376 leptocephali of Anguilla anguilla (L., 1758) from the Iberian Basin were analysed.The observed horizontal trends of abundance and particularly the mean sizes contradict the expectations based on the hypothesis of larvae distribution exclusively by drift with Gulf and North Atlantic Currents, and support the hypothesis of an active larval migration also south of the Azores.

No abstract

This is the first report on the leptocephalus catches made during the last 15 years in North-and Central Atlantic during the course of 19 cruises of five different ships from Germany and one from Poland. This report comprises identification, geographical occurrence and abundance and in some cases depth preference, migratory routes and spawning area of Congridae in the North Atlantic. The largest part of this collection consists of 876 Conger conger larvae. The likelihood that this species spawns in the Mediterranean is again confirmed. Decreasing density as well as increasing size from Gibraltar west-and north westward showed migration to be occurring in that direction. Age was determined by counting "daily rings" on the otoliths of up to 120-mm long larvae. It is suggested to be more than 300 days and is calculated to be 11/4 years for the largest larvae (TL = 140-160 mm). Some 126 specimens of three other Conger species, i.e.C, oceanicus, C. triporiceps, C. esculentus, were identified in the collection. The major part originated from the western North Atlantic. The most numerous larvae, belonging to another genus of Congridae, were Ariosoma balearicum (n --265). They showed, also in consideration of other studies, quite a wide range in number of myomeres. Their systematic status is therefore uncertain, as is also the status of those known from the NW Indian Ocean and the NW Pacific. One larva, probably of Ariosoma selenops, of unusually large size (TL = 467 ram) and captured in the Iberian Basin is described and compared with specimens known from the literature. Two larvae of unknown identity were captured off NW Africa; they resembled A. balearicum but had too high a number of myomeres. The identity of most of the Gnathophis larvae caught in the East Atlantic is uncertain. Leptocephali of Paraconger notialis in the East Atlantic, up to the area north of New Guinea, exhibited a higher number of myomeres than those known from the West Atlantic. Larvae of Xenomystax congroides (n --29), belonging to a population with a relatively high number of myomeres, were captured in the Sargasso Sea.

Strehlow, B., de Mol, F., and Struck, C. 2015. Risk potential of clubroot disease on winter oilseed rape. Plant Dis. 99:667-675. Clubroot disease caused by Plasmodiophora brassicae is an important dis ease of cruciferous plants. Although the pathogen is widespread and has been reported to cause high yield losses, the impact on winter oilseed rape (OSR) has not been experimentally verified. To quantify the risk potential of P. brassicae, we conducted two closely linked experiments. A semicontrolled experiment used artificial soil infestation at inoculum densities be tween 10® and 108 spores liter-1 of soil to detect the impact on seed yield and yield components of a susceptible and resistant OSR cultivar. A green house experiment was implemented using the soil of the semicontrolled experiment after cropping the two cultivars to quantify the influence of cultivar resistance on soil inoculum. According to cumulative link mixed models, disease rating was positively correlated with the amount of inoc ulum. Linear regression analyses revealed a negative correlation between seed yield and inoculum density. Yield losses of 60% already appeared at the lowest inoculum density. Plant losses and reduced seed per pod were accountable for yield losses. Although the resistant cultivar showed club root symptoms, seed yield was not affected by the pathogen. The green house experiment revealed that clubroot severity in subsequent OSR was reduced after cropping the resistant cultivar. This study showed signif icant yield damage of P. brassicae already at low infestation levels.

The soilborne pathogen Plasmodiophora brassicae causes clubroot on Brassica crops, a common disease in many oilseed rape growing regions. Here, we investigate genetic diversity and geographic differentiation of P. brassicae populations from different regions in Germany. We compared three regions that differ in oilseed rape cropping history, oilseed rape acreage, and incidence of clubroot. These regions were either spatially separated or separated by the former inner German border. Plasmodiophora isolates were collected from 59 fields (29, 17, and 13 fields per region, respectively) and 174 amplified fragment length polymorphism (AFLP) markers were analyzed. Every field isolate showed a unique genotype pattern; that is, no genotype was shared among the regions and different fields. The mean gene diversity was 0.27, suggesting that P. brassicae is a genetically diverse species. The comparison of indexes (gene diversity, genotypic diversity, and linkage disequilibrium) between the regions does not support our hypotheses that cropping history, oilseed rape acreage, and incidence of clubroot affect these estimates. Principal component analysis (PCA), fixation index (FST), and generalized linear model (GLM) were suitable to specify regional differences. PCA revealed two clusters of isolates based on the geographic origin of the isolates and FST showed that these clusters were highly differentiated. Hypotheses about association of genotypes with different spatial scales were tested with GLM: the region, reflecting the cropping history, and the individual field had a significant effect on the AFLP pattern. We propose that individual field isolates represent a discrete population and that geographic differentiation results from low levels of gene flow due to the limited dispersal of this soilborne pathogen and from localized selection pressure as unifying force on the genotypes.