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