Pathogenic variability and aggressiveness of Nepalese Bipolaris sorokiniana isolates causing spot blotch of wheat

Abstract

Spot blotch caused by fungal pathogen Bipolaris sorokiniana (Sacc.) Shoemaker is an important fungal disease in warm and humid wheat growing condition. Study on pathogenic variability of B. sorokinianana isolates is limited in Nepal.  Information based on host × pathogen interaction is a useful tool to devise the disease management strategy. Therefore, aggressiveness of  total 36 single spore isolates of B. sorokiniana (27 isolates from terai, 7 isolates from mid hill and 2 isolates from high hill) of Nepal were evaluated on 14 days old seedling of RR-21 (susceptible check), Guatam (moderate resistant) and Chirya 3 (resistant check) under polyhouse condition. Results revealed highly significant isolate-by-variety interaction (P<0.001) for all the disease development traits, suggesting substantial variability in the pathogenicity of the isolates. Moreover, days to disease appearance, number of lesions per leaf and disease severity was highly correlated to Area Under Disease Progress Curve (AUDPC), illustrating those traits as an important indicator of disease development and pathogen aggressiveness. RR-21 exhibited susceptible to overall isolates response followed by Gautam and Chirya 3. On the basis of AUDPC value, top ten aggressive isolates were identified (N-BS24, N-BS7, N-BS28, N-BS36, N-BS27, N-BS37, N-BS15, N-BS38, N-BS19 and N-BS16). Among them, N-BS24 and N-BS28 were able to show high disease against resistant check Chirya 3, so aggressiveness of these two isolates can be further validated through adult plant screening and genetic study and utilize it for resistant breeding program in Nepal.