Hybridization of Orchids

When the Horticultural Society of London (now the RHS) was founded in 1809, it soon began to organize flower exhibitions and competitions with prizes and awards that in due course were nationally an internationally recognized. They played an influential role in the growth of the orchid craze which swept England and continental Europe in the latter half of the century. Awards were often  based on the strange and novel character of these flowers introduced from overseas' and before hybrids made their appearance, they were given to individual species.

When, in 1856 John Dominy introduced the first horticultural hybrid ever obtained by orchid growers, the Calanthe Dominyie, it received the highest award then available. This first hybrid plan, and those which followed, were judged both for their unusual character, which completely upset contemporary attempts at classification, and for the horticultural skill displayed in their cultivation. Their intrinsic qualities were far removed from those recognized today.

Thanks to increasingly successful research into the methods of raising orchids from seed, and following the work of Bernard and Knudsen, crosses became ever more frequent. Uniform tendencies appeared and aesthetic criteria for hybrid (or cultivated) orchids were imposed. Overall forms, mixed and contrasting colours, size of flower, surface proportions of sepals and petals, structure of lip, dimension and shape of tendrils in Phalaenopsis species...these are some of the important criteria by which orchids are nowadays judged.

Apart from purely floral standards, growers also concentrate on other aspects: the harmonious distribution of flowers on the stem, mainly with a view to display, handling and transport by specialized florists, proflific flowering, strength of stem, capable of bearing a large number of flowers without support (often a problem with Cymbidium); flowering season, etc.

Some growers and orchid lovers talk to "creating" new hybrids, but this is really a misuse of language. The term "obtaining" is surely more apt for what is, after all, only a rearrangement of genes, the results of a cross which could not have occurred in nature, given the following insuperable barriers:

• Spatial isolation: separate ecological niches for species
• Temporal isolation: species flowering at different times
• Mechanical incompatibilities: e.g. pollinia too large for dimensions of stigma
• Physiological incompatibilities: only those species not too dissimilar will lend themselves to hybridization.  If the relationships (phlogenetic affinities) are weak, fertilization cannot take place or the seed will not attain maturity.

During the 1940's Carl Withner, taking a lead from methods already used for other plants, overcame this barrier in successful experiments involving the aseptic development of immature seeds, this immaturity being compatible in vitro with normal embryonic development, even though there was no natural development of the seed within the capsule. He thus made it possible to obtain hybrids from two genera markedly removed from each other (e.g. Vanda and Phalaenopsis) and opened the way to a new era in orchid cultivation.

At present, important research on orchid genetics is taking place in many countries. The main difficulty is that there is still no way of growing or multiplying a plant cell in isolation from its membrane (protoplast).

Thanks again Jean Parisot.