Morphological and Molecular Identification of Septoria apiicola Causing Late Blight on Celery in Temperate Regions

Abstract

Late blight symptoms characterized by water-soaked lesions, chlorotic spotting, necrotic blighting, and premature leaf senescence were observed on celery crops cultivated in temperate production regions. Diseased leaf samples collected from affected fields were subjected to pathogen isolation and identification using morphological and molecular approaches. Fungal isolates consistently produced slow-growing grayish colonies with dark pycnidial fruiting bodies embedded within infected tissues and culture media. Microscopic examination revealed hyaline, filiform, septate conidia characteristic of Septoria apiicola. Variability in colony growth, sporulation intensity, and pycnidial development was observed among isolates obtained from different celery-growing locations. Pathogenicity assays performed on healthy celery plants reproduced typical late blight symptoms, including foliar lesions and progressive leaf blighting, whereas control plants remained symptom-free. Re-isolation of the pathogen from inoculated tissues fulfilled Koch’s postulates and confirmed the pathogenic nature of the isolates. Molecular characterization was conducted through amplification and sequencing of the internal transcribed spacer (ITS) region and additional conserved loci commonly used for fungal identification. Sequence analysis demonstrated high similarity between the obtained isolates and authenticated S. apiicola sequences available in international databases. Phylogenetic analysis grouped the isolates within the S. apiicola lineage with strong bootstrap support, confirming species identity and close genetic relatedness among regional isolates. Disease development was favored by prolonged leaf wetness, cool temperatures, and high relative humidity typical of temperate production environments. Severe infections resulted in reduced photosynthetic area and significant decline in marketable celery yield and quality. Integrated morphological and molecular identification methods provided reliable differentiation of S. apiicola from other foliar pathogens associated with celery diseases.