Genetic diversity of Claviceps africana on sorghum and Hyparrhenia

RAPD markers were used to survey genetic variability among 140 isolates of Claviceps africana collected from Southern Africa, India, Thailand, Australia and the Americas in 1992–2002. Amplified fragment length polymorphisms were determined for a subset of the isolates. Both markers gave similar results in phenetic analysis of genetic distances between haplotypes of different geographical origin. In the Americas, a single RAPD haplotype was found throughout the various countries. The Eastern lineage consisted of two close haplotypes (one from India, the other from Thailand and Australia). Among five specialized isolates of C. africana from the alternative hosts ( Hyparrhenia spp.), three haplotypes were found. Eleven private alleles distinguished the Hyparrhenia population from that on sorghum. rDNA sequences of sorghum and Hyparrhenia isolates differed in three positions. The African sorghum population of C. africana consisted of 10, mostly closely related haplotypes. Low genotypic diversity ( H _E = 0·0337) and the fact that most of the variation originated from between populations ( G _ST = 0·866) suggested founder effects following recent invasion. In Southern Africa, no significant differentiation was found among six populations. Therefore the data were pooled and tested for prevalence of clonal or sexual reproduction. The presence of the over-represented, widespread RAPD haplotype A; gametic disequilibrium (37% loci detected by exact tests); index of association ( I _A) significantly >0; and the high proportion of compatible loci (in the clone-corrected and total data sets found to be 94 and 99%, respectively) support the hypothesis of clonality as the predominant means of reproduction.     

Ovary colonization by Claviceps africana is related to ergot resistance in male-sterile sorghum lines

Ergot, caused by Claviceps africana , has emerged as a serious threat to sorghum hybrid seed production worldwide. In the absence of gene-for-gene-based qualitative resistance in commercial cultivars, varieties with high pollen production that can escape ergot infection are preferred. Recent demonstration of differences in ergot susceptibility among male-sterile lines has indicated the presence of partial resistance. Using chitin-specific fluorescin-isothiocyanate-conjugated wheat germ agglutin and callose-specific aniline blue, this study investigated the process of sorghum ovary colonization by C. africana . Conidia germinated within 24 h after inoculation (a.i.); the pathogen was established in the ovary by 79 h a.i., and at least half of the ovary was converted into sphacelial tissue by 120 h a.i. Changes in fungal cell wall chitin content and strategic callose deposition in the host tissue were associated with penetration and invasion of the ovary. The rate of ovary colonization differed in three male-sterile lines that also differed in ergot susceptibility. This work demonstrates a possible histological basis for partial resistance in male-sterile sorghum lines that could lay the foundation for variety improvement through further breeding and selection.     

Evaluation of potential biocontrol agents against Claviceps africana in vitro and in vivo

Undiluted culture filtrates of two commercial products of Trichoderma spp., Trichopel and Trichoflow, and two isolates of Penicillium citrinum completely inhibited the conidial germination of macroconidia of Claviceps africana , the cause of ergot or sugary disease of sorghum ( Sorghum bicolor ) in vitro . Similarly, Pseudomonas aeruginosa and Burkholderia cepacia completely inhibited macroconidial germination, with the former being more effective at high dilutions. In contrast, these bacterial isolates failed to inhibit infection in vivo in glasshouse tests with ergot-inoculated sorghum, but all fungal biocontrol agents (including an isolate of Epicoccum nigrum ) reduced the severity of disease (percentage of infected spikelets per panicle), in some cases completely inhibiting the development of ergot. In a second glasshouse trial, optimum control was achieved when the biocontrol agents were applied 3–7 days before inoculation with conidia of C. africana .     

Windborne spread of ergot disease (Claviceps africana) in sorghum A-lines in Zimbabwe

Ergot disease spread rapidly in Zimbabwe amongst replicated plots of male-sterile sorghum A-lines, from a group of centrally situated and precociously inoculated plants. Prominent secondary conidiation by the pathogen, Claviceps africana , on the surface of exuded honeydew provided airborne spores which were trapped in a Burkard continuous spore trap and showed diurnal peaks of concentration in air close to the primary source of inoculum. The rate of disease spread ( r =0·2; range 0·14–0·58) closely matched that recorded for other plant pathogens such as Phytophthora infestans and Puccinia graminis tritici , and it is concluded that the characteristic secondary conidia of C. africana were the principal epidemiological agents within the experimental area. Ergot spread by windborne secondary conidia has significant epidemiological and economic implications for sorghum hybrid breeding in southern Africa.     

Patterns of release of the secondary conidia of Claviceps africana, the sorghum ergot pathogen in Australia

Trials were conducted in southern Queensland, Australia between March and May 2003, 2004 and 2005 to study patterns of hourly and daily release of the secondary conidia of Claviceps africana and their relationships with weather parameters. Conidia were trapped for at least one hour on most (> 90%) days in 2003 and 2004, but only on 55% of days in 2005. Both the highest daily concentration of conidia, and the highest number of hours per day when conidia were trapped, were recorded 1–3 days after rainfall events. Although the pattern of conidial release was different every day, the highest hourly conidial concentrations occurred between 10·00 hours and 17·00 hours on 73% of all days in the three trials. Hours when conidia were trapped were characterized by higher median values of temperature, windspeed and vapour pressure deficit, lower relative humidity, and leaf wetness values of 0%, than hours when no conidia were recorded. The results indicate that fungicides need to be applied to the highly ergot-susceptible male sterile (A-) lines of sorghum in hybrid seed production blocks and breeders' nurseries as soon as possible after rainfall events to minimize ergot severity.     

基于GIS的三江源地区物种多样性保护优先性分析

根据我们的多次科考调查和青海省对野生动物的调查结果等有关资料图件,对三江源地区的物种多样性和人类干扰因素等进行了分析和评估。选择9种鸟类、15种哺乳动物、20种植物作为本研究的指示物种,利用GIS制作了主要的珍稀濒危野生动植物分布图。选择放牧、人口、居民点、公路等因素作为生物多样性的主要干扰因素,制作出三江源地区干扰强度空间分布图。然后根据物种的丰富度和特有性、脆弱性和干扰程度等指标分析了三江源地区物种多样性保护优先性地区,做出了物种多样性保护优先地区空间分布图。     

物种多样性与病虫草害管理研究进展

农业生物多样性有许多重要的生态功能,控制农业有害生物的发生和流行是其中重要组成部分。生物多样性包括形态的多样性、功能多样性及互作的多样性,互作物质的多样性和互作方式的多样性决定了互作结果的多样性。充分利用品种之间,作物之间、作物与非作物之间的正向作用和负向作用来促进植物生长,减少病虫害的发生,是有效控制农林有害生物的重要措施。本文介绍该领域近年来的物种多样性研究的主要进展,同时提出以后研究的建议和方向,即应用宏基因组学、蛋白组学和代谢组学等后基因组学及植物生理生化等综合技术,系统分析农田生态系统中各种生物之间直接和间接互作机制的基础,根据不同的防控对象及环境条件确定多样性的结构和模式,通过大数据进行管控,才能实现病虫害的绿色防控和农业可持续发展。     

新疆棘豆属物种多样性分析

新疆棘豆属植物有98种2变种,占中国棘豆属总种数的67.1%,其中新疆特有种7种,中国新疆仅分布种58种,特有种与新疆仅分布种共占65%,所占比例较高.棘豆属在新疆的11个植被区域中均有分布,最丰富的地区为准噶尔和天山地区,尤以天山山系种类最多,它们是棘豆属现代分布与起源分化中心之一;绝大部分种类(约99%)集中分布在海拔1 001～5 000 m的山区,尤其在1 001～4 000 m最丰富,在2 001～3 000 m分布最多;植物生活型以地面芽植物为主,高达96%,地上芽植物仅占4%.植物区系与其邻近的青海省和西藏关系最为密切,相似性系数分别为28.8%和28.6%,与内蒙古和甘肃联系相对较弱;与邻国哈萨克斯坦关系最密切,相似性系数高达65.2%,其次是西西伯利亚和吉尔吉斯斯坦,相似性系数分别为41.8%和41.0%,与蒙古、塔吉克斯坦和巴基斯坦的相似性系数较低,分别为29.2%,22.8%和11.6%,联系相对较弱.     

中国花蝽科昆虫多样性及分布格局

在对中国花蝽科昆虫多样性分布统计的基础上,构建数据库,采用特有性简约分析方法,对中国花蝽科昆虫的地理分布格局和物种多样性进行探讨。结果表明,风蝶在中国8个生物地理大区均有分布,且表现出南部比北部丰富、北部比南部原始的特征,华南区和西南区的凤蝶多样性最为丰富。     

安徽大别山区绿僵菌属物种多样性

绿僵菌是一类常见且极具应用价值的生物防治材料。目前绿僵菌分类系统取得了突破性的进展,然而新分类系统在国内尚未普遍采用。本文用该系统研究了近年来分离自大别山区僵虫的21株绿僵菌的物种多样性。在对大别山绿僵菌菌株的形态学研究基础上;对其转录延长因子（EF-1a）进行了进一步的PCR扩增、测序和同源性分析,并选用MEGA软件依据简约法构建EF-1a系统发育树。结果表明,21株菌株在新系统中分别属于5个种,即贵州绿僵菌、大孢绿僵菌、蚱蜢绿僵菌、黄绿绿僵菌瘿绵蚜变种和棕色绿僵菌,并对中国新纪录棕色绿僵菌进行了形态学的描述。该研究基本明确了大别山区的绿僵菌物种多样性,为生物防治菌株提供了科学鉴定方法和丰富种质资源。     

Molecular Diversity of Agriculturally Important Aspergillus Species

Although Aspergillus species are not usually considered as serious plant pathogens, Aspergilli are frequently encountered in plant products. The most important consequence of their presence is mycotoxin contamination. The main mycotoxins produced by Aspergilli are the aflatoxins, ochratoxin A and patulin, which are produced by a variety of Aspergillus species in different plant commodities. Phylogenetic analysis of sequences of the ribosomal RNA gene cluster is useful for clarifying taxonomic relationships among toxigenic Aspergilli causing pre- and postharvest contamination of agricultural products. Molecular data has enabled us to clarify the taxonomy of black Aspergilli, A. flavus and its relatives, and sections Circumdati and Clavati, which include ochratoxin and patulin-producing species. Phylogenetically unrelated species were found to produce the same mycotoxins, indicating that mycotoxin-producing abilities of the isolates have been lost (or gained) several times during the evolution of the genus. The data also indicate that biosynthetic gene-based probes are necessary for molecular detection of these mycotoxin-producing organisms. The organisation of the biosynthetic genes of patulin and ochratoxins is unknown, although experiments are in progress in several laboratories to clarify the genetic background of biosynthesis of these mycotoxins. Identification of biosynthetic genes responsible for mycotoxin production is essential for clarifying the evolution of mycotoxin biosynthesis in Aspergilli, and to develop specific gene probes for the detection of mycotoxin-producing Aspergilli in agricultural products.     

Diversity of Hypoviruses and Other Double-Stranded RNAs in Cryphonectria parasitica in North America

ABSTRACT Double-stranded (ds) RNAs in Cryphonectria parasitica were randomly sampled from nine subpopulations in North America using an antibody-based detection system for dsRNA. dsRNA was detected in 166 (28%) of a total of 595 C. parasitica isolates sampled by immunoblotting. Incidence of dsRNA infection within subpopulations ranged from 0% in samples from New Hampshire and Ontario to 100% in County Line, MI. Most of the dsRNAs sampled were approximately 9 to 13 kb in size. dsRNAs from 72 isolates analyzed by probing Northern blots with (32)P-labeled dsRNAs were in one of three hybridization groups. One hybridization group was widespread throughout eastern North America, being found in New York, New Jersey, Maryland, West Virginia, Kentucky, and Michigan. These dsRNAs hybridized to dsRNA from the previously described C. parasitica isolate SR2 from Maryland and are referred to as SR2-type dsRNAs. The second hybridization group was found almost exclusively in Michigan. The Michigan dsRNAs cross-hybridized to Cryphonectria hypovirus 3-GH2 (CHV3-GH2) and are referred to as CHV3-type dsRNAs.One dsRNA sampled from Kentucky hybridized to CHV3-type dsRNAs from Michigan. This dsRNA was probably derived from a fungal isolate that had been intentionally released for biological control at this same site 10 years previously and had become established in Kentucky. The third hybridization group was found only in New Jersey. These dsRNAs were much smaller than all other dsRNAs (3 and 5 kb) and were found in all 11 isolates that were probed; two of these isolates also had SR2-type dsRNA in mixed infections. None of the North American dsRNAs hybridized to CHV1 from Europe, even though CHV1 has been released in numerous locations in eastern North America for biological control of chestnut blight. Similarly, no dsRNAs hybridized to CHV2-NB58, a hypovirus found previously in New Jersey. Mixed infections of SR2-type and CHV3-type dsRNAs were found in 13 of 15 isolates from Frankfort, MI, while another nearby subpopulation (County Line) was infected with only CHV3-type dsRNAs. The distribution of dsRNA hybridization groups in C. parasitica thus presents a mixed picture, since one hybridization group is widespread, whereas two others are primarily restricted to smaller geographic areas.     

克拉玛依植物群落结构和物种多样性研究

采用多样性指数,丰富度指数和均匀度指数对克拉玛依植物群落物种多样性进行了研究。结果表明:各群落类型的物种多样性指数的顺序为:梭梭+碱蓬>花花柴、胡杨>碱蓬+麻黄>柽柳>琵琶柴>猪毛菜>梭梭>芦苇>盐节木>白刺+柽柳;灌木和乔木群落多样性指数和丰富度指数大于草本群落,而均匀度指数在乔木,灌木和草本群落中则表现出多样化的趋势。     

Molecular and Morphological Diversity of Fusarium Species in Finland and North-Western Russia

In 2001 the range of the total Fusarium contamination percentage of infected seeds was between 0% and 44%, while in 2002 the contamination level was 2–25% in naturally infected Finnish samples and 5–14.5% in six samples from northwestern Russia. The most common Fusarium species in barley were F. avenaceum, F. arthrosporioides, F. sporotrichioides and F. culmorum, while in spring wheat the most common Fusarium species were F. avenaceum, F. arthrosporioides, F. culmorum, F. sporotrichioides and F. graminearum. In most cases, molecular identification with species-specific primers corresponded to the morphological analyses and allowed the identification of degenerated and otherwise morphologically difficult cultures. It was even possible to separate most of the F. arthrosporioides isolates from Finland from the closely-related F. avenaceum isolates. In the phylogenetic analysis of combined β-tubulin, IGS and ITS sequences most European F. arthrosporioides formed a separate clade from most isolates of F. avenaceum and from all isolates of F. tricinctum. Most of the species-specific primers also amplified DNA extracted from grain samples. It was, for instance, possible to detect F. avenaceum in all barley samples with contamination levels higher than 1% and in all spring wheat samples with contamination levels higher than 3%. The detection level for F. graminearum was at a contamination level of 3–5% and that for F. culmorum at a contamination level of 1–5%. In addition, the first Finnish F. langsethiae isolate was found by means of species-specific primers.     

烟粉虱寄生蜂种类及繁殖方式多样性

本文列举了烟粉虱Bemisia tabaci寄生蜂种类,共计74种,其中恩蚜小蜂属Encarsia 47种,桨角蚜小蜂属Eretmocerus24种,埃宓细蜂属Amitus 2种及新姬小蜂属Neochrysocharis 1种;从生殖方式、寄生行为及寄主发育阶段喜好程度等方面论述了烟粉虱寄生蜂种类及繁殖方式的多样性;介绍了目前烟粉虱寄生蜂的引种工作;最后提出了今后有关烟粉虱寄生蜂的研究方向.     

敦煌阳关自然保护区鸟类多样性调查及分析

敦煌阳关自然保护区地处我国西北内陆腹地,主要保护对象为湿地、候鸟和荒漠生态系统。2006年3月~2007年4月,对该保护区鸟类的种类、数量、分布和生境等进行了多次科学调查。综合文献记载,得知阳关自然保护区共有鸟类86种,隶属13目,30科,57属,其中留鸟13种,夏候鸟47种,冬候鸟5种,旅鸟21种,国家重点保护鸟类10种。鸟类区系以古北界成分为主,占繁殖鸟总数的70%,而东洋界种类仅2种。生境类型包括湿地、草原、灌丛和居民点等。近年来保护区内珍稀鸟类数量不断减少,主要影响因素是栖息地丧失,人类活动和气候变化等。     

荒漠河岸生态系统退化与物种多样性恢复研究

通过塔里木河下游生态输水后植物群落及其环境因子的调查,采用聚类分析与多样性指数,分析生态系统退化程度与时空维上物种的恢复速率差异。结果表明:塔里木河下游生态退化可以归为3类,轻度退化、中度退化、重度退化。3种退化类型的地下水埋深依次增大,物种多样性与植被盖度依次减小,沙漠化指数也依次增强。物种多样性差异与环境水分条件有着密切的关系,在地下水埋深小于5 m时,物种恢复速率的发生率达100%,而在地下水埋深大于5 m时,多样性恢复速率达46%。根据退化程度的不同与物种多样性的恢复差异,提出该区域的生态恢复应分阶段进行。     

艾比湖地区植被分布及物种多样性研究

应用重要值计算多样性指数、均匀度指数、优势度指数,对艾比湖流域植被分布及物种多样性进行分析。结果表明：① 研究区域内可划分出10个群落,其中多枝柽柳群落(Form.Tamarix ramosissima)分布最为广泛。② 湖岸植被表现出明显的带状分布特点,并且群落物种多样性随地势发生变化,地势高的地方,物种多样性较高,均匀度较好。③ 在南北断面内,影响植物生长的主要因素为土壤含盐量。随着土壤盐分的增加,物种种类趋向单一,群落结构趋向简单。相反物种多样性随着土壤盐分的减少而增大。④ 受风况和土壤含盐量的影响,南北断面植被组成差异较大,且在近湖岸范围内,南断面植物群落物种多样性和植物生长状态明显优于北断面。     

中国瓢虫的物种多样性

瓢虫是生物防治蚜虫、介壳虫等农、林害虫的天敌昆虫,对瓢虫的多样性研究是进行分类、生物防治的重要基础。本文对中国迄今记录的约680种瓢虫起源、进化、食性、分布作了综述,并说明了研究生物多样性的意义。     

防护林下草本植物层片物种多样性与环境因子的关系

沿塔里木沙漠公路防护林白北向南设置了10个调查样地,对草本植物的多度、盖度、丰富度进行调查,记录和测定各样地内地下水的埋深、电导率、矿化度,土壤电导率、灌木平均冠幅、灌木层郁闭度等环境因子.分析各样地物种多样性、样地间相似性的差异,以及草本植物层片物种多样性与环境因子的关系.结果表明:塔里木沙漠公路防护林下草本植物层片...