Characterization of Blast Resistance in BRRI released rice varieties of Bangladesh

Rice quite often affected by blast disease through transboundary pathogen Pyricularia oryzae results significant yield reduction. The reaction of BRRI-released rice varieties to blast is little known; however, the most popular and mega varieties BRRI dhan28, and BRRI dhan29, along with local and improved aromatic rice varieties are vulnerable to blast disease. This study sought to detect the existence of resistance genes (R genes) in cultivated BRRI varieties for effective deployment of R genes. A total of 84 BRRI-released rice varieties were genotyped using gene-specific tightly linked seven markers for Pi9, Pia, Pib, Pik, Pish, Pii, and Pita. It revealed that Pia and Pib genes were highly frequent in Bangladeshi cultivars (77.38% and 75%, respectively), while 40.48% of cultivars contained Pik alleles, and the lowest frequency of Pish gene (7.14%) existed in the varieties. The minimum frequencies of the remaining three resistance genes (Pi5, Pi9, and Pita2) were also present at 17.86%, 16.67%, and 10.71%, respectively. In addition, the average value of gene diversity was 0.30, with a range of 0.13 to 0.48. Here, the highest gene diversity value (0.48) obtained for the Pia gene revealed Pia gene was quite diverse within the population, followed by the Pik gene; while the Pib gene was comparatively least diverse within the population. In addition, the polymorphic information content (PIC) of the seven markers, which ranged from 0.12 to 0.37 with an average of 0.25, showed that the seven gene-specific markers had a low amount of polymorphism. Additionally, all the BRRI varieties were clustered into five distinct groups, where cluster I being enriched with the Pia and Pib genes (44.05%), cluster II had Pik allele (16.67%), cluster III had Pita-2 allele (7.14%), cluster IV contained Pi9, Pi5, Pia, Pik, Pib, and Pita-2 alleles (25%), and cluster V confined to Pish allele (7.14%). However, in the irrigated ecosystem, the highest frequency was observed for Pia (91.67%), followed by Pib (83.33%), and Pik (38.89%), but least frequency of Pi9, Pita and Pish genes revealed cultivated varieties under irrigated ecosystem had ample scope to introgression blast resistance genes for ensuring food security in the long run. Keywords: Rice, Blast, resistance gene (R gene), markers, ecosystem.