Abstract
Pierce's disease (PD) of grapevine is caused by the bacterium Xylella fastidiosa. In this study, an integrated approach was applied to assess PD susceptibility among different Vitis vinifera cultivars that incorporated disease severity, bacterial pathogen abundance and loss of stem xylem hydraulic conductivity. It was hypothesized that levels of PD susceptibility in V. vinifera can be attributed in part to the host anatomical features that are shaped by its pedigree background. Two popular wine grape cultivars were initially selected from the occidentalis group, Merlot and Cabernet Sauvignon, and one from the orientalis group, Thompson Seedless. The more recently bred table grape cultivar Scarlet Royal, that has mixed pedigree parentage, was also included. PD susceptibility was compared to the known PD resistant b43‐17 V. arizonica/candicans wild grape species from North America. The data indicated that Thompson Seedless was ranked as the most susceptible to PD because it significantly exhibited the most severe disease symptoms at 12 weeks post‐inoculation and hosted the highest X. fastidiosa titre of the cultivars, and lost over 90% of its stem hydraulic conductivity. In contrast, the other three cultivars displayed less susceptibility to PD. The way in which the xylem anatomy could impact PD susceptibility in V. vinifera cultivars is discussed, together with how grape pedigrees and their cognate centre of domestication may have influenced xylem anatomical features. This work provides a reference framework to further test the hypothesis that V. vinifera cultivars with wide xylem vessels may be more prone to PD decline.
Highlights
Pierce’s disease (PD) is a severe vascular disease of grapevine caused by the Gram-negative bacterium Xylella fastidiosa (Wells et al, 1987) and costs $104 million in annual losses to the Californian grape industry (Tumber et al, 2014)
Breeding programmes focused on evaluating PD resistance of wild Vitis species and introgressing resistance into existing susceptible V. vinifera cultivars are well established (Krivanek & Walker, 2005; Fritschi et al, 2007; Riaz et al, 2018)
Experiments designed to comprehensively assess PD susceptibility in V. vinifera cultivars have been limited in scope
Summary
Pierce’s disease (PD) is a severe vascular disease of grapevine caused by the Gram-negative bacterium Xylella fastidiosa (Wells et al, 1987) and costs $104 million in annual losses to the Californian grape industry (Tumber et al, 2014). This disease was first described in California vineyards in the late 19th century by Newton Pierce (Pierce, 1892) and its bacterial causal agent probably originated from Central America (Nunney et al, 2010). At the whole plant level, PD symptomology manifests into scorched leaves, irregular periderm development, irregular petiole abscission, raisining of berries, canopy stunting and vine death (Varela et al, 2001)
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