First reports of Colletotrichum theobromicola in the United States and C. fioriniae in Florida associated with celery anthracnose

Celery leaf curl, or anthracnose, is characterized by leaf curling, leaf spots, and stem lesions, leading to stunted growth and plant death. Colletotrichum fioriniae has been reported as the main causal agent of anthracnose in celery. In the fall of 2022, 2023, and 2024, anthracnose symptoms were observed on 5-20% of celery plants in commercial farms in southern Florida. Eighteen strains were collected and based on phylogenetic analysis of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH), chitin synthase 1 (CHS1), and β-Tubulin (TUB2) genes, 17 of them were identified as C. theobromicola and one as C. fioriniae. Four genetically and phenotypically representative strains were selected to spray-inoculate two celery cultivars, Duda 71 and M9, and confirmed Koch’s postulates, by reproducing symptoms and re-isolating the same species. However, spots caused by Colletotrichum theobromicola were generally larger than those caused by C. fioriniae, whereas leaf curl was more pronounced in plants inoculated with C. fioriniae. Although some symptom overlap was observed, C. theobromicola consistently produced petiole lesions, whereas C. fioriniae was uniquely associated with crown necrosis. This study represents the first report of Colletotrichum fioriniae causing celery anthracnose in Florida and C. theobromicola causing the disease worldwide. These findings enhance our understanding of the distribution and diversity of Colletotrichum species in Florida and provide a foundation for developing effective disease management strategies for growers in southern Florida.