Xylem Sap Mycobiota in Grapevine Naturally Infected with : A Case Study: Interaction of with .

Grapevine () is a key crop in Mediterranean agriculture, now increasingly threatened by subsp. (), the causal agent of Pierce's disease. This study investigated: (1) the diversity of culturable fungal endophytes in the xylem sap of naturally -infected grapevines, and (2) the interaction between and the pathogenic fungus identified in the sap. The xylem sap was collected from Cabernet Sauvignon vines in Mallorca, Spain, and fungal communities were characterized using culture-dependent methods. Both beneficial fungi (e.g., , ) and pathogenic species (e.g., , sp., , and the complex) were isolated from both -positive and -negative plants, indicating similar community profiles. Although limited by small sample size, these findings offer preliminary evidence of complex ecological interactions between and the xylem-associated mycobiota, with potential implications for grapevine health and disease development under varying environmental and management conditions. Further experiments under controlled conditions revealed that grapevines co-inoculated with and showed increased disease severity, suggesting a synergistic interaction. These preliminary results highlight the complex interplay between and the fungal endophytic microbiome, which may modulate grapevine susceptibility depending on environmental and management conditions.