Allozyme analysis was performed on 83 wild Phaseolus vulgaris accessions, representing a wide geographical distribution from Mesoamerica to Argentina, to determine levels of genetic diversity and geographic patterns of variability at nine polymorphic isozyme loci. The collection can be divided into two major groups, one consisting of accessions from Mexico, Central America, Colombia and Peru, and the other consisting of accessions from Peru and Argentina. One accession from northern Peru is distinct from the two major groups, and may delineate a transition zone between the two divergent groups. The level of genetic diversity within wild P. vulgaris (Ht=0.132) is comparable with those found in other Phaseolus species. There was no significant within-accession gene diversity (Hs=0.006); however, there is a moderate level of genetic diversity (Dst=0.126) between accessions. Our results are consistent with previous studies on the genetic diversity of wild P. vulgaris using phaseolin, the major seed storage protein of beans.

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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Beet necrotic yellow vein virus (BNYVV)-infected sugarbeets were obtained from many parts of Europe and also from some sites in Asia and the U.S.A. Reverse transcription (RT)-PCR products of more than I kbp were obtained for four different regions of the viral genome which may be particularly important with respect to the pathogenic properties of the virus, i.e. for the coat protein and the 42K protein-encoding regions on RNA 2 and for major parts ofRNAs 3 and 4. Restriction fragment length polymorphism (RFLP) patterns obtained with these PCR products revealed the existence of two major strain groups of BNYVV, named type A and type B. The A type was detected in Greece, the former Yugoslavia, Slovakia, parts of Austria, Italy, Spain, parts of France, Belgium, The Netherlands and England as well as in Asia (Turkey, Kazachstan, China and Japan) and the U.S.A. The B type occurs in Germany and parts of France. Mixed infections were detected at the borderline regions between areas of the A and B types. Comparisons of published and newly determined nucleotide sequences of the respective parts of the BNYVV genome indicate that the percentage of nucleotide differences between the A and the B type is approximately 3 % for the respective regions of RNAs 2 and 3 and approximately 1.5 % for RNA 4. Nucleotide sequences appear to be remarkably stable within each of the two strain groups. The majority of the nucleotide differences between the A and B types occur in the third triplet position. The amino acid changes in the coat protein area are outside the four previously determined antigenic regions that are accessible on the surface of the virus particles and are involved in the formation of continuous and presumably also discontinuous epitopes. This may explain why serological differences between the two strain groups have not been found.

SUMMARYIndirect ELISA on plates not precoated with antibodies enabled the detection of cross-reactions among a wider range of serologicaUy related viruses in the tymo-, tombus-, como-, tobamo-, potex-, carla-and potyvirus groups than was possible with the direct double-antibody-sandwich method. Used with purified virus preparations and unfractionated antisera which have to be preabsorbed with crude plant sap the method seems promising for the detection of serological relationships among plant viruses, especially when the latter can be purified only with a low yield or when antisera are in short supply and immuno-electron microscopy is not possible. The quantitative outcome of the test was influenced by the concentration of the reactants, the purity and specific adsorption characteristics of the virus and the length of the immunization period. Strains of Andean potato latent virus (APLV) were detected reliably in crude plant sap when indirect ELISA was done on plates precoated with antiviral antibodies from rabbit or guinea-pig ('first antibodies'). The" trapped virus particles were reacted with antiviral antibodies from chicken ('second antibodies') which were then detected by enzyme-labelled rabbit anti-chicken antibodies. Other combinations of 'first' and 'second' antibodies resulted in non-specific reactions in the presence of crude plant sap. The specificity of direct ELISA was not sufficiently broadened to enable the routine detection of APLV strains when antisera were used which, due to altered immunization schemes, were expected to have an especially broad cross-reactivity.