to have evolved in South America but now have a worldwide distribution and can be major and persistent pests except in the warmest soils. Both species contain pathotypes and their correct identification, although difficult, is important when planning control with resistant potatoes. Some closely related and very similar species are of minor economic importance. Resistant cultivars available at present are effective against only some pathotypes and except where high crop values make use of nematicides economic, it is important to combine extended crop rotation with such cultivars.     

Unkrautbekämpfung in Lupinen – Erkenntnisse aus 10 Jahren Lückenindikation

In Germany, cultivation of lupines traditionally takes place only in few federal states at sites with light/sandy soil conditions. Due to this fact, there only exist a small number of field trials to close gaps in chemical weed control via herbicides. The existing pre-emergence herbicides are not able to control all of the most common weed species sufficiently-they all show efficiency gaps against single weed species. Not any of the pre-emergence herbicides tested could achieve high efficiencies against Polygonum convolvulus. The best efficiency against P. convolvulus can be achieved after a sequence of a pre-emergence spray of 0,8–1,0 l/ha Fenikan and a post-emergence spray of 0,2 l/ha Tacco. Since Fenikan and Tacco are not approved for lupine, after approval the application only in lupine stocks for seed production is possible. By taking into account only the currently legal permitted herbicides, Gardo Gold and the tank mix Boxer?+?Stomp Aqua show the best broad effects. Benefits resulting from Gardo Gold can be obtained against Chenopodium album, Viola arvensis, Centaurea cyanus, while the tank mixes Boxer?+?Stomp Aqua show advantages against Galium aparine. From the pre-emergence herbicides tested, Successor T could be applied as an addition to improve the broad effect. In tank mixes with Gardo Gold, the most common weed species can be controlled well. However, with permission also this tank mix can currently only be applied in lupine seed stock production. In the near future weed control will only be possible with the currently existing and approved herbicides, because there are no new herbicides to expect that are compatible with corn, grain and lupine. Under suboptimal application conditions of soil herbicides, weeded lupine stocks can only be harvested after siccation.     

Precipitation changes in the mid-latitudes of the Chinese mainland during 1960–2014

Based on daily precipitation data from 163 meteorological stations, this study investigated precipitation changes in the mid-latitudes of the Chinese mainland(MCM) during 1960–2014 using the climatic trend coefficient, least-squared regression analysis, and a non-parametric Mann-Kendall test.According to the effects of the East Asian summer monsoon on the MCM and the climatic trend coefficient of annual precipitation during 1960–2014, we divided the MCM into the western MCM and eastern MCM. The western MCM was further divided into the western MCM1 and western MCM2 in terms of the effects of the East Asian summer monsoon. The main results were as follows:(1) During the last four decades of the 20~(th) century, the area-averaged annual precipitation presented a significant increasing trend in the western MCM, but there was a slight decreasing trend in the eastern MCM, where a seesaw pattern was apparent. However, in the 21~(st) century, the area-averaged annual precipitation displayed a significant increasing trend in both the western and eastern MCM.(2) The trend in area-averaged seasonal precipitation during 1960–2014 in the western MCM was consistent with that in the eastern MCM in winter and spring. However, the trend in area-averaged summer precipitation during1960–2014 displayed a seesaw pattern between the western and eastern MCM.(3) On an annual basis,both the trend in rainstorms and heavy rain displayed a seesaw pattern between the western and eastern MCM.(4) The precipitation intensity in rainstorms, heavy rain, and moderate rain made a greater contribution to changes in the total precipitation than precipitation frequency. The results of this study will improve our understanding of the trends and differences in precipitation changes in different areas of the MCM. This is not only useful for the management and mitigation of flood disasters, but is also beneficial to the protection of water resources across the MCM.     

A field investigation of wind erosion in the farming–pastoral ecotone of northern China using a portable wind tunnel: a case study in Yanchi County

The farming–pastoral ecotone in northern China is an extremely fragile ecological zone where wind erosion of cropland and rangeland is easy to occur. In this study, using a portable wind tunnel as a wind simulator, we conducted field simulated wind erosion experiments combined with laboratory analysis to investigate wind erosion of soils in trampled rangeland, non-tilled cropland and tilled cropland in Yanchi County, China. The results showed that compared with rangeland, the cropland had a higher soil water holding capacity and lower soil bulk density. The wind erosion rate of trampled rangeland was much higher than those of non-tilled cropland and tilled cropland. For cropland, the wind erosion rate of the soil after tilling was surprisingly less than that of the soil before tilling. With increasing of wind speed, the volume mean diameter of the eroded sediment collected by the trough in the wind tunnel generally increased while the clay and silt content decreased for all soils. The temporal variation in wind erosion of the trampled rangeland indicated that particle entrainment and dust emission decreased exponentially with erosion time through the successive wind erosion events due to the exhaustion of erodible particles.