Epidemiology of Okra Mosaic Virus on Okra Under Tropical Conditions

Abstract

Okra [Abelmoschus esculentus (L.) Moench] is susceptible to at least 19 plant viruses with Okra mosaic virus (OkMV) being reported to be the most severe. Alternative host plants have been suspected to harbor OkMV which have contributed in its transmission. A study was carried out to determine the incidence of OkMV in weed species found near cultivated okra. Weed species growing around okra field, and exhibiting virus, or virus-like disease, symptoms were sampled and serologically analyzed to determine whether they harbored OkMV. Vector transmission tests were carried out with Aphis craccivora, A. spiraecola, Podagrica unifoma, P. sjostedti and Syagrus spp. to determine if the virus was insect-transmitted from the weeds to healthy okra and indicator plants. In the second experiment, healthy okra plants were inoculated with OkMV, at 14, 21, and 28 days after emergence and the effect of OkMV on yield components was estimated. Presence of OkMV in some weed samples was confirmed by symptom expression, host range, and serology. Leaf extract from the weeds produced symptoms on at least two common indicator hosts upon mechanical inoculation. Datura spp. exhibited the greatest ability to harbor OkMV. Cucumber mosaic virus (CMV; genus Cucumovirus), a non-persistently transmitted virus was isolated as a result of differential transmission tests with candidate vectors of CMV from Datura sp. The effect of OkMV infection on okra growth and yield varied with time of inoculation. There was a positive correlation between fruit weight and numbers of fruit for all inoculation times. There was reduction in yield components due to infection with OkMV in all time of inoculation.