Tetraploid Arils

Iris 'Tel Hashi'distribution of aril (oncocyclus and regelia) irises There are two commonly grown types of aril irises: the oncocyclus that range from the southern Caucasus through eastern Turkey, Syria, Jordan, Iran, Lebanon, and Israel, and the regelias from Turkestan and Afghanistan. The oncocyclus group includes the most spectacular flowers in the genus Iris, and has inspired the devotion of enthusiasts for centuries. The regelias, although less dramatic, are nonetheless interesting irises, with their elongated petals and unusual coloring. Two of the regelia species, Ii. hoogiana and stolonifera, are natural tetraploids with 44 chromosomes. The other regelias are diploids, as are all oncocycli, with 20 chromosomes. Although the regelias have chromosomes in sets of 11 and the oncocycli in sets of 10, the chromosomes pair readily and diploid or tetraploid hybrids are usually perfectly fertile.

Tetraploid arils would be expected to produce fertile seedlings when crossed with the 48-chromosome bearded irises or with I. pumila, thus bypassing the sterility barriers that arise when the diploid arils are used. There are a few tetraploid aril hybrids with some oncocyclus ancestry, of which 'Persian Pansy' is perhaps the best known example. In the 1970s and 1980s, John Holden and Sam Norris used colchicine to induce tetraploidy in oncocyclus and oncogelia hybrids.The process is a difficult one, as many seedlings either die or revert to the diploid state. Eventually, though, a number of tetraploid seedlings of mostly oncocyclus ancestry were produced, and a small handful were named and registered.

It is unlikely that anyone will take up the work with colchicine again soon, so expanding the genetic base of this family requires crossing diploids with the available tetraploids, and hoping for an unreduced gamete or a triploid seedling with enough fertility to continue the line. This is extremely important work, not only to facilitate arilbred breeding, but because the oncocycli have very narrow habitats in a region of the world threatened by war and development.

My own priority with this group is to cross them with as many different oncocyclus species and hybrids as I am able to grow, in the hope of obtaining an occasional tetraploid. Given the difficulty of the crosses involved and the expected low germination rates, this is work that will require a great deal of patience. At the same time, I am crossing the tetraploid arils with I. pumila and 48-chromosome medians to produce fertile arilbred dwarfs and medians.

I've compiled a listing of tetraploid arils that may be of use in building a collection of these irises.

 

Hall of Fame

 

Bronze Beauty Van Tubergen (Van Tubergen by Aril Society International, R. 2001) AR/RH, 20-24” (51-61cm), E. S. pale lavender, golden bronze veining around edge, lavender basal midrib flush; F. deep wine red, golden bronze around edge, beards white, hairs tipped yellow. I. hoogiana x I. stolonifera. Introduced in Holland prior to 1950; in commerce in America as ‘Hoogiana Bronze Beauty’ also known as ‘Bronze Beauty’. [44 chr.]

The Dutch firm of Van Tubergen introduced many aril hybrids over the years. 'Bronze Beauty' was one such. It combines the two tetraploid regelia species, Ii. hoogiana and stolonifera into an attractive plant with hoogiana form but interesting, blended coloration. I've included it in the Hall of Fame as a kind of placeholder for the contribution of these two species to modern tetraploid aril breeding. It was finally registered by the Aril Society International in 2001. The long name 'Bronze Beauty Van Turbergen' was used because 'Bronze Beauty' was already taken, but it is unfortunately awkard. The plant has long been known as 'Bronze Beauty' and will continue to be referred to as such in informal contexts.

Persian Pansy (Lloyd Austin by Aril Society, R. 1969). AR/RC, 12-16” (30-41 cm), M-L. Pansy purple, veined deeper; yellow throat; large black signal; beard dark yellow, tipped tan. I. nigricans x Late Amethyst. Court of Iris, 1960. [42 chr.]

An accidental tetraploid resulting from an unreduced gamete from I. nigricans, this has long been the most onco-looking of tetraploid RCs, with form and coloration much more reminiscent of I. nigricans than I. hoogiana. It is fertile both ways, and has produced several registered offspring. Even after tetraploid oncogelias were produced via colchicine treatment, 'Persian Pansy' remains a fine and important member of the tetraploid aril family.

Werckmeister's Beauty (Peter Werckmeister by Sharon McAllister, R. 1992). Sdlg. 1916–1. AR/RC, 20" (51 cm), E–M. S. lavender gray, finely veined medium violet; F. lavender gray, intensely veined and dotted medium violet and washed violet; deep violet signal; orange yellow beards. Bronze Beauty Van Tubergen x (Teucros x I. susiana). Aril Society, 1992.

This tetraploid aril was produced by crossing 'Bronze Beauty Van Tubergen' with a colchicine-induced tetraploid oncogelia seedling. 'Werckmeister's clone #2' (unregistered) has the same parentage, but is not a sibling, since the oncogelia parents of the two were not the same plant, but sibling seedlings. Although these tetraploids show their regelia ancestry in their elongated flower form, they carry important oncocyclus genes and have proven durable garden plants and valuable breeders. Werckmeister's study of the meiosis of these plants indicated that they are aneuploids, nearer to triploid than tetraploid, despite an initial chromosome count indicating tetraploidy. Nevertheless, many years of hybridizing experience has verified that they breed as fully functional tetraploid arils.

Norris T-N85G ((I. camillae x (T-N78R: (C-N73B: (((I. susiana x Andromache) x (I. susiana x I. gatesii)) x I. sari) x C-N73A: ((Bagdad Beauty x (I. susiana x Andromache)) x I. sari) x I. sari )) x ((C-N73A x (B66T x I. sari)) x T-N78R))

Samuel Norris and John Holden produced a substantial number of tetraploid oncogelia seedlings by line breeding colchicine-induced tetraploids (indicated by seedling numbers beginning with "C" in the parentage). I have rather arbitrarily selected Norris T-N85G as a representative of this group, on account of it being used recently by Lawrence Ransom to produce the new tetraploid arils 'Tadzhiki Bandit' and 'Tadzhiki Eclipse'. It appears that most of these tetraploid seedlings have been lost, although perhaps a few are still being grown by specialists.

Gallery

 

'Bronze Beauty Van Tubergen'

'Werckmeister's Beauty'

'Dunshanbe'
(Wilkes, 1977)
Iris stolonifera 'Chocolate'
'Tadzhiki Bandit'
(Ransom, 1997)
'Tadzhiki Eclipse'
(Ransom, 1997)
'Vera'
(Van Tubergen)
I. stolonifera 'Merlin's Magic'
(Jensen, 1986)
Iris stolonifera 'Network'

'Ballalaika Music'
(Mathes, 1992)

 

Plant List

The list below shows the name of each plant I currently grow, the source, and the year acquired.

I. hoogiana

Paul Christian Rare Plants

2011

I. hoogiana purpurea

Paul Christian Rare Plants

2011

I. hoogiana alba

Paul Christian Rare Plants

2016

I. stolonifera

Odyssey Bulbs

2010

I. stolonifera

Paul Christian Rare Plants

2011

I. stolonifera Brown Standard

Janis Rukšans

2014

I. stolonifera Chocolate

Janis Rukšans

2011

I. stolonifera Claudius

Paul Christian Rare Plants

2016

I. stolonifera Merlin's Magic

Janis Rukšans

2011

I. stolonifera Network

Lithuanian Rare Bulb Garden

2013

I. stolonifera Sina Dark

Janis Rukšans

2014

I. stolonifera Tiberius

Paul Christian Rare Plants

2016

I. stolonifera White Flag

Janis Rukšans

2011

Amphion

Paul Christian Rare Plants

2016

Antiope

Lithuanian Rare Bulb Garden

2013

Ballalaika Music

ASI

2011

Bronze Beauty Van Tubergen

Odyssey Bulbs

2010

Coffy River

Lithuanian Rare Bulb Garden

2013

Dunshanbe

Odyssey Bulbs

2010

Hippolyta

Paul Christian Rare Plants

2016

Tadzhiki Bandit

ASI and Iris-au-Trescols

2011

Tadzhiki Eclipse

Iris-au-Trescols

2011

Vera

Lithuanian Rare Bulb Garden

2013

Werckmeister's Beauty

Iris-au-Trescols

2011

Holden Ht-33-T

Pete McGrath

2014

Mathes T-99-2

Iris Colorado

2014

Illustration: 'Tel Hashi' (Kellie '68) a tetraploid aril hybrid (I. acutiloba x unknown).

Tom Waters

September 2010

updated October 2016

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Unless otherwise noted, all text and illustrations copyright Tom Waters and all photographs copyright Tom or Karen Waters. Please do not reproduce without permission.