Preliminary
tests showed that when pepper and melon
were preinoculated with CMV-S + SCARNA 5 at the first true leaf or early
cotyledonary stage, respectively, more than
96% of the plants became infected as determined by ELISA (data not shown) but
were visually symptomless. To determine
the best time for challenge inoculation,
plants were challenged with the severe
strains 1, 2, or 3 weeks after preinoculation
with CMV-S + S-CARNA 5 and maintained in the greenhouse. There was a
maximum decrease in disease incidence for
preinoculated pepper plants when challenged after 3 weeks, as compared to
plants challenged 1 and 2 weeks after preinoculation (Fig. 1). The satellite RNA
protection of vaccinated pepper and melon
plants against the challenge of the severe
virus strain CMV-16 in the greenhouseexperiments is shown in Figure 2B and C.
CMV-D caused pinpoint necrotic local
lesions on the inoculated leaves of the
melons and little if any systemic spread
was observed up to 3 weeks after challenge
inoculation in greenhouse experiments
(data not shown); therefore, CMV-D was
not used as a challenge strain for melon in
the field experiment.