Identification of inoculum sources of Fusicladium eriobotryae in loquat orchards in Spain

Abstract

Fusicladium eriobotryae is the causal agent of loquat scab, the main disease damaging fruit, leaves and young twigs of this crop. A two growing seasons study (2015-2016 and 2016-2017) was carried out in two loquat orchards (cv "Algerie") to determine the inoculum sources of F. eriobotryae by direct observation of conidia, pathogen isolation on culture media and detection using a new real time PCR protocol developed in this study. One-year-old twigs, fruit peduncles and fruit mummies were randomly sampled three times per growing season on each orchard, and inflorescences only at flowering. Conidia of F. eriobotryae were not found and the isolation of the pathogen was neither possible from any sample in both seasons. Specific primers FUG2F and FUG2R, were designed to detect and quantify DNA of F. eriobotryae on plant material, with a limit of detection (LOD) established at 48.6 fg/μl. The DNA of the pathogen was not detected by real time PCR in fruit mummies neither inflorescences, but it was detected in fruit peduncles and twigs in the season 2016-2017 with concentrations ranging from 50 to 2742 fg/μl, confirming that this two loquat organs might act as potential inoculum sources for F. eriobotryae. The detection of F. eriobotryae only in this season agrees with the predictions of an epidemiological model for this pathogen. Our results indicate that in years with a high disease pressure, fruit twigs and peduncles might act as a source of inoculum of new infections the following year.