Viruses of herbaceous legumes in the moist savannah of West Africa

Virus diseases of herbaceous legumes have been relatively little studied even though the legumes play an important role in the maintenance of soil fertility and pest/disease management as well as providing fodder in sub-Saharan Africa. Leaf samples exhibiting virus-like symptoms from nine herbaceous legume genera (Aeschynomene, Arachis, Calopogonium, Centrosema, Chamaecrista, Cratylia, Dicolea, Stylosanthes and Zornia) were tested for 12 viruses reported to occur in herbaceous legumes. Although six viruses (blackeye cowpea mosaic, peanut mottle, bean common mosaic and bean yellow mosaic potyviruses, cucumber mosaic cucumovirus and tobacco mosaic tobamovirus) were detected, some symptomatic samples tested negative. These were examined by electron microscopy and virus-like particles were observed

First report of banana streak badnavirus in plantain landraces in southern Cameroon, Central Africa

Banana streak badnavirus (BSV) has been reported from Musa spp. in many parts of West Africa, including Benin, Côte d'Ivoire, Ghana, and Nigeria (1). Symptoms of BSV infection in Musa spp. are sometimes similar to and confused with those caused by cucumber mosaic virus (CMV). BSV is prevalent in areas of southern Nigeria bordering Cameroon, and the disease may also be present in other Central African countries. In June 1996, six leaf samples with viruslike yellow/chlorotic streak symptoms were collected from plantain in the four villages, Awae, M'Balmayo, Nkolfep, and Nkolfoulou, within a 60-km radius of Yaoundé, Cameroon's capital. The samples were indexed for BSV and CMV by both triple antibody sandwich indirect enzyme-linked immunosorbent assay (TAS-ELISA) and immunosorbent electron microscopy (ISEM) to ascertain the presence of these two viruses. The TAS-ELISA was performed with rabbit polyclonal antiserum (obtained from B. E. L. Lockhart, University of Minnesota) for trapping and mouse polyclonal antiserum (obtained from G. Thottappilly, IITA) for detection. Out of the six samples, one tested strongly positive (>×2 A405 of the healthy control) and four were weakly positive (×1.5 A405 of the healthy control) for BSV by TAS-ELISA. However, all six samples contained BSV particles when examined by ISEM with rabbit polyclonal antiserum (from B. E. L. Lockhart) for trapping. None of the samples tested positive for CMV. These results confirm that BSV is present in Cameroon and that BSV is likely to be the causal agent of the symptoms

Responses of white yam (Dioscorea rotundata) cultivars to inoculation with three viruses

The responses of 24 white yam (Dioscorea rotundata) cultivars to mechanical and vector transmission with each of three viruses infecting yams were assessed through enzyme-linked immunosorbent assay (ELISA) and symptom development. The viruses were Dioscorea alata virus (DAV), genus Potyvirus; Dioscorea alata bacilliform virus (DaBV), genus Badnavirus; and Cucumber mosaic virus (CMV), genus Cucumovirus. Only TDr 95-128, a landrace cultivar from Nigeria, developed symptoms of infection with CMV and DaBV following mechanical and vector transmission, respectively. PAS-ELISA showed that nine genotypes remained uninfected by DAV and 11 were uninfected by CMV or DaBV. Genotypes TDr 747 and TDr 1640 both showed resistance to all three viruses

Evaluation of micropropagated plantain and banana (Musa spp.) for banana streak badnavirus incidence under field and screenhouse conditions in Nigeria

Between 1991 to 1996, more than 50 Musa hybrids and 10 landraces were evaluated under field and screenhouse conditions for virus symptoms resembling those caused by banana streak badnavirus (BSV). The symptoms included chlorotic streaks, leaf deformation, stunting, cigar leaf death, distortion of the peduncle, bunch or fruits, and internal pseudostem necrosis. Immunosorbent electron microscopy (ISEM) of randomly selected plants with one or more of these symptoms confirmed the presence of BSV particles in 15 tropical Musa plantain hybrids (TMPx) and five Musa landraces. Under both field and screenhouse conditions, the incidence of symptomatic plants in the hybrids was significantly higher than in the landraces. The hybrids also generally had a higher concentration of BSV antigens, as determined by enzyme‐linked immunosorbent assay (ELISA). By contrast, most BSV‐infected landraces were symptomless and had very low or undetectable amounts of BSV antigens. There was a significant variation in incidence of symptomatic plants between genotypes, experiments and year of observation. These results are discussed in relation to the higher natural BSV incidence observed on some Musa hybrids as compared with their parental genotypes