Efforts Underway to Develop Ringspot-Resistant Papaya Hybrid

***Updated 9:43 a.m. Friday, Oct. 11, with the grant amount.***

While the debate rages on about the pros and cons of genetically modified crops, a Hawai`i research facility is working on developing a ringspot virus-resistant papaya – the “old-fashioned” way.

The Oahu-based Hawaii Agriculture Research Center has received a federal grant to assist in cross-breeding a hybrid that would be resistant to the disease that ravaged the Big Island papaya industry in the 1990s.

Center Executive Director Stephanie Whalen said the effort involves what she describes as a distant cousin of the papaya that is native to South America.

The mountain papaya.

The plant, Vasconcellea pubescens, is also known as the mountain papaya. HARC is working with an Australian researcher using a variety of the fruit that has shown resistance to the virus.

“We’re trying to move that resistance to papaya,” Whalen said.

But the fruit of V. pubescens is a far cry from Carica papaya, the species that papaya lovers love. While it looks similar to a Hawaiian papaya and can be eaten raw, it is usually cooked as a vegetable.

The popular Sunrise variety of papaya. UH photo.

In fact, V. pubescens is so genetically diverse from C. papaya that when the two are crossed the result tends to be sterile.

One method researchers are trying is to cross V. pubescens with Vasconcellea parviflora, another distant cousin of the papaya. The latter is susceptible to the ringspot virus but the mix is capable of making fertile seeds.

Researchers hope to find an offspring of that match that is fertile yet carries the virus-resistance gene. If that happens, then they will cross that with non-genetically-modified Hawaii papayas. If those produce offspring they will be repeatedly “backcrossed” with non-GMO Hawaii papayas, all the while testing the plants for resistance to the disease.

The trick is retaining the virus-resistance while achieving a fruit with the quality that is acceptable to consumers, Whalen said.

She said even if there is success, it can take decades to achieve.

Another research project in the Philippines, which has also been hard-hit by the ringspot virus, is reporting some success crossing papaya with another Vasconcellea species – after 50 years of trying.

“Traditional breeding takes a long time,” Whalen said, “and it’s not always successful.”

Whalen cited previous efforts by the HARC when it was known as the Hawaiian Sugar Planters Association.

She said the organization’s research on sugar cane varieties at times involved the planting of two million cane seedlings a year. Out of those sometimes only one or two had the qualities desired.

Also, despite the recent funding from the US Department of Agriculture Specialty Crop Block Grants, money for this research is hard to come by.

Whalen said the current grant is $20,000 a year for two years — nominal for this type of research.

“That doesn’t pay for one full-time technician, let alone the professional who is directing the work,” she said.

“If people are adamant about non-GMO papayas, this is the project to send money to,” she said.

Her organization can be contacted at http://www.harc-hspa.com/, and funds can be used solely for this research if the donor so desires.

HARC also received funding from the latest grants to help develop blue and purple pest-tolerant anthuriums, and also to refine methods of propagating cacao.

Other recipients of the Hawai`i grants totaling $347,000 include the University of Hawaii to work on methods to fertilize pineapples to optimize shipping, the Hawaii Homegrown Food Network for a public education campaign to increase consumption of breadfruit, and the Kohala Center to improve Hawai`i tea production.

The Hawai`i funding was part of $52 million in USDA grants issued this year to support America’s specialty crop producers.