Effect of okra mosaic virus disease on the above-ground morphological yield components of okra in Tanzania

Abstract

The effect of virus and virus-like diseases on the above-ground morphological yield components of okra was determined in farmers’ fields in June 2001. Virus and virus-like disease symptoms were found in all the surveyed fields with disease incidence that averaged 55% and ranged from 30 to 89%. There was a significant ( P<0.05) variation in the above-ground yield components between virus-infected and healthy plants. Compared to healthy ones, diseased plant height was reduced by 19.5%, number of fruits by 34.7% and petiole length by 32.1%. A striking exception was noticed on stem girth which was larger by 27% in diseased plants. Virus disease severity score was 3.1±0.13 on average using a 1–4 scoring scale (where 0: no symptoms and 4: severe symptoms). Okra mosaic virus (OMV) was identified in 97% of the total affected samples using double-antibody-sandwich enzyme-linked immunosorbent assay (DAS ELISA), the first time it has been identified in the Lake Victoria basin of Tanzania. Infected plants exhibited diffuse mosaic on leaves and at times veinal mottling and banding. Fruit malformation was observed particularly in plants with disease severity score of 4.0. There was no significant difference ( P>0.05) in the yield components among the different fields. The reduction in the yield components incurred by virus disease emphasised its damaging potential on currently grown okra cultivars in Tanzania.