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Differential Protection Against Papaya Ringspot Virus Isolates in Coat Protein Gene Transgenic Papaya and Classically Cross-Protected Papaya. P. F. Tennant, Department of Plant Pathology, Cornell University, Geneva, NY 14456; C. Gonsalves(2), K. -S. Ling(3), M. Fitch(4), R. Manshardt(5), J. L. Slightom(6), and D. Gonsalves(7). (2)(7)Department of Plant Pathology, Cornell University, Geneva, NY 14456; (4)U.S. Department of Agriculture, ARS P.O. Box 1057, Aeia, HI 96701; (5)Department of Horticulture, University of Hawaii, Honolulu, HI 96822; (6)Molecular Biology Research Unit 7242, The Upjohn Company, Kalamazoo, MI 49001. Phytopathology 84:1359-1366. Accepted for publication 11 August 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-1359.

Transgenic papaya expressing the coat protein gene of the mild papaya ringspot virus strain from Hawaii (PRV HA 5-1) showed high levels of resistance against the severe PRV HA isolate from Hawaii. Inoculation with high concentrations of the virus, multiple mechanical inoculations, or graft inoculations failed to break the resistance of transgenic papaya. Virus recovery assays from these inoculated plants suggested that virus replication and movement were impaired. Transgenic papaya also showed high levels of resistance against severe PRV isolates recently collected from Hawaii. Similarly, PRV HA 5-1 cross-protected papaya offered high levels of protection against two of the three isolates from Hawaii. However, neither transgenic nor mild strain-infected papaya showed good levels of protection against PRV isolates from 11 other geographical regions that were serologically related to PRV HA 5-1. A range of reactions was observed: complete resistance; delay in symptom development and symptom attenuation with PRV isolates from the Bahamas, Florida, and Mexico; and, a shorter delay in symptom development but no symptom attenuation with isolates from Brazil or Thailand.