Detection Of Viruses And The Spatial And Temporal Spread Patterns Of Viral Diseases Of Cucurbits (Cucurbitaceae Spp.) In The Coastal Savannah Zone Of Ghana

ABSTRACT

Cucurbits are susceptible to over 35 plant viruses; each of these viruses is capable of causing total crop failure in a poorly managed virus pathosystem. The objectives of this study were to detect the viruses that infect six cucurbit species in the coastal savannah zone of Ghana and to describe the spatial and temporal spread patterns of virus epidemics in zucchini squash (Cucurbita pepo L.) by the use of mathematical and geostatistical models. Cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus Thunb.), zucchini squash (Cucurbita pepo L.), butternut squash (Cucurbita moschata Duchesne), egushi (Citrullus colocynthis L. Schrad.) and melon (Cucumis melo L.) were grown on an experimental field in the coastal savannah zone of Ghana and were monitored for the expression of virus and virus-like symptoms. The observed symptoms were further confirmed by Double Antibody Sandwich Enzyme-Linked Immunosorbent Assay (DAS ELISA) and mechanical inoculation of indicator plants. The temporal spread patterns of virus disease in zucchini squash were analyzed by exponential, logistic, monomolecular and gompertz mechanistic models. The spatial patterns of virus disease spread in zucchini squash field were analyzed by semivariograms and inverse distance weighting (IDW) methods. Cucumber, zucchini squash, melon and butternut squash were infected by both Cucumber mosaic virus (CMV) and Papaya ringspot virus (PRSV-W). Egushi was infected by CMV but not PRSV-W. None of the six cucurbit species were infected by Watermelon mosaic virus (WMV) or Zucchini yellow mosaic virus (ZYMV). The temporal pattern of disease incidence in the zucchini squash field followed the gompertz function with an average apparent infection rate of 0.026 per day. The temporal pattern of disease severity was best described by the exponential model with coefficient of determination of 94.38 % and rate of progress of disease severity of

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0.114 per day. As at 49 days after planting (DAP), disease incidence and severity factor had reached 11.82 % and 1.09 respectively. The spatial pattern of disease spread in the zucchini squash field was best described by the Gaussian model with range of spatial dependence of 0.63 m.