Virus diseases of cowpea in Africa: IITA Research Guide, No. 53

Eight viruses are reported from cowpeas in Africa. Cowpea viruses are described from lowland, humid and sub-humid West Africa, as well as from mid-altitude ecological zones mainly found in eastern and southern Africa. Wherever facilities are limited and detailed characterization is not possible, a simple procedure using a combination of serology (agar-gel diffusion test), inoculation to test plants, and vector transmission studies, is proposed for the identification of the cowpea viruses reported so far from Africa. The possibilities of controlling these viruses are briefly discussed

Complex virus diseases of sweet potato

Both components of the virus complex that causes the sweet potato virus disease (SPVD) in Nigeria can individually be transmitted by their respective vectors from diseased sweet potato to healthy sweet potato and to the test plant, Ipomoea setosa. But in isolation, neither the aphid nor the whitefly-transmitted component, both latent in sweet potato, can be thus transmitted

Tissue culture in disease elimination and micropropagation

Meristem-tip culture is commonly used to eliminate viruses from plants. The fact that some viruses are more difficult to eliminate than others has led to the use of thermotherapy and chemotheraphy, along with meristem-tip culture, to increase the efficacy of disease elimination. Tissue culture material is considered to be the most suitable form to international exchange of vegetative plant material and is accepted by quarantine authorities. Micropropagation is used in both research institutions and commercial companies to produce large quantities of high quality planting materials. It is applied to vegetatively propagated crops, those crop species that are difficult to multiply, and new hybrids. It is achieved through the induction of axillary shoot formation, direct and indirect adventitious shoot formation, somatic embryogenesis, and storage organ formation. This paper describes tissue culture techniques used for both disease elimination and micropropagation and discusses the advantages and disadvantages of different technique

Strain-Typing of Potato Virus Y Isolates from Potato in Nigeria by Infectivity Tests and Elisa

In a survey of potato viruses in Nigeria, five isolates of potato virus Y (PVY) were obtained. Two of these, PVY-BL and PVY-BL2, produced symptoms in indicator plants that resembled those caused by PVYN strains, particularly with their ability to incite systemic veinal necrosis in Samsun tobacco. Two isolates, PVY-BK and PVY-KR, reacted positively in ELISA with polyclonal antibodies prepared against PVY-BL and also shared some pathogenic properties with PVYC and PVYO strain groups. They could, however, not be detected in ELISA using monoclonal antibodies specific for PVYC and PVYO strains, an indication that they may be strains that have not previously been described or are antigenic deviants of existing ones

Incidence and Distribution of Potato Viruses in Plateau State, Nigeria

Potato farms and backyard holdings in Plateau State were surveyed for potato viruses S,X,Y and leaf roll in 1990-1992. Random and biased field samples as well as leaves from sprouted seed tubers from local markets were tested for the four viruses by the enzyme-linked immunisebent assay (ELISA). The incidence of viruses in the fields in four districts was between 45 and 62%, although it reached 90.9% at Chisu in one occasion. Potato virus X (PVX) was the most prevalent while potato virus Y (PVY) and potato leaf roll virus (PLRV) were the least. Virus incidence in plants sprouting from seed tubers in the screen house was more or less comparable to field incidence. Mixed infections by viruses were common, those containing PVX being the most prevalent. PVY scarcely occurred in mixed infections with potato virus S or PLRV

Incidence and Distribution of Potato Viruses in Plateau State, Nigeria

Potato farms and backyard holdings in Plateau State were surveyed for potato viruses S,X,Y and leaf roll in 1990-1992. Random and biased field samples as well as leaves from sprouted seed tubers from local markets were tested for the four viruses by the enzyme-linked immunisebent assay (ELISA). The incidence of viruses in the fields in four districts was between 45 and 62%, although it reached 90.9% at Chisu in one occasion. Potato virus X (PVX) was the most prevalent while potato virus Y (PVY) and potato leaf roll virus (PLRV) were the least. Virus incidence in plants sprouting from seed tubers in the screen house was more or less comparable to field incidence. Mixed infections by viruses were common, those containing PVX being the most prevalent. PVY scarcely occurred in mixed infections with potato virus S or PLRV