The fungus Magnaporthe oryzae causes rice blast disease leading to substantial yield losses in Uganda. Therefore, it is necessary to test the reaction of R-genes to the strains of the fungus prevalent at a particular area to these genes before incorporating the carrier lines of such genes into a rice breeding programme through gene pyramiding. This study was aimed at understanding the effectiveness of R-genes to the isolate of M. oryzae from Namulonge such that appropriate breeding strategies can be deployed to increase resistance durability to rice blast disease. In this study, eighty-three genotypes including 73 lines with monogenic resistance and 10 local varieties were evaluated twice along with two susceptible and one resistant check in the screen house in a 10 X 8 alpha lattice design with two replications. The genotypes were inoculated by spraying and scored using the standard evaluation system (SES) of 0-9 at 7, 14 and 21 days after inoculation (DAI). The data was analyzed using the restricted maximum likelihood (ReML) in Genstat. The tested genotypes were significantly different at a level of (P<0.001) for the first, second and across experiments at 7, 14 and 21 DAI for disease severity, severity percentage, disease incidence, and relative area under disease progression stairs (rAUDPS) indicating genetic variability among the tested germplasm for rice resistance to blast disease caused by the Namulonge isolate of M. oryzae through gene pyramiding. Twenty-five (including the six local resistant varieties whose R-genes are not known and nineteen monogenic lines) out of eighty-three (22.9%) genotypes had consistently low disease severity scores during the two experiments with a range between 0-3. The R genes Pi3, Pi5 (t), Pi7 (t), Pi-b, Pik, Pi54, Pik-m, Pit, Pita, Pita-2, Piz, Piz-4, Piz-5 was considered effective to this particular isolate. The results of this study set the basis of a breeding program for rice resistance to blast disease caused by the Namulonge isolate of M. oryzae through gene pyramiding.
Keywords: Rice, Blast disease resistance, monogenic differential lines, reaction profiles, R-genes