Morphological and cultural diversity of Alternaria brassicae (Berk.) Sacc. isolates cause of black leaf spot of Crucifers

Forty isolates of Alternaria brassicae were collected from different cauliflower, cabbage and mustard growing locations of India and characterized for cultural, morphological, pathogenic variations. All the isolates showed high level of variability in vitro in respect to mycelia growth, growth pattern and sporulation. The Jaipur isolate (AB-16) showed higher growth (86 mm) in PDA and Coimbatore isolate (AB-37) showed least growth (35mm) in PDA. All the isolates depicted high growth rate and high number of spore production on Cauliflower Leaf Extract Agar (CLEA) followed by (PDA) and Czapek Dox Agar (CDA). Substantial variation was found in spore morphology in respect to conidial length, width and number of septa. Average conidial length and width were varied from 34.2–99.2 μm and 6.1–14.8 μm, respectively. Horizontal septa showed higher degree of variation than vertical septa. Number of horizontal and vertical septa ranged between 4.0–8.2 and 0.2 -1.8, respectively.