苦瓜枯萎病菌的鉴定及其遗传多样性分析

 对分离获得的32株苦瓜枯萎病菌菌株进行形态学特征和寄主专化型测定, 结果表明, 测试的苦瓜枯萎病菌株均为尖孢镰刀菌苦瓜专化型 (Fusarium oxysporum f. sp. momordicae), 这些菌株可以侵染苦瓜和瓠瓜幼苗, 但不侵染其他葫芦科瓜类作物。对苦瓜枯萎病菌菌株的rDNA-ITS区 (ITS1、5.8S和ITS2)序列进行扩增测序, 结果显示其序列长度均为456 bp;聚类分析表明测序菌株与镰刀菌属中尖孢镰刀菌不同专化型的菌株聚为一群。利用RAPD标记技术分析苦瓜枯萎病菌的遗传多样性, 结果显示苦瓜枯萎病菌株与其他葫芦科瓜类作物枯萎病菌株间的遗传相似系数范围为0.59~0.99, 当遗传相似系数为0.85时, 供试的48个菌株分成10个类群 (G_1~10)。在RAPD聚类树中所有苦瓜枯萎病菌株聚在一个分支上 (G₁群), 菌株间的遗传相似系数范围为0.92~1.00, 具有较高的遗传相似性, 且菌株的聚群与地理来源存在一定的相关性。     

巴拿马进口香蕉上的尖孢镰刀菌对玉米苗期侵染试验简报

在巴拿马进口香蕉上分离获得的尖孢镰刀菌,编号为 NP1800,哈尔滨医科大学和中国科学院微生物所合作进行“串珠镰刀菌和尖孢镰刀菌对玉米苗期侵染的接种试验”,用该菌作试验菌种,在他们试验的9种尖孢镰刀菌中,NP1800是对玉米幼苗致病性最强的菌株。尖孢镰刀菌是广寄主专化型的。我们认为该菌除为害香蕉之外,还有可能为害其他农作物。因此我们进行了尖孢镰刀菌对玉米苗期的侵染试验。获得了以下4方面的数据:(1)不同玉米品种注射接种的发病情况(2)尖孢镰刀菌对不同玉米品种发病回收统计(3)注射接     

尖孢镰刀菌双链RNA的分离鉴定

 对尖孢镰刀菌10个专化型18个菌株进行分析发现,在尖孢镰刀菌大豆专化型Fusarium oxysporum f.sp.Glycines 1193-31中存在双链RNA,由6种成分组成,其大小分别为3.8kb,3.0kb,2.4kb,0.48kb,0.43kb和0.21kb,该菌株气生菌丝少,形成大量的粉红色分生孢子堆,并发生角变。     

甘肃定西地区甘蓝枯萎病病原菌的分离与鉴定

自2009年起,甘肃定西地区出现了甘蓝植株矮化、叶片黄化、枯萎甚至死亡的现象。2015年8月,我们采集了田间病株样本,使用常规组织分离法对病原菌进行了分离和纯化,依据柯赫氏法则进行了病原菌确认,并通过形态学和分子生物学方法对病原菌进行了鉴定。结果表明病原菌的形态学特征与尖孢镰刀菌Fusarium oxysporum一致,其rDNA-ITS、rDNA-IGS以及EF-1α序列与尖孢镰刀菌F.oxysporum相似性达99%,基于病原菌及尖孢镰刀菌各代表专化型EF-1α序列构建的系统发育树将该菌与尖孢镰刀菌黏团专化型F.oxysporum f.sp.conglutinans聚为一类,故引致甘肃定西地区甘蓝枯萎病的病原菌为尖孢镰刀菌黏团专化型F.oxysporum f.sp.conglutinans。     

大蓟总黄酮对尖孢镰刀菌甜瓜专化型生长、生理的影响及其田间防治效果

为探究大蓟总黄酮对尖孢镰刀菌甜瓜专化型Fusarium oxysporum f. sp. melonis的抑制效果,采用微波超声法提取大蓟种子中的总黄酮,并测定其对其尖孢镰刀菌甜瓜专化型生长、生理指标的影响及其田间防治效果。结果显示,大蓟总黄酮浓度为10 mg/mL时,对尖孢镰刀菌甜瓜专化型的菌丝生长抑制率和孢子萌发抑制率达到100.0%,菌丝畸变、断裂;尖孢镰刀菌甜瓜专化型OD650 nm和pH最小,分别为0.3和5.5;其电导率是对照组1.2倍。不同浓度大蓟总黄酮处理下尖孢镰刀菌甜瓜专化型呼吸强度、超氧化物歧化酶(superoxide dismutase,SOD)和过氧化氢酶(catalase,CAT)活性均呈现先上升后下降的趋势,羧甲基纤维素酶和β-葡萄糖苷酶活性降低,浓度为10 mg/mL大蓟总黄酮处理尖孢镰刀菌甜瓜专化型60 h后,呼吸强度、SOD和CAT活性均降至最低,分别为7.8 mgCO2·cm-2·h-1、22.9 U/mL和20.8 U/mL。田间防治结果表明,浓度为10 mg/mL大蓟总黄酮处理下,甜瓜枯萎株数最少,防治效果最佳,为93.5%。表明大蓟总黄酮能够有效地抑制尖孢镰刀菌甜瓜专化型生长,具有进一步发展为绿色新型植物源尖孢镰刀菌甜瓜专化型防治剂的能力。     

水花生病原菌——蕉斑镰刀菌菌株的筛选及其致病性测定

蕉斑镰刀菌 Fusarium stoveri是从自然界水花生植株上分离的、可致水花生表现萎蔫、地上茎腐烂、叶片上呈现褐色斑或黄化的生防真菌.室内研究表明,蕉斑镰刀菌菌丝生长和产孢的适宜温度范围在25～28℃,多数菌株的最适温度为28℃;菌株间的产孢量有较大差异.在供试菌株中,32-6菌株的产孢量最大;供试的9个蕉斑镰刀菌菌株对水花生均有较强的致病力,但菌株间的致病力有所差异.根据菌株的生长速率、产孢量和致病力等因素,菌株32-6被选为水花生生防菌的优选菌株.采用生产上常见农作物、蔬菜、经济作物及物候上与水花生一致的杂草等42种植物对菌株32-6进行寄主专化性测定,结果表明,蕉斑镰刀菌菌株32-6具有高度的寄主专化性,只对水花生表现出较强的致病性,对其他植物均不致病.     

西瓜枯萎病菌遗传多样性的相关序列扩增多态性分析

对30个西瓜枯萎病菌Fusarium oxysporum f.sp.niveum菌株基因组DNA进行相关序列扩增多态性(SRAP)分子标记分析,以探究其遗传多样性与地理来源的关系。采用尖孢镰刀菌西瓜专化型Fusarium oxysporumf.sp.niveum0、1、2号生理小种的基因组DNA为模板,对225对SRAP引物进行筛选,筛选出20对多态性、重复性较好且条带清晰的引物,对30个菌株进行PCR扩增,共扩增出386条带,其中多态性条带有371条,多态性比率为96.11%,平均每对引物扩增出19.3个位点和18.55个多态性位点。UPGMA法聚类分析结果显示,供试菌株两两之间的遗传相似系数范围为0.69~0.90,平均为0.79,说明尖孢镰刀菌西瓜专化型的遗传多样性较为丰富。基于SRAP标记聚类分析表明,30个菌株在遗传相似系数为0.70处被划分为3个类群,I类群包含24个菌株,其中18个来自湖南省,Ⅱ类群只包含1个来自黑龙江省哈尔滨市的菌株,它和另一个来自黑龙江地区的菌株被划分到不同的类群,且遗传距离相对较远;Ⅲ类群包含了5个菌株,其中3个来自海南三亚,其余两个来自湖南省。根据菌株的分布情况来看,菌株的聚集与地理来源没有明显的相关性。     

香蕉枯萎病菌生理小种鉴定及其SCAR标记

 通过室内人工接种蕉类鉴别寄主,对采集于广东蕉区的18个蕉类枯萎病菌菌株进行鉴定,KP021、KP022、GZ981和JL021 4个菌株属Racel,其余14个菌株属Race4,说明广东蕉区同时存在尖孢镰刀菌古巴专化型Race1和Race4。用RAPD技术对上述18个菌株进行分析,从200条随机引物中筛选出8条引物可产生生理小种RAPD标记12个,其中标记Racel的8个,标记Race4的4个。对这些RAPD标记带分别进行回收、克隆、测序,根据这些特异片段序列分别设计相应的SCAR引物,通过对18个菌株的PCR扩增检验,有4个RAPD标记成功地转化为SCAR标记,其中Race1-SCAR标记1个、Race4-SCAR标记2个、同时能鉴定出2个小种的SCAR标记1个。应用这4个SCAR标记同时对采自田间的9个病菌分离物进行检测,能够准确地鉴定出广东蕉区的尖孢镰刀菌古巴专化型Racel和Race4,这为下一步开展香蕉枯萎病菌生理小种的分子鉴定及各生理小种田间流行动态监测奠定了基础。     

尖孢镰刀菌的遗传多态性

 尖孢镰刀菌是重要的植物维管束病原真菌。近年来,有关该菌的遗传多态性研究报道很多,本文着重综述了利用营养体亲和群、DNA多态性技术研究尖孢镰刀菌专化型、小种及其相互关系等方面的进展,同时介绍了对棉花枯萎病菌、瓜类枯萎病菌及尖孢镰刀菌小种起源等的研究概况。     

晋南地区黄瓜、黑籽南瓜死秧的病原菌鉴定及品种抗性研究

经分离、培养对不同菌种培养性状的观察,确定了侵染黄瓜、黑籽南瓜造成死秧的镰刀菌主要为尖镰孢菌黄瓜专化型、尖镰孢菌西瓜专化型、串珠镰刀菌和腐皮镰孢菌4种。经致病性测定,4种镰刀菌均能侵染黄瓜,引起发病造成死秧,可分为强致病类型和中强致病类型。经抗病性鉴定,黑籽南瓜种子只有南瓜4号为耐病品种;黄瓜种子也只有津优31号为耐病品种。     

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).     

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     

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.     

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.