Pathogenicity of Botryosphaeriaceae and Phytophthora species associated with Paulownia dieback, canker and root rot in Italy

Abstract

In recent years, an unusual decline and mortality has been observed in Paulownia plantations throughout the Marche region (Central Italy). Given the economic importance of this emerging forest crop, a study was conducted to determine which pathogens are directly involved in this syndrome. Field surveys performed in two plantations revealed the widespread occurrence of severe disease symptoms such as leaf chlorosis, crown thinning, shoot and branch dieback, sunken cankers, epicormic shoots and root rot. Disease incidence was also assessed by aerial remote sensing (RS) technologies using drones. Symptomatic samples collected from both stem and root tissues yielded fungal and fungal-like colonies representing two distinct families: Botryosphaeriaceae and Peronosporaceae. Morphological and DNA sequence data revealed five distinct species, identified as Macrophomina phaseolina and Botryosphaeria dothidea (Botryosphaeriaceae), Phytophthora pseudocryptogea, P. citrophthora and P. erythroseptica (Peronosporaceae). Given that all species are reported here for the first time on Paulownia, Koch’s postulates were satisfied inoculating the three Phytophthora species and two Botryosphaeriaceae at the collar of the stem of potted 1-year-old rooted cuttings in June 2023. Thirty days after inoculation, all plants showed the same symptoms as those observed in the field.