蔬菜日光温室栽培条件下土壤养分累积特性研究

测定了陕西杨凌示范区不同日光温室栽培土壤剖面的养分含量及变化。结果表明,日光温室土壤有机质、硝态氮、有效磷和速效钾含量呈现显著累积趋势,其中以0~20 cm土层有机质、0~40 cm土层有效磷和速效钾以及0~200 cm土层硝态氮累积量尤为突出。蔬菜生长过程中温室土壤剖面中铵态氮含量的变化相对较小,而硝态氮含量呈逐渐降低趋势。蔬菜收获后土壤剖面(0~200 cm)硝态氮残留量在707~1 161 kg/hm2之间,平均达954kg/hm2,明显高于农田土壤。温室栽培条件下土壤电导率明显高于农田土壤,以土壤表层尤为突出。土壤硝态氮、有效磷和速效钾与土壤电导率之间的关系均达显著水平,其中硝态氮含量与土壤电导率间的关系最为密切,说明过量施用肥料特别是氮肥,是引起土壤盐分累积的主要原因。     

不同肥料类型对土壤硝态氮时空变异的影响

采用土柱法研究不同肥料类型对土壤硝态氮时空分布动态的影响.结果表明,在不同肥料类型处理下,各土层中硝态氮含量出现峰值约在灌浆盛期,低谷在扬花期.在不同土层中,0～20 cm土层中硝态氮含量最高,并随土壤剖面深度的加深而下降.配施肥料处理中0～20 cm土层的硝态氮含量各生育时期均最高,20～40 cm除灌浆盛期和成熟期外也以配施处理最高,40～120 cm土层中硝态氮含量在处理间无明显规律.土壤硝态氮主要累积在0～40 cm土层中,深层土壤中含量较少.尿素处理下,0～20 cm和20～40 cm土层中硝态氮含量分别占全生育期1.2 m土层总含量的5.6%和24.9%;有机肥处理下,分别占23.8%和24.8%;配施处理下,分别占8.2%和20.2%.1.2 m土体中的硝态氮含量在小麦生长旺盛期降低,生育后期升高.三种肥料类型处理,1.2 m深处硝态氮含量最高值为3.441 mg/kg,最低值为0.944 mg/kg,基本不存在由于淋失造成地下水污染的可能性.综合考虑小麦产量、品质与生态环境效益,三种肥料类型以尿素与有机肥配施为最佳.     

水氮用量组合对冻融期土壤相变区硝态氮迁移与累积的影响

为了研究冻融期水氮用量对土壤硝态氮迁移及累积的影响,设置了两个灌水量(375、750 m~3·hm~(-2))、三个施肥水平(100、300 kg·hm~(-2)和500 kg·hm~(-2))组成6种水氮组合,进行田间冬灌试验。结果表明,水氮处理显著增加了相变区(0~60 cm)土壤硝态氮水平,各处理下硝态氮累积量差异显著。未冻期和冻结期0~60 cm土壤硝态氮累积量随水、氮量的增加而增加,消融期硝态氮累积量随肥量的增加而增加。冻结前、后期土壤剖面聚氮区(特指硝态氮)由0~30 cm逐渐下移至30~60 cm。硝态氮向相变区的迁移量随水氮量的增加而呈增加态势,在N500下迁移趋势更明显。封冻前0~30 cm土壤硝态氮的相对累积量随灌水量增加而降低,30~60 cm土层则增加。冻结期,随施氮量的增加,0~30 cm土层硝态氮相对累积量增加,30~60 cm土层则降低。消融期0~30 cm土层硝态氮相对累积量随施氮量的增加而增加,随灌水量的增加而减少,而30~60 cm土层则呈现相反规律。     

玉米膜孔灌农田土壤水氮分布特性

通过大田玉米灌水试验,研究了畦灌和膜孔灌条件下农田土壤水氮运移特性。结果表明:在相同灌水定额条件下,膜孔灌土壤剖面含水率比畦灌土壤剖面含水率变化均匀,0~30 cm土层灌水后1天和灌水后5天膜孔灌土壤含水率比畦灌土壤含水率高19.2%和18.3%;在相同灌水定额条件下,土壤铵态氮含量受土壤水分运动的影响较小,主要分布在30 cm以上土壤层,膜孔灌条件下土壤铵态氮含量随时间分布比畦灌均匀,其含量最大值为41.6 mg/kg,同畦灌相比铵态氮含量增加了4.3%;硝态氮含量受灌水方式的影响较大,在相同灌水定额条件下,10~50 cm各土层硝态氮含量膜孔灌比畦灌分别增加了41.3%、96.3%、55.3%、50.7%和46.5%,膜孔灌土壤硝态氮含量随时间和垂直土壤剖面分布均匀,其硝态氮含量主要集中在0~50 cm土层,有利于作物对氮素的吸收,提高氮素利用率。     

基施尿素对片麻岩新成土旱地谷子生长及土壤硝态氮时空分布的影响

本试验在片麻岩新成山地土壤上,设置0(CK)、N 120kg/hm2(N120)、N 225 kg/hm2(N225)、N 300kg/hm2(N300)4个施氮水平,布置田间微区试验,小区面积为10m2,研究了尿素不同施用量对旱地谷子生长及土壤硝态氮时空分布的影响。定位试验第二年的结果表明:在该试验条件下,N120处理谷子产量达到最高为4.76 kg/10m2,之后提高施肥量N225和N300处理的谷子产量并没有显著增加;从0~60 cm土壤剖面中硝态氮时空分布的差异可以看出:在施肥20 d后,N120、N225和N300处理NO3--N含量在0~40 cm土层显著增加,其中N225和N300处理NO3--N已经下移到40~60 cm土层。施肥80 d后,各施肥处理的硝态氮有一部分已经移出60 cm土层。到施肥96 d(谷子收获),N120、N225和N300处理比CK处理土壤剖面中NO3--N含量显著增加,且氮肥用量越高,土壤中NO3--N含量越高。     

宁夏不同地区农田土壤矿质氮的空间变异特征

在宁夏灌区和旱区共计选定肥力水平不同的30块农田,分别采集了0~120 cm深土壤剖面样品和小麦植株样品,测定了土壤铵、硝态氮含量和小麦地上部含氮量,分析了土壤矿质氮的空间变异性及其与小麦吸氮量的关系。结果表明,在0~120 cm深土壤剖面中,NH4-N、NO3-N和矿质氮含量及其累积量,灌区土壤显著高于旱区土壤,测点之间存在极显著差异,变异系数相当高。但在土层间不论灌区还是旱区变化不明显,在剖面上下分布比较均匀。矿质氮含量在土层间存在着正相关。在0~120 cm深土壤剖面中,矿质氮累积量在灌淤土、黑垆土、黄绵土和灰钙土间差异较大,平均分别为370.0、155.1、117.5和61.0 kg/hm2。其累积量与小麦籽粒产量、生物学产量、地上部总吸氮量之间呈极显著正相关,表明土壤较深层次的矿质氮对作物吸氮量也具有重要贡献。     

三江源区土地利用方式对土壤氮素特征的影响

以三江源区曲麻莱县高寒草甸草原、退化高寒草甸草原、退化高寒草原和人工草地4种土地利用方式为研究对象,研究了不同土地利用方式的土壤全氮、有效氮、铵态氮、硝态氮、无机氮总量及比例,结果表明:4种利用方式土壤的氮素含量均处于较低水平,在0~10 cm土层,土壤全氮与有效氮含量表现出相似的规律性,人工草地最高,退化高寒草甸草原最低。与高寒草甸草原相比,退化高寒草甸草原0~10 cm土层全氮和有效氮含量分别降低了52.4%和76.2%,而10~40 cm土层的全氮和有效氮含量却明显增加。对土壤铵态氮和硝态氮含量的研究结果进一步表明,研究区域土壤中无机氮以硝态氮为主,退化导致0~10 cm土层的铵态氮和硝态氮含量降低,退化和人工种植均导致0~10 cm土层硝态氮含量明显降低,而10~20 cm和20~40 cm土层的硝态氮含量明显升高,且这两个土层之间差异不显著,40~60 cm土层又明显降低。因此,退化和人工种植均导致土壤硝态氮沿土壤剖面淋溶下移,并且淋溶主要发生在0~40 cm深度的土壤中。土壤无机氮总量与硝态氮表现出相似的规律性,对土壤无机氮总量和比例的研究也表明退化加剧了土壤氮素的矿化过程。     

不同水肥管理措施对春玉米产量和土壤硝态氮时空分布的影响

采取大田结合小区试验的方法,研究了不同水肥管理措施对春玉米产量和土壤硝态氮时空分布的影响。结果表明:水肥一体管理区春玉米产量为17 107 kg·hm-2,显著高于传统水肥管理区(13 349 kg·hm-2);从春玉米出苗期到收获期,无肥区0~90 cm各土层硝态氮含量不断降低,累积总量也从452.5 kg·hm-2降低到279.1 kg·hm-2,传统水肥管理区和水肥一体管理区0~90 cm各土层硝态氮含量和累积总量均呈先上升后下降的趋势,但水肥一体管理区分次追肥避免了传统水肥管理大喇叭口期过量追氮带来的淋溶风险;春玉米大喇叭口期和收获期随着土层深度的增加,0~180 cm土层硝态氮含量呈下降趋势;不同水肥管理措施0~180 cm土层硝态氮累积总量传统水肥管理区最高,大喇叭口期和收获期分别达到1 119.3 kg·hm-2和945.5 kg·hm-2,淋溶风险最大。因此以水肥一体化为核心的水肥管理措施可实现冀西北地区春玉米高产和环境友好。     

不同覆盖措施对塿土碳氮及水分的影响

通过田间试验,研究了陕西关中塿土区地膜覆盖和秸秆覆盖对表层土壤有机碳、全氮和微生物量碳氮,以及0~200 cm土壤剖面水分及硝态氮分布的影响。结果表明:与不覆盖(NM)相比,白色全膜覆盖(WF)、黑色全膜覆盖(BF)和秸秆覆盖(SM)的表层土壤有机碳分别降低了19.8%、26.3%和20.9%,土壤全氮也分别降低了4.8%、9.6%和10.6%。与NM相比,覆盖处理(WF、BF和SM)可以提高表层(0~20 cm)土壤硝态氮的含量,增加0~40 cm土层的硝态氮累积量(BF的差异不显著),降低40~120 cm土层的硝态氮累积量,但120~200 cm土层的硝态氮累积量差异不显著。SM和BF显著降低0~200 cm土层的硝态氮总累积量,而WF没有显著差异。与NM相比,地膜覆盖(WF和BF)和秸秆覆盖(SM)均可以提高表层0~40 cm土壤水分含量和储水量,但SM的效果低于地膜覆盖;WF可以降低深层土壤水分含量和储水量,而SM和BF与NM无显著差异。0~200 cm土层的总储水量,SM显著高于NM,而地膜覆盖则与NM无显著差异。各覆盖处理均显著降低了表层土壤微生物碳(MBC)和微生物氮(MBN)的含量,与NM相比,MBC分别降低了27.4%、55.4%和66.5%,MBN分别降低了4.6%、4.8%和6.8%。地膜覆盖(WF和BF)和秸秆覆盖(SM)均能够加速土壤有机碳的矿化分解,降低土壤微生物,减少土壤硝态氮的深层淋溶,其对塿土碳氮和水分的长期影响值得进一步研究关注。     

(土娄)土区不同蔬菜对钾肥的肥效反应

在陕西省关中土娄土区布置线辣椒、甘蓝、白菜、芹菜钾肥大田试验,研究不同蔬菜对钾肥的肥效反应。结果表明,增施钾肥可使蔬菜硝态氮含量降低11.8%～116.0%,维生素C含量增加0.4～147.4mg/kg;产量增加9.3%～33.8%;明显促进营养生长和生殖生长;400cm深土壤剖面硝态氮累积量减少22.7～48.0kg/hm2,尤其在80～220cm剖面减少最为明显。     

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.     

Diagnostics,genetic diversity and pathogenic variation of ascochyta blight of cool season food and feed legumes

Molecular diagnostic techniques have been developed to differentiate the Ascochyta pathogens that infect cool season food and feed legumes, as well as to improve the sensitivity of detecting latent infection in plant tissues. A seed sampling technique was developed to detect a 1% level of infection by Ascochyta rabiei in commercial chickpea seed. The Ascochyta pathogens were shown to be genetically diverse in countries where the pathogen and host have coexisted for a long time. However, where the pathogen was recently introduced, such as A. rabiei to Australia, the level of diversity remained relatively low, even as the pathogen spread to all chickpea-growing areas. Pathogenic variability of A. rabiei and Ascochyta pinodes pathogens in chickpea and field pea respectively, appears to be quantitative, where measures of disease severity were based on aggressiveness (quantitative level of infection) rather than on true qualitative virulence. In contrast, qualitative differences in pathogenicity in lentil and faba bean genotypes indicated the existence of pathotypes of Ascochyta lentis and Ascochyta fabae. Therefore, reports of pathotype discrimination based on quantitative differences in pathogenicity in a set of specific genotypes is questionable for several of the ascochyta-legume pathosystems such as A. rabiei and A. pinodes. This is not surprising since host resistance to these pathogens has been reported to be mainly quantitative, making it difficult for the pathogen to overcome specific resistance genes and form pathotypes. For robust pathogenicity assessment, there needs to be consistency in selection of differential host genotypes, screening conditions and disease evaluation techniques for each of the Ascochyta sp. in legume-growing countries throughout the world. Nevertheless, knowledge of pathotype diversity and aggressiveness within populations is important in the selection of resistant genotypes.     

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.     

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.