A benign viral satellite RNA, in combination with a mild strain of cucumber mosaic virus
(CMV-S), was used as a “vaccine” or “preinoculum” to demonstrate the feasibility of protecting
pepper (Capsicum annuumcv. California Wonder) and melon (Cucurbita melocv. Janus des
Canaries) against two severe CMV strains, CMV-D and CMV-16, in the final 2 years of a 4-year
pilot field and greenhouse experiment. In the field, healthy pepper and melon seedlings challenged with CMV-D and CMV-16 reduced yields by 33 to 60%; CMV-S caused only limited
yield reduction in pepper and had no effect on the yield of melon. Different time intervals between preinoculation of pepper and melon seedlings with CMV-S and challenge inoculation
with the severe CMV strains were tested. All plants challenged 3 weeks after vaccination
showed nearly complete protection from subsequent infection by severe strains. The yield from
preinoculated and challenged pepper plants was 80% that of untreated plants, while the yield
from preinoculated and challenged melon plants was increased slightly over the untreated control plants. The use of this technology for biological control of plant viruses is discussed.