A total of 139 isolates representing 8 Agro Ecological Zones (AEZs of 1,2,9,11,13,19,23 and 28) of Bangladesh were characterized for their pathogenicity using 25 monogenic lines (MLs) as differential varieties (DVs) targeting 23 resistant genes and two susceptible checks LTH and US2 (having no blast resistant gene or R-gene).Considering significant higher plant height (28.7 cm) and higher leaf color chart reading (3.4), higher disease incidence (20.4%) and lower seedling mortality (0.7) the treatment T8 (3/4th soil, 1/4th CD and NPK of total volume) was considered as standard soil medium for screening of blast isolates against DVs. Virulence frequency of blast pathogens to DVs was higher for the isolates from AEZ11 (47%) followed by AEZ23 (46%) and lower for the isolates of AEZ28. The virulence spectrum of tested blast isolates differed significantly. Under control condition (controlled temperature and humidity) virulence frequencies of blast isolates, collected from rain fed ecosystem (Transplanted Aman season), against DVs was higher than the blast isolates those were collected from irrigated ecosystem (Boro season) specially for Pii, Pi3, Pi5(t), Pik-m, Pi1, Pik-h, Pik, Pik-p, andPi7(t) genes. Isolates clarified on MLs through pathogenecity test indicated that Pi9, Pish, Pita and Pita2 were the major genes responsible for blast resistance in Bangladesh. Among them Pi9, Pish showed resistance frequencies of 90% and above while Pita and Pita-2 showed 80-87% against all blast isolates.
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