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

<i>Xylella fastidiosa</i> (<i>Xf</i>) is the etiological agent of Pierce's disease (PD), a major threat to viticulture worldwide. The <i>Xf</i> 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 <i>Vitis vinifera</i> '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 <i>Xf</i> prtA^-. Our findings suggest that different resistance mechanisms are present against the planktonic and biofilm phenotypes of <i>Xf</i>, as represented by the prtA^- <i>Xf</i> mutant and the wild-type Temecula1 <i>Xf</i> 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 <i>Xf</i>. The resistance assessed in the U0505 line against <i>Xf</i> prtA^- infection provides valuable insights into potential genetic and molecular targets for breeding PD-resistant grapevine cultivars and developing effective disease management strategies.