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To quantify the magnitude and the spatial spread of grapevine downy mildew secondary sporangia, 4685 Plasmopara viticola single lesion samples were collected from 18 plots spread across central Europe. Disease symptoms were collected on two to 22 sampling dates per plot between 2000 and 2002. Four multiallelic microsatellite markers were used for genotypic identification of pathogen samples. Genetic analysis showed more than 2300 site-specific P. viticola genotypes, indicating that populations are genetically rich demographic units. Approximately 70% of the genotypes were sampled once and 14% were sampled twice throughout the various epidemics. In the 18 populations only seven genotypes (0.3%) were identified more than 50 times. Three genotypes particularly successful in causing disease through secondary cycles showed mainly a clustered distribution. The distance of sporangial migration per secondary cycle was less than 20 m and their plot colonization rate was calculated at around 1-2 m 2 day -1 . Downy mildew epidemics of grapevine are therefore the result of the interaction of a multitude of genotypes, each causing limited (or a few) lesions, and of a dominant genotype able to spread stepwise at plot-scale. These findings contrast with current theories about grapevine downy mildew epidemiology, which postulate that there is massive vineyard colonization by one genotype and long-distance migration of sporangia.

In view of the ongoing revival of the chestnut orchards in southern Switzerland, evaluation of chestnut quality represents an important issue. Chestnuts are mainly consumed roasted. Three native varieties and a French one were roasted and submitted to sensory and chemical analysis in comparison to a commercial marrone variety imported from Italy. Weight loss due to roasting ranged from 23 to 30%. Roasted chestnuts contained 260±350 g kg À1 starch, 50±102 g kg À1 sucrose, 0.5±4.4 g kg À1 fructose, trace amounts of glucose and 9±15 g kg À1 total fatty acids. The main fatty acid in chestnuts was linoleic acid, amounting to 49% of total fatty acids. Sensory analysis showed that acceptance of chestnuts was highly dependent on sweetness, which was related to sucrose content. It should be at least 90 g kg À1 .Varietal differences were observed in this study and it was shown that roasting caused little change in composition. Thus chestnut varieties used for roasting have to be selected accordingly. The commercial variety Marrone di Cuneo con®rmed its superiority with regard to suitability for roasting. Among the Swiss varieties, only Lu È ina exhibited satisfactory quality.

Southern Switzerland has a long tradition of chestnut cultivation as a staple food. Local inhabitants constantly selected varieties according to the ripening period, the type of use, and the adaptability to the territory. As a result, the panorama of chestnut varieties is very complex, as reflected by more than 120 different variety names in an area of 26,000 ha. Since 1994, 47 varieties have been conserved in the chestnut germplasm of southern Switzerland (CSS), including Marroni, Euro-Japanese, and French varieties. A selection of 164 individuals from the CSS was analysed by 8 SSR markers (4 of which were developed in this study). Microsatellite analysis indicated that the CSS was accurately established, as 86% of the individuals grafted were correctly labeled. The identification of 98 genotypes, 10 clonal chestnut groups, 4 synonym groups, and 12 homonym groups reflected the complex ethnogeographical structure of the chestnut distribution. The 17 Marroni individuals considered clustered in 2 differentiated genetic groups instead of only 1 as expected. The fundamental problem of the frequent cases of homonymy and synonymy is discussed, as is the need for criteria for discriminating between polyclonal varieties and distinct homonymous varieties.

Breeding of resistant apple cultivars (Malus x domestica) as a disease management strategy relies on the knowledge and understanding of the underlying genetics. The availability of molecular markers and genetic linkage maps enables the detection and the analysis of major resistance genes as well as of quantitative trait loci (QTL) contributing to the resistance of a genotype. Such a genetic linkage map was constructed, based on a segregating population of the cross between apple cvs. Fiesta (syn. Red Pippin) and Discovery. The progeny was observed for 3 years at three different sites in Switzerland and field resistance against apple scab (Venturia inaequalis) was assessed. Only a weak correlation was detected between leaf scab and fruit scab. A QTL analysis was performed, based on the genetic linkage map consisting of 804 molecular markers and covering all 17 chromosomes of apple. With the maximum likelihood-based interval mapping method, eight genomic regions were identified, six conferring resistance against leaf scab and two conferring fruit scab resistance. Although cv. Discovery showed a much stronger resistance against scab in the field, most QTL identified were attributed to the more susceptible parent 'Fiesta'. This indicated a high degree of homozygosity at the scab resistance loci in 'Discovery', preventing their detection in the progeny due to the lack of segregation.

With a view to enhancing the quality of local chestnut in southern Switzerland, the impact of three treatments ['soaking', 'cold bath' (hydrotherapy) and 'warm bath' (thermo-hydrotherapy)] on the qualitative, chemical and sensory characteristics of the nuts during 90 days of cold storage was evaluated. Weight and water content decreased significantly with increasing duration of storage. Starch content decreased following a negative logistic trend. Sucrose, however, increased steeply according to a monomolecular trend and was significantly higher between 0 and 60 days of storage in the soaked chestnuts than in the cold-bath treated nuts. The mean proportion of mouldy fruit remained constant at 27% for the warm-bath treated nuts and increased from 16 to 30% for the cold-bath treated fruit and from 28 to 63% for the soaked nuts during the 90 days of cold storage. The most frequently isolated moulds were Ciboria batschiana, Penicillium spp. and Mucor hiemalis. Warm and cold baths were successful in eliminating the larvae of Cydia splendana but the cold bath was inadequate to control Curculio elephas. Cold bath significantly reduced the sensory qualities (sweetness, aroma, texture) of the nuts, but made them easier to peel, as did the warm bath.

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