Multiple Inoculation with Three Attenuated Viruses for the Control of Cucumber Virus Disease

Multiple inoculation of cucumber seedlings with attenuated isolates of cucumber mosaic virus (CMV), zucchini yellow mosaic virus (ZYMV), and watermelon mosaic virus 2 (WMV-2) somewhat reduced yield loss due to mixed infection by virulent strains of these viruses in field experiments under severe epidemic conditions in 1994 and 1995. In addition, this protective inoculation largely protected grafted cucumber plants from viral wilt syndrome. In greenhouse experiments, no significant differences were observed between single and multiple inoculations in the cross-protection effects of the attenuated viruses against their respective virulent strains. Triply inoculated plants developed synergistic yellow leaf mosaic symptoms and 15% fewer marketable fruits compared with healthy plants. Thus, multiple inoculation is appropriate for the summer-early autumn production, when economic losses due to the concurrent incidence of CMV, WMV-2, and ZYMV are significantly greater than the loss in yield due to the inoculation.