by Tom Waters
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| 'Aladdin's Gem' (Thoolen, 2002) OGB/ABD |
Most arilbred medians are produced by crossing standard
dwarfs (SDBs) with fertile halfbreds (OGB). The results of such crosses tend to
be pleasing garden subjects, occupying about the same niche as intermediates
(IBs), but with the added interest of arilbred color patterns. Unfortunately,
arilbred medians produced this way are usually infertile, or have very limited
fertility at best. Also, being only ¼ aril (OGB-), they don’t always show
enough pronounced aril characteristics to really stand out as arilbreds.
For those of us who enjoy the smaller arilbreds, the holy
grail would be diminutive fertile arilbreds that are half aril in content. We
might imagine miniaturized versions of the taller arilbreds that have come from
breeding arils with tall bearded (TBs). One approach to realizing this dream is
through the creation of “arilpums”: hybrids between arils and the tiny dwarf
bearded species Iris pumila. This
type of cross produces true arilbred dwarfs, around 10-12 inches (25-30 cm) in
height, fertile, and half aril. Additionally, Iris pumila is expected to confer winter hardiness on its seedlings.
The potential of such breeding was first appreciated in the
mid 20th century, when iris breeders became aware of the
cytogenetics of irises, and the possibility of creating “fertile families” of
irises from wide crosses, if the parents are chosen to have the right
chromosome configurations to produce fertile offspring. Both the SDBs (from TBs
crossed with Iris pumila) and the
fertile arilbreds (from TBs crossed with arils) are examples of such fertile
families, and show how varied and successful they can be.
The most direct way to build a fertile family of arilpums is
to cross Iris pumila with tetraploid
arils. In nature, the only tetraploid arils are the Regelia species Iris hoogiana and Iris stolonifera. Indeed, the pioneering hybridizer Paul Cook (who
also introduced the first SDBs from TB x pumila
crosses) produced two hoogiana/pumila
hybrids in the 1950s: ‘Hoogpum Blue’
(Cook, 1956) and ‘Hoogpum Purple’
(Cook, 1956). Both were fertile, but Iris
hoogiana doesn’t have many characteristics that most of us think of as
epitomizing the “aril look”, and these little offspring were not very
distinguishable from MDBs, and in fact were registered as such.
The first approach to arilpums with oncocyclus ancestry came
from Peter Werckmeister, the great expositor of cytogenetic theory to
English-speaking irisarians. In the 1970s, he produced “Miltonia” (not
registered) from a lucky cross, in which the aril parent (an oncogelia from
‘Teucros’ x Iris susiana), although a
diploid, acted as a tetraploid by producing an unreduced gamete. Werckmeister
reported eventually creating a whole array of fertile arilpums from “Miltonia”.
Alas, they were not widely distributed and are now lost to us.
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| Thoolen arilpum seedling AP9007-1 |
Interest in arilpums underwent something of a revival in the
1990s, after Samuel Norris and John Holden created a line of tetraploid
oncogelias from using colchicine treatment. Crossing these with Iris pumila
produced arilpums with much more “onco look” than had been possible previously.
The first of these to be introduced was ‘Barbarella’
(Mathes, 1991), followed by ‘Aladdin’s
Gem’ (Thoolen, 2002). Both Harald Mathes and Francesca Thoolen raised a
number of different arilpum seedlings, but these were the only two registered
and introduced into commerce. Both ‘Barbarella’
and ‘Aladdin’s Gem’ produce fertile
pollen, but are unwilling pod parents. Mathes and Thoolen noted similar
difficulties with their other arilpums, and their breeding programs were
eventually abandoned.
The lack of pod fertility was an unfortunate setback,
because the simplest way to build up this family would be to cross the existing
arilpums among themselves, rather than repeating the initial aril x pumila crosses.
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| 'Topaz Talisman' (Jensen, 2015) RB/ABD |
The most recent arilpum is the lovely stolonifera/pumila hybrid ‘Topaz Talisman’ (Jensen, 2015). It has
not yet been tested extensively for pod fertility.
Why has this family not made more progress? It has been more
half a century since its potential was first understood, theoretically. I do
not believe the pod fertility issue is insurmountable, although it is a setback
and perhaps kept the family from taking off in the 1990s, when interest was
greatest. Since then, the number of hybridizers working with arilbreds has
declined, and not all are interested in such an experimental project. The
parent plants, tetraploid arils and Iris
pumila, are not easy to grow in all locations: the arils need a very dry summer,
and pumila needs a cold winter.
Another obstacle is that the initial crosses are difficult,
not many viable seeds are produced, germination is poor, and so a lot of
persistence is needed to bring arilpum seedlings to bloom. Since I began
working in this area six years ago, I have made 365 pollinations, resulting in
525 seeds, and at long last four seedlings which I hope to see bloom this year
or next.
I would love to see others get involved; the prospects for
eventual success obviously depend on a number of people working with
determination over the course of a number of years. Here is the recipe:
- Acquire tetraploid arils, such as Iris stolonifera, ‘Tadzhiki Bandit’, ‘Tadzhiki Eclipse’, ‘Werckmeister’s Beauty’, ‘Balalaika Music’, and ‘Dunshanbe’. Keep in mind that you must use tetraploid arils – crossing Iris pumila with random arils and arilbreds offers no special hope of fertility in the seedlings.
- Acquire Iris pumila, either from seed exchanges, or named cultivars such as ‘Royal Wonder’, ‘Wild Whispers’, ‘Little Drummer Boy’, ‘Hobbit’, and others.
- Make crosses between these two groups, as often as possible, and mixing and matching parents as much as possible.
- Also get any available arilpums (pretty much just ‘Aladdin’s Gem’ and ‘Topaz Talisman’ these days), to cross amongst themselves or with arilpum seedlings you produced from the aril/pumila crosses.
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| Hildebrandt arilpum seedling 11-4-2 (photo: George Hildebrandt) |
I think this a project that offers enormous potential in the
long term, and is ideal for a small, backyard hybridizer who does not have the
resources to grow thousands of seedlings and does not need to worry about
immediate commercial success. There is a whole new world waiting to be opened
up!
