CULTURAL, MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF STEMPHYLIUM VESICARIUM CAUSING WHITE BLOTCH OF ONION

Abstract

An investigation comprising a set of experiments were conducted at the Molecular Plant Pathology Laboratory of the Department of Plant Pathology, Sher-e-Bangla Agricultural University and in the Plant Breeding and Biotechnology Laboratory of the Department of Botany, University of Dhaka during February’13 to July’14. A total of 24 isolates of Stemphylium vesicarium collected from different onion growing areas were characterized in terms of cultural, morphological and molecular aspects. Front colony colors were greenish brown to dirty white, deep grey to whitish, light grey to whitish, deep greenish white, light grey and dirty white to greenish. Reverse colony colors were brown, deep brown and light brown. Colony shapes were circular and irregular with umbonate, raised and flat type colony elevation. Colony texture were cottony, fluffy and velvety with entire, undulate and filiform type colony margin. Among the culture media, V-7 juice agar found to be the most suitable culture media for mycelial growth of S. vesicarium. The sporulation of the fungus was remarkably influenced by V-7 juice mixed with Potato Dextrose Agar, this media exhibited the highest sporulation 2 to 15.7 µm. Maximum breadth of conidia was 12.55 µm found in isolate DSSA and minimum 9.760 µm in isolate CCKH 02. The horizontal septation varied from 1-3. The longitudinal septation varied from 0-4. DNA extraction was successfully done by using CTAB method from 18 isolates out of 24 isolates for studying molecular variability. Testing of seven