Assessing regional scale weed distributions, with an Australian example using Nassella trichotoma

Knowledge of the spatial distribution of weed infestations over regional scales is essential for effective management of source populations and to assess future threats. To this end, the distributions of Nassella trichotoma across a study area in south‐east New South Wales, Australia, were analysed using the geographically local Getis–Ord G_i* spatial hotspot clustering statistic. The clustering of N. trichotoma observations was analysed at three infestation levels: presence (at any density), patch level and the occasional plant level. The results indicate that there are c. 578 km² of cells containing N. trichotoma in strongly clustered infestations, 11.2 km² within weakly clustered infestations distinct from the main clusters, and 55 km² that are not clustered. There are 117 km² of strongly clustered patch level cells, 3 km² in distinct but weak clusters, and none outside of a cluster area. Of the occasional plant level cells, 329 km² are strongly clustered, 6.2 km² are in distinct but weak clusters, and 19 km² are not clustered. These results provide a mechanism by which control efforts can be prioritized. The analysis approach described in this paper provides a consistent, quantitative and repeatable approach to assess weed infestations across regional scales and can be applied to any weed species for which spatial distribution data are available.     

Genetic diversity of the weed species,Stellera chamaejasme,in China inferred from amplified fragment length polymorphism analysis

Stellera chamaejasme is a perennial weed with a wide geographic range that is found from the Altai of eastern Russia, northern China and Mongolia southwards as far as the western Himalayas of the Qinghai–Tibet and Yungui Plateaus. The genetic diversity and population structure of 17 populations of S. chamaejasme, represented by 349 individuals, were assessed by using amplified fragment length polymorphism markers. The results showed a relatively high level of genetic variation at the species level. The proportion of total diversity among populations was 0.4370, suggesting significant genetic differentiation and a low gene flow among the populations of this species. The Mantel test indicated that genetic differentiation among populations was significantly correlated with geographic distance. Genetic drift through range expansion and a low gene flow among populations might result in a lower diversity in peripheral populations, compared to central populations. A Bayesian analysis revealed two potential gene pools in S. chamaejasme, which was confirmed by neighbor‐joining clustering and principal coordinate analysis. These results demonstrate that it is necessary to develop suitable biocontrol agents for populations with different gene pools.     

基于MODIS的和田河夏季漫流监测分析

在ENVI中采用目视解译和监督分类相结合的方法,以及ArcGIS的定位、量测、图层叠加,对和田河中下游夏季漫流状况进行监测分析。结果表明:① 和田河中下游漫流已经到了相当严重的程度。② 中游绿洲边缘和其他河段相比漫流较少,94.4%的监测日期内漫流面积均在35 km²以下,45%的监测日期里没有漫流痕迹。两河交汇处科什米什至古河道与和田河的交汇处,45%的监测日期内漫流面积均在35 km²以上,只有2004年8月5日和2008年7月29日的监测面积为0。古河道与和田河的交汇点至肖塔水文站漫流最严重,大部分监测日期都在 70 km²以上,最大的达到111 km²。③ 全流域共有漫流点10处,其中和田河主河道段左侧有4处,1个新增水域漫滩,右侧出现4处,1个新增水域漫滩;喀拉喀什河左侧出现1处。漫流主要发生于主河道上。     

Evolution of resistance to simazine in Senecio vulgaris L.

Fruits were collected from populations of S. vulgaris growing on commercial fruit farms and progenies were tested for susceptibility to simazine. The five least susceptible populations, which originated from sites where simazine had been applied annually for periods ranging from six to ten years, were subjected to two generations of artificial selection for simazine resistance. Two control populations which originated from unsprayed sites were treated similarly. One population originating from Malpas, Cheshire showed a significant response to selection. The simazine resistance of the other six populations was not improved by artificial selection. Selected progenies of the Malpas population were completely unaffected by simazine at 2.8 kg ha^?1. The potential for evolution of resistance to simazine in S. vulgaris is discussed and the effects of ecological and genetic factors on the rate of evolution are assessed.     

基于DNA条形码技术的湖南省柑橘主产区实蝇幼虫分子鉴定

为明确湖南省柑橘主产区的实蝇入侵为害现状,从该省7个市(自治州)22个地点收集柑橘蛆果中的幼虫,利用DNA条形码技术对其进行分子鉴定,并以DNA条形码序列作为分子标记探究橘大实蝇Bactrocera minax的20个中国地理种群(湖南省6个组群共16个种群、其它3省市4个种群)以及1个印度地理种群间的亲缘地理关系,分析橘大实蝇在我国的遗传进化关系。结果表明,仅采集自邵阳市城步苗族自治县柑橘蛆果中的5头幼虫被鉴定为蜜柑大实蝇B. tsuneonis,其余21个地点采集的595头幼虫均被鉴定为橘大实蝇。21个橘大实蝇地理种群的平均单倍型多样性为0.75,核苷酸多样性为0.0032,核苷酸差异数为2.13,中国所有地理种群均具有较高的遗传多样性;单倍型网络进化图显示湖南、重庆、贵州种群共享的单倍型H3为原始单倍型,表明其为比较原始的种群;AMOVA分析结果显示种群内个体间遗传变异占总体变异的59.04%,是遗传变异的主要来源;遗传分化结果表明湖南省6个组群间均出现了中度至高度的遗传分化,FST在0.0521～0.7795之间。表明DNA条形码技术可用于蜜柑大实蝇和橘大实蝇幼虫的分子鉴定及其种群遗传进化分析。     

Spatial aggregation in Fusarium pseudograminearum populations from the Australian grain belt

Previous studies have evaluated the overall structure of populations of Fusarium pseudograminearum (teleomorph, Gibberella coronicola ), causal agent of cereal crown rot, but there is no information available on spatial relationships of genetic variation in field populations. Three 1-m-row sections in crown-rot-affected wheat fields in the Australian grain belt were intensively sampled to estimate population genetic parameters and the spatial aggregation, or clustering, of disease aggregates and genotypes. Estimates of population genetic parameters based on amplified fragment length polymorphisms (AFLPs) indicated that the genetic diversity in isolates from the 1-m-row populations described a significant portion of the diversity recorded for corresponding field and regional populations. In point pattern analysis, there was physical clustering and aggregation of F. pseudograminearum isolates from two of the three sites. Analysis of the spatial distribution of clonal haplotypes (DICE similarity ≥ 97%) indicated significant aggregation of clones in all three 1-m-row populations. Based on matrix comparison tests, both mating types and genetic distances had significant spatial aggregation for at least two of the three 1-m-row populations. This is consistent with the presence of non-random spatial genetic structure due to clonal aggregation. High levels of genetic diversity and spatial structuring of disease and genotypes in at least two of the three 1-m-row populations is consistent with the hypothesis that stubble is a primary inoculum source in no-tillage farming systems, resulting in aggregated patterns of disease and allowing for haplotypes to be maintained in the field over a number of annual cropping cycles.     

Genetic diversity of Solanum elaeagnifolium,an invasive problematic weed in Jordan

Solanum elaeagnifolium (silverleaf nightshade) is a problematic weed that is common in Jordan and difficult to control. The weed exhibits distinct morphological variations in growth habit, leaf shape, leaf margins, flower colour and presence or absence of spines between individuals among and within populations suggesting genetic differences. Genetic variations among 61 samples of S. elaeagnifolium collected from heavily infested sites in the central Jordan Valley were investigated using six simple sequence repeat (SSR) markers and eight amplified fragment length polymorphism (AFLP) primer combinations. Results showed that 111 out of 675 AFLP bands were polymorphic generating polymorphism information content (PIC) of 38.0%, while 23 SSR polymorphic alleles were detected generating a PIC of 30.8%. Phylogenetic analysis using RaxML software identified four major clades with a clear clustering of the samples with their collection sites. Genetic analysis using both techniques revealed high level of genetic diversity among S. elaeagnifolium samples collected from a small geographical area indicating that a range of genetic diversity may be detected in weed populations across the country that may complicate its management.     

Influence of host resistance on the genetic structure of the white pine blister rust fungus in the western United States

Cronartium ribicola, the causal agent of white pine blister rust, has been devastating to five-needled white pines in North America since its introduction nearly a century ago. However, dynamic and complex interactions occur among C. ribicola, five-needled white pines, and the environment. To examine potential evolutionary influences on genetic structure and diversity of C. ribicola in western United States, population genetic analyses of C. ribicola were conducted using amplified fragment length polymorphism (AFLP) molecular markers. The fungus was sampled at six sites. Collections for two of the six sites were from separate plantings of resistant-selected western white pine and sugar pine. Heterozygosity based on polymorphic loci among populations ranged from 0.28 to 0.40, with resistant-selected plantations at the extremes. Genetic differentiation was also highest between these two populations. Principal coordinates analysis and Bayesian assignment placed most isolates that are putative carriers of virulence to major-gene resistance into a discernable cluster, while other isolates showed no clustering by site or host species. These results indicate that C. ribicola in western North America is not genetically uniform, despite its presumed single site of introduction and relatively brief residence. Moreover, major-gene resistance appears to have imposed strong selection on the rust, resulting in reduced genetic diversity. In contrast, no evidence of selection was observed in C. ribicola from hosts that exhibit only multigenic resistance.     

Genetic structure of Mycosphaerella graminicola populations in Iran

To provide insight into the genetic structure of Mycosphaerella graminicola populations in Iran, a total of 221 isolates were collected from naturally infected wheat fields of five major wheat‐growing provinces and analysed using AFLP markers and mating‐type loci. All populations showed intermediate to high genotypic diversity. In the Golestan and Ardabil populations two mating types were found at near‐equal frequencies, whilst all populations were in gametic disequilibrium. Moreover, clonal haplotypes were identified in different sampling sites within a field in both the Khuzestan and Fars provinces, demonstrating that pycnidia are probably the primary source of inoculum. All five populations had low levels of gene diversity and had private bands. Low levels of gene flow and high genetic differentiation were observed among populations and different clustering methods revealed five genetically distinct groups in accordance with the sampling areas. The Golestan and East Azarbaijan populations were more genetically differentiated than the others. Random genetic drift, selection and geographic barriers may account for the differentiation of the populations. The results of this study indicate a population structure of M. graminicola in Iran contrasting to that of most other countries studied.     

策勒绿洲地下水和地表覆被时空变化的研究

策勒绿洲是新疆典型的荒漠绿洲区,地下水是维持该绿洲及过渡带植被生长的关键因素,以绿洲灌区为主体,以2008—2015年地下水时空变化为主线,采用遥感、GS+地统计学、优化K-means聚类和空间信息叠加等方法分析绿洲地下水和地表覆被的变化特征。结果表明：（1）绿洲地下水埋深变幅最大是11号井,为9.66 m;变幅最小是25号井,为0.1 m;地下水埋深存在明显的空间自相关,相关距离为11.852 km;绿洲东北部地下水埋深明显下降,下降区域面积为184.85 km²,占绿洲面积的72%;（2）对绿洲地下水埋深进行优化K-means聚类分区,结果分为4个子区,其中第一、第二聚类中心的地下水埋深均呈现下降趋势;（3）2000—2015年绿洲土地覆盖类型发生较大转变,林地面积显著性减少了26.02 km²,草地面积增加了11.15 km²,农田向东北部明显扩增;（4）绿洲不同地表覆被类型的地下水埋深从深到浅依次为：农田>林地>草地。     

Genetic Variability and Population Structure of the Wheat Foot Rot Fungus, Fusarium culmorum, in Tunisia

The random amplified polymorphic DNA (RAPD) method was used to investigate the genetic variability and population structure of Fusarium culmorum isolated from wheat stem bases. A total of 108 isolates, representing seven geographically distinct populations, was collected from five climatic regions in Tunisia. Pseudo-allelic frequencies were estimated at each of the 25 putative RAPD loci analyzed by scoring for the presence or absence of amplified fragments; 92 haplotypes were found among the 108 strains. The analysis of the population structure did not reveal any trend with regard to geographic origin. Total gene diversity (H_T ^* = 0.318) was mostly attributable to diversity within populations (H_S ^* = 0.308). Analysis of molecular variance confirmed that most of the genetic variability was within populations. Genetic differentiation among populations was low to moderate (G_ST ^* ranged from 0 to 0.190 and averaged 0.041 over all loci). Cluster analysis with UPGMA using genetic distances did not reveal any spatial clustering of the isolates collected from the different geographic regions. Based on these results, we conclude that the F. culmorum isolates recovered from different regions in Tunisia might be part of a single population pool.     

The large‐scale removal of mammalian invasive alien species in Northern Europe

Numerous examples exist of successful mammalian invasive alien species (IAS) eradications from small islands (<10 km²), but few from more extensive areas. We review 15 large‐scale removals (mean area 2627 km²) from Northern Europe since 1900, including edible dormouse, muskrat, coypu, Himalayan porcupine, Pallas' and grey squirrels and American mink, each primarily based on daily checking of static traps. Objectives included true eradication or complete removal to a buffer zone, as distinct from other programmes that involved local control to limit damage or spread. Twelve eradication/removal programmes (80%) were successful. Cost increased with and was best predicted by area, while the cost per unit area decreased; the number of individual animals removed did not add significantly to the model. Doubling the area controlled reduced cost per unit area by 10%, but there was no evidence that cost effectiveness had increased through time. Compared with small islands, larger‐scale programmes followed similar patterns of effort in relation to area. However, they brought challenges when defining boundaries and consequent uncertainties around costs, the definition of their objectives, confirmation of success and different considerations for managing recolonisation. Novel technologies or increased use of volunteers may reduce costs. Rapid response to new incursions is recommended as best practice rather than large‐scale control to reduce the environmental, financial and welfare costs. © 2016 Crown copyright. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Roadside surveys support predictions of negligible naturalisation potential for cotton (Gossypium hirsutum) in north-east Australia

A survey of cotton (Gossypium hirsutum) volunteers was conducted along the 1400 km of a cottonseed transport route in north‐east Australia to determine the extent of naturalisation from spilt seed. In each year, 1% of the road distance was inspected for volunteer plants. The survey results were juxtaposed with the eco‐climatic suitability predictions from inferential modelling. Over 3 years, 22 cotton plants were found at eight sites. Within the cotton production region, volunteers averaged 2.28 plants km⁻¹ of road; their most likely source was seed cotton spilt during the previous harvest. Further north, three plants were found over 3 years, at an average density of 0.089 plants km⁻¹ of road; all three plants were found in locations with a positive Ecoclimatic Index. No secondary spread was detected. Roadside slashing reduced plant survival and the potential to produce seed. In the wet tropics, weed competition and slashing prevented volunteers establishing. The surveys indicate that roadsides in north‐east Australia are a hostile environment for the establishment of cotton plants, with no evidence of naturalisation or secondary spread. Current transport practices utilizing fully covered loads present negligible risk of producing naturalised populations of cotton (either transgenic or non‐transgenic) on roadsides in north‐east Australia.     

The influence of simulated immigration and chemical persistence on recovery of macroinvertebrates from cypermethrin and 3,4‐dichloroaniline exposure in aquatic microcosms

BACKGROUND: Chemical dissipation and organism immigration are considered important factors that influence recovery potential from perturbation of aquatic macroinvertebrates. Experiments were conducted to investigate the effect of simulated immigration on recovery of aquatic macroinvertebrates exposed in outdoor microcosms to ecotoxicologically similar concentrations of the rapidly dissipating pyrethroid insecticide cypermethrin (70 ng L⁻¹) or the more persistent herbicide intermediate and degradate 3,4‐dichloroaniline (10 mg L⁻¹). Microcosms were covered with light‐permeable mesh to prevent recolonisation. Immigration was simulated by the regular addition of organisms after treatment. RESULTS: Microcosms exposed to 3,4‐dichloroaniline treatment suffered substantial loss of taxon richness and by 10 months after treatment had only recovered where invertebrates had been added. Those treated with cypermethrin underwent an initial decline in certain crustacean and insect populations. These populations showed some signs of recovery over a period of 5 months through internal processes alone. However, rate of recovery was further enhanced where immigration was simulated, and in this case recovery had occurred around 100 days after treatment. CONCLUSION: Although not the only factors involved, simulated immigration and chemical fate clearly influence the ability of communities to recover from chemical exposure. Consideration of immigration processes and development of models will help to increase the realism of risk assessments. Copyright © 2009 Society of Chemical Industry     

Comparison of natural populations of Mycosphaerella graminicola from single fields in Kansas and California

Kansas and California wheat-growing regions differ dramatically in soils, climate, wheat cultivars, crop rotation patterns, and cultural practices, which could select for different fungal populations of Mycosphaerella graminicola. Our objective in this study was to use amplified fragment length polymorphism (AFLP) loci to assess the genetic diversity of M. graminicola populations within single fields in two widely separated, and geographically isolated sites in Kansas and California. Three primer-pair combinations were used to resolve polymorphism at 177 loci in 67 and 63 isolates from Kansas and California, respectively. Genotypic variability was high, which is consistent with a genetically diverse initial inoculum. There was no evidence of genetic disequilibrium in either population, with only 4.6% of the locus pairs in Kansas, and 5.4% of the locus pairs in California in detectable disequilibrium. The migration rate calculated between the two sites was as low as 1.8 individuals per generation, and significant differences in allele frequencies were observed. Therefore, these two populations do not represent mere subsamples of a larger, randomly mating population. This is a rare report of isolation by distance occurring between two North American populations of M. graminicola, indicating that at least some of these populations may be differentiating. Although genetic isolation by distance may occur, we cannot exclude movement of new gene combinations such as fungicide resistance or virulence between these two locations.     

我国小麦落选短体线虫群体遗传多样性分析

 为了明确我国落选短体线虫群体的遗传多样性,利用mtCOI基因标记对落选短体线虫9个地理群体的遗传结构及遗传分化进行分析。结果显示,9个地理群体中共得到101条mtCOI序列,发现28个碱基变异位点,形成14个单倍型。其中,H1单倍型最常见,为7个地理群体的59个个体共有,推测其可能为祖先单倍型。全部地理群体在物种水平呈现中等遗传多样性(H_T = 0.706±0.131),聚类分析显示其可分为类群Ⅰ与类群Ⅱ两个类群,AMOVA分析揭示落选短体线虫整体水平的遗传分化主要来源于种群间。Mantel检验表明落选短体线虫群体的遗传距离与地理距离存在正相关性,但是不同种群之间的遗传分化程度与地理距离没有显著关系。中性检验和错配分布检验均揭示落选短体线虫在整体水平和两个类群上的群体历史动态都处于相对稳定的状态。     

What have we learned from studies of wild plant-pathogen associations?—the dynamic interplay of time,space and life-history

The interplay of host and pathogen life history traits with disease epidemiology and the selective pressures exerted on hosts drives genetic change and the long-term coevolutionary trajectories of host-pathogen associations. Many studies have addressed various aspects of the ways in which hosts and their pathogens interact but have tended to focus on individual populations, on comparisons made at single points in time, or on broader comparisons that confound patterns from different epidemiological and evolutionary units. While such studies provide valuable information, their essentially ‘static’ snap-shot nature limits the ability to interpret the nature of the underpinning coevolutionary processes. An increasing number of long-term studies involving repeat sampling of multiple interaction demes distributed across space are giving insight into the complexity of the numerical and genetic dynamics of host and pathogen interactions. These illustrate: (a) the ephemerality of disease in individual populations in contrast to its predictability at the metapopulation scale; (b) the spatial and temporal dynamics of selection ‘hot-spots’, rates of extinction and recolonization; and (c) differences in coevolutionary dynamics among demes within a metapopulation. Such long-term studies further emphasise the interplay between life history traits, time and space, and the importance of developing a framework to classify the seemingly daunting diversity of host-pathogen associations.     

基于线粒体COI基因序列的大豆食心虫不同地理种群遗传分化

为揭示大豆食心虫Leguminivora glycinivorella不同地理种群间的遗传分化情况,通过测定19个地理种群214头老熟幼虫的线粒体COI基因序列,利用MEGA 6.0和Dna SP 5.0软件对不同地理种群间序列变异和遗传分化进行分析。结果表明,在214条408 bp的COI基因序列中发现46个变异位点,获得49种单倍型。总群体单倍型多样度为0.8277,固定系数为0.59,基因流为0.17。总群体Tajima’s D检验结果不显著,说明在较近时间内大豆食心虫未经历群体扩张。大豆食心虫不同地理种群间基因交流较少,贵阳种群、都安种群与其它地理种群分化明显,整体的遗传多样性和遗传分化程度较高,地理距离是影响不同地理种群间遗传距离的重要因素。     

Resistance to anticoagulant rodenticides in Germany and future strategies to control Rattus norvegicus

Widespread anticoagulant resistance was discovered in populations of the brown rat (Rattus norvegicus Berk.) in an area of roughly 8000 km² in north-west Germany. Resistance testing was performed by feeding tests and/or by measuring blood clotting response after intraperitoneal injection of a sublethal testing solution. A hierarchical resistance system was found with warfarin resistance at the base followed by bromadiolone/coumatetralyl resistance to difenacoum resistance at the top. Warfarin resistance was spread over the whole area with reduced incidence towards the edges. Difenacoum resistance represented the highest level found so far and was restricted to the inner zone of the resistance area where it occurred with a frequency of 6% of all individuals tested. Breeding experiments with bromadiolone-resistant rats showed that expression of the bromadiolone resistance gene differed in the two sexes, suggesting additional sex-linked modifying effects to the resistance gene. Control strategy within the resistance area with respect to prevention of further selection for resistance is discussed.     

Interpopulation variability and adaptive potential for reduced glyphosate sensitivity in Alopecurus myosuroides

Glyphosate use in the United Kingdom has more than doubled in the last 20 years. Much of this increase is driven by efforts to control herbicide resistant weeds, particularly Alopecurus myosuroides, prior to crop drilling. There is precedent for evolution of glyphosate resistance in similar situations, raising concerns over the sustainability of glyphosate use in the UK. We used dose–response experiments to examine variation in glyphosate sensitivity amongst 40 field‐collected A. myosuroides populations. No populations were resistant to glyphosate, but ED₉₀ values ranged between 354 and 610 g a.i. ha^?1. Five populations had ED₉₀ values significantly higher than the unexposed control population collected from a site at Rothamsted Research with no previous glyphosate exposure. Recurrent selection experiments were performed to determine whether variation in glyphosate sensitivity had a heritable basis. Following two rounds of selection, five of six field populations evolved significantly reduced sensitivity to glyphosate, with R/S ratios, based on estimated ED₅₀ values, ranging from 1.2 to 1.5. These results confirm that there is a heritable basis to variation in glyphosate sensitivity. The response to selection was modest. Evolved populations were not highly resistant to glyphosate, although some twice‐selected individuals survived recommended field rates. These results do not represent definitive proof of the potential of A. myosuroides to evolve glyphosate resistance, although they do indicate caution is needed when considering the sustainability of increased glyphosate use to control this herbicide resistance‐prone species.