Morpho-phylogenetics and pathogenicity tests reveal a new species of Fusarium infecting Cannabis sativa L. (hemp) in Northern Thailand

Cannabis sativa L., widely known as hemp or cannabis, has been cultivated for centuries and also legalized in several countries around the world. In Thailand, permits to use cannabis only for medical and licensed purposes are allowed, and hemp (tetrahydrocannabinol [THC] < 0.2%), is legal for general use. The rapid expansion of hemp cultivation has increased the crop's susceptibility to fungal diseases. Species of the genus Fusarium are major phytopathogens, although they may also exist as endophytes. During a survey of pathogenic fungi in Northern Thailand, diseased stems of C. sativa were collected, from which a novel Fusarium species, F. flavens sp. nov., was isolated. Identification was performed using both morphological features and analyses of DNA sequence data. Phylogenetic trees were constructed based on analyses of combined dataset of the translation elongation factor 1-α (tef1-α), RNA polymerase II second largest subunit (rpb2), and calmodulin (cal) gene regions. A combined taxonomic approach of morphological comparisons and multi-locus phylogenetic analyses confirmed the distinctiveness of the species. Pathogenicity was assessed by inoculating spore suspensions and mycelium plugs on hemp leaves, stems, and seedlings. Typical symptoms were reproduced, including leaf and stem wilting and root rot. Re-isolation and re-identification of the same fungus confirmed Koch's postulates. Based on this comprehensive approach, F. flavens was identified as the causal agent of stem and root rot in hemp. This study highlights the significance of F. flavens as a novel pathogen of hemp and emphasizes the importance of integrating morphology, molecular phylogenetics, and pathogenicity tests to clarify its role in hemp diseases.