Effect of road density on abundance of white-footed mice

While several studies have demonstrated that roads can act as barriers to small mammal movement, the relationship between road density and small mammal abundance has not yet been investigated. In southeastern Ontario, Peromyscus leucopus (white-footed mice) suffer high over-winter mortality rates, resulting in small springtime populations and frequent local extinctions. Peromyscus leucopus movement is known to be inhibited by roads, which should result in lower rates of immigration into and recolonization of habitats in landscapes with high road density. We tested two predictions: (1) Forest sites situated in landscapes with high road densities have a higher chance of P. leucopus being absent during the early spring than forest sites situated in landscapes with low road densities and (2) P. leucopus populations during the summer are smaller in forest sites situated in landscapes with high road densities than in landscapes with low road densities. We sampled P. leucopus in focal patches within nineteen landscapes (7 rural, low-road-density landscapes; 7 rural, high-road-density landscapes; 5 urban landscapes). There was no significant relationship between road density and the presence/absence of P. leucopus during the early spring. We found a significant positive effect of road density on P. leucopus relative abundance during the summer, even when we excluded the urban landscapes and based the analysis on only the 14 rural landscapes. Our results suggest that any negative effect of roads on P. leucopus populations, created by their inhibition to moving across roads, is far outweighed by some positive effect of roads on P. leucopus abundance. We suggest that the two most likely explanations are that roads are positively correlated with an important as-yet-undetermined component of habitat quality, or that roads positively affect P. leucopus by negatively affecting their predators.     

Development of <Emphasis Type="Italic">Peronospora parasitica</Emphasis> epidemics on radish as modelled by the effects of water vapour saturation deficit and temperature

Epidemics of Peronospora parasitica are strongly affected by temperature and air moisture, and the interaction of these factors. Because a significant percentage of radish plants are grown in greenhouses, it may be possible to influence epidemics by altering the greenhouse climate. The objective of this study was to test the hypothesis that epidemics of P. parasitica can be modelled by the effects of air temperature and moisture in the greenhouse. Such a model could then be used to analyse greenhouse climate control strategies with regard to managing downy mildew. Five radish crops were grown under greenhouse conditions with set-points for heating and ventilation intended to obtain favourable conditions for disease development during the first part of the growing cycle. Subsequent to this first phase, unfavourable conditions were set until harvest. Disease incidence was measured once a week until the radishes reached marketable size. In addition, experiments were carried out in growth chambers in which inoculated plants were subjected to air temperatures between 8 and 27°C, and disease incidence and sporulation intensity were measured. Data from these two experiments were then used to estimate model parameters. In this model, the interactions of air temperature (T) and water vapour saturation deficit (SD) were adequately described by a multiplicative relationship. The simulated epidemics by the fitted model were highly correlated with the observed epidemics (r = 0.91, R ² = 0.83, n = 29). Parameter estimates indicated that T of ca. 20°C and SD < 0.03 hPa resulted in the highest rates of disease development and that the rate was zero when SD > 2.0 hPa. Both experimental data and simulations showed that epidemics of P. parasitica can be effectively controlled by managing the greenhouse climate.     

N-terminal domain including conserved flg22 is required for flagellin-induced hypersensitive cell death in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Flagellin in Pseudomonas syringae is a potent elicitor of defense responses including hypersensitive cell death in dicot plants. The oligopeptides flg22 consisting of 22 conserved amino acids near the N-terminus of flagellins is reported to induce plant defense responses. Because glycosylation of the central domain of flagellin affects its elicitor activity, we investigated whether any peptide sequence in addition to flg22 is required for flagellin-induced hypersensitive reaction. A study of recombinant flagellin polypeptides indicated that the N-terminal domain including the conserved flg22 is required for flagellin-induced hypersensitive cell death in Arabidopsis thaliana.     

Occurrence of <Emphasis Type="Italic">Phaeoacremonium</Emphasis> spp. and <Emphasis Type="Italic">Phaeomoniella chlamydospora</Emphasis> in grape propagation materials and young grapevines

During a 6-year study, grapevine propagation materials and young grapevines were analysed to evaluate the presence of internal wood discolouration and the occurrence of fungal species involved in Petri disease. The intensity of wood discolouration increased with the ageing of the plants. The maximum incidence of dark streaks was observed in the rootstock while necrosis originating from buds or nodes were notably present in the trunk and cordon of older vines. In contrast, the highest levels of brown-red halo symptoms, defined as discoloured areas around the pith, were recorded in the early growth stages. Phaeoacremonium spp. and Phaeomoniella chlamydospora were usually isolated from the rooted-grafts and the 3-year old plants, respectively. The number of infected grapevines increased with age. Most of the P. chlamydospora strains were isolated from dark streaks or dots, while Phaeoacremonium spp. were detected in brown-red halo symptoms and other symptomatic or asymptomatic wood. The greatest incidence of the two fungal taxa was recorded in the lower parts of the grapevine, including the roots and rootstock.     

AFLP analysis of Russian <Emphasis Type="Italic">Alternaria tenuissima</Emphasis> populations from wheat kernels and other hosts

Alternaria tenuissima is a common pathogen on a number of plants described in several geographic regions of the world. Genetic variation within and between Russian Far East, North West and Caucasus populations of A. tenuissima from wheat was examined. In addition, genetic differences between isolates from various hosts were estimated. In total, 101 isolates of A. tenuissima were studied using amplified fragment length polymorphism (AFLP) with four primer combinations. Wright’s fixation index (F _st), gene flow (N _m) and gene diversity (H _s) were calculated. AFLP banding patterns indicated significant genetic distance and at the same time a low level of gene flow between the Far East and the two other groups of isolates originating from the European part of country. The degree of similarity between the North West and Caucasus populations was very high, as was the migration rate. Isolates analysed by UPGMA-based cluster analysis were grouped according to location of origin but irrespective of plant host. Based on the F _st value, the group of isolates originating from wheat and barley were not found to differ significantly from each other.