Symptoms Diversity Elicited by Rice Yellow Mottle Virus (RYMV) Infection on Oryza Species in Nigeria
*J. T. Onwughalu1, 2, M. E. Abo1, 2, A. O. Nwankiti2, and J. K. Okoro2
1National Cereals Research Institute (NCRI), Badeggi, Niger State, Nigeria
2Department of Crop and Environmental Protection, University of Agriculture, Makurdi
E-mail: tobechi44@yahoo.com
ABSTRACT
RYMV is endemic in Africa and assumes great economic challenge to rice production in the region where rice is a staple food. The disease is available in all rice growing areas in Nigeria, and constitutes great threat to self-sufficiency in the country’s rice development sector. Rice genotypes were screened for resistance to RYMV infection in the screenhouse at Badeggi, Niger State between 2008 and 2016, using virus isolates from farmers’ fields in north central Nigeria. Based on the Standard Evaluation Scale (SES) score, Back Inoculation Test and Enzyme Linked Immunosorbent Assay (ELISA) results, the disease was present in rice genotypes evaluated and elicited diversity of symptoms. Symptom expression varied from 2 to 4 weeks in all infected plants; producing usual yellow mottle symptoms, bunchy or dispersed tiller formation, orange or pink coloration, stunted growth (height reduction) streak and dots formation as well as hypersensitive reactions on leaves. RYMV infections appeared to have also delayed senescence leading to multiple unproductive tillering. Irrespective of the levels of symptom expression based on the SES score, leaf extracts of all inoculated entries were highly infectious, and elicited similar symptoms on SES score of 7 on FARO 29 (BG 90-2) in a back inoculation test. Leaf extract from Gigante, which showed symptoms of localized infection to the virus was also infectious and elicited clear RYMV symptoms on back inoculation to BG 90-2. Degree of symptom expression did not correlate with virus content and all screened rice genotypes contained varying levels of the virus (RYMV) based on ELISA. NERICA-L 22 had the highest virus content of 62.5%, followed by NERICA-L 21 (56.3%) and NERICA-L 14 (52.1%); whereas, a low virus content (%) of 2.1%, 4.2% and 14.6% were recorded by NERICA-L 17, 23, 26, 36, & 42, FARO 44, NCRO 48 and Gigante respectively. The result showed that Gigante and NIL 54 are the most reliable resistant rice genotypes against the virus.
Keywords: RYMV; Symptomatology; ELISA; Hypersensitivity; Badeggi
