Originally published in Hawaii Homegrown Food Network Newsletter on April 21, 2014.

A large percentage of open pollinated papayas contain genetically modified DNA.A large percentage of open pollinated papayas contain genetically modified DNA.

Do you know if your papaya trees are GMO? I thought I did. I thought that since I raised trees from organic papaya seeds from a seed exchange or health food store, they were pretty certainly non-GMO. But I wasn’t positive, so last February I attended a “Seedy Saturday” workshop that included free testing of papaya trees. I learned about papaya genetics, cross-pollination, and how to ensure you grow non-GMO. And I learned that at least 6 of our roughly 50 trees were GMO.

However you feel about eating GMO papaya, organic growers must avoid planting GMO seedlings or seeds if they want to produce fruits that can be marketed as organic. That may not be as simple as it sounds.

 The purpose of this article is to reduce the unwanted spread of GMO papaya by sharing information about:

  • how to test papaya trees to determine if they are GMO;
  • how to greatly decrease your chance of having trees that pick up GMO pollen; and
  • how to ensure you have a source of non-GMO papaya seed.

The recent “Papaya Testing, Tasting and Talk Story” workshop in Pahoa was organized by Lyn Howe of the Hawaii Public Seed Initiative (see – http://kohalacenter.org/publicseedinitiative/about.html) and hosted by Councilman Greggor Illigan. The main speaker was Dr. Richard Manshardt, Professor of Horticulture, Tropical Fruit Crops-Genetics and Breeding at the University of Hawaii, Manoa, one of the team of researchers that genetically engineered the ringspot-virus resistant papaya, aka the GMO papaya.

We were invited to bring in leaf samples of our papaya trees for testing. I brought in 16 samples (2 from neighbors), and within a few days received the news that 2 of our trees were GMO. I then followed up with testing 10 more trees at the Hilo Extension office and found that 4 of those were also GMO. How was it possible that seeds I planted from organic, non-GMO papayas grew into GMO trees?

Here’s how: If a non-GMO flower is pollinated by a GMO tree, seeds inside the fruit will be GMO. The fruit itself will still be non-GMO, but planting those cross-pollinated seeds will result in GMO trees. There are ways to intervene in this process and make sure your papaya fruits aren’t cross-pollinated. But you have to understand the sex life of the papaya.

Papaya Sex Primer

Papaya plants come in three sexes: male; female; and hermaphrodite, which has both male and female parts on the same flower.

If your goal is to ensure your trees don’t pick up genetically engineered pollen, you need to be able to tell the sex of your trees. Papaya seedlings all look the same, so (unless you are able to do DNA fingerprinting) you have to wait for the tree to be old enough to flower, and then you can tell the sex by looking at the flowers.

 MG 4150Male papayas produce many flowers on long stalks.

The male papaya tree has no fruit, just a big cluster of flowers on long stalks (see photo).

The buds are thin and shaped like a stretched-out spoon. Occasionally – just to be confusing – a male tree can produce a hermaphrodite flower and fruit at the end of the long stalk. This seems to happen during unusual weather conditions.

Female papaya trees have fruits, but if not pollinated, they will have fruits with no seeds. The flower is rounder shaped (see photo), puffed out by the fat ovary inside. The flower has an ovary with branching lemon-yellow stigma (where the pollen from a male or hermaphrodite lands), but no bright orange male anthers. The fruits can have many shapes, depending on variety, but are always somewhat rounded, like a pear or a globe.

Hermaphrodite papaya trees have fruits with seeds. The flowers are thinner than females, with a tubular shape. Hermaphrodite papaya flowers contain both male and female parts within each flower, very close together. This arrangement nearly always ensures that the flowers will self-pollinate. The male part (stamen) has orange pollen-containing anthers on the ends of short white filaments. The pollen can drip right down onto the female part of the flower (pistil). Thus, all hermaphrodites bear fruit. The fruit is elongated, somewhat football-shaped, compared to the rounder fruit the female trees produce.

FemalepapayaflowerFemale papaya flower. Note the long petals and fat ovary with branching yellow stigma on top. Credit: Richard Manshardt 2014.

HermaphroditepapayaflowerHermaphrodite papaya flower. Note the orange male anthers, and cylindrical ovary with no branching on top. Credit: Richard Manshardt 2014.

Farmers will plant three papaya seedlings where they want one tree. They wait for them to reach flowering age, and cut down any males, females, or extra hermaphrodites, leaving one hermaphrodite per planting spot. This usually works because due to being a dominant trait, hermaphrodites are the most common papaya sex, followed by females, with males being the rarest.

Increase Your Chance of Having Non-GMO Seeds

Here’s the major tip: only let hermaphrodites grow. If you let males grow, you don’t get fruit. (Also, if it’s a GMO male, you could be spreading GMO pollen throughout the community.) If you let females grow, they are open to picking up pollen wherever they can get it, and this could be wind- or insect-borne pollen from a GMO papaya. Manshardt conducted a pollen-drift study (Manshardt et al., 2007) in which GMO embryos were found in seeds of non-GMO ‘Sunrise’ papaya trees growing within 100 feet of a GMO ‘Rainbow’ field. Most (70%) of the female trees were affected but a few hermaphrodites were, too (13%). A study by Hawaii SEED (Bondera and Query, 2006) found extensive contamination of non-GMO papaya seeds by GMO pollen.

So although just growing self-pollinating hermaphrodites will greatly reduce the risk of cross-contamination, it is not assured, especially if there are GMO papayas growing nearby. To be really sure, you have to physically keep stray pollen from reaching your papayas.

How to Grow Your Own Non-GMO Papaya Seed

Dr Russell Nagata, CTAHR’s Hawaii County Administrator at the Komohana Research & Extension Center in Hilo, and also present at the Pahoa workshop, described how to ensure that papaya seed you are growing yourself will stay non-GMO.

Start with a hermaphrodite papaya tree that you are sure is not GMO, possibly one you have had tested, and that is a good strong tree bearing papayas you find delicious. When a new flower bud is not yet open, and while it remains on the tree, enclose it in a special glassine envelope. These are the kind of envelopes stamp collectors use. You can purchase them on-line or contact Dr Nagata at Extension and he can provide you with a few per person. Staple the envelope closed to prevent pollen from other trees getting in, and mark with a tag the spot where the bud attaches to the tree. As the flower opens, it will self-pollinate, and a fruit will grow. Eventually the bag will tear and fall off as the fruit grows – this is why marking the spot on the stem is important! Once this fruit is ripe, save the seeds as a source of your own non-GMO papayas.

Nagata also encourages people who only want to grow non-GMO papaya to purchase non-GMO papaya seeds sold by the University. You can order organically grown, non-GMO Sunrise and Waimanalo Low-Bearing papayas through the Extension Service either on-line, here,http://www.ctahr.hawaii.edu/seed/ or by visiting their office at the Komohana Extension Office, 875 Komohana Street, Hilo. Hawai’i SEED tested the University’s non-GMO papaya seeds in 2006 and found less than 0.1% GMO contamination of the Solo Waimanalo seeds (Bondera and Query, 2006), but the University states on its 2014 updated website “We had our papaya seeds tested by an independent Genetic Test Lab on the mainland and we’re happy to report that we are GMO free.”

How Do You Know It’s GMO?

For your existing trees, you have to test them to know they aren’t GMO. There are no visual outward positive clues. On our trees, the presence of disease was not a clue – none of our trees have ringspot virus. The size and shape of the fruit was not a clue on our trees, either. And while all the GMO trees we had were female, there can be GMO hermaphrodites, too. The only way to know you have a GMO tree is to get it tested.

In order to test for GMO papayas, the team that developed ‘Rainbow’ attached a “reporter” gene to the genetically engineered papaya sequence. This is the beta-glucuronidase (GUS) gene, from a type of E. coli bacterium. When a section of GMO papaya is placed in a special reagent, the GUS gene makes it turn blue. The GUS test is what the Extension Service uses to test samples for being GMO.

As Dr Manshardt demonstrated to us at the workshop, it is possible to do the GUS test at home, with the appropriate chemicals and equipment. At the Extension lab they use a microscope to be sure of results, but you can also see the change to blue with the naked eye. For someone with many trees it could be worth the effort.

How To Get Your Trees Tested

The CTAHR Komohana Research & Extension Center in Hilo tests papaya trees for being GMO at a cost of $3.00 per sample. Take a quarter-sized piece of a very young papaya leaf, at the top of the tree where the newest growth is, still in the pale green, translucent stage, and put it in a zip-lock baggie. (The light green color of the new leaves allows the lab technician to see clearly the change to blue.) Label each sample and corresponding tree so you can identify which tree the sample came from once you receive your test results. The lab will report your results with whatever label you designate the sample (for example, “Lower Orchard, Row B #3).  They do the GUS bioassay and if it turns blue, it’s GMO. They’ll send you a letter in a week or sooner, or may also email you more quickly with the results.

The Extension Service in Hilo is open 7:45 am – 4:30 pm Monday – Friday and accepts only exact cash or a check. The address is 875 Komohana Street, Hilo 96720. Phone (808) 981-5199.

If you follow these steps it will greatly reduce the chances of unwittingly spreading GMO seeds. It may also save you from having to cut down papaya trees and destroy seedlings, as we just had to do.


Bondera, M. and M. Query. 2006. Hawaiian papaya: GMO contaminated. Hawaii SEED.

Manshardt, R., C. Mello, S. Lum and L. Ta. 2007. Tracking papaya pollen movement with the GUS transgene marker. Acta Horticulturae 740: 183-187.

 One of our Exotica papayas, all hermaphroditesWith one of our Exotica papayas, all hermaphrodites.