VARIABILITY OF RICE YELLOW MOTTLE VIRUS IN A SET OF ISOLATES ORIGINATING FROM NORTH-CENTRAL NIGERIA

VARIABILITY OF RICE YELLOW MOTTLE VIRUS IN A SET OF ISOLATES ORIGINATING FROM NORTH-CENTRAL NIGERIA

^*Onwughalu, J. T.^1, & Abo, M. E.¹

¹National Cereals Research Institute (NCRI), Badeggi, Niger State, Nigeria

²Chukwuemeka Odumegwu Ojukwu University, Igbariam Anambra State

*Email: tobechi44@yahoo.com

ABSTRACT

The study was carried out to determine the resistance-breaking ability of six RYMV isolates collected from the north central Nigeria. Seven rice genotypes obtained from AfricaRice Center were used for the experiment in a Split-plot designwith three replications under screenhouse environment at Badeggi, Niger State. The result showed that the resistant alleles – rymv1-1 was circumvented by the six virus isolates, which also expressed the characteristic symptoms of RYMV at 42 Days after inoculation (DAI). The rymv1-4/rymv2 and rymv1-3 were showed to be moderately resistant with isolates from Mararaba-Obi and Gulu at 42 DAI respectively. The breakdown of resistance observed in the traditional resistant rice genotype (Gigante) appeared first as hypersensitivity reaction and later (≥42 DAI) as symptom expressed breakdown. Rymv1-5 found in Tog 5674 was not affected by the six virus isolates in terms of symptom expression; however, saps from earlier inoculated test plants (Tog 5674) were infective on the susceptible genotype (Bouake 189). Virus isolates from Obubu-Ofu and Makurdi, belonging to Ser1 reacted differently and circumvented the resistance in the conventional resistant check (Gigante) with obvious yellow mottle symptoms of RYMV at 42 DAI. The serological profile analysis of the virus isolates indicated they belonged to Serogroups 1 and 2 (Ser1 and Ser2). The present study has reported significant differences in the aggressiveness of isolates of same serogroup, and the overall RYMV isolates existing in north central Nigeria. The pathogenicity effect of the virus isolates onnumber of panicles and yield at harvest for susceptible test plant indicated 100 % yield loss with Gulu, Makurdi and Edozhigi isolates. Moreover, the four virus isolates from Mararaba-Obi, Edozhigi, Gulu and Obubu-Ofu contributed more than 60 % yield loss in Tog 5672, which only showed moderate resistance with Mararaba-obi and Gulu isolates. This study has reported the resistance gene/alleles holding in north-central Nigeria to include rymv1-5, rymv1-3, and rymv1-4+ rymv2.

Keywords: Rice yellow mottle virus; Resistance-breaking; isolates; Nigeria