First Report of Xylella fastidiosa Infection and Pierce’s Disease in Resistant Grape Cultivars in Texas, United States

All commercially cultivated European grapevines (Vitis vinifera) are considered susceptible to Pierces disease (PD) caused by the xylem-limited bacterium Xylella fastidiosa (Wilcox et al. 2015). PD causes vine losses and is the primary limiting factor to grape production in Texas (Perry & Hollis, 1974). Recently, grapevine cultivars described as PD resistant were released commercially (Walker et al. et al. 2021). In 2021, bare root grape vines of cultivars, ‘Errante Noir’(EN, n=25 ), ‘Paseante Noir’(PN, n=16), ‘Camminare Noir’ (CN, n=15), ‘Ambulo Blanc’(AB, n=25), and ‘Caminante Blanc’ (CB, n=25), grafted on1103p rootstock, were planted in a research vineyard with a history of PD in Gillespie County, TX. In late July 2024, poor growth, chlorosis, leaf scorch, green islanding and retained petioles consistent with PD were observed in all cultivars (Wilcox et al. 2015). As PD was suspected, observations on incidence and severity were taken. By November 1, 2024, collected data on PD scorch symptoms showed an incidence of 17 (EN) to 63(PN) percent across cultivars . Symptomatic vines were rated as ≥2 according to the scale described in Krivanek et al. 2005. In Oct. 2025, PD symptoms were observed again in all five cultivars with increased incidence of 21(EN) to 75(PN) percent across cultivars with ratings of ≥2 in severity . To investigate cause of symptoms, leaf petioles were collected from 12 symptomatic vines (n=3 AB, n=2 CB, n= 3 EN, n=4 PN) .Each sample was halved and split into 2 sets. One set was sent blind to the Texas Plant Disease Diagnostic Lab (Texas A& M AgriLife Extension, College Station, TX) for real time PCR (qPCR) testing (Schaad et al. 2002). The second set was used in isolation trials and tested with the AmplifyRP® XRT for X. fastidiosa (RPA) test (Agdia Inc., Elkhart, IN; Cesbron et al. 2023) following manufacturer’s protocol. Both methods yielded similar results, finding positive tests for X. fastidiosa in 9 of the 12 samples. Isolation attempts were successful in 6 of 11 samples representing all tested cultivars. qPCR of pure cultures confirmed the isolates as X. fastidiosa (Shaad et al. 2002). To further characterize the pathogen, bacteria were isolated from fresh samples from positive AB, EN and PN plants. Isolates were cultured on PWG media and DNA extracted from single clones using the Monarch genomic DNA kit (NEB, Ipswich, MA). Sequencing and genome assembly was done following Vanhove et al. 2019. LINgroup (Tian et al. 2020) and MLST (Jolley et al. 2018) sequence comparisons placed all strains in the ST1 group of X. fastidiosa subsp. fastidiosa; strains clustered most closely to CCPM1 , an X. fastidiosa subsp. fastidiosa genome from Georgia , USA ( NCBI accession SAMN09941435). All sequences were deposited to NCBI bioproject PRJNA1278688 under accessions PD_Tx24_C284: SAMN49192511 (PN), PD_Tx24_C281: SAMN49192510 (EN), and PD_Tx24_C279: SAMN49192509 (AB). PD symptomatology, positive identification of X. fastidiosa by RPA and qPCR, pathogen isolation and whole genome sequencing, warrant a report on these cultivars. We believe this is the first report of X. fastidiosa associated with these cultivars under field conditions in Texas. The consistent presence of X. fastidiosa, and PD symptoms at this site, raises significant concerns about the role these varieties may play , as pathogen reservoirs and the resulting impact on grapevine planting recommendations. The consequences of these observations to the spread and management of PD are not fully understood and continued investigation of their resistance traits is encouraged.