In this article we will discuss about the micropropagation of ferns for commerce and industry.
Pteridophytes, in general and ferns in particular, occupy a place of prominence amongst ornamental plants. This is basically because of their evergreen foliage and its elegance. Since time immemorial, ferns have been an object of beauty and human fascination. Ferns produce an abundance of spores consequently an infinite number of progeny- gametophytes as well as sporophytes- is possible under controlled conditions.
Despite this, ferns are being multiplied vegetatively to avoid heterogenity. Vegetative propagation of ferns remains a time-honoured approach for multiplication by florists. The basis for vegetative multiplication of a plant lies in its regenerative capacity.
An extension of this regenerative capacity to a large number of cells is possible through in vitro technique. Therefore, of late, ferns are being multiplied in vitro, employing the techniques of tissue and cell culture. Vegetative multiplication of plants through in vitro technique is described as micropropagation.
Protocols have been worked out for micropropagation of ferns; Alsophila, Microlepia, Adiantum and Nephrolepis. Another fern added to this list is Matteuccia, ostrich fern.
Besides being of interest as garden ornamental in Europe as well as America, the ostrich-fern is a commercial source of croziers which are sold, fresh as well as frozen, in USA and Canada. In the last few years this industry has expanded manyfold. There is demand for about one million kg of crosiers (fiddle-heads) per year in these parts of world.
In this account will be given details of micropropagation of N.falcata forma furcans, the fish-tail-fern, and N. exaltata cv bostoniensis, the Boston-fern, and Matteuccia struthiopteris, the ostrich-fern, because of their ornamental and commercial value.
Unfortunately, due to its commercial implications in vitro multiplication of ferns has lapsed into a secret, before becoming a science. A nutrient medium is available for commercial multiplication of ferns. It is known as Murashige-Fern Multiplication Medium (Grand Island Biological Company, New York). This medium (MFMM) is different from routinely employed MS nutrient formulation; in having an enhanced level of phosphate.
In general three stages of experimentation are involved to achieve in vitro micropropagation of plants. Stage I, is establishment of aseptic culture on hormone-free nutrient medium. Stage II, is mutiplication of shoot propagules on hormone-enriched medium. Stage III, is induction of roots on shoots, and finally there is transfer of plantlets to soil.
For fish-tail fern the explants employed were 2 cm runner tips from stock plants maintained in a growth chamber. Buds were not possible when runner internodes served as explants. The nutrient media were Murashige-shoot-multiplication-medium or Murashige- Fern-Multiplication-medium (MFMM). The overall growth appeared to be better on latter (MFMM) than the former.
Stage one lasted for about 30 days, this was characterized by production of usually 2-3 to several shoots per explant. These new shoots, when they had 2-3 leaves, were dissected from parent explants and sub-cultured on hormone-enriched medium. At stage II on kinetin medium (10-5, 5 x 10-5M) were produced maximum number of shoots (about 8).
Lower concentration of kinetin supported single shoots which eventually resulted in single plants. At this stage inclusion of NAA was of no help. Only kinetin is the major factor involved in shoot production and NAA is not essential.
However, NAA was promotory for root production; at specific level of Kinetin specific concentration of NAA must be there for shoot production. No roots were formed on medium with very high kinetin (10-4M) and NAA; regardless of its concentration. Roots were also possible even without NAA.
This protocol was also true for Boston cultivar of this fern. This fern even produced stolons in culture. On medium with high level of kinetin and high level of NAA callus-like moruloid masses were produced, they were in fact individual growth areas. On transfer to hormone-free medium these developed into individual shoots.
Vegetative propagation of Matteuccia struthiopteris, the ostrich fern, from nursery stock is very low. However, an in vitro micropropagation method evolved, indicated that it is possible to achieve the results within 10 weeks. For this, three part protocol was followed.
The explants were shoot apices, the nutrients were a defined formulation; Knudson’s salts supplemented with Nitsch’s trace elements. Kinetin at 10-6 and 10-5M brought about highest number of buds (average about 15 per explant). For rooting NAA was helpful. Plantlets bearing roots on transfer to milled peat containers covered with transparent plastic showed 100% survival, after uncovering.