CULTURAL, MORPHOLOGICAL, PATHOGENIC AND MOLECULAR CHARACTERIZATION OF Alternaria porri CAUSING PURPLE BLOTCH OF ONION

Abstract

Purple blotch of onion samples collected from different onion growing regions of Bangladesh and studied their cultural, morphological, pathogenic and molecular characterization. Colony color varied between light to dark olivacious and grayish white. Shapes of colonies were irregular, regular with and without concentric ring. Margin of colonies were entire, irregular and wavy with effuse, fluffy and velvety texture. Isolates impregnated media with color ranging between grey to brown. 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 7.720×10 3 to 47.02×10 3 per mm 2 with sporulation time 3.33 to 11.00 days. The conidial shape was straight to curve with light to deep brown color. 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