Characterization and Pathogenicity of Alternaria porri

Purple blotch of onion (Alternaria porri) causes severe foliar damage to onion plants. Twenty seven (27) isolates of Alternaria porri were isolated from diseased samples collected from different onion growing regions of Bangladesh and studied their cultural, morphological, pathogenic and molecular characterization. Growth rate of isolates was between 2.43 to 3.95 mm/day with fast growth in isolate DSTR 02 and least in MMBH. Morphological variation in conidia production was between 7.720×103 to 47.02×103 per mm2 with sporulation time 3.33 to 11.00 days. Conidial septation ranged from 3.00 to 6.00 × 1.00 to 2.00 with size from 11.20 to 39.20 × 4.76 to 11.43 µm. Isolates shown variations in lesions size exhibited the pathogenic variation exist in the environment. In molecular study no band were found by using seven (7) RAPD primers in polymerase chain reaction (PCR) but band found by using ITS primer ITS1F and ITS4 from three isolates (DSSA, DSTR 02 and RBHR 02). The results demonstrated the existence of considerable variation in cultural, morphological, pathogenic and molecular characters of Alternaria porri isolates prevalent in Bangladesh environment.