Gal-On, A., Department of Virology, Agricultural Res. Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50-250, Israel
Antignus, Y., Department of Virology, Agricultural Res. Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50-250, Israel
Rosner, A., Department of Virology, Agricultural Res. Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50-250, Israel
Raccah, B., Department of Virology, Agricultural Res. Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50-250, Israel

A full-length cDNA clone of the RNA genome of the cucurbit potyvirus zucchini yellow mosaic virus (ZYMV) was constructed downstream from a bacteriophage T7 RNA polymerase promoter. A single extra guanosine residue not present in ZYMV RNA was added to the 5' and 3' ends. Capped (m7GpppG) ZYMV RNA transcripts were infectious in 10 of 91 Cucurbita pepo test plants; uncapped RNA transcripts were not infectious. The appearance of symptoms in plants inoculated with the infectious transcript was delayed for more than a week compared to plants inoculated with native viral RNA. The progeny virions recovered from infected plants had the same biological properties (aphid non-transmissibility and typical symptoms) as the parental virus. The progeny virions also reacted positively with ZYMV antiserum and ZYMV-specific probes by dot blot hybridization. The authenticity of the progeny virus was verified by identifying a specific molecular marker (C substituted for T in the 3' non-coding region) using nucleotide sequence analysis.