Study on the genetic variability and pathogenicity assessment among isolates of spot blotch causing fungi (Bipolaris sorokiniana) in wheat (Triticum aestivum L.)

Wheat is the second largest consuming crop in the world. The yield attributes are hit by many biotic as well as abiotic stress for this crop. Spot blotch which is caused by Bipolaris sorokiniana, a major disease infests into this crop. This fungus flourishes in the humid conditions and mostly affects the Indo-Gangetic plain area. So we have done this extensive research to characterize the fungus and its pathogenicity. The experiment was laid out into Randomized Block Design with three replications to screen the genotype under field conditions for spot blotch susceptibility in the Rabi season of 2016–2017 at Borlaug Institute for South Asia. The greenish grey group had a maximum frequency of 31.25 among all the isolates in the natural population. Radial growth was maximum in RAU-GTL-34 (40.66 mm) having cottony growth pattern and dull white with rings like marking. The mean pathogenicity value showed that isolates were more pathogenic on Sonalika (3.7) than Chiriya 3 (2.5). Colony color and level of exudations were also observed to be related to the level of pathogenicity and aggressiveness. Area under disease progress curve of isolates on Chirya 3 varied from 198.77 (white group) to 730.25 (black group) in both natural and polyhouse condition, while for Sonalika it varied from 458.02 (white group) to 134.83 (black group) in natural condition, whereas from 458.02 (white group) to 1374.07 (black group) in polyhouse condition. Fungus specific primer Cos A_F/R was identified for all isolates as B. sorokiniana. Two Internal transcribed spacer (ITS) primer gave a total of 22 alleles out of which twelve were monomorphic and ten were polymorphic with an average of eleven alleles per loci. The Polymorphism Information Content values varied from 0.884 to 0.915 with an average of 0.88. PCR–RFLP analysis gave a total sixty-six allele out of which thirty unique alleles and thirty-six shared alleles with an average of 7.3 alleles per loci in both the region. The Polymorphism Information Content values varied from 0.331 (ITS-2 and Hinf-I) to 0.809 (ITS-2 and Hind III). Pair-wise genetic similarity coefficients widely varied from 0.54 to 1.0 indicating similarity among the isolates.