Updated: Sep 16
Papaya (Carica papaya)
GE contamination of papaya is classified as either air contamination or seed contamination. Papaya flesh always has the same genetic make-up as the seed of the tree that it came from. Trees grown from GE seeds will have GE leaves and fruit flesh, and at least 75% GE seeds. Planting a GE seed unwittingly in a non-GE operation is an example of seed contamination.
Air contamination refers to GE contamination of developing seeds as a result of inadvertent cross-pollination of a non-GE fruit by GE pollen. A papaya tree planted from an organic, or non-GE, papaya seed will always bare GE-free flesh but can still yield contaminated seed. The potential for cross-pollination exists each growing season.
Seed contamination avoidance can be mitigated from sourcing clean seed. Planting of GE papayas legally requires signing a technology agreement. However, GE papaya seed has been sold and traded without these legal parameters. The initial contamination is complicated in that most producers seed-save for future generations from what may be an already contaminated gene pool.
Air contamination avoidance is dependent on papaya biology. Depending on whether the plant is dioecious or gynodioecious, they have different modes of pollination and therefore have specific risks. Cultivars have variances in pollen viability as well.
Outcrossing is likely if female plants are present in fields adjacent to other papaya fields. Studies have shown that hermaphroditic plants, if separated by a distance of 1/4 mile or more, have less potential for outcrossing.
Alternatively, with gynodioecious (hermaphroditic) plants, seed purity can be maintained by bagging unopened hermaphrodite flowers that typically self-pollinate prior to opening. Bags can be left on the blossoms until the petals fall off. This practice prevents receptivity to foreign pollen, GE or otherwise.
Hawai‘i Seed’s protocol suggests that growers first test their tree to ensure it is not GE. To do so, growers should collect the newest leaves of the papaya plant and subject them to GUS testing. Then they should bag the flower, and mark the developing fruit so it is clear later on for seed collection.
Female plants in general are much more susceptible to cross-pollination, as they produce no pollen of their own. A study of GE papaya contamination in Hawai‘i concluded that 70% of traditional papaya plants within 85 ft. of a GE crop were contaminated by GE pollen. Some experts suggest therefore removing female plants from organic production.
Decrease your crop’s risk of GE contamination, and read the full papaya chapter in Protecting Organic Seed Integrity: The Organic Farmer’s Handbook to GE Avoidance and Testing. The handbook is available as a free download.
Keeping Papaya GE-free…
Trees planted prior to 1997 will be GE-free. Otherwise GUS test papaya trees and rogue out any that test positive as GE.
Remove male trees and consider removing female papaya trees, which are much more susceptible to contamination. Instead grow hermaphroditic cultivars.
Do not trust any seed sources in Hawaii as GE-free. Instead save your own clean seed.Save
clean seed to plant by bagging a hermaphrodite plant on a known non-GE tree just prior to flower.
Following pollination, remove the bag and flag the developing fruit for later identification.
Harvest when the fruit is ripe; either plant seeds or dry and store them.