Occurrence and Virulence of Rice Yellow Mottle Virus in Lowland Rice Growing Areas of Uganda
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Rice yellow mottle virus (RYMV) continue to be the most important viral disease causing 20-100% yield loss on farmers’ rice fields. This study was carried out to contribute towards identification of RYMV isolates for resistance screening in Uganda. Field surveys were done from three regions of Uganda which include Eastern Uganda (Iganga, Kaliro, Mbale, Busia, Mayuge, Budaka, Bukedea, Busembatia, Bukedea, Tororo, Kamuli, Namutumba, Pallisa & Bugiri), Northern (Apac, Lira & Dokolo) and Western (Hoima & Kasese) identifying occurrence of rice yellow mottle virus isolates. Severity and incidence levels of different farmers’ rice fields were established using observational approaches of plant leaves and samples collected for use as inoculum source in experiment at NaCRRI research station. Findings revealed that RYMV is present in all the surveyed districts of Uganda with grand mean severity for isolates of 2.583 (P= 0.05). The highest incidences and severity of 73% and 6.6 respectively was reported in Tororo district while the lowest values of incidences and severity were reported in Kasese district i.e. 0.64% and 1.8 respectively. At NaCRRI, rice genotypes (TOG 5672, TOG 5681, TOG 5674, TOG 5307, local Supa, NERICA 6, Gigante & IR64) were raised, mechanically inoculated with RYMV isolates from nine districts (Mbale, Lira, Kasese, Apac, Kaliro, Tororo, Butaleja, Mayuge and Iganga) and observed for data collection up to 51days post inoculation. The three susceptible cultivars: local Supa, NERICA 6 and IR64 as well as Gigante all succumbed to disease while the four cultivars from West Africa: TOG 5672, TOG 5681, TOG 5674 & TOG 5307 were resistant. Isolates from Kaliro and Tororo were the most aggressive in breaking the resistance of rice genotypes. The rice genotypes should be used as sources of resistance to improve selected farmer- preferred varieties in Uganda while Tororo district should be used as a screening area for newly developed varieties for RYMV resistance.