Identification and Quantification of Pathogenic Pythium spp. from Soils in Eastern Washington Using Real-Time Polymerase Chain Reaction

ABSTRACT Traditional methods of quantifying Pythium spp. rely on the use of selective media and dilution plating. However, high variability is inherent in this type of enumeration and counts may not be representative of the pathogenic population of Pythium spp. Variable regions of the internal transcribed spacer of the rDNA were used to design species-specific primers for detection and quantification of nine Pythium spp. from soils in eastern Washington. Primer pairs were designed for Pythium abappressorium, P. attrantheridium, P. heterothallicum, P. irregulare group I, P. irregulare group IV, P. paroecandrum, P. rostratifingens, P. sylvaticum, and P. ultimum and used with real-time polymerase chain reaction. Standard curves were generated for each of the species using SYBR Green I fluorescent dye for detection of amplification. Seventy-seven isolates of Pythium were screened to confirm specificity of each primer set. DNA was extracted from soil and standard curves were generated for P. irregulare group I, P. irregulare group IV, and P. ultimum to correlate populations of each species in the soil with quantities of DNA amplified from the same soil. Examination of raw field soils revealed results similar to those observed in previous studies. This new technique for the quantification of Pythium spp. is rapid and accurate, and will be a useful tool in the future study of these pathogenic Pythium spp.     

黄河流域城镇生活污水回用农业的潜力和对策

黄河流域是我国典型的干旱和半干旱地区,流域缺水、支流水质污染和污水灌溉面积的增加对环境、农业生产和农产品安全造成了潜在的威胁。适当处理的城镇生活污水是一种稳定的水资源、在很大程度上缓解水资源的紧缺状况,利用污水资源的主要用途之一是灌溉农田。处理后的城镇生活污水回用农业的潜力极大、具有经济、环境和社会效益。然而,城镇生活污水对人类健康和环境(地下水和地表水)可以造成潜在的影响、必须制定处理后回用农业的标准、使用技术和管理规范。     

Identification of Phytophthora spp. isolated from plants and soil samples on strawberry plantations in Poland

Journal of Plant Diseases and Protection - Crown and leather rot of strawberry caused by Phytophthora spp. are major soil diseases of cultivated strawberry...     

Observations of Phytophthora spp. in Water Recirculation Systems in Commercial Hardy Ornamental Nursery Stock

Samples of water and sediment were taken from drains, reservoirs and wells from four commercial hardy ornamental nurseries with water recirculation systems. The samples were taken on seven different dates throughout a single year from August 1994 to July 1995. The samples were screened for Phytophthora species using five different methods: direct plating, three bait tests (using lupin seedlings, apples and Rhododendron leaves) and a DAS-ELISA (double-antibody sandwich enzyme-linked immunosorbent-assay) with two antisera. In the nurseries with old water recirculation systems, Phytophthora species were detected in the drains and in the reservoirs. In the nursery with a new recirculation system, the pathogens were only present in the drains. None of the water samples from wells in any of the nurseries were contaminated. Phytophthora species were present in the water as well as in the sediment samples from drains and reservoirs. They were detected in the water recirculation systems irrespective of the season. The number of isolates increased about sevenfold between late summer and spring. At least 12 different Phytophthora species were identified: some isolates were previously unrecorded species. The epidemiology of the pathogens in outdoor water recirculation systems as well as the importance of the results for commercial nurseries is discussed.     

三工河流域水量转换特征及水资源利用

三工河流域从源头至尾流经了不同的地质单元,在河流的不同地段上,水资源表现形式各不相同,或由地下水补给地表水,或由地表水给地下水。本文分析了不同地段上的水量转化特征,并在此基础上探讨了该区水资源利用现状,存在的问题,提出了有效的对策。     

汉江河谷地区椪柑急性炭疽病发生特点及其综合防治技术

汉江柑橘带是我国柑橘北缘重要优势产区之一,近年来,随着农业产业内部结构的大幅调整,尤其是国家南水北调中线核心水源区生态环境保护和生态经济试验区的逐步建立,使地处核心水源区的湖北省郧县和湖北省丹江口市这两个柑橘主产区,每年以4000m2的规模发展柑橘产业,并利用汉江河谷沿岸小区气候环境适度发展优质桠柑和优质脐橙。     

绞股蓝疫病的发生与防治技术

绞股蓝又称七叶胆、五叶参、小叶五爪龙等,俗称母猪藤。为葫芦科绞股蓝属植物。以全草供药、食兼用。含有多种氨基酸和微量元素,并含50多种皂甙。其中有5种绞股蓝皂甙和人参皂甙结构相同,因此,有“南方人参”之称。陕西安康为绞股蓝原产保护地,全市有4个县、区大面积种植。目前人工栽培面积6900hm2,为农民增收发挥了重要作用,也是安康市委、市政府提出“药、水、游”战略决策的内容之一,为安康一大主导产业。但是,随着人工栽培面积扩大,时间增长,加之气候异常变化,田间管理粗放,绞股蓝病害逐年加重,特别是疫病常造成绞股蓝成片死亡,一般病田…     

疫霉菌对霜脲氰抗性遗传及对霜脲氰和甲霜灵的交互抗性

就疫霉菌对霜脲氰抗性的产生和遗传，以及疫霉菌对霜脲氰和甲霜灵的交互抗性进行了研究。结果表明，苎麻疫霉容易对霜脲氰产生抗药性突变，但抗性在连续３代单游动孢子分离过程中逐渐丧失。大雄疫霉对霜脲氰不易产生抗性突变，恶疫霉、大雄疫霉和苎麻疫霉对甲霜灵和霜脲氰不存在交互抗性     

球孢白僵菌对两种植物病原镰孢的拮抗作用

体外测定了球孢白僵菌Beauveria bassiana对两种棉花病原镰孢——棉花枯萎病菌Fusarium oxysporium f.sp.vasinfecturn和棉花红腐病菌Fusarium verticillioides的拮抗作用。平板对峙培养时,两种镰孢的生长均受到明显抑制。不同含孢量的球孢白僵菌对两种镰孢的抑制效果不同,且抑制率与孢子浓度成显著的线性量效关系;在接种量为6×107孢子.mL-1时,对两种菌的抑制率均达到90%以上,对红腐病菌的抑制率稍高。白僵菌代谢液对两种植物病原菌也表现出抑菌作用,并且抑制率与代谢液浓度呈显著的线性量效关系。综上述,球孢白僵菌对两种镰孢拮抗作用的机制主要涉及营养和空间竞争以及抗生作用,其中抗生作用对拮抗作用的贡献更大。对抗生性代谢液的初步分析发现,醇沉后的上清液冻干粉经4种有机溶剂浸提后,无明显的抑菌作用;而向培养基中添加球孢白僵菌多糖和蛋白粗提物均能显著抑制两种镰孢菌的菌丝生长。因此,抑菌活性物质主要是大分子的多糖和蛋白。     

新疆伊犁河谷玉米田杂草发生现状及防除对策

新疆伊犁河谷玉米田杂草有9科17种,其中发生普遍、危害严重的优势种有田旋花、稗、金狗尾草、灰绿藜、狗尾草5种。杂草的防除,以清选种子,使用腐熟粪肥,加强栽培管理,合理密植,轮作倒茬等农业防除为基础,化学防除为主要手段,可把杂草危害控制在最低程度。     

A Species-Specific Polymerase Chain Reaction Assay for Rapid Detection of Phytophthora nicotianae in Irrigation Water

ABSTRACT Phytophthora nicotianae is a common and destructive pathogen of numerous ornamental, agronomic, and horticultural crops such as tobacco, tomato, and citrus. We have developed a species-specific polymerase chain reaction (PCR) assay for rapid and accurate detection of this pathogen in irrigation water, a primary source of inoculum and an efficient means of propagule dissemination. This PCR assay consists of a pair of species-specific primers (PN), customization of a commercial soil DNA extraction kit for purification of DNA from propagules in irrigation water, and efficient PCR protocols for primer tests and sample detection. The PN primers proved adequately specific for P. nicotianae in evaluations with 131 isolates of P. nicotianae, 102 isolates from 15 other species of Phytophthora, and 64 isolates from a variety of other oomycetes, true fungi, and bacteria. These isolates originated from a wide range of host plants, three substrates (plant tissue, soil, and irrigation water), and numerous geographic locations. The detection sensitivity is between 80 and 800 fg DNA/mul. The assay detected the pathogen in naturally infested water samples from Virginia and South Carolina nurseries more rapidly and accurately than standard isolation methods. Use of this PCR assay can assist growers in making timely disease management decisions with confidence.     

云南干热河谷旱坡地两种覆盖措施对土壤水分的影响

针对干热区气候特点,设置了旱坡地地表盖沙和覆膜两土壤水分处理方武,2003～2005年连续测定其土壤水分变化情况.在地面覆盖物作用下,耕作层40 cm以上土壤水分随降雨量和蒸发强度变化而变化,土层40 cm下土壤水分较稳定;土壤原本含水量的高低影响土壤水分的变化程度.盖膜、盖沙措施使土壤水分只在土壤表层40 cm内有不同程度增加.总体来说,盖膜增加最多,比CK多5%;其次是盖沙,比CK多2.612%.深层土壤水分总体趋势是随土壤深度增加而增加,增加幅度随深度增加不断减少.     

Genetic Analysis of a Pathogenic Erwinia sp. Isolated from Pear in Japan

ABSTRACT Four Erwinia strains, originally isolated in Japan from pear trees with bacterial shoot blight symptoms, were analyzed to determine their genetic relationship with Erwinia amylovora and E. pyrifoliae. When genomes were characterized with amplified fragment length polymorphism markers and by comparative groEL sequence analysis, the Japanese Erwinia sp. and South Korean E. pyrifoliae strains were placed in the same group, which was phylogenetically distinct from a group of 15 strains of E. amylovora. Sequencing of the 29,593-bp plasmid pEJ30 from Erwinia strain Ejp556 revealed that this plasmid was nearly identical to plasmid pEP36 from E. pyrifoliae and was closely related to the nontransferable ubiquitous plasmid pEA29 from E. amylovora. Twenty-one presumptive genes and their order in pEP36 were highly conserved in pEJ30; however, transposon Tn5394, which was present in pEP36, was not found in pEJ30. Short-sequence DNA repeats were conserved between pEJ30 and pEP36, and were different from short-sequence repeats in pEA29. Despite base-pair mismatches, primer pairs used in pEA29 polymerase chain reaction assays for E. amylovora amplified plasmid DNA from the Japanese Erwinia Ejp556 and Ejp562. Like E. pyrifoliae and a few strains of E. amylovora, Japanese Erwinia Ejp617 contained plasmids related to E. pyrifoliae ColE1-related plasmid pEP2.6. Based on these genetic analyses, we conclude that the Erwinia pathogen of pear in Japan is closely related to E. pyrifoliae and that both of these pathogens are demonstrably distinct from E. amylovora.     

Occurrence and characterization of a Phytophthora sp. pathogenic to asparagus (Asparagus officinalis) in Michigan

A homothallic Phytophthora sp. was recovered from asparagus (Asparagus officinalis) spears, storage roots, crowns, and stems in northwest and central Michigan in 2004 and 2005. Isolates (n = 131) produced ovoid, nonpapillate, noncaducous sporangia 45 microm long x 26 microm wide and amphigynous oospores of 25 to 30 microm diameter. Mycelial growth was optimum at 25 degrees C with no growth at 5 and 30 degrees C. All isolates were sensitive to 100 ppm mefenoxam. Pathogenicity studies confirmed the ability of the isolates to infect asparagus as well as cucurbits. Amplified fragment length polymorphism analysis of 99 isolates revealed identical fingerprints, with 12 clearly resolved fragments present and no clearly resolved polymorphic fragments, suggesting a single clonal lineage. The internal transcribed spacer regions of representative isolates were homologous with a Phytophthora sp. isolated from diseased asparagus in France and a Phytophthora sp. from agave in Australia. Phylogenetic analysis supports the conclusion that the Phytophthora sp. isolated from asparagus in Michigan is a distinct species, and has been named Phytophthora asparagi.     

Sensitivity to Protectant Fungicides and Pathogenic Fitness of Clonal Lineages of Phytophthora infestans in the United States

ABSTRACT Since 1991, dramatic changes have occurred in the genetic composition of populations of Phytophthora infestans in the United States. Clonal lineages recently introduced into the United States (US-7 and US-8) are more common now than the previously dominant lineage (US-1). To help determine why these changes occurred, four clonal lineages of P. in-festans common during the early 1990s in the United States and Canada were evaluated for sensitivity to the protectant fungicides mancozeb and chlorothalonil using amended agar assays for isolates collected from 1990 to 1994. No isolate or lineage was resistant to either mancozeb or chlorothalonil. There were significant differences among isolates for degree of sensitivity to one fungicide individually, but there were no significant (P = 0.05) differences among the US-1, US-6, US-7, and US-8 clonal lineages for degree of sensitivity to both fungicides. Therefore, resistance to protectant fungicides cannot explain the rapid increase in frequency of the US-7 and US-8 clonal lineages. Three components of pathogenic fitness (latent period, lesion area, and sporulation after 96 h) were tested for the three clonal lineages that were detected most commonly during 1994 (US-1, US-7, and US-8). All but one of the isolates in this analysis were collected during 1994 and evaluated within 10 months of collection by inoculating detached leaflets of the susceptible potato cultivar Norchip. There were significant differences between the US-1 and US-8 clonal lineages for lesion area and sporulation, and between US-1 and US-7 for latent period. The US-6 clonal lineage was excluded from the pathogenic fitness experiments, because no isolates of this lineage were collected during 1994. Compared with US-7 and US-8, US-1 had the longest latent period and the smallest lesions with the least sporulation. Incorporation of the differences between US-1 and US-8 in computer simulation experiments revealed that significantly more protectant fungicide (e.g., 25%) would be required to suppress epidemics caused by the US-8 clonal lineage compared with US-1. These differences in pathogenic fitness components probably contribute to the general predominance of the "new" clonal lineages (especially US-8) relative to the "old" US-1 lineage.     

石羊河流域民勤盆地深层淡水资源

本文利用已有的水文地质资料,在2005年水文地质勘探及试验及综合物探资料的基础上,针对民勤盆地淡水资源匮乏,解决人畜饮用水困难问题,利用水均衡法对民勤盆地的深层地下淡水资源进行了计算评价。经计算淡水天然资源量为1072.85万m3/a,30年可采资源量为847.78万m3/a。     

Characterization of the Phytophthora infestans Population in the Columbia Basin of Oregon and Washington from 1992 to 1995

ABSTRACT Isolates of Phytophthora infestans collected from 1992 to 1995 from potato fields in the Columbia Basin of Oregon and Washington were analyzed for compatibility type, metalaxyl sensitivity, and glucose-6-phosphate isomerase (Gpi) genotype. In 1992, 30 of 31 isolates were of the US-1 multilocus genotype. A single metalaxyl-resistant isolate of the US-6 (A1 Gpi 86/100) genotype was found near the end of the growing season. In 1993, only 2 of the 59 isolates collected were A1 isolates with Gpi 86/100. Ten isolates were of the A2 compatibility type, seven with Gpi 100/111, two with Gpi 100/100, and one was undetermined. The remaining isolates were metalaxyl-resistant A1 compatibility types with either Gpi 100/100 or 100/111. The first A2 isolates in the Columbia Basin were found in 1993. In 1994, 10 of 18 isolates were of the US-1 genotype. The remaining isolates were US-6 and US-8 genotypes. In 1995, 97% of 268 isolates tested were of the US-8 genotype. Five isolates were A2 compatibility type with Gpi 100/122. One A2, metalaxyl-resistant isolate was Gpi 100/100/111, and two A1 isolates were Gpi 100/111/122. The population of P. infestans quickly changed between 1992 and 1995, from a population comprised almost exclusively of the US-1 genotype to a population represented by new or recombinant genotypes.     

Characterization of Phytophthora spp. Causing Outbreaks of Citrus Brown Rot in Florida

ABSTRACT Epidemics of citrus brown rot from 1994 to 1997 in the south-central and east-coast citrus areas of Florida were characterized and the causal Phytophthora spp. identified. Two species of Phytophthora, P. palmivora and P. nicotianae, were consistently associated with brown rot. Epidemics caused by P. palmivora appeared to be initiated on immature fruit dropped on the orchard floor. The soilborne fungus infected and sporulated on these fruit and was then disseminated to fruit above 1 m in the canopy. In contrast, infection by P. nicotianae, the common cause of root rot, was confined to the lowest 1 m of the canopy. Fruit infected by P. palmivora produced large amounts of ellipsoidal sporangia available for splash dispersal, whereas those infected by P. nicotianae produced far fewer spherical sporangia. Isolates from brown rot epidemics were compared with P. nicotianae from citrus in Florida and Texas, P. citrophthora in California, P. palmivora, and selected Phytophthora spp. from other hosts. Brown rot symptoms produced by the different pathogenic citrus isolates on inoculated fruit were indistinguishable. Morphology, mating behavior, and isozyme patterns of brown rot isolates from 1988 to 1997 matched P. palmivora from citrus roots, other host plants, and other locations, but were different from characterized isolates of P. citrophthora in California and P. nicotianae in Florida and Texas. Cellulose acetate electrophoresis of the isozyme glucose-6-phosphate isomerase rapidly identified the causal citrus pathogen from infected fruit and soil isolation plates. Although P. palmivora is an aggressive pathogen of citrus roots, bark, and fruit, populations in orchard soils were low compared with P. nicotianae.     

Role of Phytophthora spp. in citrus decline in Apulia and Basilicata,Italy1

The results of field surveys carried out in citrus groves of Apulia and Basilicata in Italy to clarify the etiology of a decline condition associated with root and foot damage of citrus are reported. Field observations and laboratory tests have shown that the most frequent causes of citrus decline are root and foot infections by Phytophthora spp. The species isolated were P. nicotiunae var parasiticu and P. citrophthora; the former was the species most often isolated from both the soil and the feeder roots. Less frequently, ArmiNuria sp., frost damage and rodents were identified as additional causes ofdecline. Finally the role ofcultural factors in the decline caused by Phytophthora spp. is discussed.