不同体色生物型烟蚜的取食特性分析

为探究不同体色生物型烟蚜Myzus persicae取食行为的差异,明确其在烟田的分布特征,利用刺探电位图谱(EPG)技术测定了红色型、绿色型和褐色型3种体色生物型烟蚜在烟草上的取食行为。结果表明:红色型烟蚜刺探取食之前对烟草寄主所花费的识别时间最短,为2.20 min,极显著短于褐色型烟蚜的10.09 min。绿色型烟蚜在刺探过程中pd波平均持续时间为7.45 s,显著长于红色型烟蚜的6.85 s,极显著长于褐色型烟蚜的3.95 s,但3种体色生物型烟蚜的pd波次数无显著差异。首次刺吸至第1次出现E2波所需时间,绿色型和褐色型烟蚜均约为红色型烟蚜的2倍。韧皮部取食阶段,3种体色生物型烟蚜分泌唾液(E1波)的时间无显著差异;红色型烟蚜被动吸食汁液(E2波)时间为112.28 min,显著长于绿色型烟蚜的70.02 min和褐色型烟蚜的75.15 min。褐色型烟蚜在木质部主动摄取汁液(G波)的时间最短为8.58 min,与另外2种体色生物型烟蚜差异显著。表明3种体色生物型烟蚜各自具有不同的取食策略,但总体而言红色型烟蚜对烟草的适应性最强。     

4个苜蓿品种对两种体色豌豆蚜的抗生性

在抗蚜鉴定的基础上,在室内20℃条件下,选用4个抗蚜性不同的苜蓿品种,测定了不同苜蓿品种上两种体色豌豆蚜的生物学参数。结果显示,两种体色豌豆蚜在‘金皇后’上的发育历期、净生殖率、平均世代周期差异显著(P0.05),绿色豌豆蚜若虫的发育历期长于红色型,而红色豌豆蚜的净生殖率、平均世代周期大于绿色型;在‘甘农5号’上两种色型豌豆蚜的内禀增长率、周限增长率、种群加倍时间差异显著(P0.05),绿色豌豆蚜的内禀增长率、周限增长率高于红色型,种群加倍时间低于红色型。以内禀增长率作为测定抗生性的指标,4个苜蓿品种对两种色型豌豆蚜的抗性表现不同,其中‘金皇后’对绿色豌豆蚜的抗性较高,‘甘农5号’对红色豌豆蚜的抗性较高,‘猎人河’对两种色型豌豆蚜的抗性均较低,4个苜蓿品种对绿色豌豆蚜抗性的大小顺序为‘金皇后’‘甘农5号’‘甘农3号’‘猎人河’,对红色豌豆蚜抗性大小依次为‘甘农5号’‘甘农3号’‘金皇后’‘猎人河’。     

不同寄主植物上烟蚜DNA多态性的RAPD-PCR分析

用RAPD-PCR技术研究了桃树、油菜和烟草上烟蚜的DNA多态性。结果表明,用相似性指数(SI)和Nei的遗传距离(D)及聚类分析对本研究筛选的三个引物OPX-04、OPX-06和OPX-19的扩增结果进行比较,除OPX-06的D值聚类可将各寄主植物上的烟蚜分开外,其余均可将样本分为两类,即来自桃树的烟蚜和来自油菜、烟草上的烟蚜。这说明与桃树的烟蚜相比,在DNA水平上,油菜上的烟蚜与烟草上的烟蚜更为接近。结果还表明,在烟蚜的体色方面,与黄绿色相比,红色与褐色更为接近。     

茶丽纹象甲的发生规律与防治

茶丽纹象甲（ＭｙｌｏｃｅｒｉｎｕｓａｕｒｏｌｉｎｅａｔｕｓＶｏｓｓ）是近几年在我县茶园中新发现的一种害虫。由于该成虫的体色为灰黑色,体背覆有黄绿色鳞片集成的斑点和条纹,腹面散生黄绿或绿色鳞毛;鞘翅上具黄绿色纵带,近中央处有较宽的黑色横纹,故又名茶小绿...     

棉尖象的发生与防治

棉尖象是南通棉区棉花苗期主要害虫之一。过去发生少,为害轻。六十年代中期以来,玉米大面积夏改春,棉尖象也随之暴发,给棉田全苗造成一定威胁。 一、形态特征 1.成虫 体色灰黄至灰褐,翅鞘上分布不规则褐色斑块,并散布鳞片毛,左右各有刻点纵沟10条。虫体腹面呈黄绿色金属光泽。雄体长3.8毫米,雌虫4.1毫米(不包括     

基于EPG分析无翅型和有翅型柑橘蚜虫的取食行为

为明确无翅型、有翅型柑橘蚜虫取食行为的差异,采用EPG技术对褐色橘蚜Toxoptera citricida(Kirkaldy)和棉蚜Aphis gossypii Glover的有翅型、无翅型成蚜在柑橘苗上的取食行为进行测定。结果表明,褐色橘蚜无翅型和有翅型的EPG均记录到7种取食波形,依次为非刺探波np、路径波A、B和C、电位下降波pd、韧皮部取食波E1和E2;棉蚜无翅型和有翅型的EPG记录到9种取食波形,除上述7种外,还包括木质部主动吸食波G和口针阻碍波F。褐色橘蚜有翅型和无翅型的np波持续时间为25.73 min和8.39 min,二者间差异显著;棉蚜有翅型的np波持续时间、刺探次数、C波次数分别为27.34 min、19.16次、20.21次,显著高于无翅型,而刺探总持续时间为332.66 min,显著低于无翅型。棉蚜的C波次数及总持续时间、刺探次数、pd波次数及总持续时间均显著高于褐色橘蚜,而E2波总持续时间及平均持续时间均显著小于褐色橘蚜。表明棉蚜无翅型比有翅型在柑橘上更容易取食,影响有翅型蚜虫取食的抗性因子可能位于柑橘表面;褐色橘蚜比棉蚜对柑橘的适应性更强。     

基于Holdridge分类系统的东北地区主要树种的水热分布类群

根据东北地区树种分布资料和233个气象站资料,利用Holdridge生命地带分类系统计算了东北地区50种主要树种的Holdridge生命地带分类系统的年生物温度(BT)、可能蒸散(APE)、年降水量(PREC)和可能蒸散率(PER)。构建了Holdridge指标与树种分布的纬度、经度和海拔高度的回归模型,定量的分析了东北地区树种分布的气候规律。综合年生物温度(BT)和可能蒸散率(PER)两个气候指标将50种主要树种划分为8个水热指标类群,分别为寒温耐旱型、寒温湿润型,寒温潮湿型,中温耐旱型,中温湿润型,中温潮湿型,暖温耐旱型和暖温湿润型。     

朱砂叶螨和二斑叶螨

朱砂叶螨Tetranychus cinnabarinus和二斑叶螨T.urticae是两个较难区分的种。 卵:后者为乳白色、半透明;而前者微黄、不透明。但3天后均为黄色,且逐渐出若现两个红色眼点,难区分。 若螨:活动期体色及体背两侧斑纹两种无差异。但静止期近羽化时前者为橙红色,后者绿或墨绿色,静止期体色稳定。     

不同体色棉蚜的体色变化规律与繁殖特征

黄、绿两种体色棉蚜在不同温度下的体色变化规律表明,绿色干母的黄色后代在18℃和22℃下经1代分化后全部稳定产绿色个体,而在26℃下则分化为绿色和黄色两种个体。棉田采集的黄、绿个体在不同温度下的体色筛选表明,黄色个体在18℃和21℃下能分化出黄色和绿色两种个体,但在24℃和27℃下保持黄色不变;而绿色个体在18℃和21℃的低温下连续4代基本上保持绿色不变,24℃和27℃的高温下却全分化为黄色。棉蚜在棉株新叶上的绿色蚜比例明显高于老叶。田间黄、绿两种体色棉蚜在相同温度下的产仔前期、平均寿命无显著差异,但平均产仔量表现为绿色蚜高于黄色蚜,并在26℃下差异显著。     

旋幽夜蛾在通榆县大面积发生为害

2005年6月9日在通榆县新华镇发现1种新的害虫为害。该害虫群集、迁移为害,虫龄不整齐,体色多变。在葵花、蓖麻田密度24头/m2,在灰菜上达70～80头/m2。取食量大,2d内造成本县新华镇2000hm2农作物受灾,其中绝收毁种面积944hm2,造成直接经济损失126万元。根据2d的田间实地考察和标本形态特征观察,经省农业大学昆虫专家鉴定,认定该害虫为旋幽夜蛾(Scotogramma trifoliiRottemberg),别名藜盗虫、绿虫子、剜心虫等。该虫食性与草地螟相似,体形与黏虫相仿。田间幼虫体长20～30mm(老熟幼虫31～35mm),头褐色或褐绿色,随虫龄及食性不同,体色变异大,有…     

Tumours of Begonia and some other ornamentals,induced by Corynebacterium fascians

In 1975 many tumours were observed in plants ofBegonia Schwabenland grown in Aalsmeer. Submersion of the roots ofNicotiana megalosiphon seedlings in a homogenate of tumorous tissue, induced tumours after two weeks. Short periods of submergence yielded results similar to those obtained after longer periods. Tumour homogenates lost their infectivity after ten min at 50°C. Aphids transmitted the infectious agent.Treatment with propylene oxide did not inhibit infectivity completely. Filtration through a 450 nm filter removed the infectious agent.Tobacco tumor virus or a viroid could not be isolated. Cultures ofCorynebacterium fascians, isolated from tumours ofN. megalosiphon were highly infectious and induced tumours in healthyN. megalosiphon andBegonia. Tumorous tissue homogenates ofPelargonium zonale, Dahlia sp.,Gladiolus sp., andLilium sp. also caused tumours inN. megalosiphon, from whichC. fascians was isolated. It was not possible to produce tumours inN. megalosiphon with homogenates from roses with symptoms of bud proliferation.Samenvatting In 1975 werden vele tumoren waargenomen inBegonia Schwabenland op Aalsmeerse bedrijven (Fig. 1). De infectiositeit van tumorweefsel kon goed en snel worden vastgesteld door de wortels van zaailingen vanNicotiana megalosiphon in een homogenaat van tumorweefsel te dompelen. Tumoren ontstonden na twee weken, de eindbeoordeling geschiedde na een maand (Fig. 2). Ook verschillende andereNicotiana spp.,Melilotus officinalis (Fig. 3) enPisum odoratum (Fig. 4) werden aangetast.Bij de infectiositeitstoets gaven zeer korte dompeltijden even goede resultaten als langere (Tabel 1). Infectieus sap verloor zijn infectievermogen na 10 min verhitting bij 50°C. Bladluizen brachten de smetstof over. Propyleenoxide verminderde de infectiositeit wel, doch onderdrukte deze niet totaal. Bij filtratie door een 450 nm filter bleef het infectieuse agens op het filter achter. Het tumor-inducerende agens was ook aanwezig in die delen van planten met tumoren welke gezond leken en het ging voor een gering deel over met zaad (Tabel 2).Uit tumoren konden wij geen tabakstumorvirus of een viroïde isoleren. Culturen vanCorynebacterium fascians, geïsoleerd uit tumoren vanN. megalosiphon bleken zeer infectieus en veroorzaakten tumoren inN. megalosiphon enBegonia. Homogenaten van tumorweefsel vanPelargonium zonale, dahlia (Fig. 5), gladiool (Fig. 6) enLilium Mid Century Hybrid Enchantment (Fig. 7) veroorzaakten ook tumoren opN. megalosiphon, waaruitC. fascians werd geïsoleerd. Met sap van kroeskopzieke rozen konden wijN. megalosiphon niet besmetten.     

Plant Viruses Transmitted by Whiteflies

One-hundred and fourteen virus species are transmitted by whiteflies (family Aleyrodidae). Bemisia tabaci transmits 111 of these species while Trialeurodes vaporariorum and T. abutilonia transmit three species each. B. tabaci and T. vaporariorum are present in the European–Mediterranean region, though the former is restricted in its distribution. Of the whitefly-transmitted virus species, 90% belong to the Begomovirus genus, 6% to the Crinivirus genus and the remaining 4% are in the Closterovirus, Ipomovirus or Carlavirus genera. Other named, whitefly-transmitted viruses that have not yet been ranked as species are also documented. The names, abbreviations and synonyms of the whitefly-transmitted viruses are presented in tabulated form together with details of their whitefly vectors, natural hosts and distribution. Entries are also annotated with references. Whitefly-transmitted viruses affecting plants in the European–Mediterranean region have been highlighted in the text.     

Identification,incidence and characterization of <Emphasis Type="Italic">Fusarium proliferatum</Emphasis>on ornamental palms in Spain

During a survey conducted from 1998 to 2002, Fusarium proliferatum was found associated with young and adult palms belonging to the genera Chamaerops, Phoenix, Trachycarpus and Washingtonia showing symptoms of wilt and dieback. The fertility and toxicological profile of 36 strains representing different locations and hosts were studied. All of them except two, which were infertile, belonged to mating population D. Both mating types (MATD-1 and MATD-2) were isolated from the same host species, showing a high potential of genetic recombination in the field. Additionally, eight strains were fertile once crossed as female. Toxin analysis showed differences in the ability of strains to produce fumonisin B₁, moniliformin, beauvericin, fusaric acid and fusaproliferin. Only 17 of them produced all the toxins analyzed. Pathogenicity tests were conducted on Phoenix dactylifera and P. canariensis using nine F. proliferatum Spanish strains and two reference strains from Saudi Arabia. Eight months after inoculation all strains caused disease, with palms showing lesions on the bases of leaves and development of wilt symptoms similar to those originally observed in affected plants. This is the first report on the occurrence of F. proliferatum on P. dactylifera in Spain and also the first report of this pathogen on C. humilis, P. canariensis, P. reclinata, T. fortunei, W. filifera and W. robusta.     

Epidemiology and simulation of population development of Sitobion avenae in winter wheat

The epidemiology ofSitobion avenae and its natural enemies in winter wheat was studied in 1975, 1976 and 1977. Immigration was important until the end of flowering. The alate immigrants had apterous offspring. These became the driving force in population growth. Their offspring were mostly alatae which usually left the field. A model of the epidemic was developed. Quantitative relations between the aphids and their environment were obtained from literature or established in laboratory trials. The model simulated population development and population composition from the beginning of June till the population peak at the end of June or early in July. Because quantitative data on relations between aphids and their natural enemies and pathogens are scarce, and since the knowledge on wing formation is still limited, the population collapse could not be predicted. In the future, prognosis over a period of three weeks seems possible.Samenvatting De toenemende betekenis van graanbladluizen (vooralSitobion avenae) gepaard gaande met een sterke toename van het gebruik van insecticiden op granen maakte verbetering van de prognose over het schadelijk optreden wenselijk. Door gedetailleerde tellingen in het veld (Fig. 1–7) werden gegevens verkregen over het verloop van de epidemie en het optreden van natuurlijke vijanden in 1975, 1976 en 1977.Een immigratieperiode tot in de bloei kon worden vastgesteld. Daarna lijkt de aantrekkelijkheid van het gewas voor alate luizen te verminderen. De alate immigranten krijgen aptere nakomelingen. Deze vormen de stuwende kracht van de populatiegroei. De nakomelingen van apteren zijn merendeels alaat. Zij verlaten het gewas.Een model van de populatieontwikkeling gedurende de epidemie werd opgesteld. De relatiediagrammen Fig. 9 en 10 laten groei en ontwikkeling vanS. avenae en een predator (Syrphus corollae) zien. Kwantificering van de betrekkingen werd mogelijk door literatuurgegevens en laboratoriumexperimenten.Met het model kon de populatieontwikkeling vanS. avenae vanaf begin juni tot aan de populatiepiek in 1975, 1976 en 1977 vrij goed worden gesimuleerd (Fig. 12). Ook de populatieopbouw kon worden gesimuleerd (Fig. 14). De teruggang van de populatiedichtheid blijkt moeilijker te voorspellen door het ontbreken van gegevens over natuurlijke vijanden.Het lijkt waarschijnlijk dat in de toekomst met het model een prognose over de piek van de bladluispopulatie circa 3 weken tevoren mogelijk zal zijn.     

A new <Emphasis Type="Italic">Rhizoctonia</Emphasis> sp. closely related to <Emphasis Type="Italic">Waitea circinata</Emphasis> causes a new disease of creeping bentgrass

Isolates of an unidentified Rhizoctonia sp. (UR isolates) were obtained from creeping bentgrass and Kentucky bluegrass with reddish brown sheath and foliar rots. Because the UR isolates anastomosed with isolates of three varieties of Waitea circinata (var. oryzae, var. zeae, and var. circinata), colony morphology, hyphal growth rate at different temperatures, pathogenicity, sequence analysis of the internal transcribed spacers (ITS) region of ribosomal RNA genes (rDNA) were compared. The colony color of mature UR isolates was distinct from isolates of the other three varieties of W. circinata. In pathogenicity tests on creeping bentgrass, the severity of the disease caused by UR isolates was significantly higher than that caused by the three varieties of W. circinata. Sequence similarities of the rDNA-ITS region between UR isolates and between isolates within each variety were high (97–100%), but they were lower among isolates from UR and the varieties of W. circinata (88–94%). In a phylogenetic tree based on the rDNA-ITS sequences, UR isolates formed a cluster separate from each of the clusters formed by the three varieties of W. circinata. These results indicate that the UR isolates clearly differ from the three varieties of W. circinata. We therefore propose that the UR isolates be classified as new Rhizoctonia sp. that are closely related to W. circinata and that the disease on creeping bentgrass should be called Waitea reddish-brown patch disease (Sekikasshoku-hagusare-byo in Japanese).     

Broad bean mottle virus in Morocco; curculionid vectors,and natural occurrence in food legumes other than faba bean (Vicia faba)

Broad bean mottle virus (BBMV) was transmitted from infected to healthy faba-bean plants by the curculionid weevilsApion radiolus Kirby,Hypera variabilis Herbst,Pachytychius strumarius Gyll,Smicronyx cyaneus Gyll, andSitona lineatus L. The latter appeared to be an efficient vector: acquisition and inoculation occurred at the first bite, the rate of transmission was c. 41%, and virus retention lasted for at least seven days.S. lineatus transmitted the virus from faba bean to lentil and pea, but not to the three genotypes of chickpea tested. This is the first report on the generaHypera, Pachytychius, andSmicronyx as virus vectors, and onA. radiolus, H. variabilis, P. strumarius, andS. cyaneus as vectors of BBMV.Out of 351 samples of food legumes with symptoms suggestive of virus infection, 16, 11, 19, and 17% of the samples of chickpea, lentil, pea, and common bean, respectively, were found infected when tested for BBMV in DAS-ELISA. This is the first report on the natural occurrence of BBMV in chickpea, lentil, pea, and common bean. The virus should be regarded as a food-legume virus rather than a faba-bean virus solely, and is considered an actual threat to food legume improvement programmes.     

Relationships of <Emphasis Type="Italic">Barley yellow dwarf virus</Emphasis>-PAV and <Emphasis Type="Italic">Cereal yellow dwarf virus</Emphasis>-RPV from Iran with viruses of the family <Emphasis Type="Italic">Luteoviridae</Emphasis>

Barley yellow dwarf disease is one of the most important problems confronting cereal production in Iran. Barley yellow dwarf virus-PAV (BYDV-PAV) and Cereal yellow dwarf virus-RPV (CYDV-RPV) are the predominant viruses associated with the disease. One isolate of BYDV-PAV from wheat (PAV-IR) and one isolate of CYDV-RPV from barley (RPV-IR) were selected for molecular characterisations. A genome segment of each isolate was amplified by PCR. The PAV-IR fragment (1264 nt) covered a region containing partial genes for coat protein (CP), read through protein (RTP) and movement protein (MP). PAV-IR showed a high sequence identity to PAV isolates from USA, France and Japan (96–97%). In a phylogenetic analysis it was placed into PAV group I together with PAV isolates from barley and oats. The fragment of RPV-IR (719 nt) contained partial genes for CP, RTP and MP. The sequence information confirmed its identity as CYDV. However, RPV-IR showed 90–91% identity with both RPV and Cereal yellow dwarf virus-RPS (CYDV-RPS). Phylogenetic analyses suggested that it was more closely related to RPS. These data comprise the first attempt to characterise BYD-causing viruses in Iran and southwest Asia. The nucleotide sequence data reported appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession numbers AY450425 and AY450454     

Recent observations on leafy gall in Liliaceae and some other families

Corynebacterium fascians, which causes leafy gall, has been shown to be responsible for the unusual symptoms recently found in lilies. The symptoms are described and the different bacterial isolates compared by biochemical, serological and pathogenicity experiments. No evidence could be found for the existence of specialized strains even though considerable variation in virulence could be demonstrated. Although the role of variation in susceptibility of the different lily cultivars should not be underestimated, it would appear that high inoculum levels ofC. fascians in the soil may be largely responsible for these outbreaks.Also included in this study are the results of biochemical, serological and pathogenicity experiments ofC. fascians which has been isolated fromKalanchoe, Euphorbia, Brodiaea, Hebe andVerbascum.Samenvatting Reeds een aantal jaren was in lelies een woekering in stengelbollen bekend, die echter sporadisch voorkwam en economisch van weinig betekenis was. Tijdens de zomer van 1977 echter trad de ziekte op één enkel perceel zo ernstig op dat zeer aanzienlijke oogstderving het gevolg was. Behalve de stengelbol kan ook de hoofdbol misvormd zijn. Bovendien kunnen misvormde stengelbollen lange spruiten vormen, zgn. sabeltandvorming. Soms is het wortelstelsel gereduceerd; in de kas zijn verdikte stengels waargenomen. De ziekte staat nu bekend onder de naam woekerziekte.Door de PD te Wageningen en het LBO te Lisse werd de bacterieCorynebacterium fascians (Tilford) Dows. uit het zieke materiaal geïsoleerd. In gezamenlijk onderzoek werd nagegaan of de bacterie de veroorzaker is van bovengenoemde symptomen en of hier sprake is van een op lelie gespecialiseerde stam.Biochemische en serologische vergelijkingen tussen isolaten vanC. fascians uit lelie,Kalanchoe, Euphorbia, Brodiaeea, Hebe enVerbascum laten zien dat er zeer weinig verschillen bestaan. Alle isolaten reageren op een standaard antiserum met titers variërend tussen 1: 640–1: 5120.Een oriënterende inoculatieproef werd uitgevoerd op het LBO in 1977. Daarna werden op de PD 10 van de 25 isolaten uit lelie en 8 uit andere waardplanten getoetst op lelie, chrysant en lathyrus. Uit de inoculatieproeven blijkt, dat de bacterie de veroorzaker is van de waargenomen symptomen. Tussen de isolaten blijkt een groot verschil in pathogeniteit te bestaan (12–100% aantasting), zonder dat dit aan herkomst gebonden is. Het voorkomen van op lelie of andere waardplanten gespecialiseerde stammen is daarom niet aan te nemen.In hoeverre de hevige aantasting een gevolg is van een opbouw van de bacterie-populatie door een te nauwe vruchtwisseling en mechanische rooimethoden moet worden nagegaan.     

Survey of Bacterial and Fungal Seedborne Diseases in Imported and Domestic Potato Seed Tubers

Potato seed tubers are imported to Israel from northern Europe and planted in spring; tubers harvested early from the spring crop are used as seed for the autumn crop. Although only seed lots registered as certified are imported, a previous survey (1984–1994) indicated that most imported lots were affected by latent or active infections caused byErwinia carotovora,Streptomyces scabies, Rhizoctonia solani, Fusarium spp. andSpongospora subterranae. The survey was extended until 1998, and included additional pathogens:Ralstonia solanacearum,Helminthosporium solani, Colletotrichum coccodes andVerticillium dahliae. Most of these pathogens were also monitored in domestic seed tubers, and are reported for the first time. Brown rot was not observed in any of the imported lots. Blackleg and soft rot caused byErwinia spp. were detected in most of the imported lots; however, less than 7% of the lots were contaminated at high levels, while approximately 65% were contaminated at moderate levels. Common scab was detected in most of the imported lots; 51% of the imported lots were contaminated at moderate or high levels, whereas only 6.5% of the domestic seed lots were contaminated at these levels. Black scurf was detected in most of the imported lots; on average, 47.3%, 44.2% and 1.4% of the lots were contaminated at low, moderate and high levels, respectively, and only 7.1% were disease-free. In contrast, most of the domestic lots were either disease-free (45.4%) or had a low disease incidence (37.3%). Only 16.7% of the lots were moderately infected and 0.2% were highly contaminated. Silver scurf was observed in most of the imported lots during all years of the survey, with no differences among the producing countries; on average, 22.7%, 66.1% and 7.5% of the lots were contaminated at low, moderate and high levels, respectively, and only 3.7% were disease-free. Most of the domestic lots (76%) were disease-free and only 6.6% were infected at moderate or high levels. Black dot was observed in a considerable portion of the shipments from Holland during all years of the survey, particularly in 1998, when 34% of the lots were infected. The shipments from France and Germany were infected at low levels, except in 1998, when 19% and 11% of the lots, respectively, arrived infected. In shipments from Scotland and Ireland low incidences of the disease were observed in 1994 and 1995. In the domestic lots, black dot incidence was low (<2.4%) except in 1996, when 11% of the lots were infected.V. dahliae was monitored only in domestic seed tubers. The incidence of disease-free lots was 56–64%, whereas in 20–30% of the lots the level of infection was <5%, and in 6–16% of the lots the level was >5%. The survey findings demonstrate transmission of seedborne pathogens; most of these pathogens can become established in the soil and eventually cause severe outbreaks of disease in potatoes grown in Israel. http://www.phytoparasitica.org posting May 16, 1999.     

Pathogenic fungi involved in root rot of peas in the Netherlands and their physiological specialization

Research on root rot pathogens of peas in the Netherlands has confirmed the prevalence ofFusarium solani, F. oxysporum, Pythium spp.,Mycosphaerella pinodes andPhoma medicaginis var.pinodella. Aphanomyces euteiches andThielaviopsis basicola were identified for the first time as pea pathogens in the Netherlands. Other pathogens such asRhizoctonia solani andCylindrocarpon destructans were also found on diseased parts of roots. F. solani existed in different degrees of pathogenicity, and was sometimes highly specific to pea, dwarf bean of field bean, depending on the cropping history of the field.A. euteiches was specific to peas, whereasT. basicola showed some degree of physiological specialization.