UPRAWA / ROZMNAŻANIE / 3

Asymbiotic micropropagation of orchids from seeds (flasking)

1.
The first and almost the only crops which are popagated by tissue culture (in vitro) from seeds are orchids. This laboratory exercise may appeal to you simply because of the potential beauty of the orchids you will be propagating, but also because the techniques you will be learning (invitro propagation from seed) are very important in the commercial orchid industry and in modern orchid breeding. This exercise in in vitro seed propagation of orchids is pedagogically justified for several reasons:

2.
With this exercise you will have an opportunity to become acquainted with the rather unique sexual reproductive strategy which has evolved in the Orchidaceae family:

Orchid seeds are extremly tiny, almost dust like, and the rudimentary embryo contains essentially no stored food reserve directly available as an energy source for seed germination or seedling growth.

3.
Instead orchids have evolved a somewhat unique variation on the theme of mycorrhizal symbiosis. Orchid seed germination in nature is absolutely dependant upon the formation of an association between the tiny rudimentary embryo and an appropriate mycorrhizal fungus. The fungus digests (non living) soil organic matter, such as cellulose and converts it to simple sugars which become available to support orchid seed germination and embryo growth. Germination in association with a mycorrhizal fungus is known as symbiotic germination.

Historical note, and the basis for this laboratory exercise: In 1922 Louis Knudson, at Cornell University, demonstrated that it was possible to germinate orchid seeds in vitro in the absence of the mycorrhizal fungus as long as the nutrient medium contained a suitable soluable carbon source, which Knudson provided in the form of sucrose. This non mycorrhizal technique is known as ASYMBIOTIC germination and today is the basis for a substantial horticultural industry involved in the production of orchid hybrids and many species like thoes in the genus Paphiopedilum.