THE IN VITRO TECHNIQUES: THEIR CONTRIBUTION TO BREEDING AND MULTIPLICATION OF ORNAMENTALS

1. Micropopagation

   1.1. Importance for ornamental horticulture

For different reasons micropopagation is important for ornamental horticulture.

A large number of ornamental species are out crossing, vegetatively propagated species.
The consequence is a high level of heterozygosity and frequently sterility and incompatibility as well, thus limiting the number of selfings that can be made.

Moreover, many ornamentals, if not most, originated as sports (e.g. 55% of the actual assortment of Rhododendron simsii are flower color mutants) or induced mutations.
Therefore, many have a chimaeral structure, and then only vegetative propagation can be envisaged.

rapid introduction of new valuable plants to the market is very important in the ornamental horticulture industry, and the lifetime of most varieties or cultivars is rather short, due to fashion.

For all these reasons the required breeding work, preceeding the development of a functional generative propagation system, is most often too time consuming or not possible.
Vegetative propagation remains the method of choice, amongst which micropropagation is a very important tool in the production (commercialization) of many ornamentals.

Probably orchids were the first horticultural plants to be propagated by tissue culture, and nowadays most orchids originated in a test tube.
Either they were sown in vitro or they were cloned.

After orchids, foliage plants, is the second most important group that benefits from tissue culture in general.
Originally tissue cultured plants were used directly for production, this changed with time and nowadays a lot of tissue cultured material is used as minimotherplants from which minicuttings are harvested (Debergh and Maene, 1981). The most representative families and genera to which micropropagation techniques are applied are : Ficus, Maranthaceae, Araceae, Cordyline, ferns.

In recent years there hasm been considerable interest in the development of tissue culture techniques for the rapid propagation of healthy stocks of bulbs and corms.
Micropropagation procedures are available for many species, but the only bulbous species fro which large scale micropropagation programs are functional are lilies.
For the very important genera of tulips no adequate micropropagation system is available (Cyclamen).

For some flowering pot plants the impact of micropropagation is considerable (Anthurium, Saintpaulia, Spathiphyllum). For others a performant technology is still not available (Cyclamen).

With carnation and chrysanthemum tissue culture is a necessary step in the production of virus indexed material, that will serve as a nuclear stock for the delivery of high quality cuttings.
Most planting material of gerbera is micropropagated.
The impact is less considerable in rose production, results are not