Morpho-molecular characterization based diversity analysis of Bipolaris isolates infecting graminaceous hosts.

The genus Bipolaris is found to be commonly associated with leaf spots, leaf blights, root rots, foot rots and other disease symptoms mainly in high value field crops in the family Poaceae. Spot blotch caused by Bipolaris sorokiniana (Sacc.) Shoemaker is one of the most important diseases of wheat and barley. The fungus causes germination failure, seed mortality and spot blotch development with small, dark brown lesions without chlorotic margin. Therefore, in the present study, attempts were made to investigate the morphological variations among different Bipolaris isolates collected from the different graminaceous hosts in north-western regions of India and to assess the genetic diversity of the fungus using SSR markers. The results revealed that all the 50 isolates exhibited various levels of morphological and cultural variations. Colony colour varied from dark ash to white with raised and irregular margins in most of the isolates. The size of the conidia varied from 31–75 µm × 15–27 µm, slightly curved, elliptical or oblong, mostly tapering towards ends, light to dark brown in colour, 3–12 distoseptate, having bipolar germination. The molecular identification of the pathogen associated with all the test isolates carried out using B. sorokiniana-specific primer pair, i.e. COSA_F/R, also cross-identified the pathogen to be B. sorokiniana by producing one sharp band (519 bp) in all the test isolates. All the ten SSR primers exhibited different levels of polymorphism among the different isolates. The PIC values revealing allelic diversity and frequency among all the isolates varied from 0.153 in the case of primer pair BS051 to 0.493 in primer pair BS065 and this variation in PIC values among the ten primer pairs indicated variability in amplified product and allelic frequency among the isolates. [ABSTRACT FROM AUTHOR]