Curly top survey in the Western United States

Curly top in sugar beet continues to be a challenging disease to control in the western United States. To aid in development of host resistance and management options, the curtovirus species composition was investigated by sampling 246 commercial fields along with nursery and field trials in the western United States. DNA was isolated from leaf samples and the species were identified using species-specific polymerase chain reaction primers for the C1 gene. Amplicons from 79 isolates were also sequenced to confirm identifications. Beet severe curly top virus (BSCTV) and Beet mild curly top virus (BMCTV) were widely distributed throughout the western United States, while only a few isolates of Beet curly top virus (BCTV) were found. In phylogenetic analysis, BSCTV, BMCTV, and BCTV isolates formed distinct groups in the dendrogram. Seven isolates not amplifiable with species-specific primers did amplify with curly top coat protein primers, indicating novel curtovirus species or strains may be present. Given the wide host range of the viruses responsible for curly top, frequent co-infections, and genetic diversity within and among species, establishing better host resistance, and controlling curly top will continue to be a challenge.     

Genotypic diversity of beet curly top virus populations in the Western United States

ABSTRACT The genotypic diversity of beet curly top virus (BCTV) present in the western United States has been examined by the analysis of 58 field isolates and eight laboratory or nursery isolates of the virus. Full-length clones for each isolate have been characterized for genotype by restriction endonuclease mapping. The results indicate that most of the genotypes examined may be classified as variants of the CFH, Worland, or Cal/Logan strains of BCTV. Two genotypes were recovered that appear to share certain genotypic markers of both Worland and CFH strains. Genotypic variants of the CFH and Worland strains and the two genotypes sharing markers of both strains were recovered from field isolates collected during 1994 and 1995. In contrast, the Cal/Logan strain was recovered only from isolates maintained in laboratories or nurseries. Comparisons of restriction endonuclease maps of cloned BCTV genomes revealed considerable variability both within and between strains. Although a total of 43 distinct genotypes of BCTV were identified, only 36 (84%) were recovered from field isolates. Of 37 field isolates for which more than a single clone was recovered, 16 (43%) contained more than a single genotype of one strain, whereas 4 (11%) harbored mixed infections of the CFH and Worland strains. A phylogenetic analysis using 43 characters derived from restriction endonuclease mapping data supported the grouping of 41 genotypes into three taxa consistent with the three currently recognized strains of BCTV. The relationships of the two genotypes sharing genotypic markers of both the Worland and CFH strains to other BCTV genotypes was unresolved in the phylogenetic analysis. Based on the mild symptom phenotype of the isolates from which these two genotypes were recovered and the presence of Worland genotypic markers in portions of the genome containing both cis- and trans-acting elements determining replication specificity, these two genotypes were tentatively considered as variants of the Worland strain.     

Characterization and Distribution of Two Races of Phialophora gregata in the North-Central United States

ABSTRACT Genetic variation and variation in aggressiveness in Phialophora gregata f. sp. sojae, the cause of brown stem rot of soybean, was characterized in a sample of 209 isolates from the north-central region. The isolates were collected from soybean plants without regard to symptoms from randomly selected soybean fields. Seven genotypes (A1, A2, A4, A5, A6, M1, and M2) were distinguished based on DNA fingerprinting with microsatellite probes (CAT)(5) and (CAC)(5), with only minor genetic variation within the A or M genotypes. Only the A1, A2, and M1 genotypes were represented by more than one isolate. The A genotypes dominated in the eastern Iowa, Illinois, and Ohio samples, whereas the M genotypes were dominant in samples from western Iowa, Minnesota, and Missouri. In growth chamber experiments, isolates segregated into two pathogenicity groups based on their aggressiveness toward soybean cvs. Kenwood and BSR101, which are relatively susceptible and resistant, respectively, to brown stem rot. In both root dip inoculation and inoculation by injecting spores into the stem near the ground line (stab inoculations), isolates of the A genotypes caused greater foliar symptoms and more vascular discoloration than isolates of the M genotypes on both cultivars of soybean. All isolates caused foliar symptoms in both cultivars and in three additional cultivars of soybean with resistance to brown stem rot. Greater differences between the A and M genotypes were seen in foliar symptoms than in the linear extent of xylem discoloration, and greater differences were seen in Kenwood than in BSR101. Inoculation of these genotypes into five cultivars of soybean with different resistance genes to brown stem rot showed a genotype x cultivar interaction. A similar distinction was found in an earlier study of the adzuki bean pathogen, P. gregata f. sp. adzukicola, and consistent with the nomenclature of that pathogen, the soybean pathogens are named the aggressive race (race A) and the mild race (race M) of P. gregata f. sp. sojae.     

Characterization of Pyricularia grisea in the United States Using Independent Genetic and Molecular Markers

ABSTRACT A total of 540 isolates of Pyricularia grisea from rice in the United States were examined for vegetative compatibility, MGR586 DNA fingerprint diversity, and mating type based on hybridization with the mat1-1 and mat1-2 sexual mating type alleles. The collections contained both archived and contemporary field isolates representative of the known MGR586 lineages and races that occur throughout the United States. Complementary nitrate nonutilizing (nit) or sulfate nonutilizing (sul) mutants were used to assess vegetative compatibility in P. grisea. There was a complete correspondence between vegetative compatibility groups (VCGs), MGR586 lineage, and mating type among 527 contemporary isolates (collected between 1991 and 1997) from Arkansas, Louisiana, Missouri, Mississippi, and Texas; all isolates in MGR586 lineages A, B, C, and D belonged to VCGs US-01, US-02, US-03, and US-04, respectively. In addition, all isolates tested in VCGs US-01 and US-04 had the mat1-1 mating type allele whereas those in VCGs US-02 and US-03 had the mat1-2 allele. The strict association of independent markers during this sample period was consistent with a strictly asexual mode of reproduction. However, examination of archived isolates collected in the 1970s and 1980s and contemporary isolates revealed an incongruent relationship between the independent markers. MGR586 C and E isolates were vegetatively compatible which indicated that multiple robust MGR586 delineated lineages could be nested within certain VCGs. Although isolates in lineages C and E were vegetatively compatible, they were of opposite mating type. Several hypotheses, including recombination, could account for the incongruence between the various markers. Among the eight MGR586 lineages (A through H) that occur in the United States, all isolates in lineages A, D, E, G, and H had the mat1-1 allele, whereas isolates in lineages B, C, and F had the mat1-2 allele. Nit mutants can be recovered relatively easy from P. grisea and should allow large numbers of individuals within a population to be assessed for vegetative compatibility. VCGs may prove to be an effective multilocus marker in P. grisea. Thus, VCGs should be a useful means for characterizing genetic structure in populations of the rice blast fungus worldwide, provide a useful genetic framework to assist in interpreting molecular population data, and may provide insight into potential sexual or asexual recombination events.     

Molecular and Biological Characterization of Tomato chlorotic mottle virus Suggests that Recombination Underlies the Evolution and Diversity of Brazilian Tomato Begomoviruses

ABSTRACT Tomato chlorotic mottle virus (ToCMoV) is an emerging begomovirus species widely distributed throughout tomato-growing regions of Brazil. ToCMoV appears to have expanded its geographic range recently, invading tomato-growing areas that were free of begomovirus infection before 2004. We have determined the first complete genome sequence of an infectious ToCMoV genome (isolate BA-Se1), which is the first begomovirus species isolated in the northeast of Brazil. When introduced by particle bombardment into tomato, the cloned ToCMoV-[BA-Se1] DNA-A and DNA-B components caused typical chlorotic mottle symptoms. The cloned virus was whitefly-transmissible and, although it was infectious in hosts such as Nicotiana benthamiana, pepper, tobacco, and Nicandra physaloides, it was unable to infect Arabidopsis thaliana, bean, N. glutinosa, and Datura metel. Sequence and biological analyses indicate that ToCMoV-[BA-Se1] is a typical New World begomovirus sp. requiring both DNA-A and DNA-B components to establish systemic infections. Although evidence of multiple recombination events was detected within the ToCMoV-[BA-Se1] DNA-A, they apparently occurred relatively long ago, implying that recombination probably has not contributed to the recent emergence of this species.     

Genotypic and Pathogenic Diversity Among Pea-Infecting Strains of Aphanomyces euteiches from the Central and Western United States

ABSTRACT Pathogenic and genotypic variability among four populations of Aphanomyces euteiches from individual fields in Minnesota, Wisconsin, and Oregon were investigated using pathogenicity and randomly amplified polymorphic DNA (RAPD) analyses. About 50 strains were isolated from each of two pea fields in Minnesota, and 11 and 6 strains from pea fields in Wisconsin and Oregon, respectively, using pea (Pisum sativum) as a baiting host. Pathogenic variability and host range were evaluated in greenhouse studies with five pea lines or cultivars having different levels of resistance to Aphanomyces root rot and one cultivar each of alfalfa and snap bean. All strains were pathogenic on one or more pea cultivars, and 18 and 14% were pathogenic on alfalfa and bean, respectively. Disease severity incited by different strains varied significantly on individual pea cultivars and on all hosts combined. The percentage of strains pathogenic on different hosts varied among locations. Genotypic variation among all 114 strains was evaluated with RAPD analysis. Ten decanucleotide primers detected 92 polymorphic bands. Cluster and principal coordinates analysis revealed one large group containing 102 of the 114 strains from all locations. Two closely related minor groups of strains (12 strains) were genotypically distinct, with about 55% similarity to the main group of 102 strains. The strains in the minor groups were all isolated from the Minnesota locations and were pathogenic on two disease-resistant pea breeding lines (MN313 and MN314). Estimates of genetic diversity based on RAPD analysis ranged from 0.24 to 0.33 within populations to 0.35 among all strains from all populations. A. euteiches populations were genotypically and phenotypically variable, but no distinct genotypic differences were identified among populations from the four isolated locations.     

美国旱农的几点经验

通过对美国西部旱地农业的实地考察分析,介绍了当地旱地农业耕作种植制度,平整土地,自然喷灌,土壤保护,旱地机械及饲养业,可供有关同类地区参考。     

Molecular and Biological Characterization of Lettuce mosaic virus (LMV) Isolates Reveals a Distinct and Widespread Type of Resistance-Breaking Isolate: LMV-Most

ABSTRACT Lettuce mosaic virus (LMV) causes an economically important seedborne and aphid-transmitted disease of lettuce and ornamental crops worldwide. The genetic diversity among 73 LMV isolates was examined based on a 216-nucleotide sequence at the variable region encoding the NIb-coat protein junction. Three clusters of LMV isolates were distinguished: LMV-Yar, LMV-Greek, and LMV-RoW. In the latter cluster, two subgroups of isolates, LMV-Common and LMV-Most, accounted for a large proportion of the LMV isolates analyzed. These two subgroups included the seedborne isolates, consistent with this property contributing a selective advantage and resulting in widespread distribution. In addition to being seedborne, LMV-Most isolates overcome the two resistance genes commonly used in lettuce, mo1(1) and mo1(2), and thus represent a potential threat to lettuce cultivation. The complete sequence of an LMV-Most isolate (LMV-AF199) was determined, allowing a better definition of the genetic relationships among LMV-Most, LMV-Common, and an additional isolate of the LMV-RoW cluster.     

Groundnut Rust in the United States and the Caribbean

Abstract

Groundnut rust, caused by Puccinia arachidis Speg., is endemic in the West Indies and has occurred with increasing frequency in the United States in recent years. Since 1970 this highly destructive fungus has become established throughout Asia and Oceania, in Australia, and in much of Africa. Rust, together with the leaf spots, greatly restricts production of groundnuts in the Caribbean and in Central America. However, it has not been a major cause of crop losses in the USA except in South Texas during 1971. The fungus does not overwinter in the USA but airborne uredospores are blown in from subtropical areas. Several fungicides currently recommended for leaf spot control are also effective against rust. Three distinct groundnut genotypes are known sources of marked resistance: Tarapoto (P.l.s 259747, 341879, 350680, 381622, 405132); Israel Line 136 (P.l.s 298115 and 315608); and DHT 200 (P.l. 314817). The resistance is physiological and apparently bigenic and recessive. Variation in reaction to different isolates suggests that races of groundnut rust occur. Rust-resistant lines with acceptable agronomic traits are under development in several breeding programmes.     

美国农药残留监控概述

美国农药残留监测工作始于１９６３年 ,至今已有３８年的历史 ,而有些州开展农药残留监控的历史更长。如加州于１９０２年实行农药登记管理 ,１９２６年开始农药残留监控工作 ,目前已长达７５年之久。他们在长期的工作中建立了一套完整的农药残留监控法律法规和监测体系 ,积累了丰富的经验。１机构体系健全 ,职责分工明确美国农药残留监控工作由环保局 (ＥＰＡ)、食品与药品管理局 (ＦＤＡ)、农业部 (ＵＳＤＡ)三个部门共同负责。环保局负责农药登记和农药最高残留限量 (ＭＲＬ)的制定 ;食品与药品管理局监督实施农药残留限量 ,并负责对进口…     

Isolation and Characterization of Derivative Lines of the Onion Yellows Phytoplasma that Do Not Cause Stunting or Phloem Hyperplasia

ABSTRACT Two lines of onion yellows phytoplasma producing milder symptoms were isolated from the original line (OY-W). One has an additional characteristic, non-insect-transmissibility (OY-NIM), compared with the other (OY-M). OY-M was established after maintaining OY-W for 11 years on a plant host (Chrysanthemum coronarium) with an insect vector (Macrosteles striifrons), and OY-NIM was isolated after subsequent maintenance of OY-M in plants by periodic grafting. Polymerase chain analysis suggested that OY-NIM cannot traverse the gut or survive in the hemolymph of the leafhopper. OY-W results in witches'-broom formation and stunted growth in the host plant. In contrast, OY-M and OY-NIM do not cause stunting in the host plant, although they result in witches'-broom. Histopathological analysis of these lines revealed that the hyperplastic phloem tissue and severe phloem necrosis seen in OY-W did not exist in OY-M and OY-NIM. This was attributed to a reduction in the population of phytoplasma in tissues in both OY-M- and OY-NIM-infected plants. The results suggest that the cause of stunting and phloem hyperplasia may be genetically different from the cause of witches'-broom. Pulsed field gel electrophoresis analysis showed that OY-M had a smaller genome size ( approximately 870 kbp) than OY-W ( approximately 1,000 kbp). Thus, some of the OY-W genes responsible for pathogenicity may not be present in OY-M.     

美国EPA登记的生物农药有效成分名录

本文列出了截止2009年4月1日。美国环保局农药项目办公室公布登记的319种生物农药有效成分名单。     

美国杀鼠剂的登记应用现状

目前在美国环保署登记应用的杀鼠剂商品共有302个,有效成分13种。其中磷化锌、氯鼠酮、敌鼠酮、α-氯代醇和马钱子碱等全部或部分产品被列入限制使用农药产品名录,和其他限制使用农药一样受到限制使用政策的约束。同时,美国杀鼠剂产品的销售、流通和使用主要受到EPA《杀鼠剂风险消减决定》的限制,特别是第二代抗凝血类药剂只允许在特定专业领域流通和使用。     

美国生物农药的主要类别

美国登记注册的生物农药主要分为生物化学农药和微生物类农药,其中生物化学农药包括引诱剂、驱避剂、天然昆虫/植物生长调节剂及除草剂、信息素、其他生化农药等;微生物类农药包括细菌、真菌、病毒、酵母、原生动物、工程菌、转基因植物等。     

柑桔突发型生理性病害发生原因与矫治

近年来,由于异常气候和不合格农资产品大量销售使用的影响,在柑桔生产上常常出现一些突发型的生理性病害,柑农大都不能及时正确地采取矫治办法,致使发生病害的地方产量损失大.为解决这一问题,我们对宜昌市近年来发生的两种突发型生理性病害进行了调查研究和会诊求证,并指导柑农实施正确的矫治方法,取得了较好的效果.现就两种突发型生理性病害的发生原因、症状表现和矫治方法报道如下,供农业技术人员及广大柑农在生产实践中参考.     

Monitoring pesticides in agricultural and urban soils of the United States.

Organochlorine pesticides were monitored annually in the major agricultural areas of the United States from 1968 to 1973. Results show that agricultural soils are widely contaminated with low levels of organochlorine residues. Residue concentrations are decreasing as applications of the compounds decrease. Annual monitoring of urban areas since 1969 has demonstrated that urban soils generally have higher pesticide residue concentrations than do agricultural soils in the same locations. High concentrations of mercury, cadmium, and lead have also been observed in urban soils.     

美国对药肥产品的登记管理

本文通过对相关网站资料、文献的查阅、分析,初步勾勒出美国EPA及部分州对药肥产品管理的现行基本做法,为中国建立和形成对药肥产品的管理规范提供借鉴。     

葡聚烯糖和Harpin蛋白对两种番茄病害的防治效果

葡聚烯糖是一种在寄主 病原互作过程中来自病原菌的可诱导植物抗病性的激发子[1],具有调控植物的生长、发育和增强抗病性等功能。迄今已知寡糖类制剂可提高芹菜对萎蔫病、黄瓜对猝倒病、大豆对根腐病等的抗性,对采后病害如辣椒和草莓烂果也有显著的防病效果。Ｈａｒｐｉｎ蛋白是植物病原菌ｈｒｐ基因编码的非特异性激发子,已证明多数病原Ｈａｒｐｉｎ蛋白能诱导烟草、马铃薯、番茄、大豆、黄瓜及拟南芥产生过敏反应[2]。该蛋白已于2000年在美国注册并商品化生产,主要用于防治烟草黑胫病、葡萄灰霉病、马铃薯叶斑病等多种病害。番茄是重要的…     

Integrated pest management and weed management in the United States and Canada

There is interest in more diverse weed management tactics because of evolved herbicide resistance in important weeds in many US and Canadian crop systems. While herbicide resistance in weeds is not new, the issue has become critical because of the adoption of simple, convenient and inexpensive crop systems based on genetically engineered glyphosate‐tolerant crop cultivars. Importantly, genetic engineering has not been a factor in rice and wheat, two globally important food crops. There are many tactics that help to mitigate herbicide resistance in weeds and should be widely adopted. Evolved herbicide resistance in key weeds has influenced a limited number of growers to include a more diverse suite of tactics to supplement existing herbicidal tactics. Most growers still emphasize herbicides, often to the exclusion of alternative tactics. Application of integrated pest management for weeds is better characterized as integrated weed management, and more typically integrated herbicide management. However, adoption of diverse weed management tactics is limited. Modifying herbicide use will not solve herbicide resistance in weeds, and the relief provided by different herbicide use practices is generally short‐lived at best. More diversity of tactics for weed management must be incorporated in crop systems. © 2014 Society of Chemical Industry