MONITORING VIRULENCE PATTERNS OF XANTHOMONAS ORYZAE PV. ORYZAE IN TERAI REGION OF NEPAL.

Bacterial blight (BB) of rice, caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the destructive rice diseases in Nepal. Use of host plant resistance is the most effective method of BB management. However, breakdown of resistance of a variety often occurs after few years of release due to genetic adaptation of the pathogen. So, understanding of pathogen population virulence is required to deploy a suitable variety with effective gene in the target areas. Considering the point, BB isolates were collected from five different districts of Nepal Terai during 2012-2013 and were tested on BB near-isogenic lines during 2014 at Regional Agricultural Research Station, Khajura, Nepalgunj, Banke, Nepal. The occurrence of BB pathogen was highly variable and diverse on the tested genotypes and over locations. No single gene showed resistance to all the BB pathogen population available in Nepal Terai. Xa21 was effective to isolates of Bardiya, Banke, Kailali, and Morang except to the isolate from Rupandehi. The BB pathogen from Rupandehi was the most virulent to all single genes except Xa3; and also to two gene pyramids (IRBB-50, IRBB-51, IRBB-53, IRBB-54 and IRBB-55). Three gene-, four- and five gene-pyramids were resistant to all isolates of five different locations. IR-24 got the longest lesion length and could be used as susceptible check in the screening nursery. Thus, three genes or four genes combination could be deployed for stable management of BB disease and minimize crop losses.