小麦纹枯病菌对三唑酮不同敏感性菌株的生物学特性及对不同杀菌剂的敏感性

为预测小麦纹枯病菌对三唑酮抗药性的发展趋势,采用菌丝生长速率法测定了2013年分离自河南省16个地市的98株菌株对三唑酮的敏感性,比较不同敏感性菌株的生物学性状差异,并分析了其中22株菌株对其它10种杀菌剂的敏感性。结果表明:小麦纹枯病菌群体中已出现对三唑酮敏感性下降的菌株,其中有90株菌对杀菌剂的敏感性属于正态分布,以其EC_(50)均值1.91μg/mL作为小麦纹枯病菌对三唑酮的敏感性基线。敏感菌株菌丝生长速度较快,可达8.50~12.86 mm/d,菌核产量较多,为35.80~42.90 mg/皿,生存适合度较高;敏感性下降及抗性菌株的致病性及菌核萌发等都未发生改变,但菌丝生长速率仅为5.36~10.02 mm/d,菌核产量为9.00~36.90 mg/皿,均下降明显,生存适合度降低;低抗菌株与敏感菌株在菌落形态上相同,但菌丝分枝数增多且分枝菌丝变短。三唑酮对小麦纹枯病菌的毒力较小,EC_(50)大于其它10种杀菌剂;戊唑醇、氟环唑、烯唑醇、咯菌腈和噻呋酰胺的毒力均较大,其EC_(50)≤0.10μg/mL;其余5种杀菌剂的EC_(50)在0.13~0.69μg/mL之间;小麦纹枯病菌对三唑酮的敏感性与其它10种杀菌剂间的决定系数为0.003~0.200,存在微弱的正相关性,表明在生产中这些杀菌剂可与三唑酮轮换或交替使用。     

几种杀菌剂对玉米顶腐病菌的抑制作用

用平板菌落法测定了杀菌剂对玉米顶腐病菌菌丝生长、产孢、孢子萌发及芽管伸长的抑制作用。结果表明:浓度为1000μg/mL的60%氟吗·锰锌可湿性粉剂、15%三唑酮可湿性粉剂、47%腈菌·锰锌可湿性粉剂3种杀菌剂对菌丝生长抑制率为100%。1000μg/mL和500μg/mL供试各杀菌剂能抑制分生孢子萌发,50%多菌灵可湿性粉剂和77%氢氧化铜可湿性粉剂抑制孢子萌发EC50分别为0.2719μg/mL和762.8854μg/mL。供试杀菌剂抑制芽管伸长的EC50差异显著,47%腈菌·锰锌可湿性粉剂EC50为0.1268μg/mL,70%甲基硫菌灵可湿性粉剂EC50为383.9653μg/mL。杀菌剂对分生孢子产生抑制作用显著,产孢量显著小于对照,60%氟吗·锰锌可湿性粉剂能完全抑制孢子形成。     

短萼仪花炭疽病病原鉴定及其药剂筛选

采用组织块分离法分离了短萼仪花病叶上的病原菌,通过针刺回接法确定了其致病性,进一步采用形态学和分子生物学相结合的方法对短萼仪花炭疽病的病原进行鉴定。同时,采用菌丝生长速率法测定了7种不同的杀菌剂对短萼仪花炭疽病病菌的室内毒力。结果表明,引起短萼仪花炭疽病的病原为胶孢炭疽菌(Colletotrichum gloeosporioide)。7种杀菌剂对短萼仪花炭疽病病菌的室内毒力明显不同。其中,97%吡唑醚菌酯表现出最好的抑制作用,EC_(50)为(9.67±1.20)μg/mL。     

苯并烯氟菌唑对尖孢炭疽菌的毒力及对其所致辣椒炭疽病的防效

为评价苯并烯氟菌唑对辣椒炭疽病的防治潜力，采用菌丝生长速率法和孢子萌发法分别测定苯并烯氟菌唑对108株辣椒炭疽病病原菌尖孢炭疽菌Colletotrichum acutatum菌株菌丝生长和孢子萌发的抑制活性，通过辣椒活体接种试验比较苯并烯氟菌唑对辣椒炭疽病的相对保护防效和相对治疗防效，测定其对辣椒炭疽病的室内相对防效和田间相对防效。结果表明，苯并烯氟菌唑对尖孢炭疽菌孢子萌发的抑制活性高于对其菌丝生长的抑制活性，对孢子萌发及对菌丝生长的有效抑制中浓度EC₅₀分别为0.005～0.196μg/mL和0.073～3.398μg/mL；苯并烯氟菌唑对辣椒炭疽病的相对保护防效优于相对治疗防效，240 g (a.i.)/hm²苯并烯氟菌唑对辣椒炭疽病的相对保护防效可达85.64%。240 g (a.i.)/hm²苯并烯氟菌唑喷雾处理对辣椒炭疽病的田间相对防效均在75.31%以上，显著高于相同剂量的氟吡菌酰胺、氟啶胺和多菌灵的相对防效。总之，苯并烯氟菌唑对尖孢炭疽菌有较高毒力，对辣椒炭疽病有稳定的田间防效，有开发为防治辣椒炭疽病新药剂...     

辣椒炭疽病病原鉴定及其杀菌剂毒力测定

从贵阳市花溪区磊庄村辣椒基地采集疑似炭疽病的典型的自然发病辣椒果实,采用组织分离、培养、形态学观察、致病性测定以及多基因分子系统学,确定病原菌的种类;采用菌丝生长速率法研究了8种杀菌剂对该病菌菌丝生长的抑制作用。结果表明,引起贵阳市花溪区磊庄村辣椒炭疽病的病原菌为尖孢炭疽菌Capsicum acutatum。室内毒力测定发现8种杀菌剂对尖孢炭疽菌均有一定的抑制作用,其中25%咪鲜胺EC和30%吡唑醚菌酯SC抑制效果最好,EC_(50)分别为0.253 5 mg/L和0.720 3 mg/L;其次为22.5%啶氧菌酯SC和22.7%二氰蒽醌SC,EC_(50)分别为7.249 5 mg/L和21.664 5 mg/L。将30%吡唑醚菌酯SC和22.7%二氰蒽醌SC按照9∶1、6∶4、3∶7、4∶6的比例混配,联合毒力测定和评价结果显示两者混配对该病菌具有协同增效作用,且25%咪鲜胺EC和22.5%啶氧菌酯SC以6∶4、4∶6、8∶2的比例进行混配时也表现出明显的增效作用。引起贵阳市花溪区磊庄村辣椒基地辣椒炭疽病的致病菌为尖孢炭疽菌。咪鲜胺、吡唑醚菌酯、啶氧菌酯和二氰蒽醌对该菌具有较好的抑制作用,可为辣椒炭疽病的田间防治提供参考依据。     

草莓丝核菌根腐病病原菌鉴定及7种杀菌剂的抑菌作用测定

为了解草莓丝核菌根腐病的病原种类及筛选防治丝核菌根腐病的有效杀菌剂,本研究基于形态学特征、细胞核荧光染色、菌丝融合群测定以及rDNA-ITS的序列分析,对北京和河北承德地区的草莓丝核菌根腐病的病原菌进行了鉴定,并利用菌丝生长速率法测定了7种杀菌剂对丝核菌的抑菌作用。结果发现,北京地区的丝核菌为双核丝核菌(binucleate Rhizoctonia,BNR),属于融合群AG-A;河北的丝核菌为立枯丝核菌Rhizoctonia solani,属于融合群AG-4。氟啶胺、吡唑醚菌酯、噻呋酰胺、戊唑醇、咯菌腈、氟硅唑对2种丝核菌均有很强的抑制作用,EC_(50)值为0.063 9～2.485 7μg/mL,抑霉唑的抑制作用较差,EC_(50)值为9.966 8～11.236 8μg/mL。同一种杀菌剂对不同丝核菌的抑制作用存在差异,噻呋酰胺、戊唑醇、氟硅唑、咯菌腈和抑霉唑对立枯丝核菌的抑制作用强于对双核丝核菌。试验结果为生产上合理选用杀菌剂防治草莓丝核菌根腐病提供了科学依据。     

莲雾灰斑病病原菌鉴定及室内药剂筛选

为了探明莲雾灰斑病病原菌和对该病有效的杀菌剂种类,采用组织分离法进行病原菌分离,同时借助形态学特征和ITS序列进行鉴定,测定了病原菌菌丝生长的最适环境和碳氮营养条件,并进行室内药剂筛选。结果表明,莲雾灰斑病病原菌菌丝白色绒毛状,产孢结构为分生孢子盘,分生孢子梗无色瓶状,分生孢子单胞无色,椭圆形至长椭圆形,大小(13.2～23.16)μm×(4.8～7.5)μm,ITS序列长为553 bp,系统进化发现该菌与胶胞炭疽菌(Colletotrichum gloeosporioides)归为一支。该菌在25～30℃生长较快,中性和偏碱条件适宜菌丝生长,最适碳氮源分别为蔗糖和蛋白胨。5种杀菌剂对莲雾灰斑病病原菌具有较强的抑制效果,按其毒力高低排序:250 g/L丙环唑乳油(EC_(50)为0.003 mg/L)250g/L吡唑醚菌酯乳油(EC_(50)为0.264 mg/L)75%肟菌酯戊唑醇水分散剂(EC_(50)为0.610 mg/L)50%戊唑嘧菌酯悬浮剂(EC_(50)为0.834 mg/L)37%苯醚甲环唑水分散剂(EC_(50)为2.370 mg/L)。因此,莲雾灰斑病的病原为胶胞炭疽菌(Colletotrichum gloeosporioides),适生性较强,250 g/L丙环唑乳油和250 g/L吡唑醚菌酯悬浮剂可作为田间防治该病害的候选药剂种类。     

不同生育阶段黄瓜菌核病菌对几种三唑类杀菌剂的敏感性

采用菌丝生长速率法测定了6种三唑类杀菌剂和4种其他杀菌剂抑制黄瓜菌核病菌Sclerotinia sclerotiorum(Lib.)de Bary菌丝生长的毒力,同时测定了其对菌核形成及萌发的抑制作用。结果表明,甲基硫菌灵抑制菌丝生长的毒力最低,EC50值为65.75 μg/mL;己唑醇和戊唑醇的抑制活性较高, EC50值分别为0.09和0.16 μg/mL,毒力分别是甲基硫菌灵的763.7和423.4倍;其次是丙环唑、氟硅唑、腈菌唑,毒力是甲基硫菌灵的137.3~286.6倍;再次为三唑酮,毒力仅为甲 基硫菌灵的20.6倍;腐霉利、菌毒清抑制菌丝生长的毒力较低,EC50值均大于10 μg/mL。在EC50值 浓度下,所有供试药剂对菌核形成及其数量均没有影响,但三唑类杀菌剂对菌核单重影响较大,各处理所形成的菌核单重降低率均在70%以上;而当药剂浓度在10 μg/mL以下时,己唑醇等三唑类杀菌剂对菌核萌发均没有影响。     

香榧果实褐斑病病原菌鉴定及防治药剂筛选

为明确近年来在香榧Torreya grandis果实上出现的一种新病害——褐斑病的病原菌,通过分离物致病性测定、形态学观察、rDNA-ITS序列分析及病原菌生物学特性进行鉴定,并对苯醚甲环唑、嘧菌酯、甲基硫菌灵、咪鲜胺、肟菌酯及吡唑醚菌酯6种防治药剂进行了初步筛选。结果表明,从病样中分离到的菌株XF01在回接试验出现的症状与田间自然感病症状一致,证明菌株XF01为香榧果实褐斑病的致病菌。该病原菌菌丝初为灰白色,后为深灰色或青褐色;分生孢子梗单生或簇生,无分枝,淡褐色;分生孢子多倒梨形或卵形,大小平均为19.258μm×9.048μm,横、纵隔膜分别为1~7个和0~3个,无喙或具柱状短喙,形态特征与链格孢菌Alternaria alternata一致。该菌ITS序列(Gen Bank登录号为KU525533)与链格孢菌株ITS序列(Gen Bank登录号为KR864893.1)同源性为100%,并聚为一簇,分子鉴定结果与形态学鉴定结果一致,确定引起该病害的病原菌为链格孢菌。该病菌菌丝生长、产孢和孢子萌发的最佳温度均为28℃,最适生长pH均为7。室内毒力测定结果显示,咪鲜胺对该菌菌丝生长的抑制效果最好,EC50为0.065μg/mL;吡唑醚菌酯对其孢子萌发的抑制效果最好,EC50为0.002μg/mL,表明这2种药剂可用于香榧果实褐斑病的田间防治。     

黄淮麦区假禾谷镰刀菌对3种杀菌剂敏感性测定

以假禾谷镰刀菌Fusarium pseudograminearum为主要病原菌引起的小麦茎基腐病已经成为黄淮麦区的主要小麦病害之一,对小麦生产安全带来严重威胁。为了解假禾谷镰刀菌对氰烯菌酯、戊唑醇和咯菌腈3种杀菌剂的敏感性,采用菌丝生长速率法对采自河南、河北、山东的108株假禾谷镰刀菌进行了室内毒力测定。试验结果表明：氰烯菌酯对假禾谷镰刀菌的EC₅₀为0.088～0.929μg/mL,EC₅₀均值为(0.471±0.181)μg/mL;敏感性分布为连续单峰曲线,经Shapiro-Wilk正态性检验符合正态分布(W=0.988,P=0.437>0.05),所以将所有菌株的EC₅₀平均值0.471μg/mL定为假禾谷镰刀菌对氰烯菌酯的敏感基线;戊唑醇对供试菌株的EC₅₀为0.015～0.961μg/mL,EC₅₀均值为(0.384±0.219)μg/mL,敏感性分布不符合连续单峰的正态分布;咯菌腈对供试菌株的EC₅₀为0.029～0.354μg/mL,E...     

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.     

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.     

Nematicidal Activity of Chrysanthemum coronarium

Organic amendments and green manure are potential alternatives to the harmful chemical control means currently used against plant-parasitic nematodes. In this work, Chrysanthemum coronarium was applied to the soil as a green manure to control the root-knot nematodes Meloidogyne incognita and M. javanica. Chrysanthemum coronarium significantly reduced nematode infection of tomato roots and improved plant-top fresh weight, both in the greenhouse and in microplots. Other green manures, derived from Anthemis pseudocotula, wild chickpea (Cicer pinnatifidum), Geranium spp. and wheat, were not as effective as C. coronarium. Chrysanthemum coronarium, retained its nematicidal activity even when applied as a dried material. Only mature C. coronarium plants, in their flowering stage, exhibited nematode control activity, but the green plant parts were more effective than the flowers. An aqueous extract of C. coronarium exhibited in vitro, nematostatic activity towards M. incognita and M. javanica second-stage juveniles and inhibited their hatching from eggs and egg-masses; its nematostatic activity was expressed also against other phytonematode species such as Heterodera avenae and Pratylenchus mediterraneus, but did not affect the beneficial entomopathogenic nematode Steinernema feltiae.     

Inactivation of soil-borne plant pathogens during small-scale composting of crop residues

Samples of heavily infested crop residues were incorporated in static compost heaps (2.5–4.6 m³) of the Indore type. Temperature increased to 50–70°C within 6 days depending on the type of crop residues used and the location within the heap. The heat phase (>40 °C) lasted 2–3 weeks and was followed by a c. 5-months maturation phase (<40 °c).=" among=" the=" 17=" pathogens=" tested,=">Olpidium brassicae and one of the four formae speciales ofFusarium oxysporum that were tested survived composting, but also their inoculum was greatly reduced.Survival during specific phases of composting was studied by incorporation and retrieval of samples at various stages of the process.F. oxysporum f. sp.melonis was completely inactivated andO. brassicae andPlasmodiophora brassicae were almost completely inactivated during the short heat phase. The three pathogens survived the long-lasting maturation phase without loss of viability. Heat evolved during composting was found to be the most important factor involved with sanitation of crop residues. The possible involvement of fungitoxic conversion products and microbial antagonism is discussed.     

Effects of the saprophytic leaf mycoflora on growth and productivity of winter wheat

The effects of the saprophytic mycoflora and its interference with cereal aphids on growth and yield of winter and spring wheat was studied in field experiments in 1980, 1981 and 1982.Yields varied between 5000 and 8000 kg dry matter of kernels per ha. The effect of the saprophytic mycoflora on yield was determined in different treatments: A) no control measures against cereal aphids and saprophytic and necrotrophic fungi, B) no control of cereal aphids, control of saprophytic and necrotrophic fungi, C) control of cereal aphids and control of saprophytic and necrotrophic fungi, D) control of cereal aphids and stimulation of saprophytic mycoflora and E) control of cereal aphids, no control of saprophytic and necrotrophic fungi nor stimulation of saprophytic mycoflora.Considerable differences in top densities of saprophytic mycoflora (10 times as large in A and D as in B and C) were determined. The consequences of these differences for the growth and productivity of wheat were minor. A negative effect of saprophytic mycoflora on the yield could not be detected in 1981 and 1982, whereas a small positive significant effect was found in 1980. This stimulation may have been due to competition between necrotrophic fungal pathogens and saprophytic mycoflora. As a result of favourable weather conditions necrotrophic fungal pathogens were very numerous in 1980 and could form an important yield reducing factor. Yield levels may effect the importance of the necrotrophic and saprophytic mycoflora as yield reducing factors. Additionally, in the presence of aphid honeydew captafol was found to be relatively ineffective against saprophytic fungi.     

浅黄恩蚜小蜂和丽蚜小蜂对温室白粉虱的寄生潜能分析

浅黄恩蚜小蜂Encarsia sophia GiraultDodd和丽蚜小蜂Encarsia formosa Gahan是防治粉虱类害虫的优势寄生蜂,通过生命表技术方法分析了2种寄生蜂对温室白粉虱Trialeurodes vaporariorum(Westwood)的防治潜能。结果表明,丽蚜小蜂在羽化第3天和第10天出现2次寄生高峰,占其总寄生量的13.7%和8.0%,在2次高峰之间逐日寄生粉虱数量比较平稳,单雌逐日平均产雌数保持在10.6~13.4头,10 d后寄生量呈明显的下降趋势;而浅黄恩蚜小蜂羽化10 d内逐日寄生粉虱量变化不大,单雌逐日产雌数稳定在4.2~5.4头,羽化14 d后寄生量呈明显下降趋势。丽蚜小蜂和浅黄恩蚜小蜂的R0、T、rm、λ值分别为171.5、18.0、0.2854、1.3303和61.6、16.2、0.2544、1.2897;粉虱若虫充足时,丽蚜小蜂平均单雌寄生若虫数是浅黄恩蚜小蜂的2.7倍,而后者平均单雌取食若虫数为60.6头,明显高于前者42.7头,总的来看,丽蚜小蜂通过寄生和取食杀死粉虱总量220.8头,明显高于浅黄恩蚜小蜂的127.9头。表明在应用寄生蜂防治温室白粉虱时,单独释放丽蚜小蜂比浅黄恩蚜小蜂显示出更好的防治潜能。     

Aetiology and causal agents of mango sudden decline disease in the Sultanate of Oman

Mango sudden decline is a recently introduced, economically serious disease in Oman. Affected mango trees have wilting symptoms that usually begin on one side and later spread to involve the entire tree. Trees exude amber-coloured gum from the bark of their trunks or branches and vascular tissues are discoloured. Having entered Oman in the recent past, survey data is presented that shows the disease to have spread throughout the northern part of the country. Evidence is presented that the vascular wilt pathogen Ceratocystis fimbriata causes mango sudden decline disease in Oman, possibly in concert with Lasiodiplodia theobromae and the recently described Ceratocystis omanensis. Isolates of these fungi from affected trees, cause infection and can be recovered from inoculated seedlings. Bark beetles (Hypocryphalus mangiferae) are shown to carry C. fimbriata and L. theobromae and are presumably responsible for transmitting both pathogens to healthy mango trees. Acting as a wounding agent and vector, the bark beetle is likely to have assisted the rapid spread of the disease across Oman.     

Identification and pathogenicity of Pythium species causing damping-off of kidney bean

Five Pythium species (Pythium irregulare, P. mamillatum, P. myriotylum, P. spinosum and P. ultimum var. ultimum) were isolated from the hypocotyls and roots of kidney bean plants with damping-off from a commercial field and from experimental plots that have undergone either continuous cropping with kidney bean or rotational cropping with arable crops. In inoculation tests, all five Pythium species were pathogenic to kidney bean. This is the first report of damping-off of kidney bean caused by Pythium species; we named this disease damping-off of kidney bean. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession numbers AB291811, AB291944 and AB291945.     

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.     

Relationship Between Production of the Phytotoxin Prehelminthosporol and Virulence in Isolates of the Plant Pathogenic Fungus Bipolaris sorokiniana

A gas chromatographic method was developed to quantify the phytotoxin prehelminthosporol, which is a sesquiterpene metabolite of the plant pathogen Bipolaris sorokiniana. The toxin was extracted from mycelium or culture filtrates, pre-cleaned using solid phase extraction, and analyzed by gas chromatography as a trimethylsilyl-derivative. The detection limit of the method was 5ngl^–1 (signal to noise ratio 4:1) which corresponds to ca. 15ng prehelminthosporol per mg dry weight of mycelium or 15ng prehelminthosporol per ml culture filtrate. The total amount of prehelminthosporol (mycelium plus culture filtrate) increased with cultivation time when examined in six isolates of B. sorokiniana after 6, 9, 12 and 15 days of incubation. The screening experiment of 17 isolates for prehelminthosporol production after 8 days of incubation revealed significant differences in the toxin production between the isolates. The isolates with low toxin production had lower virulence towards barley roots compared to those with higher production of the toxin. However, the virulence did not increase with prehelminthosporol level among the high producing isolates. Prehelminthosporol was also analyzed in a number of related Bipolaris and Drechslera species. In addition to B. sorokiniana, three out of six Bipolaris species (B. setariae, B. zeicola, B. victoriae) produced prehelminthosporol, which indicates that ability to produce prehelminthosporol is conserved among closely-related Bipolaris species.