Detection and cellular localization of Xanthomonas campestris pv. viticola in seeds of commercial 'Red Globe' grapes

Abstract

Commercial grapevine fruit (Vitis vinifera) of the Red Globe variety were collected in vineyards from Vale do São Francisco lower basin, an area of occurrence of grapevine bacterial canker. Seeds were extracted, classified as symptomatic or asymptomatic and processed in order to be observed under light (LM) and scanning electron microscopy (SEM) along with silver-enhanced immunogold labeling, to allow bacterial detection using a policlonal antibody against Xanthomonas campestris pv. viticola (Xcvi), etiological agent of the disease. The seed samples showed bacterial aggregates associated to the tegument surface and to the first parenchymal layer beneath the seed tegument. Bacterial identity was confirmed by immunogold labeling. This appears to be the first report of Xcvi associated to asymptomatic seeds and berries, suggesting a systemic mechanism to spread and colonize different tissues and sites, driving attention to seeds, presenting them as an important niche for survival and dissemination of this pathogen. These results point towards the need of including seed-bearing fruit in studies regarding Xcvi epidemiology.