Growing Orchids using Tissue Culture Technique

Orchids are among the popular cutflowers in the world. It has become the object of attention of many cutflower growers as it captures an element of beauty through its complexities and elegantly formed sepals. Different species of orchids are used widely in flower arrangements, corsage making, and as collection specimens for the hobbyists. One orchid genus, Vanilla, is commercially important as it is used as the source of the vanilla food flavoring. Through the years, with the development of new orchid species, the world-wide demand for orchids has rocketed giving the cutflower a high market value.

As a high-value crop, orchids are seen as good source of profit in the world-wide market. In the country, during the 1970’s, several commercial nurseries were established to meet to growing demand of the domestic and international market. Key production area for orchids expanded in Laguna, Batangas, Cebu, Negros Occidnetal, Davao city, and South Cotabato.

Eventually, many important hybrids of orchids from different genera such as Vanda, Renanthera, Phalaenopsis, Vandopsis, Paphiopedilum, and Aerides were propagated through different means, including tissue culture.

Tissue and embryo culture technology

Tissue culture is the technique used in culturing plant parts that result in mass production of desirable varieties. High-value crops such as banana, garlic, and macapuno are being mass-propagated through this technique. Aside from producing a large number of planting materials in a short period of time, tissue culture is the technique utilized in producing virus-free planting material, hence, ensures the growth with minimal losses from incidence of virus-caused disease. The technique is also used in the propagation of valuable plants that do not breed true-to-type by seed propagation. This means that whatever good traits the mother plant has will also be manifested in its clones.

In essence, the technique involves the propagation of plant parts with actively dividing cells in an artificial environment where they can continuously divide and form cell clusters identical with the mother plant. Active buds, roots, stems, shoot tip, leaf/flower/fruit part, embryo and meristem are some of the plant parts (also called explants) used in micropropagation. These explants are detached from a mother plant.

Depending on what type of explants used, the technique of tissue culture can be further classified as plant culture, embryo culture, organ culture, callus culture, protoplast culture, or meristem culture.

Orchids possess minute seeds devoid of endosperm to nourish the embryo. This endosperm nourishes the embryo in the form of starch which keeps the seeds alive. With the endosperm lacking in the seeds of orchids, the embryo must be cultured in an artificial medium containing the necessary nutrients it requires for growth and development.

An underlying principle in all tissue culture techniques applies the same for all, and that is performing the technique under sterile or aseptic condition. Under aseptic conditions, microbial contamination of the culture that could cause infection is minimized. This is the first step in achieving a successful embryo culture in orchids.

The Process

The process of embryo culture can be divided into two parts: first is the preparation of the medium where the embryos will be cultured and the second is the actual culture of the embryos.

The components of the culture medium include inorganic nutrients that are essential for the plant to complete its life cycle, such as sugar, vitamins, amino acid, organic supplement such coconut water, growth regulators, agar as a gelling agent, and other supplements that are deemed necessary. In the case of orchids, the Knudson medium is being utilized as it is specially formulated for the embryo culture of orchids.

The actual embryo culture proceeds after the preparation of the medium. To achieve an aseptic condition, the inoculation chamber is disinfected by spraying 80 percent ethyl alcohol on the surface where the whole process will be performed.

An orchid pod which contains the seeds of the orchid is secured and rubbed with 95 percent ethyl alcohol for preliminary sterilization. Inside the chamber, the whole pod will be dipped in a bottle 1/3 full of 95 percent ethyl alcohol for 3 to 5 seconds with the aid of a scalpel and forceps. The pod, after being dipped in an ethyl alcohol, will be flamed at least thrice until the alcohol on the surface has evaporated. Such series of steps are performed to ensure that the surface of the pod is free from contaminants.

After the surface sterilization, the pod is sectioned on a sterile petri dish with the aid of sterile forceps. Once the pod has been opened, thousands of orchid ovule will be revealed. The ovules will be carefully scraped off from the pod with the use of scalpel and will be carefully dropped into the bottle of the culture medium. Once the ovules have settled inside, the bottle will be covered tightly with cotton plugs and will be placed in a cool and well-lighted place. Tissue culture laboratories usually have their own designated shelves for the newly cultured embryo.

Signs of successful germination in the embryo culture of orchid are when the orchid seeds start to swell and turn green. Sooner, the embryo becomes bigger and assumes the shape of a top. At this point, the structure is no longer an embryo, but a protocorm. At this stage, the protocorms are ready for reflasking. The protcorms will be transferred from one culture bottle to another with the use of a spatula. Reflasking is necessary since this will provide room for further growth and development for the protocorms. Four to eight months after reflasking, the protocorms will become bigger and ready to be planted out of the culture bottle for potting.

Just like any process, this technique requires skills in performing the media preparation and culture, and knowledge, especially on stages of development of embryo.

More orchids to come

The Philippines is home to at least 941 species of the cultivated 20,000-35,000 orchid species in the world. The diverse species of orchids in the country suggest a promising future of the orchid industry.

In 2003, orchids ranked third in terms of production volume in the country with 2,487 metric tons. Meanwhile, 1996 data on cutflowers show that orchids were being exported in Japan and Italy with a total 0.41 percent share from the other four major cutflowers exported to other countries.

The potential of the country in cutflower production development is evident with the availability of appropriate technology, particularly tissue culture. With this technology, multitudes of virus-free orchids can be propagated in no time, enabling us to respond to the high demand for orchids in the domestic and export market as well. end

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Sources:
* Naranja, LR. 2005. The Development of Sustainable Commercial Floriculture Industry in the Philippines. Country paper presented at the Seminar on the Development of Sustainable Commercial Floriculture held in Islamabad, Pakistan.
* Rimando, TJ. 2001. Ornamental Horticulture: A Little Giant in the Tropics. SEAMEO Regional Center for Graduate Study and Research in Agriculture, University of the Philippines Los Baños.
* Rosario, TL. 2001. Laboratory Manual in Ornamental Horticulture. University of the Philippines Los Baños.
* Rosario, TL. “Cutflower production in the Philippines.” Cutflower production in Asia 1998.

Article and photo from Ellaine Grace L. Nagpala- bar.gov.ph, January-March 2007 Volume 9 Issue No. 1

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