Molecular and phenotypic analysis reveals cross infection of Bipolaris species in wheat and rice

Wheat ( Triticum aestivum L.) and rice ( Oryza sativa L.) are the two most important food grain crops cultivated worldwide. In present scenario of climate change as well as changing cropping system, the spot blotch of wheat caused by Bipolaris sorokiniana and brown spot of rice caused by Bipolaris oryzae have resulted in great losses to food grain yield in all parts of the country especially in regions where rice–wheat cropping system is pre-dominant. The objectives were to determine the cross infection pattern of Bipolaris spp. prevalent in rice–wheat cropping system regions and their relatedness to alternative host as well as host preference. When twenty isolates each of B. oryzae and B. sorokiniana were subjected for their pathogenicity on susceptible variety of rice (PB-1121) and wheat (Sonalika) respectively, BO-1 and BS-112 were found to be most virulent isolates with 83% and 89% disease index on their own hosts respectively. Cross infection study under artificial conditions with most virulent isolate revealed that when inoculation of BS-112 on wheat and rice was done, infection index of 89% and 80% was obtained, while BO-1 inoculation showed infection index of 85% and 78% on rice and wheat respectively. Cross infectivity was confirmed by PCR using species specific markers developed in the laboratory. Synergism between two pathogens revealed infection index of 94% on wheat and 92% on rice, which was more than individual inoculations. Cross infectivity was also identified under natural condition for both B. sorokiniana and B. oryzae on rice and wheat at certain places.