Artistic research in breeding : The Bifrost Eucalyptus project

Jens Staal

Genetic signs of domestication of plants and animals date as far back as the oldest known evidence for other artistic expressions like painting, music and sculpture. Breeding is often seen as a science or a craft and is rarely considered art. The Bifrost art project aims to combine the spectacular bark and growth rate of the rainbow gum Eucalyptus deglupta with the cold hardiness of the cider gum Eucalyptus gunnii and possibly other cold-hardy species. The cold hardiness introgression should make it possible to grow amazing rainbow-colored trees in a European or North American climate. The project has been initiated and is expected to continue for decades or centuries in a distributed, participatory, manner. The project explores breeding as an art form, and through extension landscape and ecosystem manipulations that may last beyond the time when human kind has driven itself to its extinction. The project also questions commonly held beliefs about “pristine” and “natural” as being better than “artificial” and “anthropogenic”.

Seeding Eucalyptus

Seeding Eucalyptus is easy, but some things need to be taken into account. First of all, the seeds are small and do not have much energy reserves. Because of this, the seeds need to be seeded at the surface (I use regular peat-based potting soil) and kept moist. A small in-door “greenhouse” to keep high humidity while letting through sunlight is an ideal set-up. The E. deglupta seeds to not need to be stratified and start germinating rapidly (example: 2-3 weeks after seeding)

Grafting and planning for florigen-induced flowering in the same season

Published information about E. deglupta grafting indicate that toxic phenolic compounds can be a problem in grafting to other Eucalyptus species [46], and a technique called bud grafting is recommended. This technique is also ideal for our purposes, since we will use vey young seedlings for grafing. I use parafilm to close off grafts. Since the seedlings still were very small in June with very thin branches to graft, I have also experimented with honey as a "glue" during grafting (with two theoretical advantages - high sugar (79%) which might emulate sweet sap from a wound and trace amounts of plant hormones in the honey that might promote wound healing and grafting).

A general timeline (this will be highly dependent on where you live and will have to be established by trial-and-error):

January : Seed E. deglupta (and later hybrid generations)

April-June : bud grafting (3-4 month old seedlings, lowest outside temperatures above 10 ^oC)

I will also try a few in early March after the nights are guaranteed frost-free.

June-August : E. gunnii host plants flower (1-5 months after grafting; likely that some months are needed for the florigen signal to work on the grafts)

Autum/Winter : harvest seeds before E. deglupta grafts die off from frost

backup strategy if grafts do not grow much the first season: wrap grafts to insulate against frost during winter.

Since this is a long-running project where experiences may change strategies over time, I also recommend to consult the continous updates.

Cross-pollination of Eucalyptus

A traditional manner to ensure cross-pollination is to eliminate the anthers (emasculation) and then apply pollen. If the size of the flowers (the style length) is very different or if there are prezygotic hybridization barriers, the style can also be cut to ensure successful invasion by the pollen. After pollination, the flower is sealed off using a bag to avoid other pollination events and infections (since it is outside, plastic is recommended).

An interesting alternative to emasculation is Artificially induced protogyny (AIP), which has been shown to be very efficient.

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