Mapping Determinants Within Cucumber Mosaic Virus and Its Satellite RNA for the Induction of Necrosis in Tomato Plants. David E. Sleat. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. Lee Zhand, and Peter Palukaitis, Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. MPMI 7:189-195. Accepted 29 December 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994.

A mutant of the WL47 satellite (WL47-sat) RNA of cucumber mosaic virus (CMV) constructed in vitro, induceslethal necrosis in tomato plants when associated with either of two subgroup II strain of CMV: LS- or WL-CMV (D.E. Sleat and P. Palukaitis, Proc. Natl., Acad. Sci. USA 87:2946-2950, 1990). The phenotype of this mutant (WLM2-sat RNA) has been examined on tomato plants, after co-inoculation with a wider range of CMVstrains. Necrosis was observed when WLM2-sat RNA was associated with any of the subgroup II CMV strains tested. However, WLM2-sat RNA ameliorated the symptoms induced by subgroup I CMV strains without inducing necrosis. Inoculation with WLM2-sat RNA with pseudo-recombinants formed between subgroup I and subgroup II CMV strains showed an association of the necrosis induction phenotype with RNA 2 of the subgroup II strains. In contrast to WLM2-sat RNA, infectious transcripts of the naturally necrogenic D4-sat RNA induced lethal necrosis in tomato withal CMV strains tested. Experiments D4-sat RNAs indicated that nucleotide sequences in either of two separate regions could influence the necrosis phe-notype. Thus, the subgroup-specific necrosis-inducing phenotype may be due to subtle alterations in secondary and/or tertiary structure in the satellite RNA, as well as the presence or absence of particular nucleotide sequences.