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Trabajo presentado en 15th International Symposium of Plant Virus Epidemiology “Epidemiology and management of plant viruses under a changing climate”, celebrado en Madrid (España), entre el 5 y el 8 de junio de 2022., Genetic resistance is a sustainable way of controlling plant viruses, but it requires the presence of resistance genes in the host germplasm. Besides, its durability can be reduced by resistance-breaking isolates, either pre-existing in the environment or emerging after the deployment of the resistance. In the case of cucumber vein yellowing virus (CVYV, a member of the genus Ipomovirus), an emerging virus on cucurbits in the Mediterranean Basin (1), few resistances are available in melon. The melon accession PI 164323 was found to display complete resistance to the strain CVYV-Esp, and accession HSD 2458 presented a tolerance, i.e. very mild symptoms in spite of virus accumulation in inoculated plants. The resistance is controlled by one dominant allele Cvy-11, while the tolerance is controlled by a recessive allele cvy-2 independent from Cvy-11. Upon inoculation with eight geographically diverse CVYV isolates corresponding to the known molecular diversity of the virus (2), the resistance was found to be strain-specific since many CVYV isolates induced necrosis on PI 164323, whereas the tolerance presented a broader range. A resistance-breaking isolate inducing severe mosaics on PI 164323 was obtained. It differed from the parental strain by a single amino-acid change in the VPg-coding region. The effect on the mutation was confirmed by reverse genetics using a newly-obtained CVYV infectious clone (3). Competition experiments suggested a fitness cost of the resistance-breaking mutation in susceptible melon. Our results highlight the need to combine cultural practices and/or additional genes to develop a more durable control of CVYV than the use of the Cvy-11 allele alone.

International audience; Three viruses transmitted by aphids (non-persistent transmission) are responsible of strong yield losses on squash crops in France and around the world: Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV) and Watermelon mosaic virus (WMV). For each virus, different biological, serological and molecular groups were described. The resistance is polygenic for CMV, ZYMV and with a major gene for WMV but always with an intermediate resistance.The evaluation of squash resistance to viruses and the assessment of symptoms are complex due to the partial and not complete resistance and the quantitative results observed. It is important to describe the different levels of virulence of virus strains and to identify the different levels of resistance of squash varieties. There are currently no harmonized protocols to define the levels of partial resistance of squash to these viruses.The aim of this project, in collaboration between GEVES, INRAE and breeding companies (HMClause, Gautier, Monsanto, Rijk Zwaan, Sakata, Syngenta) was to acquire a better knowledge of levels of squash resistance and to define robust resistance tests to these viruses. Based on the INRAE’s characterized collection of strains of viruses, three strains per virus (with different virulences and from different groups) were selected. These strains and different protocols from INRAE and partners (stage of inoculation, optimal conditions of test, notation scale) were compared, on a panel of commercial varieties with different levels of resistance, to define for each virus a robust resistance test.One strain per virus, making it possible to differentiate the different levels of resistance of varieties, was selected. For each virus, a resistance test and reference materials (strain and controls) were validated. The reference collection of GEVES was characterized for the three viruses. These new protocols, used for CTPS registration, will be proposed to CPVO and UPOV for a harmonized use.; Trois virus transmis par les pucerons selon le mode non-persistant sont responsables d’importantes pertes de récolte dans les cultures de courgette en France et dans le monde : les Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV) et Watermelon mosaic virus (WMV)L’évaluation de la résistance de la courgette aux virus est complexe du fait du caractère partiel (ou non complet) de la résistance et des résultats quantitatifs observés. Il est important d’identifier les différents niveaux de résistance des variétés de courgette à ces virus, et de décrire les niveaux d’agressivité des souches permettant de mieux différencier les variétés. Actuellement, il n’existe pas de protocole harmonisé pour définir les différents niveaux de résistance partielle de la courgette à ces virus.Le but de ce projet collaboratif entre le GEVES, l’INRAE et des sociétés semencières (HMClause, Gautier, Monsanto, Rijk Zwaan, Sakata, Syngenta) était d’acquérir de meilleures connaissances des niveaux de résistance de la courgette et de définir un protocole de test robuste pour ces virus. Basée sur la collection de souches de virus caractérisée par INRAE, trois souches par virus (avec différentes agressivités et appartenant à différents groupes) ont été sélectionnées. Ces souches et les différents protocoles de INRAE et des partenaires (stade d’inoculation, conditions optimales de test, échelle de notation) ont été comparées sur un panel composé de variétés commerciales avec différents niveaux de résistance afin de définir pour chaque virus un test de résistance robuste.Une souche, permettant de différencier les différents niveaux de résistance des variétés, a été sélectionnée par virus. Pour chaque virus, un test de résistance et le matériel de référence (souches et témoins) ont été validés. La collection de référence du GEVES a été caractérisée pour les trois virus. Ces nouveaux protocoles, utilisés pour les

International audience; Cucurbits are widely grown worldwide in diverse agroecosystems, from traditional gardens to soil-less glasshouses. Viruses represent one of the major threats for cucurbit production, affecting both the yield and quality of crops. The number of known cucurbit-infecting virus species has grown from 35 in 1998 to more than 80 in 2018. The prevalence and agronomic impact of these viruses 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 preexisting virus populations, sometimes resulting in an increased economical impact. In Mediterranean and tropical climates, as well as in heated greenhouses in temperate regions, Bemisia tabaci-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 favour their natural vectors, and the increased exchanges of plant material that made possible their long-distance spread. 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.

Recently, Lecoq et al (1992) reported a new yellowing disease of cucurbits in France caused by cucurbit aphid-borne yellows luteovirus (CABYV) (1). Yellowing of older leaves of cucurbits has been observed in Lebanon for the past few years. Transmission tests showed that the disease incitant could be transmitted by Aphis gossypii in a persistent, circulative manner from muskmelon plants (Cucumis melo) to cucumber (C. sativus), muskmelon (C. melo), and squash (Cucurbita pepo) plants. Extracts from these plants reacted positively in enzyme-linked immunosorbent assays (ELISAs) with an antiserum prepared to a French isolate of CABYV. Surveys conducted in 1995 and 1996 showed that CABYV was widely distributed in the major cucurbit-growing areas along the Lebanese coast from north to south, and in the Beqaa plain. It was detected year round, alone or in mixed infections with mosaic-inducing viruses. The highest frequencies were recorded between May and October. CABYV and zucchini yellow mosaic potyvirus (ZYMV) were the most commonly detected viruses in outdoor cucurbits, including squash, cucumber, and melon. However, in protected cultivations (plastic tunnels), only a small proportion of cucumber plants showing similar yellowing symptoms reacted positively with CABYV antiserum in ELISAs, suggesting another cause to account for these symptoms. Reference: (1) H. Lecoq et al. Plant Pathol. 41:479, 1992.

International audience; Are sown flower strips an efficient tool to limit aphid colonization and viral epidemics in melon crops?. 10. Conférence de la Société française de phytopathologie. 12. European foundation for plant pathology conference

UMR BFP - Equipe Virologie; Characterization of a complex of necroviruses involved in a necrotic disease of corn salad ([i]Valerianella locusta[/i]). 16. Rencontres de Virologie Végétale (RVV 2017)

International audience

International audience

International audience

National audience; The cucurbits include several important vegetables to human consumption which are threatened for epidemic diseases such as those caused by begomoviruses. The Old World begomovirus Tomato leet curl New Delhi virus (ToLCNDV) was first described in India and is currently spreading in some Mediterranean countries. Meanwhile, the New World begomovirus Melon chlorotic mosaic virus (MeCMV) has been only described in Venezuela. This work aims to evaluate melon lines in order to look for resistance sources against these viruses.

National audience; Watermelon mosaic virus (WMV, genus Potyvirus, family Potyviridae) is a serious pathogen of cucurbit crops with a worldwide distribution. It has a wide host range (>170 species) and it is transmitted non-persistently by several aphid species. Previous molecular analyses based on full-length WMV sequences indicated the presence of 3 major groups, namely G1, G2 & G3. Until 2000 in the Mediterranean basin only G1 and G2 groups were observed, with many G1-G2 recombinants. The third group (G3 or ‘‘EM’’ for emerging) probably originating from Asia was first observed in south-eastern France in 2000. Despite the occurrence of WMV in Greece at least since 1983, no information was available on its genetic variability.

National audience; More than 70 viruses infect cucurbits worldwide. Among the most common and agronomically important are several potyviruses: ZYMV, WMV, PRSV. Besides these viruses that have a worldwide distribution and present distinct biological, serological and molecular features, several viruses closely related to PRSV that could constitute highly divergent strains of this virus or related species have been defined, and could represent new threats for agriculture.

Checking for C4 clone capacity to transmit CMV on a set of Cucurbits. Percentage of plants with CMV symptoms after inoculation by five A. gossypii belonging C4 clone. n = number of plants inoculated, Symptoms were observed 3 weeks after inoculation (DOCX 14 kb)

The melon Vat gene confers resistance to the aphid species Aphis gossypii and resistance to non-persistent viruses (CMV, WMV…) when inoculated by this species. It is however ineffective in blocking the transmission of viruses inoculated by other aphid species. Its effect on non-persistent virus epidemics is thus expected to be limited when A. gossypii is not the main aphid species visiting the melon crop. On the contrary, although not documented, its effect on the persistent virus CABYV mainly vectored by A. gossypii is expected to be strong.[br/] The first objective of the study was to evaluate the effect of Vat on virus epidemics and on the genetic structure of virus populations in field conditions.[br/] The second objective was to investigate the benefit of combining Vat resistance and an appropriate management of field margins to regulate the populations of aphids and/or their virus load. Indeed, literature suggests that flower strips can participate in pest biological control by favoring natural enemies, and strips of non-host plants can protect crops from non-persistent viruses by allowing aphids to probe on healthy plants and thus to lose their virus load before reaching the crops.

Watermelon mosaic virus (WMV, genus Potyvirus, family Potyviridae) is a serious pathogen of cucurbit crops with a worldwide distribution. It has a wide host range (>170 species) and it is transmitted non-persistently by several aphid species. Previous molecular analyses based on full-length WMV sequences indicated the presence of 3 major groups, namely G1, G2 & G3. Until 2000 in the Mediterranean basin only G1 and G2 groups were observed, with many G1-G2 recombinants. The third group (G3 or ‘‘EM’’ for emerging) probably originating from Asia was first observed in south-eastern France in 2000. Despite the occurrence of WMV in Greece at least since 1983, no information was available on its genetic variability.

The cucurbits include several important vegetables to human consumption which are threatened for epidemic diseases such as those caused by begomoviruses. The Old World begomovirus Tomato leet curl New Delhi virus (ToLCNDV) was first described in India and is currently spreading in some Mediterranean countries. Meanwhile, the New World begomovirus Melon chlorotic mosaic virus (MeCMV) has been only described in Venezuela. This work aims to evaluate melon lines in order to look for resistance sources against these viruses.

International audience

International audience

International audience; In 2014, a total of 108 symptomatic watermelon samples were collected in Greece and analyzed by DAS-ELISA using polyclonal antisera (INRA, Montfavet) against the most common aphid-transmitted viruses. Cucumber mosaic virus (CMV) was detected in eight of 108 plants tested. Five of these plants collected at Lesvos were also infected with Watermelon mosaic virus (WMV), whereas three plants from Prohoma had single infections. Five samples with severe stunting and yellowing collected at Asenovgrad (Bulgaria) in 2013 and tested by DAS-ELISA for the above viruses hosted CMV and Cucurbit aphid-borne yellows virus (CABYV). To confirm CMV presence in watermelon, a nested RT-PCR assay was carried out first with the degenerated primers CMVup624a (5′-ATGGACAAATCTGRATC- 3′) and CMVdo1244a (5′-TGRTGCTCRAYGTCKACATGA-3′) followed by CMVup624b (5′-GGACAAA TCTGRA TCTCCCAA TGC-3′) and CMVdo1244b (5′- TGCTCRAYGTCRACATGAAG-3′) that amplify a 622 bp region from the viral coat protein gene. Total RNA (Chatzinasiou et al., 2010, method A) extracted from all ELISA- positive watermelon samples from both countries and from two healthy watermelon plants was used as template in nested RT-PCR. A product of the expected size was amplified from all serologically CMV-positive samples, but not from the healthy ones. The Greek CMV isolates from Lesvos (LN810059) and Prohoma (LN810060) showed 99% nucleotide sequence identity with potato (AB448694) and tomato (EF153734) CMV isolates from Syria and India, while the Bulgarian isolate (LN810058) showed 99% nucleotide sequence identity with an Indian cucumber isolate (JF279608). Phylogenetic analysis indicated that the Greek CMV isolate (LN810059) belongs to sub-group IA, while the Bulgarian isolate and a Greek isolate (LN810060) belong to sub-group IB. To our knowledge this is the first report of CMV infecting watermelons in Greece and Bulgaria.