Contribution to the occurrence and former distribution of Tephroseris palustris (Compositae) in the Central Europe

Tephroseris palustris (syn. Senecio palustris) is a circumboreal species with large distribution range. The European part of the recent distribution area extends southwards to central France, Germany, Poland, and Ukraine, while in Great Britain, Czech Republic, Hungary, Slovakia, and Romania, T. palustris has been treated as extinct species. The southern boundary of its distribution in Poland does not reach the Carpathian territory. Herbarium specimens, formerly collected in Czech Republic, were found, however, all Czech localities are extinct. No herbarium specimens confirming the old literature data from Slovakia, Hungary, and Romania have been found. Some herbarium specimens coming from this area, and declared as T. palustris (S. palustris), in fact, refer to Senecio paludosus L. Contrary to previous nomenclature review (Jeffrey & Chen 1984), the name Tephroseris palustris (L.) Rchb. seems to be correct (Reichenbach Fl. Saxon.: 146, 1842).     

A methodology for risk analysis of plurivorous fungi in biological weed control: Sclerotinia sclerotiorum as a model

In New Zealand, research is being performed on the use of the ubiquitous plurivorous ascomycete Sclerotinia sclerotiorum, as a biocontrol agent for Cirsium arvense in pasture. As a consequence of the wide host range of this fungus, the proposed biocontrol may pose a risk to non-target arable plants. Crop disease risk is primarily due to the formation of sclerotia. These perennating bodies may directly infect susceptible crops sown at the biocontrol site in years after the biocontrol event. Additionally they may cause infection in neighbouring crops through the formation of apothecia from which airborne ascospores are dispersed. A methodology for a risk analysis is proposed, embodying both temporal and spatial processes, where the relative disease risk from biocontrol is defined as the ratio of added to naturally occurring inoculum.Exponential decay is proposed as a suitable model for the survival of sclerotia in soils beneath pastures, and data from an ongoing study are used in a preliminary parameterisation. The model is applied to published data on initial sclerotium population size and unpublished data on natural levels of soilborne sclerotia, to reveal how a withholding period, defined as the interval of time that must elapse for the ratio of added to natural inoculum to equal unity, may be calculated.For quantifying escape and aerial dispersal of ascospores from a treated pasture, three mechanistic models are proposed. Firstly, a simple one-layer model of escape, giving a provisional estimation of 81% of released ascospores escaping the pasture canopy, is discussed. Secondly, ascospore dispersal within and close to the biocontrol site (<30 m) is described by a model revealing abrupt decline in the atmospheric concentration of ascospores within short distances from the biocontrol site. Thirdly, for predicting ascospore concentrations at greater distances (>100 m), a Gaussian plume model is proposed. In a first approximation, these models are used in an example calculation to show how a hypothetical safety zone might be determined. A map of the province of Canterbury showing the locations of different agricultural activities and infestations of dense populations of C. arvense, revealed that potential biocontrol sites mostly do not border arable land and that a safety zone would therefore be feasible.The study presented here provides conceptual and mathematical frameworks for risk analysis of the use of plurivorous fungi in biological weed control, using S. sclerotiorum as an example. However, before a judgement may be made about the phytosanitory risks associated with the use of S. sclerotiorum to control C. arvense in pastures in Canterbury, the models developed in this paper must be parameterized using data collected under a wide range of conditions in the field.     

Stomatal conductance in a tropical xerophilous shrubland at a lava substratum

Diurnal variation in leaf stomatal conductance (g _s) of three xerophilous species (Buddleia cordata, Senecio praecox and Dodonaea viscosa) was measured over a 10-month period during the dry and wet seasons in a shrubland that is developing in a lava substratum in Mexico. Averaged stomatal conductances were 147 and 60.2 (B. cordata), 145 and 24.8 (D. viscosa) and 142.8 and 14.1 mmol m^–2 s^–1 (S. praecox) during the wet and dry season respectively. Leaf water potential () varied in a range of –0.6 to –1.2 (S. praecox), –0.6 to –1.8 (B. cordata) and –0.9 to –3.4 MPa (D. viscosa) during the same measurement periods. Stomata were more sensitive to changes in irradiance, air temperature and leaf–air vapour pressure difference in the rainy season than the dry season. Although stomatal responses to were difficult to distinguish in any season (dry or rainy), data for the entire period of measurement showed a positive correlation, stomata tending to open as increased, but there is strong evidence of isohydric behaviour in S. praecox and B. cordata. A multiplicative model relating g _s to environmental variables and to accounted for 79%–83% of the variation of g _s in three sites (pooled data); however, the performance of the model was poorer (60%–76%) for individual species from other sites not included in the pooled data.     

Pyrrolizidine alkaloids in and on the leaf surface of Senecio jacobaea L

This is the first study showing that alkaloids are present on the leaf surface of plants. A concentration of 30-230 pmol/cm2 pyrrolizidine alkaloids (PA's) was detected in 8 different samples taken from Senecio jacobaea. PA concentration on the leaves was marginally correlated with PA concentration of the total leaf tissues. The PA spectrum on the leaf differed from the PA spectrum of the total leaf.     

Variation in pyrrolizidine alkaloid patterns of Senecio jacobaea

We studied the variation in pyrrolizidine alkaloid (PA) patterns of lab-grown vegetative plants of 11 European Senecio jacobaea populations. Plants were classified as jacobine, erucifoline, mixed or senecionine chemotypes based on presence and absence of the PAs jacobine or erucifoline. Due to the presence of jacobine, total PA concentration in jacobine chemotypes was higher than in erucifoline chemotypes. Both relative and absolute concentrations of individual PAs differed between half-sib and clonal families, which showed that variation in PA patterns had a genetic basis. Within most populations relative abundance of PAs varied considerably between individual plants. Most populations consisted either of the jacobine chemotype or of the erucifoline chemotype, sometimes in combination with mixed or senecionine chemotypes.     

Random amplified polymorphic DNA (RAPD) and quantitative trait analyses across a major phylogeographical break in the Mediterranean ragwort Senecio gallicus Vill. (Asteraceae)

Random amplified polymorphic DNA (RAPD) and quantitative trait variation of the widespread and ephemeral Senecio gallicus were surveyed in 11 populations sampled from the Iberian Peninsula and southern France. The aim of the study was to compare population relationships and levels of geographical differentiation with chloroplast (cp) DNA and allozyme variation assessed previously in the same populations. Employing multivariate statistics, a moderate level of intraspecific differentiation was observed among populations from Iberian coastal and inland regions for both RAPDs and quantitative traits. However, RAPDs provided greater resolution in identifying additional population structure within the hypothesized, Pleistocene refugial source area of the species in coastal Iberia. A major part of the geographical subdivision in RAPD and quantitative traits was concordant with the coastal vs. inland divergence as previously inferred from cpDNA haplotype frequencies, but strongly contrasted with the geographical uniformity of the species for allozymes. This concordance across various nuclear and cytoplasmic markers (RAPDs/quantitative traits, cpDNA) suggests that geographical uniformity for allozymes is more attributable to low rates of evolution and/or small genome sampling rather than high rates of pollen dispersal, slow rates of nuclear lineage sorting, or indirect balancing selection. The present study underscores the value of using additional classes of nuclear markers for narrowing the numbers of competing causal hypotheses about intraspecific cpDNA-allozyme discrepancies and their underlying evolutionary processes.     

Biological characteristics of an invasive south African species

Senecio inaequidens, a south African species that has recently invaded parts of Europe, especially human disturbed habitats, was examined under laboratory and glasshouse conditions to assess the germination of achenes, soil seed banks, growth of seedlings and its breeding system. These observations allowed identification of ecological characteristics that may contribute to the invasiveness of the species. Achenes derived from three populations of S. inaequidens were germinated over a wide temperature range (from 14/6 °C day/night temperatures to a constant temperature of 30 °C). They exhibited a rapid achene germination especially when temperatures reached 20 °C. Germination of seeds from soil samples also exhibited a prolonged germination over time suggesting therefore different types of dormancy. Growth response was studied along a nitrogen gradient from 0.33 to 16.0 mmol l^–1 and data were interpreted using growth analysis. Seedlings of S. inaequidens exhibited a slow growth in low nutrient availability and a rapid growth rate when exposed to high nutrient availability, which contributed to producing a large leaf area and biomass. Four types of pollination were studied in S. inaequidens. Hand-pollinations showed that S. inaequidens was mostly self-incompatible. Self-pollinated capitula only showed 7.6% viable achenes, significantly lower than insect-pollinated and cross-pollinated capitula. Some individuals were more self-fertile than others ensuring the production of some offspring in a situation of colonisation. Natural pollination occurred with generalist insects. Most of these results confirm the invasive ability of S. inaequidens.     

The origin of a novel form of Senecio (Asteraceae) restricted to sand dunes in southern Sicily

The taxonomy of diploid Mediterranean Senecio sect. Senecio (Asteraceae) is complex, owing to a recent species radiation, high morphological plasticity and occasional interspecific hybridization. A study was conducted to resolve the origin of a novel form of Senecio restricted to sand dunes in southern Sicily, Italy. This has been described previously as morphologically intermediate to Senecio gallicus and Senecio glaucus ssp. coronopifolius, indicating a possible hybrid origin, or as a variant of Senecio leucanthemifolius. Plants of this form grown in a glasshouse were morphologically intermediate to S. glaucus and S. leucanthemifolius, but were also similar to some cultivated individuals of S. gallicus. No evidence for a hybrid origin was obtained from a survey of random amplified polymorphic DNA variation; instead the plants surveyed were most closely allied to Tunisian S. glaucus. They were also polymorphic for the same set of cpDNA haplotypes present in Tunisian S. glaucus. We conclude that the Sicilian Senecio is a variant form of North African S. glaucus ssp. coronopifolius, which most probably dispersed to sand dunes in southern Sicily in the relatively recent past. The presence of several cpDNA haplotypes in this material indicates that there have been multiple introductions of the species to Sicily.