Polyploidy in Clivia

[Tetje]

Hier ein Beitrag im wissenschaftlichen Rahmen, mit freundlicher Genehmigung durch den Autor.

Polyploidy in Clivia:

Aart van Voorst, the Netherlands


Many important varieties in floricultural crops are polyploids. They appeared mostly by chance in the progenies of crops like Narcissus, Orchid and Alstroemeria and were selected because of superior characteristics like big flowers and strong stems. When the mitosis-arresting properties of chemicals like colchicine were identified, these substances were used to double the chromosome number in many plant species.
All Clivia species are diploid, with a chromosome number 2n = 22. To double the chromosome number in Clivia seeds or young seedlings are the best starting material for colchicine treatment. Meristems in mature plants cannot be reached easily by the toxic colchicine solution.
Mature embryos from a cross between two C. miniata hybrids were excised from seeds in vitro and treated in the dark with a colchicine concentration of 0,05% for 66 hours at 25°C. After four months the resulting plantlets were hardened in the greenhouse and tested for polyploidy by Flowcytometric analysis. Tetraploid and mixoploid plants were found. Five years after the colchicine treatment the first mixoploid plant flowered and produced 2n gametes. From the first crosses with a diploid miniata as a mother triploid plants were nursed after germination/embryo culture in vitro. Selfing of the mixoploid plant gave a tetraploid plant after germination in vitro. Crosses were made between other mixoploid plants and diploid mothers to find out whether embryoculture is needed for triploid surviving or that Clivia triploids can be grown from seed. Normal seeds are formed but the mothers used did produce some reduced pollen, so the plants that will be formed from the seeds need to be checked for ploidy level.
Triploids from seed in Clivia could speed up breeding of new interesting hybrids. Combination with other Clivia species can give rise to new kinds of interspecific hybrids. Sterility is often a problem in triploids but embryoculture may be used to breed aneuploid hybrids with special characteristics from triploids with reduced fertility.
Overall polyploid breeding in Clivia will benefit most if a broad range of tetraploid material is available. A great number of diploids can be made tetraploid or crossing colchicine tetraploids with diploid hybrids that produce unreduced gametes would accelerate the breeding process. Unreduced gametes were found in one C. miniata hybrid, but if triploids can be grown from seed only hybrids that form a high percentage unreduced gametes can successfully be used to form new tetraploids. A consequence will be that the whole progeny should be checked for ploidy level just as in the search for triploids in a tetraploid-diploid combination.
Whatever will be the result of the uncertainties in the different experiments, polyploidy will certainly open up new exciting avenues in Clivia breeding.