ABSTRACT
In Uganda, the severe Maize lethal necrosis (MLN) disease, which threatens subsistence maize production is caused by co-infection of maize plants with Maize chlorotic mottle virus (MCMV) and Sugarcane mosaic virus (SCMV). However, there is no information about natural hosts of MLN causing viruses and their role in epidemiology of MLN in Uganda. The aim of this study was to determine existence of natural alternative weed and cultivated crop hosts of MLN causing viruses. Three seasonal surveys between 2014 and 2015 were carried out in five major maize growing agroecological zones of Uganda. Weeds and cultivated crops growing in proximity to maize were observed for virus symptoms and tested for MLN causing viruses using Double Antibody Sandwich Enzyme-Linked Immunosorbent Assay and Reverse Transcriptase Polymerase Chain Reaction. Data was collected on frequency of occurrence of weeds and cultivated crop species and MLN virus disease incidence. Digitaria abyssinica, Bidens pilosa and Commelina benghalensis were the most common weed species while Phaseolus vulgaris, Manihot esculenta, Arachis hypogaea), Musa sp, Glycine max and Ipomoea batatas were most common cultivated crops. Pennisetum purpureum, Digitaria abyssinica, Cyperus rotundus, Amaranthus spinosus, Commelina benghalensis and Eleusine indica weeds species are natural hosts of Maize chlorotic mottle virus. Among the cultivated crops, Phaseolus vulgaris, Manihot esculenta and Sesamum indicum are natural hosts of MCMV. Only Sorghum (Sorghum bicolor) and sweet potato (Ipomoea batatas) tested positive for SCMV. MCMV incidence in weeds ranged from 2% to 63%% and 2% to 29% in cultivated crops. MLN causing viruses were prevalent in weeds and cultivated crops located in known hotspots for MLN in Uganda. The study has revealed that alternative hosts of MLN-causing viruses are present in major maize growing agroecological zones of Uganda and act as sources of inoculum to sustain MLN epidemics.