Control of Papaya Ringspot Disease by Cross Protection

Abstract

Papaya ringspot disease is considered as the most destructive disease of papaya in Thailand. Papaya ringspot disease caused by papaya ringspot virus (PRV) which belongs to potyvirus group. Efforts to select naturally occurring mild strain PRV began in the late 1986 by field collection and serial dilution isolation were successful. Eight isolates of mild strain PRV were obtained from this study. Papaya seedling inoculated with these mild strains remained symptomless of showed mild mottling with no reduction in plant size and leaf-shap. The mild strains designated as PRV-C1 and PRV-F1 gave better protection than the others against challenge inoculation with a severe strain (PRV-SD) under greenhouse conditions. Protection was also observed when the pre-immunized papaya seedlings with the mild strain PRV-F1 were transplanted into farmer fields. The results revealed that the naturally collected mild strain of PRV could be used for cross protection of papaya ringspot virus.