Dendrobium: Distribution, Characteristics, Plant Morphology, Growth and Flowering
Based on both species number and morphology, Dendrobium is the second most diverse genus in the Orchidaceae family, with over 1600 species, and this number is growing as new natural and synthetic hybrids are discovered. Even though lithophytic and terrestrial life forms are seen, the monocotyledonous genus is primarily epiphytic. Due to over-collection, habitat loss, and fragmentation, as well as the fact that Dendrobium is prized for both its decorative and therapeutic properties, many of its species are at risk of going extinct. As a result, it is crucial to have a thorough knowledge of taxonomy, phylogeny, and reproduction. The enormous morphological variation and vegetative similarities across the species, however, make the genus infamous for its difficulty in classification and separation based on morphology.
It is found throughout many tropical and subtropical areas, including Southeast Asia, where there are hundreds of species, and Vietnam, where there are over 100 species, all of which are extensively dispersed. With more than 16,000 species, Dendrobium is the second-largest orchid genus (Puchooa, 2004). Major producers of Dendrobium orchids include Thailand, Taiwan, China, the Philippines, Germany, the United States, Japan, and India. The majority of Dendrobium species are epiphytic, sympodial orchids that are native to subtropical and tropical areas. This genus is well-known for its ability to produce cut flowers. Commercial Dendrobium cultivation is widespread in the states of Karnataka, Kerela, Tamil Nadu, and Andhra Pradesh.
Root: Aerial roots have been modified in epiphytic orchids. Multiple layers of epidermal cells transformed into a glossy, spongy, water-absorbing structure make up the roots. Epiphytic orchid roots are notable for having chlorophyll and taking part in photosynthesis.
Leaf: To help reduce water loss, the leaves of the majority of epiphytic orchids are thick, leathery, and coated with wax. The quantity of sunshine a plant receives can be determined by the colour of the leaves. The optimal shade of green should fall between light and dark green.
Pseudo-bulb: These are organs with specialised water storage for surviving in harsh climates. These are created by the enlargement of one to several stem internodes. The pseudo-stems have smooth surfaces with lengthwise grooves and frequently have conical or oblong shapes. The pseudo-shrivelling stems are a sign that the plant is under water stress. The pseudo-bulb loses its leaves as it ages and goes dormant. It is referred to as a “rear bulb” at this point.
Flower: The typical orchid flower is bilaterally symmetrical and zygomorphic. The three sepals and three petals that make up an orchid flower are arranged in a whorl and a reproductive column. Each flower is carried on a spike that emerges from the point where the outermost leaf meets the pseudobulb.
1. One of the largest genera of orchids, mostly Dendrobium, contains 1,600 distinct species that may flourish in a variety of settings, from hot and humid lowlands to high-altitude, frigid highlands.
2. According to Khuraijam et al. (2017), 85% of the world’s trade in cut orchid flowers is made up of Dendrobium species.
3. Due to the enormous variety of flower colours, sizes, and shapes, Dendrobiums are popular as potted plants and cut flowers all over the world.
4. They bloom at various times of the year, depending on the environment. For six to eight weeks, the long-lasting sprays of flowers are in bloom and ready to be cut and used in arrangements.
5. The medium-sized flower spikes of Dendrobium are incredibly stunning. They have between 5 and 20 blossoms per spike and come in a variety of colours, including white, mauve, pink, red, blue, purple, and yellow.
6. Orchids are a hugely lucrative industry worldwide thanks to their unusual shape, stunning colours, prolonged vase and self-life.
7. Dendobriums are epiphytes, they trap wind-borne plant and animal matter, soil grains, mineral flakes, bird droppings, and other nutrients between their tangled roots where they can be absorbed by the plant from the moisture around the roots. This process allows them to create their mini-nutrient.
8. There are known and grown hybrids of more than 100,000 species worldwide (NRCO, 2015). Southern and northern states are not good locations for orchid cultivation, but in recent years, demand for orchids has multiplied across the nation.
9. Because of India’s floriculture industry, imports and exports of flower-related goods are rising worldwide. All plants, including orchids, need heavily on nutrients.
10. Plants that grow in soil or on land use their roots to absorb these nutrients.
11. Plants display deficiency symptoms when nutrient requirements are insufficient or only partially met, and in extreme cases, plants may perish. The best way to feed orchids is by frequent applications of fertilisers in low quantities. To create high-quality flowers, it is necessary to estimate the plant’s growth pattern, nutrient consumption, and the impact of various nutrient levels on flower output.
12. The type of media used to produce epiphytic orchids should offer a surface for the plants to cling to because Dendrobium stretches its roots throughout the branches of trees, totally exposing them.
In terms of all vegetative and blooming factors, a proper media composition is helpful. A healthy environment for roots is provided by an optimal growing medium, which also permits proper aeration, enough drainage, and good anchoring to the plant. It ought to be inert, permeable, and resistant to organic decay. It ought to be affordable and accessible (Bose and Bhattacharjee, 1980). The epiphytic orchid’s robust and healthy root system was the first stage in assuring optimal growth. Therefore, choosing the best rooting medium increases the likelihood that roots will grow profusely.
Orchids are divided into two categories, sympodial and monopodial, based on their growth habits.
Sympodial growth habits: The plants create a thick pseudo-bulb that typically develops along the rhizome. Examples include Bulbophyllum, Oncidium, Cattleya, and Dendrobium.
Monopodial growth habit: Each year, the plants generate a single, tall main stem. New leaves are occasionally added to the top of the stem as it grows longer, while the main stem occasionally sprouts aerial roots. As illustrations, consider Vanda, Vanilla, Rhyncostylis, and Arachnis.
The husks must be put on the benches before planting. The arrangement of husks can take many different forms. The husks can be arranged back-to-back, which is one of the easiest and most typical techniques.
The bed is surrounded by a minimum of four twines, which are used to secure and maintain the position of the individual plants. The base would need more support as the plant grows and new pseudo-stems are generated each year, thus more husks would need to be put at the base, just enough to hold the entire plant erect. The husks need to be lightly rinsed with plain water after planting. The post-planting timetable must then be adhered to starting the following day. The two-week post-planting programme, which mostly consists of fungicides, bactericides, and N: P: K balanced nutrients, is used to acclimate the plants to the new environment.
Patterns of Growth and Flowering
The sympodial growth pattern of Dendrobium orchids causes the plant to develop laterally. Along the rhizome, the lateral growth creates new shoots that eventually mature into a stem with roots and leaves and flowers. This cycle of growth is perpetually repeated.
Flowering: A hardened plant with a height of 10 to 12 cm should begin to bloom four to five months after planting under ideal conditions. The cane doesn’t produce flowering shoots until it has reached full maturity. Where the outermost leaf meets the pseudobulb is where the first flowering stalk or spike appears. The flowering spikes appear on the mature cane from top to bottom.
Dendrobiums typically produce flowering buds opposite the leaf axils from the sides of the canes. One to two new canes will be produced by each plant during the first year of cultivation. These canes will each bear three to four tiny flower spikes. Each of these flower spikes will typically have 5 florets. The number of canes generated per plant will rise during the coming years, along with the number of spikes and the length of the spikes. A plant that is three to four years old and is being grown and managed properly should yield eight to ten spikes with ten to eleven florets each.
The spikes with a length of 60 cm and 10–12 florets per spike are considered to be of the highest quality. When more than half of the florets are open, harvesting should be done in the early morning by snapping the base of the spike.