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Research Project: Characterizing and Detecting Pathogens to Ensure Safe Exchange of Plant Germplasm

Location: National Germplasm Resources Laboratory

Title: Characterization of a mild isolate of papaya ringspot virus type-P (PRSV-P) and assessment of its cross-protection potential

Author
item MEDINA-SALGUERO, ANDRES - Centro De Investigaciones Biotecnologicas Del Ecuador
item COMEJO-FRANCO, JUAN - Centro De Investigaciones Biotecnologicas Del Ecuador
item Grinstead, Sam
item Mowery, Joe
item Mollov, Dimitre
item QUITO-AVILA, DIEGO - Centro De Investigaciones Biotecnologicas Del Ecuador

Submitted to: PLoS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2021
Publication Date: 2/5/2021
Citation: Medina-Salguero, A., Comejo-Franco, J., Grinstead, S.C., Mowery, J.D., Mollov, D.S., Quito-Avila, D. 2021. Characterization of a mild isolate of papaya ringspot virus type-P (PRSV-P) and assessment of its cross-protection potential. Plant Disease. https://doi.org/10.1371/journal.pone.0241652.
DOI: https://doi.org/10.1371/journal.pone.0241652

Interpretive Summary: Papaya is a tropical fruit (family Caricaceae) used for fresh consumption, juice and jams. Fruit production in Ecuador has been declining due to diseases caused by different pathogens, including viruses. We used high throughput sequencing technology to study papaya ring spot virus (PRSV) isolates causing different degrees of symptoms and plant damage in Ecuador. We identified two distinct types, mild and severe, and evaluated their natural infectivity and interactions in co-infections. We investigated whether the mild strain can be used to confer cross protection from the severe isolate. Our findings suggest that the severe strain is more aggressive than the mild strain, and the mild strain does not offer protection against the severe strain. These results highlight the importance of rogueing plants infected naturally with the mild strain, which may be asymptomatic but still a source from which insect vectors can spread the virus. The research also reinforces the need to use laboratory diagnostic analysis in addition to visual inspection to detect asymptomatic infections early, so that long term losses caused by PRSV can be minimized.

Technical Abstract: A mild isolate of Papaya ringspot virus type-P, abbreviated as PRSV-mild, from Ecuador was sequenced and characterized. The most distinguishing symptom induced by PRSV-mild was gray powder-like leaf spots radiating from secondary veins. In greenhouse experiments, PRSV-mild did not confer durable protection against a severe isolate of the virus (PRSV-sev), obtained from the same field. Furthermore, isolate specific detection in cross-protected plants showed that PRSV-sev becomes dominant in infections, rendering PRSV-mild undetectable at 90 - 120 days post superinfection. Virus testing using isolate-specific primers detected PRSV-mild in two out of five surveyed provinces, with 10% and 48% of incidence in Santo Domingo and Los Ríos, respectively. Comparative genomics showed that PRSV-mild lacks two amino acids from the coat protein region, whereas amino acid determinants for asymptomatic phenotypes were not identified. Recombination events were not predicted in the genomes of the Ecuadorean isolates. Phylogenetic analyses placed both PRSV-mild and PRSV-sev in a clade that includes an additional PRSV isolate from Ecuador and others from South America.