Microsatellite based population structure of Plasmopara viticola at single vine scale

The genetic structure of a Plasmopara viticola population was characterized on five single vines, one for each cultivar Regent, Merlot, Isabella, Müller-Thurgau and Solaris, using four neutral specific polymorphic microsatellite markers. Five-hundred and seventy samples were collected at four dates in the period between the 10th of July and the 23rd of August 2006. On average over all five cultivars, 67% of the genotypes present on the single selected vines derived from primary infections and caused 37% of the lesions genotyped. Fifty-three percent of these genotypes occurred only once on the vine throughout the survey period, while 14% were able to asexually reproduce on the selected single vine throughout the survey period, causing 23% of the lesions. Thirty-three percent of the genotypes on the single vine derived from other vines, 28% from vines of other cultivars in the other rows, and 5% from vines of the same cultivar in the same row. New primary infections appear all along the sampling dates. The overwhelmingly quantitative role of primary infections at vineyard scale was known, however here we observed the phenomenon also at the single vine scale and the reduced contribution of secondary lesions to the populations present on more resistant cultivars compared to the susceptible cultivars. As the sampling extended almost to defoliation, the results are judged to be representative of a typical P. viticola epidemi

Gebrauch biologischer Insektizide im Kampf gegen den Scaphoideus titanus, den Vektor von Flavescence dorée

Flavescence dorée and the mandatory control of its vector Scaphoideus titanus pose important problems in organic vineyards. The goal of our field studies conducted in the Ticino was to develop a pest control strategy conform to the guidelines of organic production. Insecticides containing pyrethrin were the only organic products showing an efficacy higher than 90% against the immature stages of S. titanus. However, these products had no effect on adult leafhoppers. Repeated applications of pyrethrin proved to be toxic against the predatory mite species Amblyseius andersoni. Despite this toxicity, the only efficient and recommended control strategy in organic vineyards is their application. Pyrethrin should be applied three times at an interval of ten days after the first appearance of individuals of the 3rd nymphal stage. Symptomatic plants must be eradicated from the vineyard to remove the phytoplasma inoculum

QTL analysis for aphid resistance and growth traits in apple

The rosy apple aphid (Dysaphis plantaginea), the leaf-curling aphid (Dysaphis cf. devecta) and the green apple aphid (Aphis pomi) are widespread pest insects that reduce growth of leaves, fruits and shoots in apple (Malus × domestica). Aphid control in apple orchards is generally achieved by insecticides, but alternative management options like growing resistant cultivars are needed for a more sustainable integrated pest management (IPM). A linkage map available for a segregating F1-cross of the apple cultivars ‘Fiesta' and ‘Discovery' was used to investigate the genetic basis of resistance to aphids. Aphid infestation and plant growth characteristics were repeatedly assessed for the same 160 apple genotypes in three different environments and 2 consecutive years. We identified amplified fragment length polymorphism (AFLP) markers linked to quantitative trait loci (QTLs) for resistance to D. plantaginea (‘Fiesta' linkage group 17, locus 57.7, marker E33M35-0269; heritability: 28.3%), and to D. cf. devecta (‘Fiesta' linkage group 7, locus 4.5, marker E32M39-0195; heritability: 50.2%). Interactions between aphid species, differences in climatic conditions and the spatial distribution of aphid infestation were identified as possible factors impeding the detection of QTLs. A pedigree analysis of simple sequence repeat (SSR) marker alleles closely associated with the QTL markers revealed the presence of the alleles in other apple cultivars with reported aphid resistance (‘Wagener', ‘Cox's Orange Pippin'), highlighting the genetic basis and also the potential for gene pyramiding of aphid resistance in apple. Finally, significant QTLs for shoot length and stem diameter were identified, while there was no relationship between aphid resistance and plant trait QTL

Multiannual infestation patterns of grapevine plant inhabiting Scaphoideus titanus (Hemiptera: Cicadellidae) leafhoppers

The Nearctic leafhopper Scaphoideus titanus Ball (Hemiptera: Cicadellidae) was accidentally introduced in Europe, where it became the vector of the ‘Candidatus Phytoplasma vitis' phytoplasma causing the ‘Flavescence dorée' disease of grapevine plants. A time-varying distributed delay model, simulating the successive occurrences of egg hatching, nymph presence, and adult emergence, is extended here to represent multi-generation infestation patterns of grapevine plants inhabited by eggs, nymphs, and adults. The model extension includes intrinsic mortality, mortality caused by plant dormancy, and low temperatures, development of diapausing and post-diapausing eggs, fecundity rates, and adult longevity. Field observations and published data were used to estimate parameters. The model was validated with five years canopy infestation data from five vineyards not subjected to insecticide treatments and found to have satisfactory explicative and predictive qualities. The model output is most sensitive to a 10% variation in the upper threshold and in the shape parameters of the survivorship function and least sensitive to a 10% variation in the shape parameters of the development function and the survivorship level. Recommendations are made to take into account other factors than temperature and plant phenology and include a wider geographical area in further model developmen

Numero di trappole gialle necessarie per stimare nel vigneto la densità relativa delle popolazioni della cicalina Scaphoideus titanus Bali

The density and distribution of immature and adult Scaphoideus titanus Bali on yellow sticky traps was studied in the two vineyards of Castelrotto (Canton of Ticino, Switzerland) and Ghemme (near the town of Novara, Italy). The Aéroxon traps placed horizontally within the plant canopy is most efficient to catch S. titanus adults since they are more mobile then the immature forms.The smallest number of traps assuring a desired reliability of the estimate is calculated on the basis of formai probabilistic statements: half of the lenght of the confidence interval is equal to a proportion D of the standard error of the mean, and the confidence interval should include the true mean with a probability P. Thereby, the variance is expressed as a function of the mean according to Taylor's power law, and the distribution of both the adults and the immature individuals was aggregated. For the purpose of this study, D=0.3 and P=0.9 were assumed to produce reliable estimates. Accordingly, 9 traps are sufficient if the density is 10 specimens per trap, but 41 traps are required fora density of 1 individuals per trap.The two vineyards under study were divided into 6 blocks. Since there were generally no significant differences (P < =O. 05) between these blocks a simple random placement of traps can be envisaged.The method is useful for monitoring S. titanus populations. It permits for example a better estimate of the trials of pesticide applications.La densità e la distribuzione delle forme immature e degli adulti di Scaphoideus titanus sono state studiate in due vigneti: il primo situato nel comune ticinese di Castelrotto, il secondo nel comune novarese di Ghemme. Il metodo di cattura consiste nell'utilizzare le trappole gialle Aéroxon poste orizzontalmente nella vegetazione. Tale sistema è molto piu efficiente nei confronti degli adulti poiché piu mobili delle forme immature.Il minor numero di trappole che assicuri l'attendibilità della stima desiderata, è calcolata sui principi dell'analisi probabilistica formale: metà della lunghezza dell'intervallo di confidenza è uguale al rapporto D dell'errore standard della media e l'intervallo di confidenza deve includere il valore reale della media con una probabilità P. In tal modo la varianza è espressa come funzione della media in accordo con la legge di Taylor. La distribuzione degli adulti e delle forme immature è di tipo aggregato. Per gli scopi di questo studio, D=0.3 e P=0.9 sono stati considerati un buon compromesso per ottenere una stima attendibile. Di conseguenza 9 trappole sono sufficienti se si ha una densità di 10 individui per trappola, ma sono necessarie 41 trappole per una densità di un individuo per trappola.I due vigneti in esame sono stati divisi in 6 blocchi. Generalmente sino a quando non si verificano delle differenze significative (P> = 0.05) tra questi blocchi, si consiglia una semplice randomizzazione delle trappole.Il metodo è utile per il monitoraggio della popolazione di Scaphoideus titanus e permette pure un migliore controllo delle prove di lotta

Influence du réchauffement climatique sur la dynamique des populations de Scaphoideus titanus en Romandie

En raison du réchauffement climatique planétaire et de celui particulièrement marqué en Suisse, le déve-loppement de certains insectes sera fortement accé-léré (Bloesch et De Siebenthal 1988). La viticulture helvétique pourrait souffrir d’un impact plus pronon-cé des insectes ravageurs (OcCC 2007). Parmi ces in-sectes, la cicadelle Scaphoideus titanus Ball(Hemip-tera: Cicadellidae) a reçu une attention particulière au cours des quinze dernières années, puisqu’elle est le vecteur principal de la flavescence dorée (Schvester et al. 1961), une grave maladie de la vigne causée par le phytoplasme Candidatus phytoplasma vitis (IRPCM 2004). La maladie fait l’objet de mesures officielles visant à endiguer sa propagation, du fait de son carac-tère épidémique et d’un impact économique négatif élevé. Pour ces raisons, elle est inscrite comme orga-nisme de quarantaine et soumise à une lutte obliga-toire (OPV 2010)