Long-term effects of sheep grazing on giant hogweed (Heracleum mantegazzianum)

A meadow dominated by a mature, flowering stand of Giant Hogweed (Heracleum mantegazzianum) was grazed by sheep in the years 1987–1993. After two years Giant Hogweed cover was much reduced and a typical meadow vegetation was established. By 1993 Giant Hogweed was completely eliminated though total species diversity was much reduced. Soil sampled from the grazed area developed no Giant Hogweed seedlings in a germination test and contained no viable seeds of the species. In contrast soil from adjacent stands produced numerous seedlings with a peak emergence from samples taken after the winter. Seeds collected in October showed a viability in tetrazolium test of 88%. Germination averaged 22% after storage at room temperature and 25% following three weeks treatment at –18°C. It was concluded that the persistence of Giant Hogweed seeds in Danish meadow soils is less than seven years.     

A set of primers for plastid indels and nuclear microsatellites in the invasive plant Heracleum mantegazzianum (Apiaceae) and their transferability to Heracleum sphondylium

This study reports the isolation and polymorphism characterization of four plastid indels and six nuclear microsatellite loci in the invasive plant Heracleum mantegazzianum. These markers were tested in 27 individuals from two distant H. mantegazzianum populations. Plastid indels revealed the presence of five chlorotypes while five nuclear microsatellite loci rendered polymorphism. Applications of these markers include population genetics and phylogeography of H. mantegazzianum. A very good transferability of markers to Heracleum sphondylium was demonstrated.     

Properties of cocksfoot streak and cocksfoot cryptic, two viruses infecting cocksfoot (Dactylis glomerata) in Scotland

A Scottish isolate of cocksfoot streak virus (CSV-S) was found to have flexuous filamentous particles which, in sap of infected cocksfoot plants, had a modal length of 712 nm. It was transmitted from infected to healthy cocksfoot plants in a non-persistent manner by Myzus persicae and by mechanical inoculation of infective sap extracts containing an anti-oxidant. Apart from cocksfoot, mechanical inoculation of infective sap succeeded in infecting only four of 22 plant species tested. The infectivity of sap extracts containing 0.2% thioglycerol was lost after heating for 10 min at 55^oC but not 50^oC, storage at room temperature for 48 but not 24 hours, and after diluting 10^-2to 10^-3. Highly purified preparations of CSV-S particles sedimented as a single component with a sedimentation coefficient of 139S and had a buoyant density in rubidium bromide of 1.31 g/cm³. Virus particles were composed of one protein and one ssRNA species with estimated M_r of 31 000 and 3.2 times 10⁶respectively. In ELISA, an antiserum prepared to CSV-S detected the virus in all aerial parts of infected cocksfoot plants and, when present in the ratio of 1 infected leaf: 1000 healthy leaves. Both CSV-S-infected and -uninfected cocksfoot also contained a previously undescribed virus with isometric particles c. 30 nm in diameter. This virus, named cocksfoot cryptic virus (CCV), was seed-borne in two cvs of cocksfoot tested and its particles contained two dsRNA species of estimated M_r of 1.14 times 10⁶and 1.27 times 10⁶. Despite the fact that particles of CSV-S were largely free from CCV particles following exclusion chromatography on agarose beads prior to immunisation, immunoelectron microscopy (IEM) showed that the antiserum prepared to CSV-S also contained some antibodies to CCV. Evidence from IEM suggested a possible distant serological relationship of CCV to ryegrass and beet (BCV 1 or BCV 2, or both) cryptoviruses, all members of sub-group A of crypto viruses.     

Properties of cocksfoot streak and cocksfoot cryptic, two viruses infecting cocksfoot (Dactylis glomerate) in Scotland

A Scottish isolate of cocksfoot streak virus (CSV-S) was found to have flexuous filamentous particles which, in sap of infected cocksfoot plants, had a modal length of 712 nm. It was transmitted from infected to healthy cocksfoot plants in a non-persistent manner by Myzus persicae and by mechanical inoculation of infective sap extracts containing an anti-oxidant. Apart from cocksfoot, mechanical inoculation of infective sap succeeded in infecting only four of 22 plant species tested. The infectivity of sap extracts containing 0.2% thioglycerol was lost after heating for 10 min at 55^oC but not 50^oC, storage at room temperature for 48 but not 24 hours, and after diluting 10-2 to 10-3. Highly purified preparations of CSV-S particles sedimented as a single component with a sedimentation coefficient of 139S and had a buoyant density in rubidium bromide of 1.31 g/cm3. Virus particles were composed of one protein and one ssRNA species with estimated Mr of 31 000 and 3.2 times 106 respectively. In ELISA, an antiserum prepared to CSV-S detected the virus in all aerial parts of infected cocksfoot plants and, when present in the ratio of 1 infected leaf: 1000 healthy leaves. Both CSV-S-infected and -uninfected cocksfoot also contained a previously undescribed virus with isometric particles c. 30 nm in diameter. This virus, named cocksfoot cryptic virus (CCV), was seed-borne in two cvs of cocksfoot tested and its particles contained two dsRNA species of estimated Mt of 1.14 times 106 and 1.27 times 106. Despite the fact that particles of CSV-S were largely free from CCV particles following exclusion chromatography on agarose beads prior to immunisation, immunoelectron microscopy (IEM) showed that the antiserum prepared to CSV-S also contained some antibodies to CCV. Evidence from IEM suggested a possible distant serological relationship of CCV to ryegrass and beet (BCV 1 or BCV 2, or both) cryptoviruses, all members of sub-group A of cryptoviruses.     

On flower visitors and true pollinators: The case of protandrous Heracleum sphondylium L. (Apiaceae)

Hogweed (Heracleum sphondylium L.), a common European umbellifer, is very variable in terms of flower and inflorescence morphology. Its flowers are visited by numerous insects, yet little is known about the importance of the particular insect taxa. I observed umbels of two colour morphs (subspecies) of Heracleum sphondylium growing in NE Poland, which were visited by more than 108 insect species during two study seasons. Analysis of the insects' importance suggests that the most efficient pollinators are the medium-sized flies Eriozona syrphoides, and Lucilia spp. (Diptera). Bumblebees Bombus terrestris (Hymenoptera), beetles of genus Stenurella spp. and Dasytes spp. (Coleoptera) and flies Eristalis spp., Meliscaeva cinctella, Phaonia angelicae and Thricops nigrifrons also contribute to pollination of the studied plants, but their efficiency shows considerable seasonal variation. Although the dense umbels of the white flowered H. sphondylium subsp. sphondylium are generally more attractive for insect visitors than the loose yellowish inflorescences of H. sphondylium subsp. sibiricum, these taxa do not seem to attract different sets of the pollinators. For both subspecies, flowers in the staminate phase were visited significantly more often than those in the pistillate phase. Some flower visitors visited the staminate phase only, which suggests they may be parasites rather than pollinators.     

The Stimulation of Growth by Low Temperature in Embryos of Heracleum sphondylium L.

Low temperature of 2–5° C. accelerates the rate offormation of amino acids from reserve proteins in the endospermof Heracleum sphondylium. It also brings about the accumulationof glycine and arginine in abundance. Experimental culture ofexcised embryos on synthetic media shows that these acids areparticularly beneficial to embryo growth whilst alanine, thepredominating acid at room temperature, is not. It is suggestedthat the rapid growth following low- temperature treatment resultsfrom the action of low temperature on protein breakdown.     

The bioactive essential oil of Heracleum sphondylium L. subsp. ternatum (Velen.) Brummitt

The essential oil of Heracleum sphondylium L subsp. ternatun (Velen.) Brummit (Umbelliferae) was isolated from crushed seeds by means of hydrodistillation and analyzed by GC and GC/MS. Major components were identified as 1-octanol (50.3%), octyl butyrate (24.6%), and octyl acetate (7.3%). Furthermore, antimicrobial activity of the oil was evaluated using microdilution broth and agar diffusion methods. The bioactive constituent of the essential oil was determined as 1-octanol by using a bioautography assay.     

Plasmatic Filaments and Particles in Mature Sieve Elements of Heracleum sphondylium under the Electron Microscope

By using dimethyl sulphoxide in addition to glutaraldehyde onthe phloem of Heracleum a speedier fixative for phloem sieveelements has been developed, less disruptive to plasmatic filaments(p. f.)- Strands of p. f. under the electron microscope seemto run from sieve element to element, axially through the luminaand the sieve-plate pores. Some of these axial strands giveprofiles which suggest that they exist as tubular structuresin which a series of swellings, 20 to 60 ran in diameter, canbe detected as if microperistalsis were passing along them.Marker particles of five different types were noted, often attachedto wisps of plasmatic filaments. Many of the p. f. seemed tohave a helical substructure.     

The Mechanical transmission and some properties of a virus disease of cow-parsnip,Heracleum sphondylium L

The described virus of cow-parsnip,Heracleum sphondylium L., was found in three ruderal localities of Greater Praha. The symptoms are manifested by decolorations which consist of bright yellow areas spreading from the centre of the leaf blade along the main veins. These symptoms appear severely in May. Under higher temperatures and in a chronic stage of infection the symptoms are more or less masked. The disease is mechanically transmissible to parsley, coriander, parsnip, dill, sowbane,Chenopodium quinoa and C.giganteum. The author failed to transmit the disease to celery, carrot, caraway and to 27 species of differential host plants, he failed in the transmission of the virus by the dodder,Cuscuta campestris YUNCK., too. Thermal inactivation point of the virus lies between 51° and 55° C. Infectivity of extracted sap was lost after 2 days at room temperature.     

Epidermal features of Heracleum mantegazzianum Somm. & Lev., H. sphondylium L. and their hybrid

Leaf surfaces of the native Heracleum sphondylium, the alien Heracleum mantegazzianum and the interspecific hybrid were examined using SEM and light microscopy. The surfaces differed in hairiness, especially in the length of the hairs, although the hairs did not differ in general form, or distribution on the leaf surface. Stomata differed little in length, width or frequency, but there were differences in the sort of stomata in relation to the surrounding epidermal cells. The hybrid material was intermediate between the parental species, and sometimes displayed aberrant trichomes that were contorted in contiguous pairs. The results are discussed in relation to other work on the epidermal features of the Umbelliferae: as a means of discriminating the three taxa, and in relation to the ecological distributions of the species.     

A Physiological Study of Embryo Development in Heracleum sphondylium L: II. The Effect of Temperature on After-ripening

The action of low temperature in the after-ripening of seedsof Heracleum sphondylium is to make available the endospermreserves, without which the embryo is starved at room temperature.There is no development of 'secondary dormancy' in the embryo,since the effect of low temperature in after-ripening is strictlyadditive, and the total length of low-temperature treatmentrequired for germination is in no way influenced by periodsat room temperature before or during after-ripening.     

Isolation and phylogenetic analysis of novel viruses infecting the phytoplankton Phaeocystis globosa (Prymnesiophyceae)

Viruses infecting the harmful bloom-causing alga Phaeocystis globosa (Prymnesiophyceae) were readily isolated from Dutch coastal waters (southern North Sea) in 2000 and 2001. Our data show a large increase in the abundance of putative P. globosa viruses during blooms of P. globosa, suggesting that viruses are an important source of mortality for this alga. In order to examine genetic relatedness among viruses infecting P. globosa and other phytoplankton, DNA polymerase gene (pol) fragments were amplified and the inferred amino acid sequences were phylogenetically analyzed. The results demonstrated that viruses infecting P. globosa formed a closely related monophyletic group within the family Phycodnaviridae, with at least 96.9% similarity to each other. The sequences grouped most closely with others from viruses that infect the prymnesiophyte algae Chrysochromulina brevifilum and Chrysochromulina strobilus. Whether the P. globosa viruses belong to the genus Prymnesiovirus or form a separate group needs further study. Our data suggest that, like their phytoplankton hosts, the Chrysochromulina and Phaeocystis viruses share a common ancestor and that these prymnesioviruses and their algal host have coevolved.     

A Physiological Study of Embryo Development in Heracleum sphondylium L.: III. The Effect of Temperature on Metabolism

Low temperature brings about the conversion of storage proteinsinto soluble nitrogenous compounds in the eeed of Heracleumsphondylium. The possible mechanism of this action and its importancein relation to the phenomenon of after-ripening are discussed.     

Occurrence and distribution of viruses infecting potato in Russia

Potato viral disease has been a major problem in potato production worldwide including Russia. Here, we detected Potato Virus M (PVM), P (PVP), S (PVS), Y (PVY), and X (PVX) and Potato Leaf Roll Virus (PLRV) by RT-PCR on potato leaves and tubers from the Northwestern (NW), Volga (VF), and Far Eastern (FE) federal districts of Russia. Each sample was co-infected with up to five viruses. RT-PCR disclosed all six viruses in NW, three in VF, and five in FE. Phylogenetic analyses of PVM and PVS strains resolved all PVM isolates in Group O (ordinary) and all PVS isolates in Group O. Seven PVY strains were detected, and they included only recombinants. PVY recombinants were thus the dominant potato virus strains in Russia, although they widely varied among the regions. Our research provides insights into the geographical distribution and genetic variability of potato viruses in Russia.     

A Physiological Study of Embryo Development in Heracleum sphondylium L.: I. The Effect of Temperature on Embryo Development

Growth of embryos within the seed of Heracleum sphondylium proceedsmore rapidly at low temperature than at room temperature. At2° growth is exponential and in 9 weeks the size is increased4 times and the dry weight 25 times. At 15° there is a progressivefalling off in the rate of growth, and growth ceases when bothsize and dry weight have been only doubled.     

Identification and distribution of viruses infecting sweet potato in Kenya

Four hundred and forty-eight symptomatic and 638 asymptomatic samples were collected from sweet potato fields throughout Kenya and analysed serologically using antibodies to Sweet potato feathery mottle virus (SPFMV), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato mild mottle virus (SPMMV), Cucumber mosaic virus (CMV), Sweet potato chlorotic fleck virus (SPCFV), Sweet potato latent virus (SwPLV), Sweet potato caulimo-like virus (SPCaLV), Sweet potato mild speckling virus (SPMSV) and C-6 virus in enzyme-linked immunosorbent assays (ELISA). Only SPFMV, SPMMV, SPCSV, and SPCFV were detected. Ninety-two percent and 25% of the symptomatic and asymptomatic plants respectively tested positive for at least one of these viruses. Virus-infected plants were collected from 89% of the fields. SPFMV was the most common and the most widespread, detected in 74% of the symptomatic plants and 86% of fields surveyed. SPCSV was also very common, being detected in 38% of the symptomatic plants and in 50% of the fields surveyed. SPMMV and SPCFV were detected in only 11% and 3% of the symptomatic plant samples respectively. Eight different combinations of these four viruses were found in individual plants. The combination SPFMV and SPCSV was the most common, observed in 22% of symptomatic plants. Virus combinations were rare in the asymptomatic plants tested. Incidence of virus infection was highest (18%) in Kisii district of Nyanza province and lowest (1%) in Kilifi and Malindi districts of Coast province.     

Occurrence and relative incidence of viruses infecting papaya in Venezuela

A survey of the main papaya (Carica papaya L.) production fields in Venezuela during 1997, indicated that crops were heavily affected with various virus‐like symptoms. A total of 745 samples from papaya plants showing symptoms suggestive of virus infection were collected and analysed using electron microscopy and enzyme‐linked immunosorbent assay (ELISA). Papaya ringspot virus (PRSV) and Papaya mild yellowing virus (PMYV) were the most frequently found viruses, which also occurred, in mixed infections. Rhabdovirus‐like particles were found only in samples collected in Distrito Federal (D.F). Papaya mosaic virus (papMV) and Tomato spotted wild virus (TSW V) were not detected during the survey.     

Genetic diversity and differentiation in six species of the genus Rhinanthus (Orobanchaceae)

The intricate genus Rhinanthus L. contains many taxonomically unresolved taxa. The assessment of genetic diversity may clarify the differentiation and taxonomic relationships between species and help to determine their mating system, which is important for understanding the future prospects of populations and species. Isozymes were used to assess the mating system, genetic diversity, and differentiation in R. rumelicus, R. osiliensis, R. wagneri, R. alectorolophus, and R. angustifolius from sect. Cleistolemus and R. minor from sect. Rhinanthus. Genetic diversity at species level was found to be higher in widespread R. angustifolius and R. rumelicus compared with insular endemic R. osiliensis. Positive inbreeding coefficient revealed dominant inbreeding in endemic R. osiliensis and R. wagneri. We also detected a significant departure from Hardy–Weinberg equilibrium in some populations of R. rumelicus and R. angustifolius. The common R. alectorolophus and R. minor and several populations of R. rumelicus and R. angustifolius displayed a mixed mating mode. Six studied species divided into three distinct clusters. Rhinanthus alectorolophus was the most differentiated taxon among the investigated species. The species of sect. Cleistolemus formed two distinct groups. The first cluster consisted only of R. alectorolophus while another comprised R. rumelicus, R. osiliensis, R. wagneri, and R. angustifolius, indicating their close affinity. Thus, our isozyme results call into question the monophyly of section Cleistolemus and the taxonomic position of R. alectorolophus.