Chromosomes, present in plant cells, carry the genes that convey hereditary characteristics. Each plant species has a certain number of chromosomes in each of its cells. For lilies that number is 24, 12 from the female parent and 12 from the male parent. This number is constant and lilies with this number of chromosomes are referred to as diploid. Sometimes, through an accident in nature or through human intervention, lilies appear which have more chromosomes than normal. Those with 36 chromosomes in each cell instead of 24 are referred to as triploids, those with 48 are known as tetraploids. If they have 36 or 48 chromosomes we call them polyploids. Polyploids are not new, nature has been producing them since the beginning of time. Tetraploids have been produced through the use of chemicals by man for over 50 years.
What are the benefits of a triploid or a tetraploid? Plants are often larger and stronger. Flowers are larger and brighter in color, tepals may be thicker. Root systems may also be larger and more developed. For hybridizers, polyploids are valuable because lilies which refuse to cross with other lilies when they are at the diploid level will cross at the tetraploid level.
For those gardeners interested in trying their hand at hybridizing lilies, here are a few rules to follow. You can cross a diploid with another diploid in the same division (similar parentage, flower position and shape) without regard to which of the parents will be the pod (female) parent and which the pollen (male) parent. If one lily is a triploid, then it must be the pod parent because triploid pollen is seldom fertile. The pollen parent in this cross should be a tetraploid. If both lilies you are working with are tetraploids, then either can be the pollen parent or the pod parent. If you cross two diploids, the result will be another diploid.
If you cross a triploid and a tetraploid, you may get more triploids. If you cross two tetraploids, you should get more tetraploids. If you cross a diploid and a tetraploid, you may get either triploids or tetraploids. One final rule is to use the lily with the lower chromosome count as the pod parent.
Several polyploid varieties are commonly available. Some triploid varieties include:
- Good Night
- Rosepoint Lace
- Fire Alarm
- Santa Fe
- Gran Paradiso
- Red Velvet
- Hornback's Gold
Some tetraploid varieties include:
- Bold Knight
- Apricot Supreme
The above named polyploid varieties have occurred naturally or through breeding. There are no diploid forms of any of the above listed varieties. Now to make things confusing, many diploid lilies have been converted to polyploids by the use of chemicals after they were marketed as diploids so there are both diploid and polyploid forms of the same variety in gardens. For instance 'Malta' is a diploid but there is also a polyploid 'Malta'. Ideally, it should be listed as Tetra 'Malta'. Unfortunately, this is doesn't happen 100% of the time. At this time, tetraploid forms are relatively rare and are expensive so we can let our pocketbook be the guide.
The popularity of lilies continues to grow with good reason. Lilies are wonderful perennials for the sunny garden and long lasting cut flowers for enjoyment in a vase indoors. For the more adventuresome, try your hand at breeding. Maybe your touch will help create something nature hasn't.
This article originally appeared in the June 7, 1996 issue, p. 95.