Sustainable Strategies to Combat the Papaya Ringspot Virus

View the project final report

Commodities

• Fruits: papaya

Practices

• Pest Management: genetic resistance, integrated pest management

Viral diseases impose severe limitations on papaya production worldwide, including growing regions of southern Florida, Puerto Rico, and Hawai'i. The most significant of these is papaya ringspot virus (PRSV), which dramatically reduces marketable yield and can lead to plant stunting or death. All types of papaya are susceptible to PRSV, except where resistance has been genetically engineered. The virus cannot be directly controlled, so disease management often includes regular chemical sprays to reduce abundance of the aphid vector. The challenges of controlling pathogenic plant viruses with the associated risks to pesticide applicator, the environment, and consumers are common across most food crops. Innate genetic resistance is therefore the best defense against viral pathogens.

In the case of transgenic papaya, such resistance has been achieved through expression of the viral coat protein gene. Unfortunately, the utility of resistant varieties has been attenuated by negative public perception of “GMOs”, limited availability and diversity of resistant germplasm, and the emergence of viral strains impervious to coat protein-mediated resistance. As a result, new solutions are urgently required.

Towards this end, we have explored two potential strategies to enable papaya production that is both profitable and sustainable. First, we evaluated the use of transgenic, PRSV-resistant papaya border rows to shelter high-value plantings of susceptible varieties. Unfortunately, this technique did not effectively slow the spread of PRSV in our southern Florida field trial. Our other objective was to impart broad-spectrum virus resistance via genome editing. In the process, we developed the first CRISPR/Cas9 mediated genome editing protocol for Carica papaya, with an estimated efficiency > 80%. Papaya plants have now been successfully transformed with CRISPR/Cas9 constructs targeting eIF4E and eIF(iso)4E, genes associated with potyvirus resistance in many other plant species. Regeneration of genome-edited papaya lines is currently ongoing. After genotyping, rooting, and acclimation to the greenhouse, papaya plants will be inoculated with PRSV to assess resistance.

• Evaluate the use of PRSV-resistant border plantings to protect susceptible papaya varieties.

• Develop an efficient genome editing protocol for papaya.

• Generate virus resistant papaya accessions through consumer-friendly biotechnology.