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Tomato yellow leaf curl virus (TYLCV) DNA was used as a probe to identify and analyze virus‐related DNAs in the viral capside, in infected tomato plants and in the virus vector, the whitefly. In addition to the single‐stranded viral genomic DNA, double‐stranded virus‐related DNA molecules were detected in infected plants. Not all of the virus‐related DNA forms are present simultaneously in the infected plant. The double‐stranded molecules, which are probably the replicative form of the viral genome, have been purified from an infected tomato plant. In the viruliferous whitefly, only the single‐stranded unit‐size viral genome was detected.

A flexuous filamentous virus 750 nm in length was isolated from field-grown melons (Cucurnis rnelo L.) and squirting cucumber (Ecballiurn elateriurn L.). Infection of melon seedlings of most commercial varieties resulted in a lethal wilting, but late infections gave dieback. The virus infected systemically all economically important cucurbit crops. Its coat protein consists of a single polypeptide, 34 500 D in size, encapsidating a single stranded RNA genome of 10.1 kb.Antiserum against the Italian zucchini yellow fleck virus (ZYFV) reacted specifically with the Israeli isolate in both ISEM and Western blot. The virus was aphid transmissible in a non-persistent manner. Based on host range, host reaction and serological data, it is suggested that the virus described is an Israeli variant of ZY FV.