A micropropagation-based in vitro protocol for rapid screening of grapevine susceptibility to Xylella fastidiosa subsp. fastidiosa

In Italy, grapevine production is central to agricultural productivity and cultural heritage, but it is increasingly threatened by Xylella fastidiosa subsp. fastidiosa (Xff) the causal agent of Pierce’s disease under field conditions infection. The recently detected Xff ST1 in Apulia colonizes grapevine xylem vessels, impairing water and nutrient transport and leading to leaf scorch, wilting, and vine mortality. In this study, following inoculation with Xff, a rapid screening protocol based on shoot culture and micropropagation was developed as a preliminary in vitro approach to evaluate disease progression, symptom development under in vitro conditions, in eight Calabrian grapevine varieties: ‘Aglianico’, ‘Bianca Antica’, ‘Gaglioppo’, ‘Greco Bianco’, ‘Lacrima Nera’, ‘Magliocco Canino’, ‘Magliocco Dolce’, and ‘Zagarese’. The results highlighted significant differences in estimated bacterial population levels, expressed as log₁₀ CFU equivalents mL⁻¹, among varieties, with higher colonization observed in ‘Aglianico’, ‘Bianca Antica’, and ‘Magliocco Dolce’, ranging from approximately 4.0 to 4.5 Log₁₀ CFU mL⁻¹. Differential susceptibility to Xff was also evident over the 60-day post-inoculation period. Notably, ‘Aglianico’ and ‘Magliocco Dolce’ were the most symptomatic varieties, whereas ‘Greco Bianco’ and ‘Magliocco Canino’ showed the lowest symptom development, displaying the lowest rAUDPC values, 0.01 and 0.03, respectively, suggesting lower susceptibility under the experimental conditions tested. Substantial differences in symptom progression were also observed, with distinct temporal patterns of disease development among the eight varieties over the 60-day period. This study provides a comparative regional proof-of-concept for assessing baseline susceptibility variations among previously uncharacterized Calabrian grapevine genotypes. Furthermore, it presents a rapid in vitro method for evaluating Vitis vinifera ’s susceptibility to Xff, potentially serving as a significant preliminary screening tool to support subsequent validation studies and field assessments.