Pepino mosaic virus (PepMV), a previously undescribed virus, was found in fields of pepino (Solanurn muricatum) in the Canete valley in coastal Peru. PepMV was transmitted by inoculation of sap to 32 species from three families out of 47 species from nine families tested. It caused a yellow mosaic in young leaves of pepino and either a mild mosaic or symptomless infection in 12 wild potato species, five potato cultivars and potato clone USDA 41956 but S. stolonifrum and potato cultivars Merpata and Revolucion reacted with severe systemic necrotic symptoms. The virus was transmitted by plant contact but not by Myzus persicae. It was best propagated and assayed in Nicotiana glutinosa. Sap from infected N. glutinosa was infective after dilution to but not after 10 min at 65 OC but not 70 "C and after 3 months at 20 "C. PepMV had filamentous particles with a normal length of 508 nm; the ends of some seemed damaged. Ultra-thin sections of infected leaves of N. glutinosa revealed many inclusions containing arrays of virus-like particles some of which were banded or whorled; small aggregates of virus-like particles were also common. The virus was purified by extracting sap from infected leaves in a solution containing 0.065 M disodium tetraborate, 0-435 M boric acid, 0.2% ascorbic acid and 0.2% sodium sulphite at pH 7.8, adding silver nitrate solution to the extract, and precipitating the virus with polyethylene glycol followed by two cycles of differential centrifugation. Particles of PepMV normally yielded two proteins with molecular weights of 26 600 and 23 200, but virus obtained from infective sap aged overnight yielded only the smaller protein suggesting that it was a product of degradation of the larger one. The virus is serologically related to two potexviruses, narcissus mosaic and cactus X and its properties are typical of the potexvirus group.

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SummaryA virus causing sunken veins on ‘Georgia Jet’ sweet potato, and yellow brittle leaves and stunting on Ipomoea setosa, was purified and a specific antiserum was prepared. Flexuous particles with a normal length of 850 nm and a diameter of 12 nm with an open helical structure typical of closteroviruses were observed. The virus particle protein has an apparent mol. wt of c. 34 kD. Double‐stranded RNA isolated from SPSVV‐infected I. setosa and subjected to electrophoresis in agarose consisted of one major band with an estimated Mr of 10.5 kbp and two minor bands with Mr of 9.0 and 5.0 kbp. Fibril‐containing vesicles in phloem cells were observed in ultrathin sections of infected leaf tissues. The virus was transmitted by the whitefly Bemisia tabaci in a semi‐persistent manner and by grafting, but not mechanically. The virus could be transmitted to various Ipomoea species, to Nicotiana clevelandii, N. benthamiana and Amaranthus palmeri. The virus did not react with an antiserum to lettuce infectious yellows virus. Based on particle morphology, serology and symptom expression, the virus appears unique and different from all other reported whitefly‐transmitted closteroviruses. We propose it be named “sweet potato sunken vein virus” (SPSVV).

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