Development of qPCR-based diagnostic assays for Xanthomonas arboricola pv. corylina early detection in Corylus avellana L.

Xanthomonas arboricola pv. corylina (Xac) is the causal agent of hazelnut bacterial blight, the most severe disease for coriliculture worldwide. Current Xac detection and identification methods rely on time-consuming diagnostic assays (e.g. microbiological, serological, biochemical and pathogenicity). Molecular diagnosis of Xac assay has been limited to a duplex PCR assay originally designed for X. arboricola pv. pruni, requiring modified thermal profiles to enhance sensitivity to the disadvantage of specificity. In 2023, efforts were made to develop a series of new molecular diagnostic methods (e.g. conventional PCR, qPCR and LAMP) based on the “region 2.4” specific to pathovar corylina. Despite that, to detect latent infections in asymptomatic tissues, the PCR assay typically used, although rapid, is not sufficiently specific. Furthermore, for the identification of X. arboricola, highly pathovar-specific and sensitive methods are not yet available except for pathogenicity testing on host plants. The study aimed to development and validated a reliable qPCR-based diagnostic protocol for the early and rapid detection of Xac in asymptomatic halzenut tissues, thereby improving disease prevention and management. Primers were designed based on ftsX and xopH genes, both specific for pv. corylina. Samples from symptomatic and asymptomatic hazelnut plant material were preliminarily tested. The qPCR assays demonstrated high sensitivity and specify, enabling consistent detection allowed to achieve encouraging results for Xac identification in asymptomatic and symptomatic plant material. However, it is necessary to deepen the genetic aspects on Xac virulence and to broaden the choice and type of molecular targets to prevent and control the disease.