Abstract

The fungus Magnaporthe oryzae causes rice blast disease leading to substantial yield losses. This study aims at understanding the effectiveness of R-genes to the isolate of M. oryzae from Namulonge in Central Uganda to decide the incorporation of their carrier lines in local gene pyramiding programs. Eighty-three genotypes (73 monogenic resistance lines and 10 local varieties) were evaluated in two different experiments along with two susceptible and one resistant check in the screen house in a 10 × 8 alpha lattice design with two replications, inoculated by spraying, phenotyped at 7, 14 and 21 days after inoculation (DAI), and data on for disease severity, severity percentage, disease incidence, and relative area under disease progression were analyzed using the restricted maximum likelihood (ReML) in Genstat. The tested genotypes were significantly (P<0.001) different for the first, second and across experiments at 7, 14 and 21 DAI for all the measured traits indicating genetic variability among the tested germplasm for rice resistance to blast disease caused by the Namulonge isolate of M. oryzae. Twenty-five out of eighty-three (22.9%) genotypes had consistently low disease severity scores during the two experiments with a range of 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 were 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.

Key words: Rice, blast disease resistance, monogenic differential lines, reaction profiles, R-genes.