A procedure based on the polymerase chain reaction (PCR) has been developed to classify cucumber mosaic cucumovirus (CMV) isolates accurately into two subgroups. Two CMV-specific primers that flank the CMV capsid protein gene were used to amplify a DNA fragment of approximately 870 bp. Restriction enzyme analysis of this fragment produces distinct restriction patterns that assign the CMV isolate into one of two subgroups. These two restriction groups correlate with the previously established CMV subgroupings; this PCR-based method may provide a simple alternative to the serological assays used for typing CMV isolates.

Only a few plants in a crop are generally thought to become infected by abiotic soil transmission. In glasshouse experiments we have induced almost total infection in tomatoes growing in soil with infective debris, but levels of infection are dependent upon certain conditions. We found that as the inoculum concentration decreased (i) a greater percentage of the infections were either latent (symptomless) or restricted to roots and (ii) infection levels decreased. Thus, apparent infection (based on symptoms) of 0. 10% was in reality 0 60–70% based on enzyme‐linked immunosorbent assay and immunoelectron microscopy testing of roots and leaves. This occurred whether seedlings or seed were planted into infected mix. Under conditions in which minimal root damage was caused (planting seed) or roots were mechanically inoculated only once, almost all systemically infected plants were symptomless.

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A carlavirus was found to be widespread in commercial passionfruit (Passiflora edulis) plantings in New South Wales and Queensland. The particles observed were flexuous rods with mean dimensions of 651 × 12 nm. The particles often occurred in cells as aggregates but were never associated with pinwheel inclusion bodies, as is typical with passionfruit woodiness potyvirus. The particles showed a strong affinity (by immunoelectron microscopy) for antiserum prepared against Passiflora latent carlavirus (PLV) from Germany but increasingly less affinity for antisera against potato viruses S and M and PLV from the United States. Survey results indicated that PLV has been present in Australian passionfruit for more than 10 years and is widespread in most commercial cultivars in New South Wales and Queensland. The virus was twice found in wild Passiflora suberosa, once in wild P. subpeltata, and once in a feral seedling of P. edulis near an infected planting of P. edulis.

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