Reaction of Rice Cultivars to a Virulent Rice Yellow Mottle Virus Strain in Uganda

Rice (Oryza spp.) has long been an important food staple for many traditional rice growing communities. Key developments in efforts to improve rice production such as the development of NERICA varieties have been widely recognised. Nonetheless, emerging diseases such as the Rice Yellow Mottle Virus sobemovirus (RYMV) undermine dissemination of new technologies and sustained productivity of the crop. The RYMV is highly variable and several resistance-breaking strains have been identified. Appropriate sources of resistance to RYMV should be identified and characterised in order to pyramid genes for both complete and partial resistance. In this study, reaction of nine (9) rice cultivars to RYMV virulent strain in Uganda was determined. Four upland and three lowland NERICA varieties, an O. Sativa lowland variety, Gigante and IR64 were observed. Isolates of RYMV were collected from three “hot-spots” in Uganda (Lira, Luweero and Iganga). The isolate from Iganga was most virulent on RYMV susceptible cultivar (IR64), and thus used to constitute study treatment evaluated in the study. Cultivars were potted and raised in a screenhouse experiment arranged in a randomised complete block design (RCBD) with three replicates. Significant differences for relative area under disease progress curve (RAUDPC) (P<0.01) were detected among the cultivars. Similarly, significant positive correlations (P<0.05) were observed between mean disease score and percentage reduction in grain weight and between percentage grain weight and reduction in plant height. Susceptible cultivars were characterised based on premature death, and significantly reduced grain weight and plant height (P<0.01 and P<0.05), respectively. These results demonstrated the aggressive nature of the specific RYMV strain, and provided evidence with regard to the importance of grain weight and plant height in evaluating RYMV disease resistance.