SUMMARYTwo isolates of groundnut rosette virus from East Africa (GRVE1 and GRVE2) and from West Africa (GRVW1 and GRVW2) were transmitted by Aphis craccivora obtained from West Africa. A third isolate from West Africa (GRVW3) was not transmitted by A. craccivora from three widely separated sources. GRVW1, GRVW2 and GRVW3 caused leaf‐symptoms in groundnut of a mosaic pattern in light and dark green. GRVE1 and GRVE2 caused chlorosis or chlorosis and leaf distortion as well as mosaic symptoms. Groundnut plants with GRVW1 could not be infected by means of aphids with GRVE1, and GRVE1 gave similar protection against GRVW1, which suggests that they are strains of the same virus.All isolates were transmissible manually from groundnut to groundnut (Arachis hypogea), Trifolium incarnatum and T. repens, and caused systemic infection. Inoculated Nicotiana clevelandii and N. rustica developed symptoms but virus could not be recovered from them. Chenopodium amaranticolor, C. hybridum and C. quinoa showed local lesions on inoculated leaves. Virus could be acquired by aphids from groundnut or Trifolium repens infected by means of aphids, but not from those infected by manual inoculation. Virus could not be recovered from T. incarnatum manually or by aphids, but was transmitted by cleft‐grafting from clover to groundnut.Saps extracted in borax buffer plus zinc sulphate at pH 9 from plants infected with GRVW1 and GRVE1 remained infective at 18° C. for 1 week, and at — 20° C. for up to 4 weeks. Virus could be recovered from frozen leaves. Buffered saps lost infectivity when heated above 50° C. for 10 min.; most were still infective when diluted 1/10 and some at 1/100.Electron micrographs of partially purified preparations contained spherical particles 25–28 mμ in diameter. There were usually only about five per microscope field and they resembled those of some other viruses.

S U M M A R YFour strains of groundnut rosette virus were transmitted by a race of Aphis craccivora (Koch) from groundnut in Nigeria. Two of these strains, both from East Africa, were transmitted only by A. craccivora from Kenya. A fifth isolate, from Nigeria, was not transmissible by either race. The two races of aphids have been shown elsewhere to be distinct biotypes.

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