热带洋兰叶斑病病原菌生物学特性研究和防治药剂的筛选

对热带洋兰叶斑病病原菌串珠镰刀菌B10b开展了寄主范围、生物学特性研究,并对其进行了防治药剂毒力测定。结果表明：人工接种后该病原菌能侵染石斛兰、蝴蝶兰、大花蕙兰和文心兰叶片并引起典型叶斑病症状;其菌丝生长的最适温度范围为25~28 ℃,最适pH7~8;甘露醇、麦芽糖、可溶性淀粉是其最佳生长碳源,牛肉膏和蛋白胨是最适氮源;菌丝和孢子的致死温度为65 ℃ 30 min;异菌脲、腈菌唑对菌丝生长的抑制作用很强,其EC₅₀分别为1.12×10^-5 μg/mL和1.525 4 μg/mL,甲基硫菌灵和代森锰锌的效果较弱,其EC₅₀分别为105.879 8 μg/mL和66.830 2 μg/mL。     

青海省樱桃叶斑病菌生物学特性及室内药剂毒力测定

为明确青海省樱桃叶斑病菌链格孢Alternaria alternata的生物学特性及筛选出对其防效最佳的药剂,本研究采用菌丝生长速率法和孢子计数法研究了不同培养条件对该病原菌菌丝生长和产孢量的影响,并用菌丝生长抑制率法对9种杀菌剂进行室内毒力测定。结果表明,菌丝生长和产孢的最适培养基分别为马铃薯蔗糖琼脂(PSA)培养基和马铃薯葡萄糖琼脂(PDA)培养基,最适温度为25℃, 最适氮源为蛋白胨,最适碳源分别为肌醇和乳糖,最适pH分别为6~8和6~7,24 h持续黑暗处理更有利于菌丝生长和产孢。9种化学药剂对病原菌均有不同程度的抑制作用,其中250 g/L嘧菌酯悬浮剂抑菌效果最好,EC50为1.258 mg/L。该研究结果可为青海省樱桃叶斑病的防治提供理论依据。     

雷帕霉素对4种植物病原真菌的抑菌活性

采用菌丝生长速率法,测定了雷帕霉素对番茄灰霉病菌、油菜菌核病菌、水稻纹枯病菌和棉花枯萎病菌的抑菌活性,比较了嘧菌酯、丙烷脒及雷帕霉素对番茄灰霉病菌的抑菌效果,并通过电子显微镜观察了雷帕霉素对番茄灰霉病菌菌丝生长的影响。结果表明:雷帕霉素对供试4种植物病原真菌菌丝均表现出了极强的抑制活性,其中对油菜菌核病菌的抑制作用最强,EC50值为2.23×10-4μg/mL,对番茄灰霉病菌、水稻纹枯病菌和棉花枯萎病菌的EC50值分别为1.32×10-3、4.05×10-3及3.82×10-3μg/mL;雷帕霉素对番茄灰霉病菌菌丝的抑制活性显著高于嘧菌酯(EC50值为3.24μg/mL)和丙烷脒(EC50值为3.81μg/mL)。电镜观察发现,经雷帕霉素处理后,番茄灰霉病菌菌丝表现出提前衰老等症状。研究结果可为深入探讨雷帕霉素对植物病原真菌的作用机制奠定基础。     

两种季铵盐阳离子表面活性剂对番茄灰霉病菌的生物活性

为探讨季铵盐阳离子表面活性剂在番茄灰霉病防治中的应用潜力,室内采用菌丝生长速率法测定了五种阳离子表面活性剂对番茄灰霉病菌Botrytis cinerea的毒力作用,筛选出具有较高抑菌活性的1227(十二烷基二甲基苄基氯化铵)和C8-10(双八、十烷基季铵盐),并研究了其对该菌菌丝干重、分生孢子萌发、产孢量、菌核形成及细胞膜透性的影响。结果表明,五种阳离子表面活性剂中1227和C8-10对病原菌菌丝生长有较强的抑制作用,EC50值分别为8.39和5.82μg/mL,其毒力高于常规对照药剂腐霉利水悬浮剂,与嘧霉胺水悬浮剂、乙霉威水悬浮剂相当。两者对菌丝干重、孢子萌发均有较强的抑制作用,20μg/mL时抑制率接近或达到100%;对菌核数、菌核形态及分布有一定影响;40μg/mLC8-10对该菌产孢量的抑制率可达90%以上;1227和C8-10的浓度大于20μg/mL时均能明显影响病原菌细胞膜的通透性。     

7种杀菌剂对金钱树疫病病原菌的室内毒力测定

采用室内生长速率法测定了7种杀菌剂对金钱树疫病病原菌棕榈疫霉(Phytophthora palmivora Butler)的抑制作用.结果表明:0.15%四霉素水剂的抑制效果最好,EC50值为0.0457μg/mL,EC90值为0.2174μg/mL;其次为6.25%精甲·咯菌腈悬浮种衣剂和50%烯酰吗啉水分散粒剂,抑菌效果显著,前者的EC50值为0.0758μg/mL,EC90值为2.4683μg/mL,后者的EC50值为0.3407μg/mL,EC90值为2.0794 μg/mL;22.7%二氰葸醌悬浮剂、80%代森锰锌可湿性粉剂和50%氟码·乙铝可湿性粉剂对菌丝生长也有一定的抑制作用,其EC50值分别为0.1382 μg/mL、2.3796μg/mL和5.4602μg/mL;72.2%霜霉威盐酸盐水剂的抑制效果最差,EC50值为498 μg/mL.在供试的7种杀菌剂中,性价比以80%代森锰锌可湿性粉剂最高,其次为50%烯酰吗啉水分散粒剂.     

湖北省黄连叶斑病病原鉴定及其生物学特性

为明确湖北省黄连叶斑病病原菌种类及其生物学特性,采用常规组织分离法获得病原菌菌株HL-1,通过形态学特征并结合基于ITS序列分析对菌株进行鉴定,并研究该病原菌的生物学特性,用生长速率法测定了6种杀菌剂对该病原菌菌丝生长的抑制作用。结果表明,黄连叶斑病病原菌分生孢子器黑褐色,大小为100.5~120.0μm×175.3~210.0μm;分生孢子无色,单孢,大小为2.0~2.5μm×4.1~5.4μm;该菌株ITS序列系统发育进化分析结果表明,其与耧斗菜茎点霉Phoma aquilegiicola(HM222537.1)的同源性为100%,通过形态学特征及分子鉴定结果确定该菌株为耧斗菜茎点霉。该病原菌在4~25℃内均能生长,最适温度为20℃;不同光照条件对病原菌生长的影响无显著差异;在供试碳(氮)源中病原菌对麦芽糖和蛋白胨的利用效果最好;菌丝的致死温度为50℃、10 min。供试6种药剂中10%苯醚甲环唑对病原菌菌丝生长的抑制效果最好,其EC_(50)最小,为0.03μg/mL。     

新化合物氟醚菌酰胺的抑菌活性及其对棉花立枯丝核菌的作用方式研究

采用菌丝生长速率法测定了新化合物氟醚菌酰胺(LH-2010A)对10种常见植物病原菌的毒力,同时研究了其对棉花立枯丝核菌无性繁殖过程、菌丝形态及细胞膜通透性的影响。结果表明:氟醚菌酰胺对10种病原菌均具有较强的抑菌活性,比结构相似的选择性杀菌剂氟吡菌胺具有更广的杀菌谱。氟醚菌酰胺对棉花立枯丝核菌和番茄灰霉病菌的抑菌活性最高,EC50值均小于1.00 μg/mL,对其他8种病原菌的EC50值则在1.10~4.63 μg/mL之间;而氟吡菌胺只对辣椒疫霉和马铃薯晚疫病菌具有较高的抑菌活性,EC50值分别为0.61和0.72 μg/mL。在100.0 μg/mL下,氟醚菌酰胺对棉花立枯丝核菌抑菌作用明显,能显著抑制其菌核产生和菌丝生长量,使菌丝分支增多、变短、变粗;以不同浓度的氟醚菌酰胺处理棉花立枯丝核菌时,其细胞膜的通透性随着药剂浓度的增加而显著增大,520 min时最高处理浓度下的相对渗率为77.01%。表明氟醚菌酰胺对多种植物病原菌具有较高的抑菌活性,并能明显抑制棉花立枯丝核菌的多项生理指标。     

两种新型琥珀酸脱氢酶抑制剂的抑菌活性比较

采用菌丝生长速率法、孢子萌发法和幼苗法比较了吡唑萘菌胺和氟吡菌酰胺对23种病原菌的毒力。结果表明,吡唑萘菌胺对黄瓜褐斑病菌、黄瓜炭疽病菌、辣椒炭疽病菌、番茄早疫病菌、苹果斑点病菌、辣椒疫霉病菌、马铃薯晚疫病菌、番茄灰霉病菌、番茄菌核病菌、水稻稻瘟病菌和苹果轮纹病菌菌丝生长均有较高的抑制活性,其EC50值为0.10~9.52μg/mL,EC90值为1.87~62.23μg/mL。吡唑萘菌胺对花生白绢病菌、苹果腐烂病菌、棉花黄萎病菌、棉花立枯病菌和镰刀菌属病原菌的抑制活性均高于氟吡菌酰胺,而氟吡菌酰胺却对黄瓜褐斑病菌、番茄早疫病菌、苹果斑点病菌、番茄灰霉病菌、番茄菌核病菌和苹果褐斑病菌具有较高的抑制活性,其EC50值为0.39~3.98μg/mL,与吡唑萘菌胺相当。吡唑萘菌胺对玉米丝黑穗、花生冠腐病菌和番茄灰霉病菌的孢子有较高的毒力,其EC50值分别为0.002 9、0.07和1.38μg/mL。氟吡菌酰胺仅对花生冠腐病菌、番茄灰霉病菌的孢子有较高的活性,且它与吡唑萘菌胺活性相当。吡唑萘菌胺和氟吡菌酰胺对黄瓜白粉病菌均有较高的毒力,EC50值分别为0.04、0.05μg/mL。因此,吡唑萘菌胺比氟吡菌酰胺更加广谱,且抑菌活性相当或更高。     

三类杀菌剂对牡丹腔孢叶斑病菌生长和发育的影响

腔孢叶斑病是牡丹生产上出现的一种新病害,近几年在洛阳及菏泽牡丹种植园危害越来越重。为了筛选防治该病的化学药剂,本文采用菌丝生长速率法测定了3类8种杀菌剂对病菌菌丝生长的抑制活性,采用涂布平板法测定了多菌灵、戊唑醇及嘧菌酯对病菌孢子萌发和芽管伸长的影响,并在含药平板上测定了3种药剂对病菌产孢量的作用。结果表明:三唑类药剂对病菌菌丝生长的毒力最强,EC50为0.020~0.096μg/mL,且戊唑醇对孢子萌发和产孢也有很强的抑制活性,在0.1μg/mL时孢子即不能萌发;甲氧基丙烯酸酯类药剂对菌丝生长的毒力较强,EC50为0.408~0.939μg/mL,嘧菌酯对芽管伸长和产孢量均表现出很强的抑制活性,10μg/mL时,芽管几乎不再伸长,对产孢的抑制率可达到99%以上;而苯并咪唑类药剂对菌丝生长的毒力较弱,EC50为12.167~30.104μg/mL,多菌灵对孢子萌发的抑制作用弱,100μg/mL时孢子萌发率仍达到90%以上,对产孢的抑制作用也较弱,为63.02%。根据药剂对病菌生长和发育各阶段的影响,生产中应采用适宜的施用方法:戊唑醇和嘧菌酯可作为保护剂在病害发生前期喷施,也可作为治疗剂在病害发生流行期应用,但为防止抗药性菌株的出现,两者应当轮换或复配使用。     

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。     

Dermestid beetles in ‘evolution Canyon’, lower Nahal Oren, Mt. Carmel, including new records for Israel

Fifteen species of dermestid beetles were recorded at ‘Evolution Canyon’ (EC), Lower Nahal Oren, Mt. Carmel, Israel. They represent ~35% of known Israeli dermestid species. The following three species were recorded for the first time in Israel:Trogoderma svriaca Dalla Torre, 1911;Ctesias svriaca Ganglbauer, 1904; andAnthrenus (s.str.) jordaniens Pic, 1934. Adults of 13 species were collected on the more solar radiated, warmer and climatically more fluctuating south-facing slope (SFS); ten species were collected on the opposite, north-facing slope (NFS), which was cooler and climatically more stable. The abundance of adult dermestid beetles was 1.9 times higher on the SFS than on the NFS (86 and 47, respectively). Species richness and abundance distribution at EC (three collecting stations on each slope and one at the valley bottom) were significantly negatively correlated with the plant cover that consisted of trees and bushes (Spearmanr _s ,P=0.007 and 0.039, respectively) and perennials (Spearmanr _s ,P=0.039 and 0.077, respectively), indicating that non-woody plants were preferred by adult dermestid beetles.     

Epidemiology of Toxigenic Fungi and their Associated Mycotoxins for Some Mediterranean Crops

Recent data on the epidemiology of the common mycotoxigenic species of Fusarium, Alternaria, Aspergillus and Penicillium in infected or colonized plants, and in stored or processed plant products from the Mediterranean area are reviewed. Emphasis is placed on the toxigenicity of the causal fungal species and the natural occurrence of well known mycotoxins (aflatoxins, ochratoxins, fumonisins, trichothecenes, zearalenone, patulin, Alternaria-toxins and moniliformin), as well as some more recently described compounds (fusaproliferin, beauvericin) whose toxigenic potential is not yet well understood. Several Fusarium species reported from throughout the Mediterranean area are responsible of the formation of mycotoxins in infected plants and in plant products, including: Fusarium graminearum, F. culmorum, F. cerealis, F. avenaceum, F. sporotrichioides and F. poae, which produce deoxynivalenol, nivalenol, fusarenone, zearalenone, moniliformin, and T-2 toxin derivatives in wheat and other small grains affected by head blight or scab, and in maize affected by red ear rot. Moreover, strains of F. verticillioides, F. proliferatum, and F. subglutinans, that form fumonisins, beauvericin, fusaproliferin, and moniliformin, are commonly associated with maize affected by ear rot. Fumonisins, were also associated with Fusarium crown and root rot of asparagus and Fusarium endosepsis of figs, caused primarily by F. proliferatum. Toxigenic A. alternata strains and associated tenuazonic acid and alternariols were commonly found in black mould of tomato, black rot of olive and citrus, black point of small cereals, and black mould of several vegetables. Toxigenic strains of A. carbonarius and ochratoxin A were often found associated with black rot of grapes, whereas toxigenic strains of A. flavus and/or P. verrucosum, forming aflatoxins and ochratoxin A, respectively, were found in moulded plant products from small cereals, peanuts, figs, pea, oilseed rape, sunflower seeds, sesame seeds, pistachios, and almonds. Finally, toxigenic strains of P. expansum and patulin were frequently found in apple, pear and other fresh fruits affected by blue mould rot, as well as in derived juices and jams.     

A survey of the genera of<Emphasis Type="Italic">Microgaster</Emphasis> latreille and<Emphasis Type="Italic">Hygroplitis</Emphasis> thomson (Hymenoptera: Braconidae: Microgastrinae) from China

The genera ofMicrogaster Latreille 1804 andHygroplitis Thomson 1895 from China are presented systematically in this paper. Thirty-two species ofMicrogaster and three species ofHygroplitis are known in China. Diagnosis, character variation, distribution and host of each species among the two genera are presented, including its host and distribution. Keys to the species ofMicrogaster andHygroplitis are given. http://www.phytoparasitica.org posting Dec. 19, 2006.     

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.     

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.     

Characterization of potato potyvirus Y (PVY) isolates from seed potato batches. Situation of the NTN, Wilga and Z isolates

A collection of 38 PVY isolates from seed potato batches, originating from several Western European countries, was characterized by using current biological, serological and molecular tools differentiating PVY strains and groups. The correlation between the three kinds of tests was good but not absolute. No single serological or PCR method was able to discriminate among the five isolate groups found. Twenty-nine isolates belonged to the PVY^N strain and six to the PVY^O strain. No PVY^C was found. Two other isolates reacted serologically like PVY^O, but were unable to elicit a hypersensitive response from the Ny_tbr gene and probably represent the PVY^Z group. At the molecular level, these two isolates showed a combination of both PVY^O and PVY^N and could be recombinants of these strains. Another isolate reacted serologically like PVY^O, but induced vein necrosis in tobacco, like PVY^N-Wilga. Some PVY^N isolates caused tuber ring necrosis in glasshouse conditions. These might belong to the PVY^NTN group. The PVY^NTN, PVY^N-Wilga and PVY^Z groups probably represent pathotypes within strains PVY^N and PVY^O, respectively. The present study also confirms previous reports showing a high genetic variation at the 5 end within the PVYN strain.     

The autumn leafroller: Phenology,damage and parasitoids in a Dutch apple orchard

The phenology of the autumn leafroller,Syndemis musculana, a local pest of apple, was studied in order to forecast larval emergence. From 1983–1986, peak flight as determined with sexpheromone traps was always between 13–18 May. The duration of embryonic development was determined at various constant temperatures and used to estimate the periods of egg hatch in these four years. Each year, most eggs should have hatched in the second decade of June.Differences in attack rates between apple cultivars seem to be explained largely by the variation in picking time. Larvae are only half grown at the beginning of harvest (cv. James Grieve), and have gone into hibernation when the latest variety (cv. Golden Delicious) is picked. Moreover, the varieties Cox's Orange Pippin and Belle de Boskoop, picked about half time, are liable to receive additional damage by caterpillars brought with the picked fruits into storage.Various hymenopterous parasites were reared from caterpillars. As the only leafroller in the orchard which hibernates as mature larva,S. musculana may promote winter survival of some parasitoids, like the eulophidColpyclypeus florus.Samenvatting De fenologie van de herfstbladroller (Syndemis musculana Hübner), een incidentele plaag op appel, werd nader bepaald met het doel het uitkomen van de eieren te kunnen voorspellen. In 1983–1986 viel de piekvlucht, bepaald met behulp van feromoonvallen, steeds tussen 13 en 18 mei.De ontwikkelingsduur van de eieren bij verschillende constante temperaturen werd gebruikt om de periode van uitkomen te schatten. De meeste eieren zullen ieder jaar in de eerste helft van juni uitkomen.Geconstateerde verschillen in schade tussen appelrassen blijken goeddeels terug te voeren op verschillen in pluktijdstip. De rupsen van de herfstbladroller zijn pas half-was als de eerste appels eind augustus geplukt worden, terwijl tegen het einde van de oogst begin oktober de meeste al in winterslaap zijn. Met name tussentijdse rassen, als Cox's Orange Pippin and Schone van Boskoop, lopen extra schade op doordat grotere rupsen met de geplukte vruchten in de kist terecht komen.Uit de rupsen werden negen, al van andere boomgaardbladrollers bekende, sluipwespen gekweekt, Omdat deze bladrollersoort, als enige in de boomgaard, als volgroeide rups overwintert, lijkt zij bij uitstek geschikt als winterwaard.This study was carried out at the Experimental Orchard De Schuilenburg, Schuilenburg 3, 4041 BK Kesteren, the Netherlands, to which address correspondence should be addressed.     

Characterization of Sclerotinia minor populations in Texas peanut fields

In the summer of 2004 an epidemic of sclerotinia blight of peanut, a disease caused by Sclerotinia minor, occurred in Texas in fields where the disease was never previously detected. The disease was observed on many plants within one of the fields (>3000 disease foci), although most foci were <1 m. It is hypothesized that these observations were inconsistent with the recent introduction of a monocyclic pathogen, even if disease developed under conducive environmental conditions. The pattern of disease is most suggestive of the presence of foliar (ascospore) infections, although air temperature was above the known limits for apothecia development if the pathogen had arrived in the field in 2004 peanut seed. To further examine this epidemic, 232 isolates were collected, across a variety of spatial scales spanning this field and other Texas peanut fields, and evaluated for aggressiveness, fungicide sensitivity and genotypic diversity. There was wide variation among isolates for the phenotypic characteristics measured, but there was no evidence that a genotypically unique, highly aggressive, and fungicide resistant isolate had been introduced or evolved. The predominant genotype, TX1, which contained 154 isolates, was found in every county and field population.     

Eyespot of Cereals Revisited: ITS phylogeny Reveals New Species Relationships

Four species so far classified in Pseudocercosporella or Ramulispora (hyphomycetes) are associated with eyespot disease symptoms of cereals. Two of these have been linked to teleomorphs that were described in Tapesia. Sequence data derived from the Internal Transcribed Spacer region (ITS1, 5.8S and ITS2) of the rDNA operon showed, however, that the eyespot fungi associated with Tapesia are not congeneric with Ramulispora sorghi, the type of Ramulispora. The genus name Tapesia is now rejected in favour of the conserved name Mollisia, which appears to comprise heterogeneous fungi. Tapesia yallundae is not closely related to the type of Mollisia, M. cinerea, but clusters separately, being more closely allied to species with Cadophora anamorphs. A new holomorph genus, Oculimacula, is therefore proposed for teleomorphs of the eyespot fungi, while the anamorphs are accommodated in Helgardia gen. nov.     

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.