First Molecular Phylogenetic Identification and Report of Pseudocercospora cannabina Causing Leaf Spot Disease on Cannabis sativa in Thailand

Abstract

Cannabis sativa is gaining attention as an agronomically important crop in many countries around the world. The identification and control of leaf diseases in cannabis are very important for cannabis cultivators as leaves are the most economically important part of the cannabis plants. In 2022, several cannabis plants in cultivations showing olive leaf spot symptoms emerged from Chiang Rai province, Thailand. Preliminary studies indicated that the causal organism is Pseudocercospora sp. Species of Pseudocercospora are important plant pathogens that are now identified through morphological studies combined with DNA sequence data of Internal Transcribed Spacer (ITS), Actin (act), Translation Elongation Factor (tef), and RNA Polymerase II second largest subunit (rpb2) gene regions. We aimed to investigate and understand the emergence of olive leaf spot disease in cannabis plants in Chiang Rai province, Thailand, with a specific focus on the combined morpho-molecular identification of the pathogen. In our study, Pseudocercospora cannabina, the causal organism of olive leaf spot disease, was identified as the leaf spot-causing pathogen with both morphological and phylogenetic analyses. Our study is the first to provide molecular data for Ps. cannabina as the typenor Ps. cannabina isolates from previous studies have made molecular data available for this species. A pathogenicity test, re-isolation, and identification steps were performed to fulfill Koch’s postulates. This comprehensive approach enhances our understanding of the olive leaf spot disease and its causative agent in cannabis.