Assessing climate change impacts on the rape stem weevil, Ceutorhynchus napi Gyll., based on bias- and non-bias-corrected regional climate change projections.

Agricultural production is directly affected by projected increases in air temperature and changes in precipitation. A multi-model ensemble of regional climate change projections indicated shifts towards higher air temperatures and changing precipitation patterns during the summer and winter seasons up to the year 2100 for the region of Goettingen (Lower Saxony, Germany). A second major controlling factor of the agricultural production is the infestation level by pests. Based on long-term field surveys and meteorological observations, a calibration of an existing model describing the migration of the pest insect Ceutorhynchus napi was possible. To assess the impacts of climate on pests under projected changing environmental conditions, we combined the results of regional climate models with the phenological model to describe the crop invasion of this species. In order to reduce systematic differences between the output of the regional climate models and observational data sets, two different bias correction methods were applied: a linear correction for air temperature and a quantile mapping approach for precipitation. Only the results derived from the bias-corrected output of the regional climate models showed satisfying results. An earlier onset, as well as a prolongation of the possible time window for the immigration of Ceutorhynchus napi, was projected by the majority of the ensemble members.

Resynthesized lines and cultivars of Brassica napus L. provide sources of resistance to the cabbage stem weevil ( Ceutorhynchus pallidactylus (Mrsh.)).

The cabbage stem weevil (Ceutorhynchus pallidactylus (Mrsh.)) (Col., Curculionidae) is a serious pest of winter oilseed rape (Brassica napus L. var. oleifera Metzg.) in central and northern Europe. Although host-plant resistance is a key tool in integrated pest management systems, resistant genotypes are not yet available for this species. Resynthesized rapeseed lines (B. oleracea L.×B. rapa L.) are broadening the genetic diversity and might have potential as sources of resistance to pest insects. The host quality, of nine resynthesized rapeseed lines and six genotypes of B. napus to cabbage stem weevil, was evaluated in laboratory screening tests and in a semi-field experiment. In dual-choice oviposition tests, female C. pallidactylus laid significantly fewer eggs on five resyntheses and on swede cv 'Devon Champion' than on the moderately susceptible oilseed rape cv 'Express', indicating a lower host quality of these genotypes. Results of laboratory screenings were confirmed in a semi-field experiment, in which twelve genotypes were exposed to C. pallidactylus females. The number of larvae was significantly lower in two resyntheses and in cv 'Devon Champion' than in oilseed rape cv WVB 9. The total, as well as individual, glucosinolate (GSL) content in the leaves differed substantially among the genotypes tested. The amount of feeding by larvae of C. pallidactylus, as measured by a stem-injury coefficient, was positively correlated with the indolyl GSL compounds 3-indolylmethyl and 4-methoxy-3-indolylmethyl, and with the aromatic GSL 2-phenylethyl, whereas it was negatively correlated with 4-hydroxy-3-indolylmethyl. Thus, the composition and concentration of GSL compounds within the plant tissue might be a key factor in breeding for pest resistance in oilseed rape.

First Report of Plasmodiophora brassicae on Rapeseed in the Grand Duchy of Luxembourg.

Rapeseed (Brassica napus L.) is the third most important crop after wheat and barley in the Grand Duchy of Luxembourg. Since 2005, clubroot symptoms in this crop have been reported by farmers in the Gutland Region. In February 2009, plants of the hybrid rapeseed cv. Exocet, with stunted growth, yellow leaves, and club-shaped roots, were sampled from a field in Oberkorn village near Differdange. Microscopic observations of the rapeseed root fragments revealed the presence of the three life stages characteristic of Plasmodiophora brassicae Woronin. Plasmodia and zoosporangia were observed in the root hairs and resting spores were present in root galls. Individual spores were 2 to 3 µm in diameter. Total DNA was extracted from the root galls with a FAST DNA Kit (MP Biomedicals, Irvine, CA). The internal transcribed spacer region (ITS) and 5.8S gene of the rDNA region were amplified with ITS5 and ITS4 primers as described by White et al. (2) and part of this region was sequenced. A BLASTn search in GenBank revealed that the sequence closely resembled (98% identity) sequences of P. brassicae (Genbank Accession No. EF195335) from an isolate of the pathogen from Switzerland. To confirm the presence of the pathogen, seeds of the susceptible ecotype cvi-0 of Arabidopsis thaliana were grown in a soil sample (1 liter) collected near the infected rapeseed plants. After 55 days of growth in a glasshouse at 15 to 20°C, the roots of 11 plants were analyzed. Two showed clear clubroot symptoms and four others exhibited small swellings. The remaining five plants were symptomless, but plasmodia and zoosporangia were found in root hair cells. Clubroot caused by P. brassicae has previously been described on B. napus and other crucifers (1). To our knowledge, this is the first report of clubroot disease caused by P. brassicae in Luxembourg. Because its presence has since been observed in new fields in the Gutland Region and because of the ability of the pathogen to survive for a long period in the soil, this disease could represent a severe threat for cropping of Brassicaceae in Luxembourg and neighboring countries. References: (1) I. R. Crute et al. Plant Breed. Abstr. 50:91, 1980. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic press: San Diego, 1990.