tet

A tet is a tetraploid plant, one that carries four complete sets of chromosomes instead of the normal two (diploid). In ornamental breeding, especially with iris and daylily, tetploidy is induced deliberately to produce larger flowers, thicker petals, more robust growth, and increased pollen viability. The term is shorthand used by breeders and serious hobbyists when discussing cultivar lines.

Tetraploidy occurs naturally in some plant species but is usually created by treating seedlings with colchicine, an alkaloid from Colchicum autumnale, which disrupts spindle formation during cell division and prevents chromosome segregation. The resulting cells then double their chromosome number. Tissue culture and polyploidy-inducing chemicals like oryzalin are also used in modern breeding programs. The process is unpredictable: only a fraction of treated plants become stable tetraploids, and others may be chimeric, with tetraploid tissue in some organs but not others.

In daylilies, tetploid cultivars typically produce flowers 10 to 20 percent larger than their diploid equivalents, with noticeably heavier substance and longer bloom duration. Iris tets show similar vigor and flower size gains. The thicker cell walls confer better disease resistance and tolerance to environmental stress. However, tetploid lines often produce less pollen than diploids, and when crossed with diploid parents, they yield triploid offspring that are usually sterile.

Registration and catalog nomenclature in iris and daylily societies now distinguishes tets from standard cultivars. Some breeders consider tetploid conversion a separate achievement from the original diploid cultivar, warranting a new registered name. Others view a tet as a variant of its diploid source, sometimes noted with "Tet" appended to the cultivar name or mentioned in the description. The distinction matters for breeding strategy, since tetraploid x tetraploid crosses remain tetraploid and maintain fertility, while mixing ploidy levels complicates pedigrees and fertility outcomes.

Costs of producing and stabilizing tetraploid lines are higher than standard diploid breeding, so tet cultivars typically command premium prices at retail. The labor-intensive screening process to identify stable, uniform tetraploid plants from mutagenic treatments, combined with smaller initial seed or division quantities, drives production economics. Despite this, demand remains strong among serious gardeners and show competitors who value the visual impact of larger, heavier-textured flowers.