October 2003. Palua realised that Papaya ringspot virus is spread by aphids, but asked what is the most likely pathway between island and also countries. The SPC PestAlert No. 32 suggests that there is a slight chance that the virus is carried by seed. Can it, therefore, be spread in infected fruit?
SPC provided a comprehensive
Seed transmission. There is work from the Philippines that looks like a demonstration that seed transmission is possible at a very low rate (0.15%). If these experiments were conducted in conditions (insect proof nethouse) where aphids were excluded from the test plants, then this is indeed fairly conclusive proof.
See: Bayot RG, Villegas VN, Magdalita PM, Jovellana MD, Espino TM, Exconde SB. 1990. Seed transmissibility of papaya ringspot virus. Phillipines Journal of Crop Science 15: 107-111.
Fresh fruit. There was something recently published which MAY (if you think about the basic biology and extrapolate) be worth thinking about, if you are wondering about the potential risks associated with the importation of fresh papaya fruits. A paper in Plant Disease demonstrates that melon fruits imported into France from Costa Rica can act as virus sources in natural conditions. The cucurbit-infecting strain of PRSV (PRSV-W) was one of the viruses involved.
See: Lecoq H, Desbiez C, Wipf-Scheibel C, Girard M (2003) Potential involvement of melon fruit in the long distance dissemination of cucurbit potyviruses. Plant Disease 8: 955-959.
There is also a report by Trujillo-Pinto et al. (1989) that birds can also transmit PRSV from diseased to healthy fruits (the reference is on Ecoport: www.ecoport.org/ep.exe$EntPage – Click on ‘Get Full’).