Fungal pathogens in grapevines affected by esca in the Kakheti province of Georgia (Caucasus)

All viticultural regions of the world host vineyards that experience symptoms associated with grapevine trunk diseases. The most evident symptoms include apoplectic events (sudden wilting of grapevine leaves often followed by plant death), tiger-striped leaves, and a general loss of plant vigor and yield. Based on the visual observations recorded by Georgian scientists, in recent years, these symptoms have become increasingly widespread in the Kakheti region, Georgia's most important area for vine cultivation and wine production. In October 2023, three symptomatic grapevines ( Vitis vinifera cv. Saperavi) were uprooted, sectioned, and wood fragments were used to isolate fungal endophytes. Examination of the perennial wood sections revealed wood discoloration, brown wood streaking, necrotic lesions, and white rot, while the annual wood displayed only wood discoloration and brown wood streaking. Using molecular tools, specifically the sequences of ITS, tef-1 α, tub 2, rpb2 , LSU, act , cal gene regions, we identified several known wood pathogens and species not previously reported in grapevine wood. Pathogens include fungi associated with (i) the esca complex: Phaeomoniella chlamydospora , Phaeoacremonium minimum , and Fomitiporia mediterranea ; (ii) Botryosphaeria dieback: Botryosphaeria dothidea and Diplodia seriata ; (iii) Phomopsis dieback: Diaporthe ampelina ; as well as Cadophora luteo-olivacea and Cytospora ceratosperma . Fungi reported for the first time in grapevine wood include Biscogniauxia nummularia and Seiridium rosarum , both of which were tested for their potential pathogenicity on detached grapevine canes, revealing that the former induces vascular discoloration in grapevine wood. This is the first scientific report of fungi associated with esca-affected grapevines in Georgia, as well as the first evidence of B. nummularia pathogenicity in grapevine wood.