Phenotypic and serological screening of okra genotypes against Okra mosaic virus infection under field conditions

Okra mosaic disease (OMD) caused by Okra mosaic virus (OkMV) is an important biotic constraint to okra (Abelmoschus esculentus L.Moench) production in West Africa. Management of OMD with insecticides is very difficult and ineffective, thus making the use of host resistance the most desirable approach. However, there is no information available on host resistance to OkMV. In 2015 rainy and dry seasons, field trials were conducted to screen 21 okra genotypes against OkMV infection in order to identify sources of resistance and or tolerance. In both seasons, field trials were laid out in a randomised complete block design with four replications. Field resistance was assessed using 1-5 visual scale based on disease symptoms, 1 denoting no disease symptom while 5 denoted very severe symptoms. Enzyme linked immunosorbent assay (ELISA) was used to confirm field resistance or infection. Genotypes GH3760, GH2052, GH5332, UCC6, GH5302, GH5793 and GH2063 exhibited mild symptoms during both rainy and dry seasons. ELISA detected OkMV in all the 21 genotypes in both major and minor season crops. The mean number of fruit per plant and the mean fruit yield (t ha-1) differed significantly (P<0.05) among the okra genotypes in both major and minor cropping seasons. Genotype GH5332 with mild symptoms, had the highest fruit yield of 11.88 t ha-1. Genotype GH6105 also had very high fruit yield (9.34 t ha-1) but was very susceptible to OkMV infection. Both disease severity and yield were higher in the minor season than the major season in all the okra genotypes. It can therefore be concluded that genotype GH5332 exhibited partial resistance while genotype GH6102 was tolerant to OkMV. These two varieties are recommended for cultivation as truely resistance genotypes are sought.