Molecular Characterization of Grapevine Fanleaf Virus (GFLV) Isolates and Relationship with Xiphinema index Vector

Abstract

Grapevine fanleaf virus (GFLV), a nepovirus transmitted by the dagger nematode Xiphinema index, is one of the most destructive viral pathogens affecting grapevine productivity worldwide. The present study aimed to characterize molecular diversity of GFLV isolates and examine their relationship with the nematode vector X. index in infected vineyards. Symptomatic grapevine samples exhibiting fanleaf deformation, yellow mosaic, reduced vigor, and poor fruit set were collected from commercial vineyards. Total RNA was extracted and subjected to RT-PCR amplification targeting conserved genomic regions of GFLV RNA-2 coat protein gene. Sequencing and phylogenetic analyses revealed notable genetic variability among isolates, indicating the presence of distinct molecular variants circulating within vineyard populations. Comparative sequence analysis showed clustering of isolates with previously reported GFLV strains, suggesting both regional conservation and local divergence. Vector populations of X. index were extracted from rhizosphere soils and identified based on morphological traits including stylet length, tail shape, and esophageal structure. Correlation analysis indicated a strong association between nematode density and virus incidence, confirming the critical role of X. index in GFLV dissemination. Environmental conditions such as clay-loam soils and moderate temperatures favored nematode survival and virus transmission efficiency. The study highlights the close epidemiological relationship between GFLV genetic diversity and vector population dynamics. These findings underscore the importance of integrated management strategies targeting both virus and vector components, including the use of certified planting material, resistant rootstocks, and nematode suppression techniques. Overall, the results provide important insights into the molecular epidemiology of GFLV and its association with X. index, contributing to improved understanding of grapevine fanleaf disease spread in viticultural ecosystems.