Chapter II INTRODUCTION TO PLANT TISSUE CULTURE Plant tissue culture is one of the biotechnological tool used in the mass propagation of high value crops, specially orchids. Plant tissue culture is a broad term, which means the growing or cultivation of plantlets or plant parts in an artificial culture medium under aseptic conditions. It is a generic name which includes the following: a. embryo culture/embryo rescue - This is the culture of isolated mature or immature embryoes. These technique is the one primarily used for all orchid types, and the technique was highly improved by European and American orchid hobbyist in the 1920's in the propagation of their orchids hybrids. Since orchids have thousands of seeds per capsule, it is the most effective and efficient way of propagating a endangered or threatened species. The dry pod capsule technique (using dry matured seeds) where the first technique developed, and then the revolutionary green pod technique (using immature but fertilized ovules) was developed next. (Both technique will be discussed in detail in the guidebook). The dry pod technique is used to produce virus-free seedlings from a virused parent stock. Take note that embryo culture is a sexual means of reproduction and different from cloning which is asexual. Note: the techniques below are all asexual means of propagation techniques. b. shoot tip culture - This involves the culture of the apical meristem (part of the shoot tip) attached to some leaf primordia in an artificial medium. The shoot tip tissue is much larger than the one used for meristem culture. One disadvantage of this method is that it the breeder is risking to actually kill the mother plant where the tissue was obtained. c. meristem culture - This involves the culture of the apical meristematic dome only, which is much smaller than that of the shoot tip tissue. However, the technique is similar to that of shoot tip culture, but the leaf primordia are removed. This technique is also called mericloning, and the one primarily used in mass propagation of selected hybrids and species. It is also effectively used to produce virus-free planting materials. d. tissue (or callus) culture - This involves the culture of tissue arising from explants of plant organs like meristems, leaves, flower, flower stalks or buds. When the explants are placed inside a flask with nutrient media, they are normally induced to undergo callus formation (unorganized and undifferentiated masses of cells), wherein protocorm like bodies are formed. From this tissues, will arise whole plantlets. e. organ culture - This involves the culture of isolated plant organs like leaf, flower or inflorescent and stem. The explant are usually excised, sterilized and inoculated into flasks with artificial culture media. They usually do not undergo callus induction. It is similar in almost all aspect to tissue culture, just that organ culture uses a much larger tissue -- an organ. f. anther culture - This involves the culture of orchid anther (correctly called pollinia) or immature pollen grains in an effort to obtain a haploid cell or callus line. However, orchids callus usually automatically double in chromosome number, and literally produce diploid or sometime polyploid cell lines. From these cells or callus, complete plantlets arise. The stage of pollinia development is an important aspect in the success of this propagation technique. An application of these technique is the production of orchids with recessive traits e.g. albinism. g. cell suspension culture - These involves the culture of isolated cells or very small aggregates of cells remaining dispersed in liquid medium. The cells usually comes either in organ or tissue culture technique. From these cells, new plantlets could be regenerated. This technique could
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