Tetraploid Lilies

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tetraploid lilyGilding the Lily: Developments in Asiatic Hybrid Lilies
by Maureen Troesch

Gardeners have shared a centuries-long fascination for the lily. Chiefly prized for the beauty and elegance of their flowers, lilies have also been cultivated for their reputed medicinal properties, as sources of perfume and even as an edible (though not necessarily palatable) crop.

A number of lily species are native to Europe and North America, with our most familiar native lily being Saskatchewan's floral emblem, the western red lily (Lilium philadelphicum). Although lilies can be found growing wild in most temperate regions of the northern hemisphere, more than half (about 60%) of known lily species are native to eastern Asia, with Korea, Manchuria, and Japan having the largest number of native lilies. It was the introduction of these Asian species into North America and Europe in the nineteenth and early twentieth centuries which inspired the greatest interest in cultivated lilies, and the great profusion of lily hybrids and cultivars which followed. Plant breeders, both amateur and professional, continue their efforts to gild the lily, developing plants that are ever more robust, more disease resistant, and more spectacular in appearance than their forebears. At present, many of these efforts are directed towards the creation of polyploid lily cultivars.

So, just what is a polyploid lily? The word "polyploid" is a specific term which indicates that a plant has more than the normal quantity of genetic information. Almost all true lilies have 24 chromosomes on which the genetic information for the plant is located. On a typical plant, one set of 12 chromosomes will have been inherited from the female parent, and the other set of 12 chromosomes will have been inherited from the male, or pollen parent. When sexual cells from the female parent fuse with the sexual cells from the male parent, the total chromosome number is restored to 24, and a normal lily plant is formed. Such a plant, with two sets of genetic information is referred to as a diploid.

Alas, with lilies, as with humans, sexual reproduction is a complex process, fraught with hazards and attended by all manner of complications. Occasionally, something will go awry, and instead of producing a normal sex cell with 12 chromosomes, the egg cell or pollen grain will contain 24 chromosomes. Should these abnormal cells fuse to produce a viable seed, that seed will give rise to a plant that contains more than the normal 24 chromosomes. Such a plant would be referred to as a polyploid. Polyploids may arise in other ways as well. Now and again, a plant will spontaneously double its chromosome number, usually the aftermath of a flirtation with a member of another species. For example, wheat, which has six sets of chromosomes (hexaploid), is the result of a cross between a diploid and a species with four sets of chromosomes (tetraploid). Rather than creating offspring with three sets of chromosomes (triploid), as one might reasonably expect, their chromosome number doubled, producing a hexaploid plant. As if things were not complicated enough with natural alterations occurring, plant breeders are also able to interfere with normal seed development in plants, and deliberately generate polyploids.

No doubt the overwhelming question at this point is: Does anyone apart from botanists, who as everyone knows, are a very odd group of people, obsessed by all manner of peculiarities, really care about the sexual abnormalities of lily plants? The answer to this question is yes, because polyploid plants often possess a number of interesting, and potentially valuable, characteristics. Often polyploid plants are larger and more robust than their ordinary counterparts. Polyploid plants are also frequently sterile. This means that they flower, but the flowers produce no seeds. While grain farmers would be quick to agree that this is a bad thing in a wheat plant, those same people would probably acknowledge that it is an excellent quality in a banana or a grape. The tiny black specks you see in the centre of a banana never develop into seeds because the plant that produced the fruit is a sterile triploid. From the point of view of a lily grower, however, the most important aspects of polyploid plants includes the bigger flowers, thicker petals and stronger stems which are often found on polyploid plants. In windswept Saskatchewan, robust flowers held on sturdy stems are particularly valuable traits.

Numerous polyploid cultivars have been introduced in recent years. Some good ones to try include:

`Avignon': tetraploid, red-orange, up-facing;

`Bold Knight': tetraploid, red, out-facing;

`Apricot Supreme': tetraploid, apricot, down-facing;

`Parisienne': triploid, pink, up-facing;

`Tetra Connecticut King': tetraploid, yellow, up-facing;

`Hornback's Gold': triploid, yellow, down-facing;

`Eros': triploid, pink, down-facing;

`Rosepoint Lace': triploid, white with pink markings, down- facing;

`Red Velvet': triploid, deep red, out-facing;

`Jasper': triploid, pink, down-facing;

`Embarrassment': triploid, pink, down-facing;

`Pink Giant': triploid, light pink, down-facing;

`Tiger Babies': triploid, buff-to-pink, down-facing.

When purchasing lily bulbs, you should select large, firm bulbs reasonably free of injuries and blemishes. Plant the bulbs in spring or early autumn in well-prepared soil, choosing a sunny, well-drained site. Lily bulbs are typically planted at a depth that is roughly twice the depth of the bulb. Large bulbs are planted about 15-20 cm (6-8 inches) deep, and smaller bulbs are planted 10-15 cm (4-6 inches) deep. Approximately 30 cm (12 inches) should be left between bulbs. With reasonable care, and a little luck, your efforts should be rewarded with many seasons of fabulous flowers.

© 1995 Maureen Troesch