Monday, November 7, 2016

Arilbred Irises: A Little History

Tom Waters

'Brash and Bold' (Black, 2009),
William Mohr medal 2106
(arilbred median)
The story of arilbreds begins in the late 19th century, when the exotic aril iris species of the Middle East found their way into the gardens of European plant enthusiasts. Sir Michael Foster, England's foremost iris expert at the time, tried his hand at crossing the arils with the more familiar tall bearded (TB) irises. His motives were mainly exploratory; at the time, no one knew if the arils and bearded irises were compatible, or whether desirable garden plants might result from crossing them.

Although these early arilbreds were interesting plants, showing features of both parents, they were also quite sterile. Arils and TBs were just too distantly related to produce fertile offspring when crossed. One might expect hybridizers to simply give up on the idea, but many kept trying. The allure of the arils, with their huge globular blooms, often strikingly marked with velvety signals, veins, and stippling, was not something to be lightly set aside. Also, the arils themselves were difficult to grow in England and much of the US, demanding very dry conditions when dormant in summer and winter. So the great hope was that crossing arils with TBs could produce an aril-like bloom on a plant that could grow in any garden where TBs grow.

The famous iris breeder William Mohr, working in California, produced an arilbred iris that seemed close to fulfilling this dream. Named for him posthumously in 1925 by his friend and fellow iris expert Sidney Mitchell, the iris 'William Mohr' was an instant sensation. Its large blooms and wide falls, inherited from its aril parent Iris gatesii, proved irresistible in an era when most TBs had relatively small, narrow flowers.

Like the other arilbreds of similar pedigree, 'William Mohr' was essentially sterile. But it was so popular that hybridizers all over the country kept making crosses with it, ever hopeful. And occasionally 'William Mohr' would reward such persistence by producing a seed or two. We now understand that these seeds were the result of unreduced gametes, where an ovule is produced by bypassing the normal cell division. Usually it was TB pollen used in making these crosses, so the resulting seedlings were 1/4 aril. 'Mohrson' and 'Grace Mohr' were the first introduced, in 1935, launching a tradition of working "Mohr" into the name of these arilbreds. One of these, 'Elmohr' (P. A. Loomis, 1942) became the first and only arilbred to win the Dykes Medal. In this way, William Mohr became associated with the "quarterbreds" (arilbreds of 1/4 aril ancestry), even though he himself never produced any irises of this type.

Although less widely appreciated than the famous 'William Mohr', there was actually one truly fertile arilbred in cultivation at this time, 'Ib-Mac' produced by the Dutch firm of Van Tubergen and introduced in 1910. Unreduced gametes were once again involved, as its aril parent Iris iberica produced an ovule will two sets of aril chromosomes instead of the usual one. 'Ib-Mac' thus ended up as a balanced tetraploid, with two sets of aril chromosomes and two sets of bearded chromosomes, a configuration that is usually fertile.

Crossing 'William Mohr' with 'Ib-Mac' produced the fertile arilbred 'Capitola' (Frank Reinelt, 1940). Many hybridizers now began using 'Capitola' pollen on TBs, a much surer way to produce quarterbreds than hoping for the occasional seed from 'William Mohr'. These quarterbreds were also colloquially referred to as "Mohrs".

The frustration for hybridizers of this era was that although one could produce quarterbreds by crossing 'William Mohr', 'Ib-Mac', or 'Capitola' with TBs, there was no easy way to get more arils into the mix. The quarterbreds only showed moderate aril characteristics, and did not go very far in capturing the appeal of the aril species themselves.

The great breakthrough in arilbred breeding came from the work of Clarence G. White in the 1940s. Based in southern California, he was able to grow many pure arils and use them extensively in his hybridizing. His early hybrids, such as the perennially popular 'Oyez' (White, 1938), were infertile diploids, but eventually fertile arilbreds began to appear among his seedlings. The first to be introduced was 'Joppa Parrot' (White, 1948). In the decade that followed, a steady stream of fertile arilbreds in a remarkable range of colors and patterns issued from White's garden. We do not know exactly how this happened, because by this time White had given up on keeping records of his crosses, claiming it took too much time away from making the actual crosses. Most likely it was the sheer volume of his breeding program that made these breakthroughs possible. With an enormous number of seedlings, even unlikely events such as unreduced gametes are bound to happen from time to time. The fertile C. G. White arilbreds were later shown to be balanced tetraploids (like 'Ib-Mac' and 'Capitola') with two sets of aril chromosomes and two sets of TB chromosomes.

The 1950s saw the founding of the Aril Society International (ASI). Despite the name, its membership was largely concentrated in southern California, with a few in New Mexico and elsewhere. The ASI in its early years provided a much-needed framework for defining the arilbred class and encouraging the breeding of arilbreds with clear, strong aril flower characteristics. To be classified as an arilbred, an iris could have no less than 1/4 aril ancestry. Hybridizers had often crossed the early quarterbreds back to TBs, sometimes for several generations, promoting the progeny as "arilbreds", although their aril genes had in most cases dropped by the wayside, leaving plants that were for all intents and purposes just TBs. The ASI cooperated with the American Iris Society to establish the C. G. White award for best arilbred in 1961. In 1969, the William Mohr award was added for arilbreds of less than 1/2 aril ancestry, restricting the C. G. White award to those that are 1/2 or more aril. This further encouraged hybridizers to focus on arilbreds with strong aril characteristics. Both these awards attained medal status in 1993.

With the "fertile family" of C. G. White arilbreds firmly established, arilbred breeding at last came into its own. As breeders continued to work with these fertile arilbreds, they improved both in gardenability and in the form, color, and pattern of the flowers themselves. The original C. G. White hybrids typically had only a small diffuse signal patch, and veining that was indistinct and blended. Through the extended effort of dedicated arilbred hybridizers, we now have arilbreds with huge, dramatic signals, striking crisp veining, and an extraordinary range of bright clear colors.

Most fertile arilbreds today derive almost entirely from the original C. G. White introductions. A few notable additions to the family appeared subsequently: 'Welcome Reward' (Sundt, 1971), Henry Danielson's fertile regeliabreds such as 'Genetic Artist' (Danielson, 1972), and Harald Mathes's fertile arilbred medians beginning with 'Anacrusis' (Mathes, 1992). Fertile arilbred seedlings produced by Samuel Norris from his tetraploid arils crossed with TBs also appear in the pedigrees of some modern arilbreds.

The fertile "C. G. White type" arilbreds have also opened up other new areas of arilbred breeding. Crossed with TBs, they have given us quarterbreds that are much more aril-like than the old "Mohrs", and crossed with the standard dwarf bearded (SDB) irises, they have produced the charming arilbred medians, which are at least as popular as the taller quarterbreds today.

The history of arilbred breeding has progressed from an early period of difficulty and frustration, through the breakthrough of C. G. White's "fertile family" to a modern era of continual improvement and expanding diversity. What will the future bring?

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