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In the past decade, severe epidemics of cucumber mosaic virus (CMV) have caused significant damage to Espelette pepper crops. This virus threatens the production of Espelette pepper, which plays a significant role in the local economy and touristic attractiveness of the French Basque Country, located in southwestern France. In 2021 and 2022, CMV was detected via double-antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISAs) in Gorria pepper seed lots harvested from naturally infected fields scattered throughout the entire Espelette pepper production area. These seed lots were used in greenhouse grow-out tests to determine whether CMV could be transmitted to seedlings from contaminated seeds, using visual symptom assessment, DAS-ELISAs, and reverse transcription-polymerase chain reaction (RT-PCR). Despite the widespread occurrence of CMV in seeds of field samples, the grow-out experiments on a total of over 5000 seedlings yielded no evidence of seed transmission of local CMV isolates in Gorria pepper. Therefore, rather than seeds from infected pepper plants, sources of CMV inoculum in Espelette are more likely to be alternative hosts present in and around pepper fields that can allow for the survival of CMV during the off-season. These results have important epidemiological implications and will guide the choice of effective measures to control current epidemics. [ABSTRACT FROM AUTHOR]

Characterization of tobamovirus isolates collected from pepper crops in South East France has revealed the existance of several strains belonging to different viruses of the group. The biological and serological properties of three isolates (Vi76, Adam and Eve), selected as representative strains, have been studied. They have been compared with TMV and ToMV strains already isolated in our region as well as with other reference strains of ToMV-D and TMV-U1. They were also compared with other tobamovirus strains Pll, P8 and P14, from the Netherlands, and PMMV-W from Italy also isolated from pepper genotypes possessing the "L" gene for resistance to TMV and ToMV strains. According to biological and serological reactions, Vi76 is more related to ToMV than to TMV but it is not related to Adam and Eve which are more closely related to PMMV. On the basis of the interaction with the "L" gene for resistance in pepper genotypes we have found that the Adam and P8 strains belong to the Pl-2 pathotype and the Eve and P14 strains to the Pl-2-3 pathotype and all the 4 strains belong to the PMMV-W group. In France, there have been no reports of the isolation of the Pll strain which is distantly related to the Adam strain. [ABSTRACT FROM AUTHOR]

• We characterized viruses infecting cucurbitaceous and solanaceous crops in France. • Aphid- and thrips-transmitted viruses remain the most prevalent viruses so far. • New WMV and CMV strains have been introduced in France in the last decade. • Recombination and reassortment are frequent. • The frequency of introductions is a major driver of population genetic structure. Plant viral diseases represent a significant burden to plant health, and their highest impact in Mediterranean agriculture is on vegetables grown under intensive horticultural practices. In order to understand better virus evolution and emergence, the most prevalent viruses were mapped in the main cucurbitaceous (melon, squashes) and solanaceous (tomato, pepper) crops and in some wild hosts in the French Mediterranean area, and virus diversity, evolution and population structure were studied through molecular epidemiology approaches. Surveys were performed in summer 2016 and 2017, representing a total of 1530 crop samples and 280 weed samples. The plant samples were analysed using serological and molecular approaches, including high-throughput sequencing (HTS). The viral species and their frequency in crops were quite similar to those of surveys conducted ten years before in the same areas. Contrary to other Mediterranean countries, aphid-transmitted viruses remain the most prevalent in France whereas whitefly-transmitted ones have not yet emerged. However, HTS analysis of viral evolution revealed the appearance of undescribed viral variants, especially for watermelon mosaic virus (WMV) in cucurbits, or variants not present in France before, as for cucumber mosaic virus (CMV) in solanaceous crops. Deep sequencing also revealed complex virus populations within individual plants with frequent recombination or reassortment. The spatial genetic structure of cucurbit aphid-borne yellows virus (CABYV) was related to the landscape structure, whereas in the case of WMV, the recurrence of introduction events and probable human exchanges of plant material resulted in complex spatial pattern of genetic variation. [ABSTRACT FROM AUTHOR]