Abstract
Cowpea viruses are economically important diseases of cowpea in the major growing areas of Uganda and have inflicted negatively on food security, nutrition and income for many households. The objective of the study was to determine the prevalence and identity of viruses infecting cowpea in the growing districts of Uganda. Surveys were conducted in the field of grown cowpea, and virus symptoms were recorded on the basis of virus incidence and severity in the districts of Apac, Lira, Pader and Kumi. Symptomatic virus leaf samples were also collected from the same fields surveyed for serological test for detection of virus types using antibodies to cowpea aphid-borne mosaic virus (CABMV), cowpea mild mottle virus (CPMMV), cowpea severe mosaic virus (CPSMV), cowpea mosaic virus (CPMV), cowpea chlorotic mottle virus (CPCMV), cucumber mosaic virus (CMV) and cowpea chlorotic mosaic virus (CCMV) in double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Results showed that there was the highest percentage of incidence and severity in Kumi (85.4% and 13.8%, respectively) with the lowest percentage of incidence and severity observed in Apac (55.9% and 4.7%, respectively). Serological test revealed the presence of CABMV, CPMMV, CPSMV and CMV in the leaf samples as the major virus types in the surveyed districts. However, CPCMV, CPMV and CCMV were not detected in the leaf samples surveyed in the cowpea growing districts. Serological test also revealed that among the virus types detected, single and multiple virus types occurred in the plant samples. The highest single virus type occurring in the plant samples was CPMMV (11.6%) and the lowest was CABMV (1.8%). The virus types namely CMV, CABMV, CPMMV and CPSMV occurred in combinations with proportion of 7.1% in the infected plant samples. Therefore, this information obtained on the virus types provides an opportunity for breeders to develop cowpea variety with multiple resistance genes to control several virus types infecting cowpea.
Highlights
Cowpea crop is one of the most widely adapted and nutritious food legume crops in the tropics and subtropics of Africa
The results showed that there were highly significant (P < 0.05) differences in incidence and severity of virus symptoms on cowpea crop in the surveyed districts and fields (Table 1)
Virus symptoms were encountered in the four districts but with varying incidence levels of virus symptoms (Table 2)
Summary
Cowpea crop is one of the most widely adapted and nutritious food legume crops in the tropics and subtropics of Africa. Dry grain for human consumption is the principal product of the cowpea plant, and leaves, fresh peas and fresh pods are consumed [1]. Ehlers and Hall [1] showed that farmers in California can achieve up to dry grain yields of 4000 kg/ha of improved cowpea varieties with good resistance to virus diseases. In the case of Uganda, where the crop is intensively cultivated in the northern and eastern regions, farmers attain the yield of less than 200 kg/ha due to susceptible cultivar (Ebelat) which is ravaged by virus infection [2] [3]. In Uganda, cowpea viruses have become a major problem in the cowpea growing regions and cause a great effect on production, affecting the household livelihoods
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