Presence of Diverse Resistance Mechanisms in Grapevine Accessions Derived from Pierce's Disease U0505 Line

Xylella fastidiosa (Xf) is the etiological agent of Pierce's disease (PD), a major threat to viticulture worldwide. The Xf prtA^- mutant, characterized by its planktonic phenotype and absence of biofilm formation, has been previously labeled as hypervirulent due to its aggressive symptomatology in the PD-susceptible Vitis vinifera 'Thompson Seedless'. This study challenges the hypervirulent concept by demonstrating that a diverse range of grapevine accessions, especially the PD line U0505, exhibited resistance to Xf prtA^-. Our findings suggest that different resistance mechanisms are present against the planktonic and biofilm phenotypes of Xf, as represented by the prtA^- Xf mutant and the wild-type Temecula1 Xf strain, respectively. This study underscores the complexity of host-pathogen interactions and highlights the importance of multiple host defense mechanisms in countering specific virulence strategies of Xf. The resistance assessed in the U0505 line against Xf prtA^- infection provides valuable insights into potential genetic and molecular targets for breeding PD-resistant grapevine cultivars and developing effective disease management strategies.