Comparison of a baiting method and PCR for the detection of Phytophthora fragariae var. rubi in certified raspberry stocks*

In winter 2002/2003, a total of 136 root samples from 57 different raspberry stocks in Scotland were examined for the presence of raspberry root rot caused by the fungus‐like pathogen Phytophthora fragariae var. rubi. All stocks had been planted as propagation material entered at different grades in the Scottish certification scheme or had applied for plant passports. For detection, a modified ‘Duncan bait test’ was compared to a nested PCR method. The two tests identified the same infected stocks: PCR detected 10 positive samples from four different stocks, while the bait test picked up two additional positive samples coming from the same four stocks. The two tests had a similar level of reliability in this examination and a recommendation for one or the other depends mainly on the technical equipment and skills available in the laboratory.     

Prepenetration stages in infection of clematis by Phoma clematidina

A detailed study of conidial germination, germ-tube growth and the formation of infection structures in Phoma clematidina , the causal agent of clematis wilt, is described for two clematis varieties differing in disease resistance. On both the resistant and susceptible varieties, the fungus entered leaves and stems by direct penetration of the cuticle, often, but not always, following the formation of infection structures. More germ tubes per conidium were formed on the susceptible host, but these germ tubes were on average shorter than on the resistant host. Although germ tubes regularly entered the plant via trichomes, stomata were not found to be sites of entry. Following penetration of the cuticle of resistant plants, germ-tube growth was sometimes restricted to the subcuticular region, and halo formation occurred at the sites where penetration was attempted. Subcuticular growth and halo formation were not observed on susceptible plants. These observations may partly explain the resistance of small-flowered clematis varieties to P. clematidina .     

Development and use of a forecasting model for Cydia pomonella*

For more than 10 years, a forecasting model for Cydia pomonella in apple orchards, worked out by the French NPPO, has described the development of emergence cohorts in spring, and followed their development and descent, through the whole agricultural season. In homogeneous areas, this tool, still under development, can be used to define periods for effective treatment (ovicides, larvicides, mating disruption) and the tolerance for codling moth levels in various situations. Alternation of insecticides is provided for, so as to manage resistance phenomena. The reliability of the model is based on rigorous continuous biological checks on the forecasts made by the algorithm, on scientific surveillance by INRA and on regular collaboration between the advisers involved and the agrometeorological services. The model forms part of a wider decisional scheme, or expert system, in which the fruit grower and his adviser provide observations on the changes which cannot be provided by the model: installation of hail protection nets, night lights, fruit spreading. More parameters will be incorporated in future and the geographical validity of the model will be extended, particularly to more northerly areas.