Performance of two locally adapted okra varieties as influenced by cucumber mosaic virus disease

Abstract

The responses of two locally adapted okra varieties (Bokungi and Ikeregi) to Cucumber mosaic virus (CMV) were evaluated under field conditions during the 2014 cropping season. Seedlings weirus are inoculated with the virus at 1 week after emergence. Each genotype was evaluated as inoculated and uninoculated treatments. Disease incidence, severity of infection (scale 1-5), yield and yield related parameters were measured. Virus titre was quantified using Enzyme-Linked Immunosorbent Assay (ELISA). Data were subjected to independent t test and significance was determined at 5% level of probability. One hundred percent infection was found in both varieties but disease severity was higher in “Bokungi” (5) than in “Ikeregi” (3). Higher virus concentration was found in the inoculated leaves of “Bokungi” (ELISA value = 0.89) compared to “Ikeregi” (ELISA = 0.41). Reductions in plant height (8.8%), fruit number (33.3%) and fruit weight (37.6%) were significantly lower in “Ikeregi” than “Bokungi”. The present data reveal that both okra varieties are susceptible to CMV infection but “Ikeregi” appears to be more tolerant. Cultivation of the more CMV-tolerant okra variety would offer some level of insurance against complete crop failure in case of disease outbreak in the study area. Maize lethal necrosis disease (MLND) caused by mixed infections of Maize chlorotic mottle virus (MCMV) and Maize dwarf mosaic virus (MDMV) is currently the greatest threat to maize productivity in East African countries. Maize is a major cereal crop in Nigeria but there is no information on the status of MLND in the country. To ascertain this, a survey of maize viruses was conducted in selected States (Akwa Ibom, Cross River, Kano, and Katsina) in May and August 2017. A total of 108 maize leaves sampled from maize farms were tested serologically for MCMV, MDMV and SCMV using Antigen Coated Plate- Enzyme-Linked Immunosorbent Assay (ACP-ELISA). All the samples reacted negatively with MCMV, MDMV and Sugarcane mosaic virus (SCMV) antibodies, whereas 41 samples (38 %) exhibited strong positive reaction with Maize streak virus (MSV) antibody. The incidence of MSV disease was highest (51.2 %) in Kano, followed by Katsina (34.1 %), whereas the lowest incidence was found in Akwa Ibom and Cross River, with about 7.3 % each. This study showed that MLND is not yet in the study area. However, there is a need for continuous survey and surveillance, and pre-emptive breeding for maize germplasms that are resistant to MLND. In addition, farmers and the general public should adhere to preventive strategies in order to prevent severe yield losses.