Resolving <em>Diaporthe</em> Species Diversity Associated with Grapevine Propagation Material: An Emerging Threat to Grapevine Sustainability

The genus Diaporthe consists of saprobes, endophytes and important plant pathogens. Members of this genus are widely distributed and have a broad host range, including grapevine. This study aimed to establish a baseline survey to assess the diversity of Diaporthe species infecting propagation material and to explore their dynamics in disease development. Initially, a survey was conducted in a nursery field, and isolations were carried out from 2-months old symptomatic grafted vines of cv. Agiorgitiko grafted onto rootstock Richter 110. The initial molecular identification of the isolated mycobiome at the genus level was carried out by sequencing the universal internal transcribed spacer (ITS) locus, while subsequent species-level identification of the Diaporthe isolates was performed through phylogenetic approaches coupled with morphological characterization. Based on the combined analysis, five phylogenetically distinct Diaporthe spp. were identified in this study, taxonomically assigned to D. ampelina, D. eres, D. foeniculina, D. serafiniae and D. novem. Pathogenicity trials demonstrated that the most aggressive species were D. ampelina followed by D. eres, while the remaining species were classified as opportunistic or weak pathogens of grapevine. Overall, accurate identification and monitoring of Diaporthe species involved in propagation material infections, are critical for the development of effective management in nurseries.