Missouri researchers and hobbyists learn how to breed and preserve papayas

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“Pick up papayas, put them in your pocket…way over there in the papaya patch,” is how the traditional folk song about North America’s largest tropical fruit ends.

The singsong tune, “Way Down Yonder In The Paw Paw Patch,” has been around for decades, but recently researchers in Missouri shed some new light on the papaya plant.

Much of today’s research stems from the work of plant breeders 30 years ago, when papayas were crossed in hopes of creating an improved plant. In recent decades, these improvements have been analyzed over only one to two generations of breeding.

Several papaya orchards exist throughout the state, including two managed by the Southwest Research Extension and Education Center at the University of Missouri at Mount Vernon. Assistant Professor Andrew Thomas said there were about 112 papayas among the two orchards. This orchard setting allows researchers to carefully maintain the papayas, adjusting conditions as they see fit for enhanced breeding purposes.

One of the goals of the research is to make fruits tastier and more resilient so that they may one day end up on grocery store shelves alongside apples and bananas.

Papaya fruits are considered “highly perishable,” Thomas said, making them difficult to transport and ultimately distribute. Even newly bred papayas have a short shelf life. Part of the research conducted by the University of Missouri focuses on the effectiveness of edible coatings to understand better preservation techniques.

Why is there an interest in marketing papayas?

Named the state fruit of Missouri in 2019, papaya is a tropical fruit native to North America. They are often referred to as “Ozark bananas” due to their propensity to grow in the region.

“More and more people – the younger generation – are taking an interest in where their food comes from and sourcing (as) locally as possible,” Thomas said. “(Papayas are) also kind of a novelty, a specialty crop.”

This interest comes from the popularity of the farm-to-table movement, which promotes the consumption of local foods, preferably directly from the producer. In 2018, three-quarters of Americans said they actively try to include local foods in their diet, according to Gallup, a marketing research firm.

Marketing papayas to meet this demand could mean increased income and job opportunities in Missouri.

“Taking advantage of the processing potential (of papaya) would generate a lot of money and create new avenues for growers and others in the field of food processing,” said Bezalel Adainoo, a graduate student at the University. from Missouri. Papayas can be made into foods like bread, candy, and ice cream.

Currently, the main way people can buy papayas is at farmers’ markets. In fact, the average shelf life of an unrefrigerated papaya fruit is three to five days. This makes it difficult to distribute papayas to grocery stores. In addition, the fruit is fragile and bruised easily.

Researchers across the state are testing new ways to extend that shelf life for commercial sale, which begins with selective (natural) breeding.

Create “phenomenal” papayas

Thomas said a key player in the papaya farming game is Neal Peterson, who started farming papayas in 1975.

Today, Peterson operates Peterson Pawpaws, an education and information center. Its website offers information on growing, pollination, grafting (breeding) and harvesting papayas. Peterson has seven of his own papaya varieties: Allegheny, Potomac, Rappahannock, Shenandoah, Susquehanna, Tallahatchie and Wabash. The Susquehanna variety is Thomas’ favorite.

“It’s just phenomenal papaya,” Thomas said. “It’s very big, very tasteful, very productive. It’s wild papaya night and day.”

There are several factors that make an optimal papaya. University of Missouri horticulture field specialist Patrick Byers said these include more fruit per tree, bigger fruit, more flavorful fruit, even ripening on every tree and a higher pulp to seed ratio. These improved components make the fruit more marketable.

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In the wild, papaya fruits are small, about the size of an egg, Thomas said. Fruit from a tree is also less likely to ripen evenly, with good color and flavor. And in nature, the pulp to seed ratio of a papaya is around 25% pulp to seed. Once high, this ratio has been analyzed to almost switch to a pulp to seed ratio of 75%.

Harnessing the future of papaya preservation

A second-year student at Mizzou, Adainoo studies sustainable food processing, particularly with papayas.

Adainoo is testing the use of an edible polysaccharide coating on papayas to analyze how it affects shelf life. Although he is still researching and has no definitive results, he has noticed a difference.

Papayas with the polysaccharide-based edible coating that are refrigerated have a shelf life of about 15-25 days (that’s 10-20 days longer than without).

The polysaccharide-based edible coating is used on many types of produce found in grocery stores, such as apples. This coating not only protects the products, but makes them more attractive. If you’ve ever picked an apple from the wild, you might notice that it’s not naturally shiny. That shine you see at the grocery store is that edible coating, which is safe to eat.

Adainoo explained that when a product is harvested, it begins to breathe, releasing water and carbon dioxide. This version is what makes products dark in color and shriveled over time.

“What the edible coating does is it slows down the respiration process and the release of those gases and water from the fruit,” Adainoo explained. “It helps retain the properties (of the fruit) much longer than it would without the coating.”

As to why papayas are so perishable, Adainoo said it has to do with the pH level of the fruit. He said the papaya fruit generally has a pH level of around 6.2, which is close to the neutral level of seven. A specific enzyme, poly(p-phenylene oxide), which causes the reddening or fruit browning, can exist at this near-neutral pH level.

Others worry about what this future holds

Bo Brown, author of “Foraging the Ozarks: Finding, Identifying, and Preparing Edible Wild Foods in the Ozarks” and owner of First Earth Wilderness School, said he fears natural selective breeding will eventually turn into modification papaya genetics.

In the section of his book titled “Wild Food Versus Industrial Food,” Brown explores, through external research, how genetically modified foods have fewer natural health benefits than those found in nature.

“We literally eliminated (the natural health benefits) (of fruits and vegetables) to get bigger fruits, sweeter, easier to process fruits,” Brown said. “All the features we desire, each one (goes through a) process that takes away some of the ‘good stuff’. People are more interested in manipulating it for our use than the long-term effects of it- ci. in the great environment.”

Byers said he doesn’t know of anyone who is studying the potential of genetically modifying papayas, yet.

What are Papayas?

Papaya fruits hang from a tree in an orchard run by the Southwest Research Extension and Education Center in Mount Vernon.  Andrew Thomas, assistant research professor, said he has about 112 papaya trees in two orchards in the area.

Often called Missouri’s “forgotten fruit,” papayas are an edible type of cinnamon apple, ranging in size from a large shrub to a small tree. The plant usually grows on river banks or other wet areas.

Papayas are self-incompatible, which means pollen from one variety will not fertilize the ovaries and create fruit on the same tree. Rather, two different varieties are needed to get papaya fruit, Brown explained.

People who grow papayas may not see fruit if this cross pollination does not occur, which is why hand pollination of papayas is popular. This can be done with a small brush and bowl to transfer pollen from one variety to another. In the wild, flies and beetles pollinate papayas.

Bo Brown, a local foraging and survival educator, says he has teeth marks in the papaya fruit he collected in Dogwood Canyon.  While papaya trees do produce fruit, Brown said people need to act fast because the critters like to get to them first.

Cylindrical, banana-shaped fruits grow on the plant, harvested between late August and September.

Pickers can have trouble finding wild papaya fruit because critters, like squirrels, often catch them first.

Papayas can be eaten raw or cooked, but Thomas said if the fruit isn’t picked when it’s “perfectly ripe,” it often doesn’t taste good.

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Papayas are also the host plant for Zebra Swallowtail butterflies, which means that papayas are the only plant that this species of butterfly will lay its eggs on. Springfield resident Jody Vernay said that was why she originally planted 12 papaya trees in her garden. But over time, she also became attached to fruit.

A Zebra Swallowtail butterfly rests in Jody Vernay's garden.  Papayas are the butterfly's host plant, which means that papayas are the only type of plant that zebra swallowtails will lay their eggs on.

To learn more about growing and marketing papayas, the University of Missouri Center for Agroforestry offers a 14-page guide, available at extension.missouri.edu/publications/af1021.

What is the transplant?

Grafting is a horticultural technique where plant tissues are joined to continue growing together. Researchers like Peterson and Thomas describe the process of grafting a papaya tree as “easy” compared to other trees.

There are several ways to graft a papaya tree, including whip and tongue, bark encrustation, splitting and budding. On his website, Peterson details how to bark an inlay transplant.

With this technique, a dormant stick from a papaya tree is placed into an incision of an “optimal” papaya rootstock (the base and roots of an already grafted fruit tree). This union may take a few weeks, but eventually the two will begin to grow together as one.

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