In the case of both melon and pepper, a
limited number of untreated plants displayed disease symptoms during the course
of the field experiment. This study was
carried out in experimental fields with no
special treatment utilized to prevent endogenous viral, bacterial, or fungal pathogens, and therefore some plants may have
become infected with any number of insect-borne pathogens. In melon, although
preinoculation had no negative effect on
yield, preinoculated and challenged plants
showed a higher yield than untreated plants
(Table 2). To explain this increase in yield,
we suggest that vaccinated plants may not
be as susceptible as the control plants to
endogenous pathogens. Phenomena wherein satellite RNA-vaccinated plants offer
resistance to fungal (16) and viroid pathogens (13,26) have been described.