Assessing resistance types and levels to epidemic diseases from the analysis of disease progress curves: Principles and application to potato late blight

International audienceBoth race-specific (RS) and race-non-specific (RNS) resistances exist in potato against the late blight pathogen Phytophthora infestans. Because these resistance types do not have the same epidemiological effects, their presence, alone or combined, in potato genotypes can be deduced from the analysis of disease progress curves from field experiments, a type of data commonly available to potato breeders, and their comparison with those of standard reference cultivars. The identification of RS resistance is based on the presence of a delay in epidemic onset compared to a susceptible cultivar, whereas the identification of RNS resistance is translated into a reduction of apparent infection rates. These parameters can be easily computed after linearization of the disease progress curves. This paper assesses the reliability of this identification using sets of experimental data, discusses its limitations, and highlights potential applications for breeding and cultivar assessment purpose

Efficacy of the R2 resistance gene as a component for the durable management of potato late blight in France

International audienceMany race-specific resistance genes to potato late blight are overcome in France, but the disease appears later on genotypes carrying the R2 gene. This study examined whether R2 could contribute to durable late-blight control in France, and analysed the conditions of its performance. Plants grown from tubers of different physiological ages showed no difference in R2 expression in field and climate-chamber experiments, demonstrating that the delay in epidemic onset provided by R2 was not the result of gene inactivation in old plants. Among isolates collected at one site, those virulent on R2 were classified into three AFLP profiles. AFLP-VII comprised exclusively isolates virulent to R2, whereas AFLP-IV and AFLP-V included both virulent and avirulent isolates. No significant aggressiveness differences were observed between virulent and avirulent isolates from AFLP-V; however, isolates from AFLP-VII were significantly less aggressive than virulent isolates from AFLP-V. These r! esults indicate that: (i) the delayed onset of epidemics on R2 cultivars is the result of the breakdown of R2 by virulent isolates; (ii) aggressiveness of isolates virulent to R2 depends primarily on the genetic background of the pathogen where the mutation to virulence occurs; and (iii) this mutation does not lead per se to lower pathogenic fitness. It is suggested that R2 is unlikely to make a lasting contribution to late-blight control in France, and that diversification strategies such as cultivar mixtures might not considerably increase its durabilit

La Culture Biologique de la Pomme de Terre : Critères de Sélection Variétale et Production de Plants

Cet article passe en revue certains des problèmes techniques auxquels la culture biologique de la pomme de terre est confrontée et les solutions qui peuvent être apportées par la sélection variétale, notamment pour la lutte contre les parasites et ravageurs. Quelques idées pour réaliser un schéma spécifique de production de plants sont présentées. Mots-clés : mildiou, maladies à virus, résistance aux bio-agresseurs, adaptatio

Evaluation au champ de la résistance de la pomme de terre au mildiou du feuillage

National audienc

La lutte génétique contre le mildiou et les nématodes

National audienceDepuis la découverte de résistance chez les espèces sauvages jusqu'à la création de nouvelles variétés cultivées de pommes de terre

Projet Archidémio: Surface foliaire et mildiou étroitement liés

International audienceabsen

Host adaptation in Phytophthora infestans: a review from a population biology perspective

Phytophthora infestans behaves in natural and agricultural ecosystems as a biotrophic pathogen, although it can be cultured on artificial media. Pathogenicity and host adaptation are therefore essential traits to understand its biology and to come up with durable, efficient management of late blight. The present review focuses on adaptation to host species and host cultivars, and to both qualitative and quantitative types of resistance. It also discusses some of the patterns and population mechanisms involved in this adaptation, such as selection, genetic drift and migration. This highlights the need for an in-depth analysis of each local situation to accurately describe and understand the mechanisms responsible for observed population displacements

Development of a Potato Cultivar (Solanum tuberosum L.) Core Collection, a Valuable Tool to Prospect Genetic Variation for Novel Traits

International audienceThis study presents the development of a core collection capturing the genetic diversity of a collection of 350 tetraploid cultivated potato varieties (Solanum tuberosum L.). The core collection was established by using simple sequence repeats (SSR) data and the M strategy, which aims at maximizing the allelic diversity. A 48-core collection was defined which captured 99.5% of the SSR alleles used to establish it, and 96.9% of the SSR alleles which belonged to an independent set of markers. The defined core collection was further validated by analysing 35 agro-morphological traits. The class coverage value and the estimates of the Shannon-Weaver diversity index indicated a good representation of the phenotypic diversity in the core collection. Furthermore, the core set included accessions having the most desirable status for several agronomic traits. A linkage disequilibrium (LD) analysis, using data obtained with the SolCAP SNP array on the defined core collection, was performed. The population structure analysis showed that the core collection did not present a clear genetic structure. The linkage disequilibrium analysis carried out between markers located on the same pseudomolecule within 10,000 bp concluded that 41.3% of these pairs of SNP markers have a significant LD. We conclude that this core collection, representative of the genetic diversity of cultivated potato varieties, is a relevant tool for a first screening for genetic variation regarding novel traits of interest