Unveiling the Diversity and Virulence of Seedborne <i>Fusarium</i> Species in Lentil Production: Insights from a Two-Year Study in the Northern Great Plains

Fusarium root rot/wilt caused by various Fusarium spp. significantly threatens lentil ( Lens culinaris Medikus) production in the Northern Great Plains (NGP) region. However, the specific composition of seedborne Fusarium spp. causing this disease is not well understood. To address this gap, we conducted a comprehensive study spanning 2019 and 2020, collecting lentil seeds from 75 commercial fields across Montana, North Dakota, Washington, Idaho, and Ontario. Our analysis focused on both externalized and internalized pathogens, with particular attention to Fusarium spp., employing morphological and molecular techniques for identification. In total, 486 and 228 Fusarium isolates were recovered in 2019 and 2020, respectively. Predominant species included F. equiseti, F. acuminatum, F. oxysporum, F. tricinctum, F. graminearum, F. proliferatum, F. redolens, F. avenaceum, and F. sporotrichioides. Virulence studies conducted in the greenhouse revealed varying levels of aggressiveness among Fusarium spp., with F. sporotrichioides, F. oxysporum, and F. graminearum demonstrating the highest virulence. Further investigation into pathogen internalization within seed lots revealed that incidence was highest in the seed coat, followed by the cotyledon, with the lowest occurrence in the embryo. F. avenaceum was prevalently isolated from the seed coat, cotyledon, and embryo. Additionally, Fusarium spp. isolated from the seed coat and cotyledon exhibited higher virulence and greater diversity compared with those from the embryo. This study reports the first comprehensive assessment of both externalized and internalized seedborne Fusarium spp. in the NGP region. The insights gained from our findings will inform the development of targeted management strategies for Fusarium root rot/wilt, ultimately aiding in the preservation of lentil crop health and productivity in the NGP and beyond.