After reading this article you will learn about:- 1. Orchid Flower 2. Seed Germination of Orchid 3. Growing 4. Pots/Containers 5. Breeding 6. Pests and Diseases.
It belongs to important monocotyledons series microspermae, order—orchidales and family orchidaceous. This family includes about 800 genera and 35,000 species and is the largest family amongst flowering plants. Orchids are wide in origin and are available in abundance in tropics and temperate regions, however, main centers are: Indo—Malayan and tropical American regions like Brazil, Mexico and other areas, New Guinea and Australia.
Main regions in India are Himalaya—Sikkim, Meghalaya, Tripura, Assam, Bengal, Western Ghats of North Kanara, Malabar and Travancore. The important genera which have been found are Eria, Dendrobium, Cymbidium, Vanda, Perisylus, Calanthe, Orchis, Bulbophyllium, Liparis, Coelogyne, Paphiopedila, Vanilla, Rynchostyllus, Aerides, Microstylis, Spiranthes, Epipactis, Hemepelia, Goodyera, etc. Brazilian catteleyas. Mexican laelia and Indian dendrobium, cymbidium Vanda have played a major role in the development of orchid industry.
Orchids are perennial, terrestrial, epiphytic, saprophytic and intermediate herbs with rhizomes or pseudo-bulbs, or tuberous roots or assimilating roots or aerial epiphytic. The growth habit may be either monopodium or sympodium.
In monopodium main axis continues to grow year after year and bears flower on lateral branches e.g. Vanda, Angaecum, Polyrhiza, whereas in sympodium when main axis comprises of annual portions of successive axis each of which bears scale leaves and terminal flowers is called Acranthos sympodium e.g. Eulphia, Dendrobium and Liparis.
Another habit in which inflorescence is lateral and main axis continues to grow for current year and stop growing at the end of season is called Pleuranthos sympodium e.g. Cymbidium, Phaius, Calanthe, Bulbophyllum etc.
According to habitat, orchids are grouped into four main groups:
(i) Epiphytes:
These orchids grow on the trees and fasten their support with the help of clinging roots which arise from rhizomes and form network between orchid and support and form a reservoir for humus. These orchids have absorbing roots which are adventitious and project into reservoir containing humus.
Aerial roots hang down and are green inside and have capacity to store water and photosynthesized the food. During dry period they shed the leaves but they bear flowers and perennate with the help of pseudo bulbs e.g. Dendrobium, Vanda, Bulbophyllum, Obernia etc.
(ii) Terrestrial Orchids:
These are sympodium and usually have a rhizome or tuberous roots or pseudo-bulbs. These are xerophytic or mesophytic and are perennial in nature which store food and water in modified plant parts, enable them to overcome the dry period. Each annual shoot sprouts into leaf shoot and inflorescence.
(iii) Lithophytes:
These orchids grow on moist and shaded rocks and cervices of stony walls e.g. Cymbidium munroniamum, Diplomeris hirsuta, Geodoram durpureanum and Hernanium josephii.
(iv) Saprophytes:
These orchids lack green leaves and possess a fleshy underground rhizome with (Neotha) or without roots (Epipogium). The rhizome is usually which branched and absorb moisture from humus soil. Endotrophic mycorrhiza occurs in almost all saprophic orchids.
Orchid Flower:
Most showy part of orchid is its flower which may be produced as solitary terminal (Cyperipedium, Pogonia) or usually a spike sometimes in raceme. Flowers are usually trimerous and vary in form and size. In Angraecum sesquipedale from Madagascar the white flowers are of 25 cm in diameter and 45 cm long spur.
Perianth is usually six in two whorls, of three each and both whorls may be alike or outer whorl may be like calyx and inner may be corolla like. Many modifications are there. The posterior tepal or inner whorl is curiously modified and may be slipper like spurred, butterfly like, tubular, broad, strap shaped, shoe shaped, lobed or lacerated, sac like, spider like, etc.
This modified tapel is called lip or labium and acts as a landing place for insect. The lateral tepals of the inner series may remain separate and form wing like structure or may fuse like hood or sachete structure and are usually similar. The parianth lobes are curiously coloured and bear diverse and variegated patterns.
The androecium is made of one or two or three fertile structure and a variable number of staminoids arranged in two whorls. Stamens and style fuses to form a column or gynodrium or gynostemium. The column is present opposite the labellum. The anthers are bithectus, dehiscence, longitudinal, pollen numerous, granular normally agglutinated into mealy, waxy or bony masses called pollenia and the number of which varies 1-4 in each anther.
Gynaecium consists of stigma of three lobes, out of which two are fertile and one is fertile which is cabled rostellum. Ovary is tricarpellary, unilocular, with marginal dehisces, and ovules are minute. Pollination is done by insects and there is large variation in orchid flowers for pollination for different kind of insects.
The flowers have nectary in the spur of labellum or base of column. The insect lands on labellum and tries to reach nectary. The sticky mass of pollenia glued to its body while it is drilling for honey. Some orchid species attract males of many hymonoptrous insects by emitting feromones and their most unusual method of discharging their pollinia.
Fruit is a capsule which dehisces by means of three to six lateral longitudinal slits. Seeds are non-endospermic or endospermic or endosper nucleus and are produced in large numbers extremely light and with undifferentiated embryo. As many as 40,00,000 seeds/capsule are produced. The seeds are dispersed by wind.
Seed Germination of Orchid:
The orchid seeds being non endospermic in nature, cannot utilize their own reserves and hydrolyse larger molecules of starch or cellulose. Hence, under natural conditions seeds germinate after being affected by a fungus—the orchid mycorrhizia which supplies sugar to germinating seeds of orchids.
As a result asymbiotic germination in the absence of sugar precedes only up to the early protocorm stage. After analysing orchid salep which contained starch, proteins, sugars, minerals and germinated seeds of Cattelya, Laelia, Epidendrum or artificial media.
Lewis Knudson (1966) advocated that fungus was not necessary for seed germination. Later on many workers used different media for growing seeds of orchids; however, Kundson and Vacin and Went medium are used commonly which are available in ready form in the market.
The compositions of important media are given below:
Seeds from green pods are sown on the autoclaved media under aseptic conditions. After 15-20 days, the embryo start swelling and after 30-35 days, 2 leaf stages are achieved. At 4-leaf stage the seedlings are taken out from flasks and after thorough washing are planted in community pots in 1: 1 mixture of shredded tree fern fibre and charcoal.
The orchids are propagated through tissue culture technique for producing virus free seedlings of rare plants or hybrids which otherwise could not be propagated. Commercially nodal sections and in certain cases lateral bud meristem, or explants from shoots growing on pseudo-bulbs or flower stalk cutting or leaf tips have been used. First mericlones are raised and on transplanting them orchid plants are produced. There are commercial laboratories which propagate orchid plants on commercial basis and earn good profits. For tissue culture solid or liquid media are used.
Growing of Orchids:
The orchid houses are made for cultivating orchids. According to the orchid types proper conditions and rooting media are provided. Thus, orchid houses are made for tropical orchids or temperate orchids. Former, grow in shade or under indirect light, under high humidity and do not like sudden change in temperature, whereas latter type are grown in cool orchid houses. These houses are made running north-south from split bamboo, glass, fibre glass, etc.
The optimum requirement of light varies according to species grown. Cyperipedium and Phalaenopsis required only 2200-3200 Lux whereas genera like Vanda and Aranda require about 8500 Lux. It has been observed that filtered sunlight stimulates formation of male flowers and direct sunlight favours female flowers. Majority of orchids, are day neutral and are not influenced by day length. But in Catteleya both short day and long day plants are found.
There are also orchids which are grown in open sun in trenches filled with brick piece, charcoal. Orchids are commercial being grown in this way in Trivandrum, Ceylon, Thailand, and Singapore. The species of Vanda, Archanis, Aranda, Rananthera, etc. are being grown.
Humid and warm atmosphere is an ideal for the growth of most of the tropical orchids which do not have well established root system. The humidity in the range of 30-80% during night and day, respectively, should be maintained. For this a central tank of water is very helpful in orchid house. The plants in pots, baskets and hanging pots need watering two-three times a day with a fine spray so that plants are not hit directly.
Pots/Containers for Orchids:
Terrestrial orchids are grown in pots and its size should be used according to the size of the plant. Normally 25 cm pot is used. Orchids are not disturbed frequently until very necessary and, hence, repotting is done in 2-3 years. Orchids flower better when under potted. Pots are filled with the mixture of leaf mould. F.Y.M. and sand in the ratio of 1: 1: 1. Addition of charcoal or fern fibre or coconut husk or over burnt brick improves the aeration and ultimately growth and flowering.
Requirement of N and P depends upon the stage of growth e.g. during vegetative phase more of N is required than productive stage when P is required. Micro nutrients like Cu, Mg, Mn, B, Fe, and Zn are applied extra.
Many formulations are available; however, Ohio W.P is most commonly used. The composition is as follows. The use of readymade preparations like NPK 20: 20: 20 or NPK 10: 30: 20 with trace elements along with coconut water (20-25%) has also been recommended.
Breeding of Orchids:
In nature orchids are pollinated by insects and birds and there is free crossing in two species and two generas. There is no genetic barrier in species and genera. There also exists polyploidy and introgressive hybridization.
The important genera which have given maximum number of man-made hybrids are Cattleye, Cymbium, Paphiopedium, Vanda, Dendrobium, etc. Important generic hybrids are: Ascocenda (Ascocentrum × Vanda), Aranda (Arachnis × Vanda), Aeridovanda (Aerides × Vanda), Brassocattleya (Brassovola × Cattleya), Saphrocattleya (Cattleya × Sophronities).
Some important hybrids evolved for cut flower production on commercial scale are: Archianis—’Maggie Oei’, Aranthera—James Storie; Dendrobium—Pampadour, Walter Oume, Tomie, Spell Bound, Caesar; Vanda—Miss Jo aquim, Rothschildiana AscocendaYeh Sum Wah; Oncidium—Cymbidium—Babette (Mini), Ballerian (Mini), Broadmoor (Mini), Capella (Mini), Cassak (Mini), Cradle mont (Mini), Drumm (Mini), Fantasy (Mini), Green Queen (Mini), Lime-light, Mary Pincess, Mem Rosl Green, Miranda, Mem Rosl Green Moonglow, Pink Perfection, Princess Rose, Sabrina, Sir Cotton, Towiantot, Wendy Brown, Molly, Micke, Vanguard. Paphiopedium—King Arthur ‘Bougone’, Amer. Hybr.Phalaenopsis—Hybrids.
Pests and Diseases of Orchids:
Orchids are attacked by various kinds of pests and most common are aphids, thrips, mealy bugs, orchid weevil, snail and slugs. They attack younger shoots, leaves and buds. However, these are effectively controlled by the use of common insecticides like Malathion, or Thiodan.
Orchids are also prone to many fungal, bacterial and viral diseases. The common fungal diseases are leaf spot, caused by colletotrichum, sp. and Gleosporium, sp. leaf blight caused by pythium, sp. collar blotch—caused by Pencilliuthomii, and orchid wilt caused by Sclerotium rolfsii which can be controlled by spraying fungicides like Dithane M-45.