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.