Federal Office for Food and Agriculture

Phylogenetic relationships of the phyto-pathogenic Gibberella fujikuroi species complex were investigated by maximum parsimony analysis of DNA sequences from multiple loci. Gene trees inferred from the β-tubulin gene exons and introns, mitochondrial small subunit (mtSSU) rDNA, and 5′ portion of the nuclear 28S rDNA were largely concordant, and in a combined analysis, provide strong statistical support for a phylogeny consistent with species radiations in South America, Africa, and Asia. These analyses place the American clade as a mono-phyletic sister-group of an African-Asian clade. Africa is the most phylogenetically diverse area examined with 16 species, followed by America (12 species) and Asia (8 species). The biogeographic hypothesis proposed from the phylogenetic evidence is based primarily on the formation of natural barriers associated with the fragmentation of the ancient super-continent Gondwana. Discordance of the nuclear ribosomal internal transcribed spacer (ITS) based tree with gene trees from the other loci sequenced is due to nonorthologous ITS2 sequences. The molecular evidence suggests the divergent ITS2 types were combined by an ancient interspecific hybridization (xenologous origin) or gene duplication (paralogous origin) that predates the evolutionary radiation of the G. fujikuroi complex. Two highly divergent nonorthologous ITS2 types designated type I and type II were identified and characterized with conserved ITS and ITS2 type-specific polymerase chain reaction (PCR) primers and DNA sequence analysis. Only the major ITS2 type is discernible when conserved ITS primers are used; however, a minor ITS2 type was amplified from every strain tested with type-specific PCR primers. The evolutionary pattern exhibited by the major ITS2 type is homoplastic when mapped onto the species lineages inferred from the combined nuclear 28S rDNA, mtSSU rDNA, and β-tubulin gene sequences. Remarkably, the data indicate the major ITS2 type has switched between a type I and type II sequence at least three times during the evolution of the G. fujikuroi complex, but neither type has been fixed in any of the 45 species examined. Twenty-six of the 45 species included in this study represent either new species (23 species), new combinations (F. bulbicola and F. phyllophilum), or a rediscovered species (F. lactis). The results further indicate that traditional sectional and species-level taxonomic schemes for this lineage are artificial and a more natural classification is proposed.

Phylogenetic relationships within the Gibberella fujikuroi species complex were extended to newly discovered strains using nucleotide characters obtained by sequencing polymerase chain reaction (PCR) amplified DNA from 4 loci used in a previous study [nuclear large subunit 28S rDNA, nuclear ribosomal internal transcribed spacer (ITS) region, mitochondrial small subunit (mtSSU) ribosomal DNA, and β-tubulin] together with two newly sampled protein-encoding nuclear genes, translation elongation factor EF-1α and calmodulin. Sequences from the ribosomal ITS region were analyzed separately and found to contain of two highly divergent, nonorthologous ITS2 types. Phylogenetic analysis of the individual and combined datasets identified 10 new phylogenetically distinct species distributed among the following three areas: 2 within Asia and 4 within both Africa and South America. Hypotheses of the monophyly of Fusarium subglutinans and its two formae speciales, f. sp. pini and f. sp. ananas, were strongly rejected by a likelihood analysis. Maximum parsimony results further indicate that the protein-encoding nuclear genes provide considerably more phylogenetic signal that the ribosomal genes sequenced. Relative apparent synapomorphy analysis was used to detect long-branch attraction taxa and to obtain a statistical measure of phylogenetic signal in the individual and combined datasets.

Differences between endophytic and ectophytic bacterial communities with stress on antagonistic bacteria, were studied by comparing the composition of communities isolated from the rhizosphere, phyllosphere, endorhiza and endosphere of field-grown potato plants using a multiphasic approach. Terminal restriction fragment length polymorphism analysis of 16S rDNA of the bacterial communities revealed discrete microenvironment-specific patterns. To measure the antagonistic potential of potato-associated bacteria, a total of 2648 bacteria were screened by dual testing of antagonism to the soilborne pathogens Verticillium dahliae and Rhizoctonia solani. Composition and diversity of bacterial antagonists were mainly specific for each microenvironment. The rhizosphere and endorhiza were the main reservoirs for antagonistic bacteria and showed the highest similarity in their colonisation by antagonists. The most prominent species of all microenvironments was Pseudomonas putida, and rep-PCR with BOX primers showed that these isolates showed microenvironment-specific DNA fingerprints. P. putida isolates from the rhizosphere and endorhiza gave nearly identical fingerprints confirming the high similarity of bacterial populations. The phlD gene, involved in the production of the antibiotic 2,4-diacetyl-phloroglucinol, was found only among Pseudomonas isolates from the rhizosphere and endorhiza. Evaluation of the bacterial isolates for biocontrol potential based on fungal antagonism and physiological characteristics resulted in the selection of five promising isolates from each microenvironment. The most effective isolate was Serratia plymuthica 3Re4-18 isolated from the endorhiza.

Ten Fusarium species within the Gibberella fujikuroi complex are described and illustrated as new species: F. acutatum ex Triticum sp. (wheat) and Cajanus sp.,F. begoniae ex Begonia elatior hybrid, F. circinatum ex Pinus spp. and its teleomorph G. circinata, F. concentricum ex Musa sapientum (banana) and Nilaparvata lugens (Asian brown leaf hopper), F. denticulatum ex Ipomoea batatas (sweet potato), F. guttiforme ex Ananas comosus (pineapple), F. phyllophilum ex Dracaena, Sansevieria and Gasteria spp., F. pseudocircinatum ex Solanum sp. as well as Pinus kesiya and Heteropsylla incisa, F. pseudonygamai ex Pennisetum typhoides (millet) and F. ramigenum ex Ficus carica (figs). One variety, F. sacchari var. elongatum ex Nerine bowdenii, Vallota sp. and Haemanthus sp. is given species rank as F. bulbicola. A neotype is designated for F. lactis, a pathogen of Ficus carica. A key to the described species is provided.

Phylogenetic relationships of the phyto-pathogenic Gibberella fujikuroi species complex were investigated by maximum parsimony analysis of DNA sequences from multiple loci. Gene trees inferred from the β-tubulin gene exons and introns, mitochondrial small subunit (mtSSU) rDNA, and 5′ portion of the nuclear 28S rDNA were largely concordant, and in a combined analysis, provide strong statistical support for a phylogeny consistent with species radiations in South America, Africa, and Asia. These analyses place the American clade as a mono-phyletic sister-group of an African-Asian clade. Africa is the most phylogenetically diverse area examined with 16 species, followed by America (12 species) and Asia (8 species). The biogeographic hypothesis proposed from the phylogenetic evidence is based primarily on the formation of natural barriers associated with the fragmentation of the ancient super-continent Gondwana. Discordance of the nuclear ribosomal internal transcribed spacer (ITS) based tree with gene trees from the other loci sequenced is due to nonorthologous ITS2 sequences. The molecular evidence suggests the divergent ITS2 types were combined by an ancient interspecific hybridization (xenologous origin) or gene duplication (paralogous origin) that predates the evolutionary radiation of the G. fujikuroi complex. Two highly divergent nonorthologous ITS2 types designated type I and type II were identified and characterized with conserved ITS and ITS2 type-specific polymerase chain reaction (PCR) primers and DNA sequence analysis. Only the major ITS2 type is discernible when conserved ITS primers are used; however, a minor ITS2 type was amplified from every strain tested with type-specific PCR primers. The evolutionary pattern exhibited by the major ITS2 type is homoplastic when mapped onto the species lineages inferred from the combined nuclear 28S rDNA, mtSSU rDNA, and β-tubulin gene sequences. Remarkably, the data indicate the major ITS2 type has switched between a type I and type II sequence at least three times during the evolution of the G. fujikuroi complex, but neither type has been fixed in any of the 45 species examined. Twenty-six of the 45 species included in this study represent either new species (23 species), new combinations (F. bulbicola and F. phyllophilum), or a rediscovered species (F. lactis). The results further indicate that traditional sectional and species-level taxonomic schemes for this lineage are artificial and a more natural classification is proposed.

Crop diversity underpins the productivity, resilience and adaptive capacity of agriculture. Loss of this diversity, termed crop genetic erosion, is therefore concerning. While alarms regarding evident declines in crop diversity have been raised for over a century, the magnitude, trajectory, drivers and significance of these losses remain insufficiently understood. We outline the various definitions, measurements, scales and sources of information on crop genetic erosion. We then provide a synthesis of evidence regarding changes in the diversity of traditional crop landraces on farms, modern crop cultivars in agriculture, crop wild relatives in their natural habitats and crop genetic resources held in conservation repositories. This evidence indicates that marked losses, but also maintenance and increases in diversity, have occurred in all these contexts, the extent depending on species, taxonomic and geographic scale, and region, as well as analytical approach. We discuss steps needed to further advance knowledge around the agricultural and societal significance, as well as conservation implications, of crop genetic erosion. Finally, we propose actions to mitigate, stem and reverse further losses of crop diversity.

BIOLOG GN plates are increasingly used to characterize microbial communities by determining the ability of the communities to oxidize various carbon sources. Studies were done to determine whether the BIOLOG GN plate assay accurately reflects the catabolic potential of the inoculum used. To gain insight into which populations of microbial communities contribute to the BIOLOG patterns, denaturing gradient gel electrophoresis and temperature gradient gel electrophoresis (TGGE) were used to assess the diversity of ribotypes in the inocula and individual wells of BIOLOG plates following incubation. These studies were done with microbial communities from the rhizosphere of potatoes and an activated sludge reactor fed with glucose and peptone. TGGE analyses of BIOLOG wells inoculated with cell suspensions from the potato rhizosphere revealed that, compared with the inoculum, there was a decrease in the number of 16S rRNA gene fragments obtained from various wells, as well as a concomitant loss of populations that had been numerically dominant in the inoculum. The dominant fragments in TGGE gels could be assigned to the gamma subclass of the class Proteobacteria, suggesting that fast-growing bacteria adapted to high substrate concentrations were numerically dominant in the wells and may have been primarily responsible for the patterns of substrate use that were observed. Similarly, the community structure changed in wells inoculated with cells from activated sludge; one or more populations were enriched, but all dominant populations of the inoculum could be detected in at least one well. This study showed that carbon source utilization profiles obtained with BIOLOG GN plates do not necessarily reflect the functional potential of the numerically dominant members of the microbial community used as the inoculum.

Abstract Bacillus thuringiensis var. tenebrionis, a new pathotype effective against larvae of Coleoptera In 1982 a new strain of Bacillus thuringiensis belonging to a new pathotype “C” has been isolated in Darmstadt from Tenebrio molitor (Coleoptera: Tenebrionidae). The strain produces within each sporangium one spore and one insecticidal parasporal crystal which is of flat shape and quadrangular in outline. According to its biochemical features our strain belongs to a new subspecies: B. t. var. tenebrionis. After peroral application of spores and crystals to coleopteran larvae (for instance to the chrysomelids Agelastica alni and Leptinotarsa decemlineata ) a dosage‐dependent pathological reaction was induced: feeding stop followed by a remarkable mortality caused by B. t. ‐typical lesions of the larval midgut and subsequent septicemia. Heat‐inactivated preparations have no effect, UV‐inactivated ones are less effective. In contrast, larvae of Lepidoptera (Ephestia kühniella, Plutella xylostella) as well as larvae of Nematocera (Aedes aegypti) are not sensitive against spores and crystals of that new isolate. Zusammenfassung Es wird über einen neuen Pathotyp „C” von B. thuringiensis berichtet. Dieser wird durch den Stamm BI 256–82 repräsentiert, der 1982 in Darmstadt aus Tenebrio molitor L. (Coleoptera: Tenebrionidae) isoliert wurde. Der Stamm produziert pro Sporangium eine Spore und einen insektentoxischen parasporalen Kristall von plättchenartiger Form und quadratischem Grundriß. Nach den biochemischen Eigenschaften handelt es sich hier um eine neue Subspecies: B. t. var. tenebrionis. Während Larven von Lepidopteren (Ephestia kühniella, Plutella xylostella) sowie Larven von Nematoceren (Aedes aegypti) gegenüber dem neuen Stamm unempfindlich sind, treten bei Larven von bestimmten Coleopteren (wie den Chrysomeliden Agelastica alni und Leptinotarsa decemlineata ) nach der peroralen Aufnahme von Sporen und Kristallen dosisabhängig zuerst ein Fraßstopp und anschließend eine bemerkenswerte Mortalität auf. Diese wird durch B. t. ‐typische Läsionen am Larvendarm und eine darauffolgende Septikämie verursacht. Autoklavierte Präparate haben keine Wirkung; UV‐inaktivierte Präparate verursachen eine geringere Wirkung im Vergleich zum nativen Präparat.

Anticoagulant compounds, i.e., derivatives of either 4-hydroxycoumarin (e.g., warfarin, bromadiolone) or indane-1,3-dione (e.g., diphacinone, chlorophacinone), have been in worldwide use as rodenticides for >50 years. These compounds inhibit blood coagulation by repression of the vitamin K reductase reaction (VKOR). Anticoagulant-resistant rodent populations have been reported from many countries and pose a considerable problem for pest control. Resistance is transmitted as an autosomal dominant trait although, until recently, the basic genetic mutation was unknown. Here, we report on the identification of eight different mutations in the VKORC1 gene in resistant laboratory strains of brown rats and house mice and in wild-caught brown rats from various locations in Europe with five of these mutations affecting only two amino acids (Tyr139Cys, Tyr139Ser, Tyr139Phe and Leu128Gln, Leu128Ser). By recombinant expression of VKORC1 constructs in HEK293 cells we demonstrate that mutations at Tyr139 confer resistance to warfarin at variable degrees while the other mutations, in addition, dramatically reduce VKOR activity. Our data strongly argue for at least seven independent mutation events in brown rats and two in mice. They suggest that mutations in VKORC1 are the genetic basis of anticoagulant resistance in wild populations of rodents, although the mutations alone do not explain all aspects of resistance that have been reported. We hypothesize that these mutations, apart from generating structural changes in the VKORC1 protein, may induce compensatory mechanisms to maintain blood clotting. Our findings provide the basis for a DNA-based field monitoring of anticoagulant resistance in rodents.

Apple proliferation (AP), pear decline (PD) and European stone fruit yellows (ESFY) are among the most economically important plant diseases that are caused by phytoplasmas. Phylogenetic analyses revealed that the 16S rDNA sequences of strains of each of these pathogens were identical or nearly identical. Differences between the three phytoplasmas ranged from 1.0 to 1.5% of nucleotide positions and were thus below the recommended threshold of 2.5% for assigning species rank to phytoplasmas under the provisional status 'Candidatus'. However, supporting data for distinguishing the AP, PD and ESFY agents at the species level were obtained by examining other molecular markers, including the 16S-23S rDNA spacer region, protein-encoding genes and randomly cloned DNA fragments. The three phytoplasmas also differed in serological comparisons and showed clear differences in vector transmission and host-range specificity. From these results, it can be concluded that the AP, PD and ESFY phytoplasmas are coherent but discrete taxa that can be distinguished at the putative species level, for which the names 'Candidatus Phytoplasma mali', 'Candidatus Phytoplasma pyri' and 'Candidatus Phytoplasma prunorum', respectively, are proposed. Strains AP15R, PD1R and ESFY-G1R were selected as reference strains. Examination of available data on the peach yellow leaf roll (PYLR) phytoplasma, which clusters with the AP, PD and ESFY agents, confirmed previous results showing that it is related most closely to the PD pathogen. The two phytoplasmas share 99.6% 16S rDNA sequence similarity. Significant differences were only observed in the sequence of a gene that encodes an immunodominant membrane protein. Until more information on this phytoplasma is available, it is proposed that the PYLR phytoplasma should be regarded as a subtype of 'Candidatus Phytoplasma pyri'.

AbstractTen Fusarium species within the Gibberella fujikuroi complex are described and illustrated as new species: F. acutatum ex Triticum sp. (wheat) and Cajanus sp.,F. begoniae ex Begonia elatior hybrid, F. circinatum ex Pinus spp. and its teleomorph G. circinata, F. concentricum ex Musa sapientum (banana) and Nilaparvata lugens (Asian brown leaf hopper), F. denticulatum ex Ipomoea batatas (sweet potato), F. guttiforme ex Ananas comosus (pineapple), F. phyllophilum ex Dracaena, Sansevieria and Gasteria spp., F. pseudocircinatum ex Solanum sp. as well as Pinus kesiya and Heteropsylla incisa, F. pseudonygamai ex Pennisetum typhoides (millet) and F. ramigenum ex Ficus carica (figs). One variety, F. sacchari var. elongatum ex Nerine bowdenii, Vallota sp. and Haemanthus sp. is given species rank as F. bulbicola. A neotype is designated for F. lactis, a pathogen of Ficus carica. A key to the described species is provided.Key Words: DlaminiafungihyphomycetesHypocrealesLiseolaphytopathogenssystematics

Primer systems for PCR amplification of different replicon-specific DNA regions were designed on the basis of published sequences for plasmids belonging to the incompatibility (Inc) groups IncP, IncN, IncW, and IncQ. The specificities of these primer systems for the respective Inc groups were tested with a collection of reference plasmids belonging to 21 different Inc groups. Almost all primer systems were found to be highly specific for the reference plasmid for which they were designed. In addition, the primers were tested with plasmids which had previously been grouped by traditional incompatibility testing to the IncN, IncW, IncP, or IncQ group. All IncQ plasmids gave PCR products with the IncQ primer systems tested. However, PCR products were obtained for only some of the IncN, IncP, and IncW group plasmids. Dot blot and Southern blot analyses of the plasmids revealed that PCR-negative plasmids also failed to hybridize with probes derived from the reference plasmids. The results indicated that plasmids assigned to the same Inc group by traditional methods might be partially or completely different from their respective reference plasmids at the DNA level. With a few exceptions, all plasmids related to the reference plasmid at the DNA level also reacted with the primer systems tested. PCR amplification of total DNA extracted directly from different soil and manure slurry samples revealed the prevalence of IncQ- and IncP-specific sequences in several of these samples. In contrast, IncN- and IncW-specific sequences were detected mainly in DNA obtained from manure slurries.

Following joint tests in the Netherlands, Germany and the United Kingdom a new scheme is proposed for naming pathotypes of potato cyst-nematodes. Pathotypes of Globodera ( = Heterodera) rostochiensis and G. pallida are designated separately using a simple nomenclature Ro1 to Ron for G. rostochiensis and Pa1 to Pan for G. pallida. Currently seven clones are used to differentiate five pathotypes of G. rostochiensis and three of G. pallida. Several of the pathotypes recognised in the British, Dutch and German National Schemes are the same. Results of pathotyping tests may show considerable variation; adequate replication and standardisation of method are essential. With an internationally used scheme it is highly desirable that new pathotypes or differential clones are added only after testing at Institutes in several countries.

The phylogenetic relationships of 17 phytopathogenic mycoplasmalike organisms (MLOs) representing seven major taxonomic groups established on the basis of MLO 16S ribosomal DNA (rDNA) restriction patterns were examined by performing a sequence analysis of the 16S rDNA gene. The sequence data showed that the MLOs which we examined are members of a relatively homogeneous group that evolved monophyletically from a common ancestor. In agreement with results obtained previously with other MLOs, our results also revealed that the organisms are more closely related to Acholeplasma laidlawii and other members of the anaeroplasma clade than to any other mollicutes. A phylogenetic tree based on 16S rDNAs showed that the MLOs which we examined can be divided into the following five primary clusters: (i) the aster yellows strain cluster; (ii) the apple proliferation strain cluster; (iii) the western-X disease strain cluster; (iv) the sugarcane white leaf strain cluster; and (v) the elm yellows strain cluster. The aster yellows, western-X disease, and elm yellows strain clusters were divided into two subgroups each. MLOs whose 16S rDNA sequences have been determined previously by other workers can be placed in one of the five groups. In addition to the overall division based on 16S rDNA sequence homology data, the primary clusters and subgroups could be further defined by a number of positions in the 16S rDNAs that exhibited characteristic compositions, especially in the variable regions of the gene.

Herbogil (dinoterb), a reference herbicide, the mineral oil Oleo (paraffin oil used as an additive to herbicides), and Goltix (metamitron) were taken as model compounds for the study of impacts on microbial soil communities. After the treatment of soil samples, effects on metabolic sum parameters were determined by monitoring substrate-induced respiration (SIR) and dehydrogenase activity, as well as carbon and nitrogen mineralization. These conventional ecotoxicological testing procedures are used in pesticide registration. Inhibition of biomass-related activities and stimulation of nitrogen mineralization were the most significant effects caused by the application of Herbogil. Even though Goltix and Oleo were used at a higher dosage (10 times higher), the application of Goltix resulted in smaller effects and the additive Oleo was the least-active compound, with minor stimulation of test parameters at later observation times. The results served as a background for investigation of the power of "fingerprinting" methods in microbial ecology. Changes in catabolic activities induced by treatments were analyzed by using the 95 carbon sources provided by the BIOLOG system. Variations in the complex metabolic fingerprints demonstrated inhibition of many catabolic pathways after the application of Herbogil. Again, the effects of the other compounds were expressed at much lower levels and comprised stimulations as well as inhibitions. Testing for significance by a multivariate t test indicated that the sensitivity of this method was similar to the sensitivities of the conventional testing procedures. The variation of sensitive carbon sources, as determined by factor weights at different observation times, indicated the dynamics of the community shift induced by the Herbogil treatment in more detail. DNA extractions from soil resulted in a collection of molecules representing the genetic composition of total bacterial communities. Distinct and highly reproducible community patterns, or genetic fingerprints, resulting from application of the different herbicides were obtained by the sequence-specific separation of partial 16S rDNA amplification products in temperature gradient gel electrophoresis. Significant pattern variations were quantified. For detailed analysis, application-responsive bands from the Herbogil and Oleo treatments were sequenced and their tentative phylogenetic positions were identified. Data interpretation and the potentials and biases of the additional observation windows on microbial communities are discussed.

The complete nucleotide sequence of the RNA of an aphid non-transmissible plum pox virus (PPV-NAT) isolate has been determined from five overlapping cDNA clones. cDNA prepared by primer extension was used to determine the 5' terminus. The assembled RNA is 9741 nucleotides in length, excluding a 3' terminal poly(A) sequence. One large open reading frame starts at nucleotide positions 36 to 38 and is terminated with an UAG codon at positions 9522 to 9524. The putative start codon is located at positions 147 to 149. The encoded polyprotein has a predicted Mr of 353.8K. Comparison of cistrons from tobacco vein mottling virus and tobacco etch virus with those predicted for PPV-NAT indicated a similar genome organization. A highly conserved sequence of 12 nucleotides was found in the 5' non-coding region of these three potyviruses. The potential polyadenylation signal from yeast (UAUGU) was found in the 3' non-coding region of PPV-NAT and several other members of the potyvirus group.

Antibiotic resistance plasmids were exogenously isolated in biparental matings with piggery manure bacteria as plasmid donors in Escherichia coli CV601 and Pseudomonas putida UWC1 recipients. Surprisingly, IncQ-like plasmids were detected by dot blot hybridization with an IncQ oriV probe in several P. putida UWC1 transconjugants. The capture of IncQ-like plasmids in biparental matings indicates not only their high prevalence in manure slurries but also the presence of efficiently mobilizing plasmids. In order to elucidate unusual hybridization data (weak or no hybridization with IncQ repB or IncQ oriT probes) four IncQ-like plasmids (pIE1107, pIE1115, pIE1120, and pIE1130), each representing a different EcoRV restriction pattern, were selected for a more thorough plasmid characterization after transfer into E. coli K-12 strain DH5alpha by transformation. The characterization of the IncQ-like plasmids revealed an astonishingly high diversity with regard to phenotypic and genotypic properties. Four different multiple antibiotic resistance patterns were found to be conferred by the IncQ-like plasmids. The plasmids could be mobilized by the RP4 derivative pTH10 into Acinetobacter sp., Ralstonia eutropha, Agrobacterium tumefaciens, and P. putida, but they showed diverse patterns of stability under nonselective growth conditions in different host backgrounds. Incompatibility testing and PCR analysis clearly revealed at least two different types of IncQ-like plasmids. PCR amplification of total DNA extracted directly from different manure samples and other environments indicated the prevalence of both types of IncQ plasmids in manure, sewage, and farm soil. These findings suggest that IncQ plasmids play an important role in disseminating antibiotic resistance genes.

A rod-shaped bacterium has been isolated that kills male eggs of the wasp Nasonia vitripennis, a pupal parasite of flies. Only some wasps of this species express this son-killer trait, and these wasps have bacterial infections in various organs. The bacterium was isolated from son-killer wasp tissue and from the hemolymph of fly pupae parasitized by wasps expressing the son-killer trait. Bacteria are apparently transferred to parasitized fly pupae during wasp oviposition, and developing wasp offspring are subsequently infected perorally. Sex-ratio distortion by microorganisms is found in a variety of plants and animals. The infectious peroral transmission of this trait variety of plants and animals. The infectious peroral transmission of this trait is in contrast to the typical pattern of cytoplasmic inheritance of sex-ratio distortion in these other systems.

The ability of Acinetobacter sp. strain BD413(pFG4 delta nptII) to take up and integrate transgenic plant DNA based on homologous recombination was studied under optimized laboratory conditions. Restoration of nptII, resulting in kanamycin-resistant transformants, was observed with plasmid DNA, plant DNA, and homogenates carrying the gene nptII. Molecular analysis showed that some transformants not only restored the 317-bp deletion but also obtained additional DNA.

Sweet potato virus disease (SPVD) is the name used to describe a range of severe symptoms in different cultivars of sweet potato, comprising overall plant stunting combined with leaf narrowing and distortion, and chlorosis, mosaic or vein‐clearing. Affected plants of various cultivars were collected from several regions of Uganda. All samples contained the aphid‐borne sweet potato feathery mottle potyvirus (SPFMV) and almost all contained the whitefly‐borne sweet potato chlorotic stunt closterovirus (SPCSV). SPCSV was detected by a mix of monoclonal antibodies (MAb) previously shown to react only to a Kenyan isolate of SPCSV, but not by a mixture of MAb that detected SPCSV isolates from Nigeria and other countries. Sweet potato chlorotic fleck virus (SPCFV) and sweet potato mild mottle ipomovirus (SPMMV) were seldom detected in SPVD‐affected plants, while sweet potato latent virus (SPLV) was never detected. Isolates of SPFMV and SPCSV obtained by insect transmissions together induced typical symptoms of SPVD when graft‐inoculated to virus‐free sweet potato. SPCSV alone caused stunting and either purpling or yellowing of middle and lower leaves when graft‐inoculated to virus‐free plants of two cultivars. Similarly diseased naturally inoculated field plants were shown consistently to contain SPCSV. Both this disease and SPVD spread rapidly in a sweet potato crop.