Variation in the susceptibility of okra (Abelmoschus esculentus L. Moench) genotypes to okra mosaic virus and Podagrica species under field conditions

Abstract

A total of 21 okra (Abelmoschus escuentus L. Moench) genotypes were screened for their reactions against okra mosaic disease (OMD) and flea beetles (Podagrica species) infestations in field trials which were conducted from May to October, 2015 (wet season) and November 2015 to March 2016 (dry season), in order to identify sources of resistance and or tolerance. The trials were laid out in a randomised complete block design (RCBD) with four replications. Field resistance in the genotypes was assessed at 2, 6 and 10 weeks after planting using a 0 to 5 visual scale based on disease symptoms (where 1 denotes no symptom and 5, very severe symptom). Enzyme linked immunosorbent assay (ELISA) was performed to detect the presence of Okra mosaic virus (OkMV) in the okra genotypes. Populations of the flea beetle (Podagrica spp.), the vector of OkMV, and the associated leaf and fruit damage were also assessed. All the okra genotypes exhibited a varying range of disease symptoms and the flea beetle infestations, and lacked immunity. Genotypes GH2052, GH2063, GH2026, GH3760, GH5302, GH5332, GH5793, GH6105 and UCCC6 exhibited mild symptoms of OMD, and were less susceptible to flea beetle infestation and associated leaf damage during both seasons. Using ELISA, OkMV was detected in all the 21 genotypes. The mean number of fruits per plant and the mean fruit yield (t ha-1) differed significantly (P<0.05) among the okra genotypes. Genotype GH5332 had the highest fruit yield of 11.88 t ha-1 followed by genotype GH6105 (9.34 t ha-1). Percentage fruit damage due to the flea beetle infestation differed significantly among the okra genotypes, ranging between 43.7 and 91.2% and from 47 to 84% in both trials respectively.   Key words: Enzyme linked immunosorbent assay (ELISA), insecticides, Abelmoschus esculentus, okra mosaic disease, Podagrica species.