Absorption and metabolism of permethrin and cypermethrin in the cockroach and the cotton-leafworm larvae

Permethrin was metabolised by attack at the ester bond, in vivo by adult cockroaches, Periplaneta americana and in vitro by esterase preparations. Metabolites retaining the ester linkage could not be detected. In all cases, the (1RS)-trans-isomer (transpermethrin) was more labile than the (1RS)-cis-isomer. Cypermethrin was metabolised at one-fifth the rate for permethrin. In-vitro and in-vivo studies with synergists indicated that cleavage of the ester bond in permethrin can be both oxidative for the (1RS)-cis-isomer and hydrolytic for the (1RS)-trans-isomer. The penetration of permethrin through the cuticle of the cockroach was significantly greater than that of cypermethrin. The penetration and metabolism of permethrin and cypermethrin in sixth-instar larvae of susceptible and resistant strains of the Egyptian cotton-leafworm, Spodoptera littoralis, were studied as possible factors in resistance. No significant differences were found. It is suggested that the major resistance factor to permethrin in S. littoralis is probably non-metabolic.     

Pathogenicity and toxicity of Fusarium tucumaniae and Fusarium crassistipitatum to soybean and Arabidopsis thaliana

Sudden death syndrome (SDS) of soybean is a fungal disease caused by at least four distinct Fusarium species: F. tucumaniae, F. virguliforme, F. brasiliense, and F. crassistipitatum. All four species are present in Argentina. These fungi are soilborne pathogens that only colonize roots and cause root necrosis. However, damage also reaches the aboveground part of the plant, and foliar chlorosis and necrosis, followed by premature defoliation, can be observed. Although the pathogenicity and phytotoxicity of F. virguliforme has been well characterized, knowledge regarding disease development by other fungal species is scarce. In this study, two plant species, soybean (Glycine max) and Arabidopsis thaliana, and isolates from two fungal species, F. tucumaniae and F. crassistipitatum, were used to comparatively analyse the fungal pathogenicity and the phytotoxicity of volatile organic compounds (VOCs) and cell-free culture filtrates. Fungal inoculation had a significant effect on plant growth, regardless of the plant species. In addition, infected soybean plants showed disease incidence and foliar and root symptoms. Inhibition of A. thaliana growth was not due to VOCs emitted by fungi. Instead, both pathogens were shown to produce toxins that caused typical SDS foliar symptoms in soybean and root length reduction in A. thaliana. As far as we know, this is the first report that demonstrates that F. tucumaniae and F. crassistipitatum affect A. thaliana growth and emit VOCs, and that F. crassistipitatum produces toxins.     

The occurrence and distribution of nepoviruses and their associated vector Longidorus and Xiphinema nematodes in Europe and the Mediterranean basin1

Six nepoviruses are transmitted by five Longidorus and three Xiphinema species in Europe. The virus and vector associations are: L. apulus and L. fasciatus with artichoke Italian latent nepovirus, L. attenuatus and L. elongatus with tomato black ring nepovirus, L. elongatus and L. macrosoma with raspberry ringspot nepovirus, X. diversicaudatum with arabis mosaic and strawberry latent ringspot nepoviruses and X. index and X. italiae with grapevine fanleaf nepovirus. The distributions of the viruses and their vectors in Europe and the Mediterranean basin are described. The following points are commented: presence of non-indigenous nematode-transmitted nepoviruses in Europe; occurrence of vector nematodes in European countries in the absence of their associated nepoviruses; the possible vectors of serologically distinct strains of grapevine fanleaf nepovirus.     

Glutathione Transferase Activities and Herbicide Selectivity in Maize and Associated Weed Species

The role of glutathione transferases (GSTs) in the selectivity of the herbicides alachlor, atrazine, fluorodifen and metolachlor, which are detoxified by glutathione conjugation in plants, was determined in seedlings of maize (Zeamays L.) and the associated weed species Abutilon theophrasti Medic., Digitariasanguinalis (L.) Scop. Echinochloa crus-galli (L.) Beauv., Panicum miliaceum (L.), Setaria faberi Herrm. and Sorghum bicolor (L.) Moench. The availability of glutathione was also determined in all species and tissue concentrations were found to be in the range 120–160 μm for all species except D. sanguinalis and S. bicolor, which contained half this amount. GST activities toward the herbicides were determined in crude protein extracts from the plants using HPLC to quantify the biosynthesis of the herbicide conjugates. The specific activities of the GSTs toward the substrates were in the order alachlor>fluorodifen> atrazine>metolachlor in all species except A. theophrasti, where fluorodifen was a better substrate than alachlor. In most cases there was a good correlation between GST activities and the selectivity of the herbicides applied pre-emergence. In the case of atrazine, GST activities were also related to the relative rates of herbicide conjugation in vivo. In contrast, there was no simple relationship between glutathione availability and the selectivity of the herbicides. However, with alachlor there was evidence that glutathione availability was limiting GST activity and influencing tolerance.     

Of mushrooms and chocolate trees: aetiology and phylogeny of witches' broom and frosty pod diseases of cacao

The troubled history of the two major diseases of the chocolate tree (Theobroma cacao) in South America, witches' broom and frosty pod, is reviewed, concentrating on critical aspects of the aetiology as well as the phylogeny of the causal agents. Both diseases are caused by sister species within the genus Moniliophthora, belonging to the Marasmiaceae family of mushrooms. The witches' broom pathogen, Moniliophthora perniciosa, evolved on the Amazonian side of the Andes and induces brooms not only in cacao and its relatives in the genera Theobroma and Herrania (Malvaceae), but also in species in the plant families Bignoniaceae, Malpighiaceae and Solanaceae, on which the mushrooms (basidiomata) are produced. Moniliophthora roreri, the type species of the genus, evolved as a pod pathogen on endemic Theobroma species on the western side of the northern Andean Cordillera. Because Moniliophthora was described originally as the asexual form of an unknown basidiomycete, the generic diagnosis is amended here to accommodate species with agaricoid basidiomata. In addition, the new variety M. roreri var. gileri is designated for the morphotype occurring on Theobroma gileri, in northwest Ecuador. Cytology studies indicate that the supposed conidia of M. roreri are, in fact, sexual spores (meiospores) and it is posited that the fruiting structure represents a much‐modified mushroom. Finally, based on preliminary data from pathogenicity testing, it is hypothesized that the true causal agent of both diseases is an as yet unidentified infectious agent vectored into the host by the fungus.     

Growth and development of fall- and spring-planted populations of Conyza canadensis and C. bonariensis

The growth and phenological development of spring- and fall-planted Conyza canadensis and C. bonariensis were studied in Fresno, CA, USA. A glyphosate-resistant (GR) and a glyphosate-susceptible (GS) population of each species were used. Time taken by each plant to reach the rosette, bolting, appearance of first bud, appearance of first open flower, and initial seed set were converted to growing degree days (GDDs). The fall- and spring-planted C. canadensis required similar GDDs to complete their life cycles but the GR type required fewer GDDs than the GS type. In C. bonariensis, the GDDs required to complete its life cycle differed between the fall- and spring-plantings but not between the GR and GS types. The total aboveground biomass of both fall- and spring-planted Conyzas at initial seed set was similar but the spring-planted GS C. canadensis produced more biomass than the GR type, whereas the fall-planted GS C. bonariensis produced more biomass than the GR type. Plant development based on GDD models can have global implications and help in planning for timely applications of post-emergence herbicides.     

The hrpZ and hrpA genes are variable, and useful for grouping Pseudomonas syringae bacteria

The hrpS to hrpB regions from strains of Pseudomonas syringae were amplified by polymerase chain reaction (PCR) and the DNA sequence determined. The order of hrpS, hrpA, hrpZ, and hrpB was consistent among P. syringae strains. The sequence of hrpS was highly conserved. In a cluster analysis with the hrpS sequence, P. syringae strains were divided into four groups (I, II, III, and IV) and one undetermined strain, in agreement with previous studies. In contrast, the hrpZ sequences contained insertions, deletions, and base substitutions followed by changes in amino acids. Based on cluster analysis of hrpA, hrpZ, and hrpB, P. syringae strains could be divided into five groups. One of the four groups (group I) in the cluster analysis of hrpS could be further divided into two subgroups (groups IA and IB). Groups II, III, and IV were the same in the two analyses. Group-specific primers were designed, based on the DNA sequences of hrpZ, that could differentiate the groups of P. syringae strains. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession numbers AB112552 to AB112581     

Interactions between Fusarium verticillioides and Fusarium graminearum in maize ears and consequences for fungal development and mycotoxin accumulation

Fungal interactions of Fusarium verticillioides and F. graminearum in maize ears and the impact on fungal development and toxin accumulation were investigated in a 2‐year field study at two locations in France. Maize ears were inoculated either with a spore mixture of F. graminearum and F. verticillioides or using a sequential inoculation procedure consisting of a first inoculation with F. graminearum followed by a second with F. verticillioides 1 week later. Toxin and fungal biomass were assessed on mature kernels, using HPLC and quantitative PCR. Correlation between the levels of DNA and toxin was high concerning F. graminearum DNA and deoxynivalenol (R² = 0·73) and moderate for F. verticillioides DNA and fumonisin (R² = 0·44). Fusarium graminearum DNA either decreased in mixed inoculations or was not influenced by subsequent inoculations with F. verticillioides, compared to single inoculations. In contrast, F. verticillioides DNA either significantly increased or was not affected in mixed and sequential inoculations. In two of the replicates, it can be assumed that natural contamination by F. verticillioides was favoured by previous contamination with F. graminearum. Overall, the results suggest that F. verticillioides has competitive advantages over the F. graminearum strains. Additionally, the data provide, for the first time, key evidence that previous contamination by F. graminearum in maize ears can facilitate subsequent infections by F. verticillioides.     

Cryptic diversity,multilocus phylogeny,and pathogenicity of cercosporoid fungi associated with common bean and cowpea

In recent years, common bean (Phaseolus vulgaris) and cowpea (Vigna unguiculata) plants in the north of Iran have exhibited symptoms resembling Cercospora leaf spot (CLS) disease. This study was initiated to elucidate the taxonomy and pathogenicity of cercosporoid taxa associated with leaf spot diseases of these two legume crops in Iran. A total of 138 samples with CLS symptoms were collected from cultivated common bean and cowpea species in northern Iran and subjected to microscopic examination, resulting in identification of 98 Cercospora and 59 Pseudocercospora samples. A six-locus phylogenetic analysis (ITS, actA, tef1, gapdh, his3, and cmdA) coupled with examination of the morphology of 42 representative isolates from these samples confirmed that several cercosporoid fungi occur on common bean and cowpea in Iran. Five Cercospora species (C. iranica, C. cf. flagellaris, Cercospora sp. G, Cercospora sp. T, and C. vignigena) and two Pseudocercospora species (P. griseola f. griseola and P. cf. cruenta) were found; of these, C. cf. flagellaris was the dominant species, occurring on both common bean and cowpea. Pathogenicity tests confirmed that all seven species could infect leaves of common bean and/or cowpea. This is the first report of C. iranica, Cercospora sp. G, and Cercospora sp. T associated with common bean and/or cowpea in the world. In addition, C. vignigena was recorded for the first time in Iran. Results achieved in this study will assist strategies for the management of CLS disease of common bean and cowpea.     

The synthesis and fungicidal activity of derivatives of o- and p-Cyclohexylphenyl phosphorodichloridates and dichloridophosphorothioates

The synthesis of o- and p-cyclohexyphenyl phosphorodichloridates and dichloridophosphorothioates and their conversion into the corresponding dimethyl phosphates, phosphorodihydrazides, and phosphorodihydrazones, is discussed. o- and p-Cyclohexylphenyl N-phenylphosphoramidic chlorides were converted to the hydrazide and the O-methyl ester. The phosphorodichloridates were converted to the dihydrogen phosphates, but the dichloridophosphorothioates could not be hydrolysed in an analogous manner. Structure-activity relationships have been briefly discussed; the most active compound was o-cyclohexylphenyl O-methyl phosphoroisopropylidene hydrazone.     

Adsorption and bioactivity of di-allate,tri-allate and trifluralin*

Studies were conducled to cstmiate the adsorption parameter k and the bioactivity (in terms of G R₅₀) of di-allate [S-2,3-dichloroallyl N, N-di-isopropyl (thiocar bamate)], iri-allate [S-2,3,3-trichloroallyl N, N -di-isopropyl (thiocar bamate], and [trifiuralin (2,6-dinitro N, N-dlpropyl-4-trifluoromelhylaniline) in a number of Saskatchewan soil. The k values ratiged from 5 for di-allate adsorption m Asquilh loamy sand to 315 for trifluralin adsorption on Melfort loam and were closely related to the soil organic matter content. The relative degree of adsorption was irifluralin > tri-allate >di-allaie. For each herbicide, the G R₅₀ values were positively correlated wich organic matter conienl atid wilh k. It was suggested that these nonionic herbicides may be amenable to a predictive approach for field application rates in different soils. Among herbicides for any one soil, however, there was not the same relationship between G R₅₀andk. since the G R₅₀ was least for trifluralin and there was no significant difference between di-allate and tri-allate.     

In-vivo and in-vitro studies on DDT uptake and metabolism in susceptible and resistant strains of the mosquito Aedes aegypti L.

Twelve strains of Aedes aegypti have been compared for resistance to pp′-DDT, uptake of pp′-DDT, and dehydrochlorination of pp′-DDT to pp′-DDE in vivo and in vitro both at the larval and adult stages. Resistant larvae were shown to contain significantly more pp′-DDE than susceptible larvae after a standard exposure to pp′-DDT but also substantially more pp′-DDT in an unmetabolised state. There was a small increase in the percentage dehydrochlorinated in vivo in the resistant strains compared with the susceptible strains, but this was not correlated with the level of resistance nor with dehydrochlorination in vitro. However, dehydrochlorination in vitro was correlated with resistance. Adult resistance was correlated positively with dehydrochlorination, both in vivo and in vitro, but the resistant adults did not contain increased levels of unmetabolised DDT. By comparing resistance levels at the two stages, it was found that there were two kinds of resistant strain: four strains of Asian origin and one from West Africa were highly resistant as larvae but showed almost no resistance as adults; five strains from Central and South America were highly resistant at both stages. The different mechanisms of resistance in adults and larvae are discussed in relation to genetic studies.     

Glucosinolate aglucones and analogues: insecticidal properties and a QSAR

Naturally occurring aglucones of three glucosinolates (sinigrin, glucotropaeolin, and epi-progoitrin) were tested for fumigation activity against the house fly, Musca domestica, and the lesser grain borer, Rhizopertha dominica. A total of eight natural aglucones were evaluated in the bioassays. Two aglucones of sinigrin showed efficacy against both species which was comparable with that of a commercial fumigant, chloropicrin. None of the aglucones tested was comparable in activity to dichlorvos. Aglucones of glucotropaeolin were also insecticidal, but not to the same level as the sinigrin aglucones. The aglucones of epi-progoitrin were only slightly effective as fumigants. A quantitative structure–activity relationship (QSAR) was developed for synthetic analogues of the sinigrin and glucotropaeolin aglucones. An electronic parameter, σ*, provided the best predictor of activity in R. dominica, whereas a hydrophobicity parameter, π, best predicted activity in M. domestica. © 1998 Society of Chemical Industry     

Characterisation and toxicity of Bacillus thuringiensis strains from hazelnut pests and fields

BACKGROUND: In order to find and identify more toxic insecticidal Bacillus thuringiensis Berliner (Bt) strains, a survey was carried out of B. thuringiensis isolate pests belonging to Coleoptera, Lepidoptera and Diptera and from soils in hazelnut fields. Of 16 isolates having Bacillus cereus‐B. thuringiensis morphology, eight were classified as B. thuringiensis because of the production of parasporal δ‐endotoxin crystals. RESULTS: In this study, eight isolates of B. thuringiensis from hazelnut pests (isolates Bn1, Mm2, Mnd and Xd3) and from hazelnut soils (isolates 6, 27, 40 and 46) have been characterised in detail. These isolates were compared with reference strains by electron microscopy, SDS‐PAGE analysis, cry gene content, serological test and insecticidal activity. CONCLUSION: Results indicate that Bn1 and MnD are B. thuringiensis subsp. kurstaki, and Mm2 and Xd3 are B. thuringiensis subsp. tenebrionis. In addition, isolate 6 is B. thuringiensis subsp. israelensis, isolates 27 and 46 are B. thuringiensis subsp. kumamotoensis and isolate 40 is B. thuringiensis subsp. indiana. The four B. thuringiensis isolates from hazelnut pests may be valuable as biological control agents against coleopteran and lepidopteran insects. Copyright © 2009 Society of Chemical Industry     

Photosynthetic and accessory pigments in Cuscuta campestris Yuncker and some host species

Photosynthetic and accessory pigments (chlorophyll a and b, a and ß carotenes and xanthophylls) were evaluated in Cuscuta campestris Yuncker during the course of its biological cycle, taking into account both autotrophic and heterotrophic phases, and different parts of the parasite. Chloroplast activity in C. campestris was measured and comparisons were made with the chloroplast activity in Beta vulgaris L. and Convolvulus arvensis L. The effects of parasitization of C. campestris on the main and accessory photosynthetic pigments of B. vulgaris were also evaluated. Finally, a hypothesis was formulated to explain the different distribution of pigments in different parts and at different stages of the growth cycle in C. campestris and its chloroplast activity. Pigments photosynthétiques principaux et accessoires chez Cuscuta campestris Yuncker et des espèces hôtes Les pigments photosynthétiques principaux et accessoires (chlorophylles a et b, α et β carotènes, xanthophylles) ont été déterminés chez Cuscuta campestris Yuncker durant son cycle biologique. Les phases auttorophes et hétérotrophes ont été prises en compte et les mesures ont porté sur différentes parties des plantes. L'activité chloroplastique a été déterminée chez C. campestris et a été comparéà celles de Beta vulgaris L. et de Convolvulus arvensis L. Les conséquences du parasitisme de C. campestris sur les pigments principaux et accessoires de B. vulgaris ont aussi étéétudiées. Enfin, une hypothèse a été avancée pour expliquer les différences de distribution des pigments dans les différentes parties de C. campestrisà divers stades de son cycle biologique, ainsi que son activité chloroplastique. Photosynthese- und akzessorische Pigmentre in Cuscuta campestris Yuncker und einigen Wirstspflanzenarten Bei Cuscuta campestris Yuncker wurden im Verlaufe ihres Lebenszyklus die Photosynthese- und akzessorischen Pigmenten (Chlorophyll a und b, a- und ß-Karotin, Xanthophylle) sowohl in autotrophen als auch heterotrophen Phasen und in verschiedenen Pflanzenteilen untersucht. Die Chloroplastenaktivität wurde gemessen und mit der von Beta vulgaris L. und Convolvulus arvensis L. vergleichen. Die Wirkung der Parasitierung von Cuscuta campestris auf die Photosynthese-Pigmente von Beta vulgaris wurd erfaßt. Eine Hypothese über die Chloroplastenaktivität und zur verschiedenen Verteilung der Pigmente in den verschiedenen Pflanzenteilen und in verschiedenen Entwicklungsstadien von Cuscuta campestris wurde formuliert.     

Distribution and relative importance of lepidopteran cereal stemborers and their parasitoids in Uganda

Infestation levels and parasitism of lepidopteran stemborers on maize were assessed in four agroecological zones (AEZ) in Uganda. The indigenous noctuidBusseola fusca Fuller (Noctuidae) and the invasiveChilo partellus Swinhoe (Crambidae) were the most important stemborers recorded.C. partellus represented 77% of the stemborers in the Eastern AEZ whileB. fusca was dominant in the other AEZs, accounting for 60–79%. The proportion of infested plants was between 16% and 45% and borer density between 0.2 and 1.0 borers per plant. There was no clear relationship between damage and stem tunneling, which is often used to estimate yield loss.Telenomus busseolae Gahan (Scelionidae), the only egg parasitoid recovered, caused parasitism of up to 46% onB. fusca eggs. Several larval and pupal parasitoid species were recorded. The most common were the indigenous braconidCotesia sesamiae and the introducedCotesia flavipes, which are larval parasitoids ofB. fusca andC. partellus, respectively. Mean parasitism by the indigenousC. sesamiae ranged between 2.0% and 29.4% onB. fusca and from 0 to 13% onC. partellus. C. flavipes was recovered at most locations with parasitism of 0–30.5% onC. partellus and 0–12% onB. fusca; the latter was probably the result of multiparasitism as laboratory studies have shown that it was not a suitable host forC. partellus. Results indicated further that the parasitoid has not attained equilibrium 5 years after its introduction. http://www.phytoparasitica.org posting Nov. 20, 2006. Teddy Matama-Kauma died suddenly in an accident on Dec. 10, 2006, while this paper was in press.     

Virulence of Hymenoscyphus albidus and native and introduced Hymenoscyphus fraxineus on Fraxinus excelsior and Fraxinus pennsylvanica

Ash dieback is caused by Hymenoscyphus fraxineus, a cryptic species of the putatively harmless Hymenoscyphus albidus. Recently, H. fraxineus was found to be native to East Asia. However, the virulence of Asian H. fraxineus strains on Fraxinus excelsior and the virulence of European H. albidus on hosts other than F. excelsior and Fraxinus mandshurica have not yet been assessed. In a wound inoculation study, the virulence of four H. albidus and four European and Japanese H. fraxineus strains was assessed on F. excelsior and Fraxinus pennsylvanica in a climate chamber. Lesion lengths were measured after approximately three and a half months. No lesions were observed on the negative control or on trees inoculated with H. albidus. In contrast, inoculation with H. fraxineus induced typical symptoms of ash dieback on both tree species. Japanese H. fraxineus strains induced significantly longer lesions compared to European strains. Fraxinus excelsior was highly susceptible and developed lesions averaging lengths of 1·7 and 8·4 cm for European and Japanese strains, respectively. Fraxinus pennsylvanica was less susceptible and developed average lesion lengths of 1·6 and 4·8 cm for European and Japanese strains, respectively. Most strains were successfully reisolated from necrotic lesions or inocula, fulfilling Koch's postulates. The data show that additional introductions of H. fraxineus strains from the native range to Europe could pose a threat to the conservation of F. excelsior. In addition, introduction of H. fraxineus to North America could potentially have a negative effect on the indigenous F. pennsylvanica.     

Effects of neemgard on phytophagous and predacious mites and on Spiders

The effects of Neemgard, an acaricidal and fungicidal formulation obtained from neem (Azadirachta indica) seed kernels, on the phytophagous miteTetranychus cinnabarinus, the predacious mitePhytoseiulus persimilis, and the predatory spiderChiracanthium mildei, were investigated in laboratory experiments. Neemgard was highly toxic toT. cinnabarinus but had no toxic effect onC. mildei orP. persimilis. Another neem formulation—the insecticidal Neemix 45—caused conspicuous repellency, but no mortality, inT. cinnabarinus.     

Molecular identification and pathogenicity of Fusarium and Alternaria species associated with root rot disease of wolfberry in Gansu and Ningxia provinces,China

Wolfberry (Lycium barbarum) ranks in the top 10 best-selling medicinal plants in China and it has been used for centuries as a medicine and a food supplement. It is suggested to have benefits on human health due to the rich content of polysaccharides, carotenoids, flavonoids, and alkaloids contained in its fruits, leaves, and root bark. Recently, severe root rot diseases have been causing plant losses in major growing areas. Here, we report fungi causing root rot disease in Chinese wolfberry plants. The analysis of nucleotide sequences of the internal transcribed spacer (ITS) region revealed a total of 92 isolates isolated from both soil and plant material samples. Fusarium spp. were the most abundant (58%), followed by Penicillium spp. (9%), and Alternaria spp. (5%). Fusarium spp. included F. oxysporum (36%), F. solani (30%), F. chlamydosporum (9%), F. nematophilum (9%), and F. tricinctum (8%). Sequences from the translation elongation factor 1-α gene (TEF-1α) were used to confirm the identity of Fusarium spp. and showed the predominance of F. oxysporum and F. solani. To confirm the pathogenicity of isolates, four isolates belonging to Fusarium spp. and one isolate belonging to Alternaria spp., isolated from wolfberry root tissues with root rot symptoms, were tested in outdoor and laboratory conditions. Results revealed that the five tested isolates were pathogenic with varying degrees of aggressiveness and ability to induce symptoms of root rot in wolfberry seedlings. The five isolates were recovered from inoculated seedlings, completing Koch's postulates. This is the first report on causative agents of root rot in Chinese wolfberry.     

Reactions on Nicotiana species to potato viruses A,X and Y and tobacco mosaic virus in relation to their taxonomy and geographical origin

When testing the response of species of the genusNicotiana to 14 isolates of potato viruses A (PVA), X (PVX) and Y (PVY) and tobacco mosaic virus (TMV), sections and section parts of the genus could be divided into five groups according to the overall reaction of their species. Species from arid regions of australia and belonging to the sectionSuaveolentes (subgenusPetunioides) were most sensitive and least resistant, whereas the sectionsPaniculatae (subgenusRustica),Tomentosae (Tabacum) andNoctiflorae (Petunioides) appeared least sensitive and most resistant. Sixty-one percent of the accessions of the latter sections proved resistant to at least two of the viruses. The most resistant species have their main geographical distribution in the central Andes (southern Peru, Bolivia and north-western Argentina), where the viruses may have originated. One other resistant species wasN. africana (Suaveolentes) indigenous to south-western Africa. The most sensitive American sections, viz.Genuinae (Tabacum) andTrigonophyllae, Alatae, Acuminatae andBigelovianae (Petunioides), were generally more sensitive than species of theSuaveolentes section from outside the arid regions of Australia. The remaining part of the genus, viz. the American sectionsThyrsiflorae andRusticae (Rustica) andUndulatae, Repandea andNudicaules (Petunioides) was intermediate between the latter group ofSuaveolentes species and the resistant group of sections with regard to sensitivity and resistance, but had a high rate of tolerance to PVA, PVX and PVY and of hypersensitivity-associated resistance to TMV. The results indicate that the viral respons in the genusNicotiana is mainly determined geographically and to a lesser extent taxonomically.Samenvatting Na inoculatie van een grote collectieNicotiana-soorten met 14 isolaten van de aardappelvirussen A (PVA), X (PVX) en Y (PVY) en tabaksmozaïekvirus (TMV), konden de secties of sectiedelen van het genus op basis van de gemiddelde reactie van hun soorten in vijf groepen worden verdeeld. Soorten uit Australische woestijngebieden en taxonomisch behorend tot de sectieSuaveolentes (subgenusPetunioides) bleken het meest gevoelig en het minst resistent, terwijl de sectiesPaniculatae (subgenusRustica),Tomentosae (Tabacum) enNoctiflorae (Petunioides) het minst gevoelig en het meest resistent waren. Van de collectienummers van de laatstgenoemde secties bleek 61% resistentie tegen minstens twee van de virussen te bezitten. De meest resistente soorten hebben hun verspreidingsgebied vooral in het centrale deel van het Andesgebergte (het zuidelijk deel van Peru, Bolivia en noord-westelijk Argentinië). Mogelijk is dit het ontstaansgebied van deze virussen. De einge andere resistente soort wasN. africana (Suaveolentes) uit zuid-westelijk Afrika. De meest gevoelige Amerikaanse secties, te wetenGenuinae (Tabacum) enTrigonophyllae, Alatae, Acuminatae enBigelovianae (Petunioides), waren gemiddeld gevoeliger danSuaveolentes-soorten die niet uit de Australische woestijnen afkomstig zijn. Het resterende deel van het genus, bestaande uit de Amerikaanse sectiesThyrsiflorae enRusticae (Rustica) enUndulatae, Repandae enNudicaules (Petunioides), stond met betrekking tot gevoeligheid en resistentie tussen laatstgenoemd deel van de sectieSuaveolentes en de groep resistente secties in, maar vertoonde in hoge mate tolerantie voor PVA, PVX en PVY en met overgevoeligheid samengaande resistentie voor TMV. Uit de resultaten blijkt dat de reacties van het genusNicotiana op virussen vooral geografisch bepaald zijn en in mindere mate taxonomisch.