Screening rice (Oryza sativa) cultivars for resistance to bacterial leaf blight disease

Bacterial Leaf Blight (BLB), caused by Xanthomonas oryzae pv. Oryzae (Xoo), is a devastating disease that affects the yield and quality of rice (Oryza sativa L.) produced throughout the world. However, resistant rice cultivars do exist, and utilizing them in regions impacted by BLB is an important tool in reducing crop loss. In this study, six rice cultivars widely grown in Ghana along with controls were phenotypically screened for resistance to Xoo strain K1 under greenhouse conditions. Phenotypic assessment identified the rice cultivar Popa as the most resistant Ghanaian phenotype. To investigate cultivars carrying Xanthomonas resistance alleles (Xa-R genes), five STS/SSR markers (RM-317, RM-224, RM-13, xa-13prom and pTA248) respectively linked to Xa2, Xa4, xa5, xa13 and Xa21 were used to genotype selected cultivars. Our results revealed that Ghanaian cultivars, Tinsibe, AGRIC-1 and Krampa White, carry Xa2; Kabre and Krampa White carry Xa4; and Popa and IRAT10 carry xa5. However, none of the 10 cultivars showed the presence of xa13 and Xa21. The O. sativa subsp. indica resistant control, Tetep, contained Xa2 and xa5, whereas the susceptible control, IR661, contained xa5. Quantitative real-time PCR (qRT) results of selected cultivars revealed variable expression profiles of OsWRKY45, OsPR10b, OsJAZ8 and OsPR1a in response to Xoo infection. Though one or more genes responsible for Xoo resistance were present in Ghanaian cultivars, most still exhibited a susceptible phenotype following Xoo infection, which indicates that these Xa genes identified primarily from East Asian germplasm that typically confer resistance are not the primary source of resistance in West African rice cultivars to the Xoo K1 strain.