Le nématode à kyste Globodera pallida

National audienc

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

La pomme de terre

The Potato. When the Spaniards discovered the potato, it had already had a long history, for one finds evidence of it on the pre-Incan potery of the Chimu and Mochica civilizations. The first appearance of it in Europe, shortly after the conquest of Peru, did not proligerate because it adapted poorly to its new environment and remained restricted to botanic gardens. It took the entire length of the XVIIth Century and the beginning of the XVIIIth to create in Europe types adapted to tuberization during long days and/or introduce new genotypes from countries where the potato forms tubers during long days (Chile). Today, the potato, with its different varieties, is part of the main food resources of the entire world.Lorsque les Espagnols découvrirent la pomme de terre, elle avait déjà une longue histoire puisqu'on en trouve des témoignages sur les poteries préincaïques des cultures Chimu ou Mochica. Les premières introductions, liées à la conquête (Pérou), sont mal adaptées au milieu européen et restent confinées aux jardins botaniques. Il faudra toute la durée du X Vile siècle et le début du X Ville pour créer en Europe des types adaptés à la tubérisation en jours longs et/ou pour introduire de nouveaux génotypes de pays où la pomme de terre tubérise en jours longs (Chili). Aujourd'hui la pomme de terre, sous ses multiples variétés, fait partie des principales ressources alimentaires mondiales.Rousselle Patrick, Ellisseche Daniel, Rousselle Françoise. La pomme de terre. In: Cahiers d'outre-mer. N° 179-180 - 45e année, Juillet-décembre 1992. Les plantes américaines à la conquête du monde, sous la direction de Yves Monnier et Alain Huetz de Lemps. pp. 303-314

Les nématodes de la pomme de terre

National audienc

Resistance behaviour of potato cultivars and advanced breeding clones to tuber soft rot caused by Pectobacterium atrosepticum

International audienc

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

Pourritures molles dues aux Erwinia

National audienc

Genetics and phenotypic characterisation of the hypersensitive resistance of Solanum sparsipilum to Meloidogyne incognita

International audienceThe hypersensitive resistance of the genotype '385.484.13' of Solanum sparsipilum to Meloidogyne incognita, one of the southern root-knot nematodes and their Mi virulent populations was analysed. Genetic control of the hypersensitive reaction was assessed based on segregation of the necrotic reaction in infected roots of diploid F1 plants obtained from the cross of the genotype '385.484.13' with the dihaploid susceptible potato genotype 'Keltia H12'. Two distinct tests showed a distorted segregation compared to the hypothetical ratio expected for a monogenic control. We hypothesised that the resistance is based on one dominant gene designated Mh and linked to the self incompatibility locus-S. Hypersensitive plants prevented juveniles from feeding, developing and reproducing. Ninety percent of invading juveniles remained undeveloped 6 weeks after inoculation. Almost all the adults were males and only very rarely were females observed. Inhibition of the development of juveniles into females showed a bimodal distribution of the genotypes: hypersensitive ones allowed almost no development of females whilst all the juveniles became females in nonhypersensitive plants. That result supports the hypothesis of a monogenic control of the resistance. The resistance was broken when plants were grown at 30 degrees C. The histology of the hypersensitive reaction was very similar to that of the Mi gene of tomato and of some Me genes of pepper. Necrotic cells were localised not only around the head of the juveniles but also surrounding their bodies. In addition, healthy cells adjacent to necrotised ones underwent divisions parallel to the juveniles. Intercellular spaces between these cells and necrotised ones enlarged markedly, which is consistent with a process leading to isolation of the necrotic area from healthy tissu