Screening of Cannabis sativa germplasm for susceptibility to Septoria leaf spot.

Septoria leaf spot, caused by the fungal pathogen Septoria cannabis, is a common disease of field-grown hemp (Cannabis sativa L.). The development of disease-resistant cultivars presents a promising strategy for managing this disease. To evaluate hemp germplasm for susceptibility to Septoria leaf spot, diverse hemp entries from the USDA-ARS Plant Genetic Resources Unit, commercially available cultivars, and Cornell breeding lines were evaluated in replicated field trials in Geneva, NY. In 2023, 81 entries were screened, and in 2024, 105 entries were screened for disease severity on a weekly basis. Relative area under disease progress curve (rAUDPC) values were calculated to quantify susceptibility across two years. Significant variations in rAUDPC were observed among entries, ranging from 0.01 to 13.60 in 2023 and from 0.10 to 21.20 in 2024. Final disease severity ranged from 0.01% to 31.30% in 2023 and from 0.00% to 36.00% in 2024. Nine entries that consistently displayed low disease severity and are likely resistant to S. cannabis were identified. Disease severity was not significantly correlated with plant sex. Several resistant entries were of Asian origin. This study establishes foundational knowledge for breeding programs targeting Septoria leaf spot resistance and emphasizes the value of diverse hemp germplasm in disease management.