Morphological and Molecular Characterization of Erysiphe cruciferarum Causing Powdery Mildew on Brassica Vegetables

Abstract

Powdery mildew symptoms characterized by white to gray powdery fungal growth on leaf surfaces, chlorosis, reduced photosynthetic activity, and premature leaf senescence were observed in Brassica vegetable crops cultivated under diverse agroecological conditions. Diseased leaf samples were collected from affected fields and subjected to pathogen isolation and characterization using morphological and molecular approaches. Fungal isolates consistently produced superficial mycelial growth with abundant conidiophores and chains of ellipsoid to cylindrical conidia typical of Erysiphe cruciferarum. Considerable variation in colony density, conidial production, and disease severity was observed among isolates collected from different Brassica growing regions. Pathogenicity assays conducted on healthy host plants reproduced characteristic powdery mildew symptoms, confirming the pathogenic nature of the isolates, and Koch’s postulates were fulfilled through successful re-isolation. Molecular characterization was performed using amplification and sequencing of the internal transcribed spacer (ITS) region and additional conserved fungal barcoding loci. Sequence analysis revealed high similarity with authenticated E. cruciferarum isolates available in global sequence databases. Phylogenetic analysis grouped field isolates within the E. cruciferarum clade with strong bootstrap support, confirming species identity and indicating limited genetic variability among regional populations. Disease development was favored by moderate temperatures, low rainfall, and high relative humidity conditions typical of dense canopy microclimates. Severe infections resulted in reduced leaf area, impaired photosynthesis, and significant yield losses in Brassica vegetable production systems. The integration of morphological and molecular tools provided accurate identification and improved understanding of pathogen diversity and epidemiology.