Molecular Characterization of Bipolaris sorokiniana Isolates Collected from Wheat by SSR Markers
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Date
2016
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Rajendra Agriculrural University, Pusa (Samastipur)
Abstract
Spot blotch of wheat caused by Bipolaris sorokiniana is one of the most important fungal diseases of wheat (Triticum aestivum). The pathogen is seed and soil borne. Pusa in Bihar is considered as a hot spot for the disease. 36 fungal isolates were collected from infected leaves and seeds of different wheat genotypes grown at the research farms of RAU, BISA, IARI Regional Station at Pusa and from Patna, Muzaffarpur, Nalanda, Madhepura, Mahua and Jamaui. They were characterized morphologically on the basis of colony colour, growth pattern and exudation, and molecularly through SSR markers. The isolates were tested on two wheat cultivars, susceptible Sonalika and resistant Chirya-3 for disease severity, AUDPC and aggressiveness under natural condition in field and controlled condition in polyhouse. The isolates were divided into five morphological groups on the basis of their colony colour namely black, grey, grey cottony knot, grey white and whitish black, among which the frequency of black was the maximum and showed high aggressiveness. To examine the molecular genotypic variability among the isolates, their genomic DNA was isolated and amplified using 10 Bipolaris specific SSR (microsatellite) primer pairs. A total of 110 allelic variants were detected including 35 unique alleles, 75 shared alleles (including 7 null alleles) at 18 loci with an average number of 6.11 alleles per locus during the amplification reaction conducted with the thirty six entries. The primer pairs BSO96 and BS065 appeared to be highly polymorphic and comparatively more informative primers for molecular characterization and differentiation of thirty six Bipolaris sorokiniana isolates. The dendrogram was generated following UPGMA and the clusters were identified at appropriate pennon level. There were nine clusters A to I at eighty five similarity units. Entries R.G.T-78 and R.G.T-79 were relatively more closely related with the highest similarity coefficient amongst the thirty six entries evaluated. Analysis of divergence pattern based on amplification profile allowed differentiation of thirty six isolates. The different clusters of isolates showed differentiation for aggressiveness. Bipolaris sorokiniana of cluster A were the highly aggressive and of clusters B, C, D, F and G were moderately aggressive. Those of clusters E, H and I were the least aggressive. Thus molecular marker can differentiate the Bipolaris sorokiniana fungal isolates in general and for their relative aggressiveness.
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