Specificity of Resistance and Tolerance to Cucumber Vein Yellowing Virus in Melon Accessions and Resistance Breaking with a Single Mutation in VPg

Altres ajuts: CERCA Programme/Generalitat de CatalunyaCucumber vein yellowing virus (CVYV) is an emerging virus on cucurbits in the Mediterranean Basin, against which few resistance sources are available, particularly in melon. The melon accession PI 164323 displays complete resistance to isolate CVYV-Esp, and accession HSD 2458 presents a tolerance, i.e., very mild symptoms despite virus accumulation in inoculated plants. The resistance is controlled by a dominant allele Cvy-11, while the tolerance is controlled by a recessive allele cvy-2, independent from Cvy-11. Before introducing the resistance or tolerance in commercial cultivars through a long breeding process, it is important to estimate their specificity and durability. Upon inoculation with eight molecularly diverse CVYV isolates, the resistance was found to be isolate-specific because many CVYV isolates induced necrosis on PI 164323, whereas the tolerance presented a broader range. A resistance-breaking isolate inducing severe mosaic on PI 164323 was obtained. This isolate differed from the parental strain by a single amino acid change in the VPg coding region. An infectious CVYV cDNA clone was obtained, and the effect of the mutation in the VPg cistron on resistance to PI 164323 was confirmed by reverse genetics. This represents the first determinant for resistance-breaking in an ipomovirus. Our results indicate that the use of the Cvy-11 allele alone will not provide durable resistance to CVYV and that, if used in the field, it should be combined with other control methods such as cultural practices and pyramiding of resistance genes to achieve long-lasting resistance against CVYV

The never-ending story of cucurbits and viruses

Cucurbits are widely grown worldwide in diverse agroecosystems. Viruses represent one of the major threats for cucurbit production. More than 90 viruses have been described infecting cucurbits in natural conditions. Their prevalence and agronomic impact are highly contrasted, and the major problems at the worldwide level are related to circa 10 virus species, both “classic” - i.e., known for decades - or recently emerged on a large scale. Among the “old” mosaic-inducing viruses, aphid-transmitted viruses (potyviruses, Cucumber mosaic virus) remain agronomically important, particularly in temperate climates. Despite their long-term prevalence and apparent stability, introductions of new strains have been observed in several countries in the last years, probably via commercial exchanges of plant material. Some of these introduced strains have rapidly replaced pre-existing virus populations, sometimes resulting in an increased economic impact. In Mediterranean and tropical climates, as well as in heated greenhouses in temperate regions, whitefly-transmitted viruses (begomoviruses, ipomoviruses, criniviruses) now constitute major problems. Their rapid emergence can be explained by the combination of changes in climate and cultural practices that favor their natural vectors, and the increased exchanges of plant material that made possible their long-distance spread. Thrips-transmitted viruses are present in Asia and Latin America and can be locally very damaging. Viruses transmitted by seeds or by contact are also easily disseminated worldwide and represent important constraints for exchanges of plants or genetic material. Accurate and regular re-evaluation of the complex viral pathosystem infecting cucurbits in different countries, adaptation of cultural practices and development of resistant cultivars contribute to the continuous arm race against the introductions and local evolution of virus populations

Mémoire pour obtenir l'habilitation à diriger des recherches

1 annexe (57 p., 7 publications) Diplôme : HD

Zucchini yellow mosaic potyvirus (ZYMV) : étude de la variabilité et des interactions entre souches

* INRA, URD, Domaine St Paul, Site Agroparc, 84914 Avignon cedex 9 Diffusion du document : INRA, URD, Domaine St Paul, Site Agroparc, 84914 Avignon cedex 9 Diplôme : Dr. d'Universit

Host range evolution of potyviruses: A global phylogenetic analysis.

Virus host range, i.e., the number and diversity of host species of viruses, is an important determinant of disease emergence and of the efficiency of disease control strategies. However, for plant viruses, little is known about the genetic or ecological factors involved in the evolution of host range. Using available genome sequences and host range data, we performed a phylogenetic analysis of host range evolution in the genus Potyvirus, a large group of plant RNA viruses that has undergone a radiative evolution circa 7000 years ago, contemporaneously with agriculture intensification in mid Holocene. Maximum likelihood inference based on a set of 59 potyviruses and 38 plant species showed frequent host range changes during potyvirus evolution, with 4.6 changes per plant species on average, including 3.1 host gains and 1.5 host loss. These changes were quite recent, 74% of them being inferred on the terminal branches of the potyvirus tree. The most striking result was the high frequency of correlated host gains occurring repeatedly in different branches of the potyvirus tree, which raises the question of the dependence of the molecular and/or ecological mechanisms involved in adaptation to different plant species

Cucurbit aphid-borne yellows

International audienc

Moroccan watermelon mosaic

International audienc

Zucchini yellow mosaic virus, an emerging virus devastating cucurbit crops

International audienc

Vingt années de progrès en virologie végétale

Communication orale sur invitationNational audienceAu cours des vingt dernières années, les connaissances sur les virus de plantes ont progressé de façon spectaculaire, notamment grâce au développement de diverses techniques de biologie moléculaire. Des critères de classification facilement applicables, basés sur l'organisation des génomes et les similarités de séquence nucléotidiques ou protéiques, ont été définis, et le nombre d'espèces virales reconnues a pratiquement triplé. Les fonctions des protéines virales impliquées dans différents types d'interactions aux étapes-clés du cycle infectieux : réplication, migration dans la plante, transmission par vecteurs... sont de mieux en mieux connues. Des approches d'épidémiologie moléculaire permettent de comprendre l'évolution des populations virales à différentes échelles de temps et d'espace. Des modèles d'évolution suggèrent que la diversification et la spéciation des virus de plantes, au moins chez certains genres, serait concomitante aux débuts de l'agriculture il y a plus de 6000 ans. Enfin, l'utilisation des virus dans le domaine des biotechnologies et notamment des nanotechnologies a été initiée au cours des dernières décennies, et constitue un domaine particulièrement prometteur pour les années à venir

Emergence des recombinants dans les populations naturelles de virus de plantes

National audienc