2019 ASHS Annual Conference

Xylella fastidiosa (Xf) causes phony peach disease (PPD), which is incurable, vector-transmitted, and periodically rampant in affected peach production regions. In this presentation, we compared the effect of tissue type and sampling season on PCR detection of Xf in phony peach trees using newly developed primers. Among the four peach tissue types tested, only root samples demonstrated reliable and consistent detection of Xf; stem, petiole, and leaf samples, regardless of source trees, primers used, sampling times, or PCR methods, were unreliable for detection, due to insufficient quantity of DNA of Xf in these samples based on the relative quantification assay. Among the three sampling seasons, differences in detection were not obvious in terms of conventional PCR product band intensities, or not significant in terms of quantitative PCR qualification cycle (Cq) values. Furthermore, the Cq means and ratios were analyzed to compare the effects of source tree, tissue type, sampling time, and primer on detection sensitivity. In summary, only samples of root contained sufficient DNA of Xf for reliable and consistent PCR detection of Xf in phony peach trees. The newly developed primers are a useful resource for accurate detection and quantification of Xf, which is needed for epidemiological studies of the pathogen and disease, large-scale surveys of infected trees, and identification of resistant genotypes for use in breeding.