First report of root rot caused by Pythium aphanidermatum on industrial hemp (Cannabis sativa L.) in Bulgaria

Abstract

Worldwide, thegrowers suffer serious losses from mycoses caused by Pythium, Rhizoctonia, and Fusarium. Due to the root rot disease, the whole plant dies, regardless of the phenophase at the moment of infection. The increase in Cannabis sativa acreage in Bulgaria and the accompanying problems associated with the severity and incidence of various diseases necessitated this study. The study aimed to survey the root rot symptoms on field and greenhouse plantations and monitoring the plant`s health status of cannabis-planted areas in Bulgaria during 2021-2022. The main problem was darkening at the base of the stem, yellowing, dieback, and wilting of whole plants from the seedling stage to flowering. Following the Koch's postulates and morphological characteristics by microscopic observation, all collected samples corresponded to genus Pythium. For complete identification, a molecular diagnostic was performed with primers ITS1 and ITS4 using four isolates from different regions of the country, which confirmed Pythium aphanidermatum as the causative agent. Based on the molecular analyses, this is the first report of root rot caused by Pythium aphanidermatum on cannabis in Bulgaria. Keywords: Pythium aphanidermatum, root rot, Industrial hemp, Cannabis sativa