Plant growth is a sum total of anabolic and catabolic reactions with addition of dry matter
Plant growth is a sum total of anabolic and catabolic reactions with addition of dry matter. The plant growth is regulated by several intrinsic and extrinsic factors. There are several other factors promoting growth and productivity of food crops, fibres and oil yielding plants (Kumar et al., 1995 and Kumar and Roy, 1996).
The plants used in ayurvedic drugs were mostly collected from the field conditions and this has resulted in considerable loss of biodiversity and endangering several plant species. Conservation of these valuable plant species has become imperative (Dhar et al., 2000) due to interest in herbal medicines for healthcare all across the world (Franz, 1993).
Cultivation of medicinally important plants has been recently started in several countries like Japan, China, Europe and America. However, the detail parameters on the mode of propagation, nursery techniques, nutrient cycles, growth regulator requirements and regulation of partitioning of photosynthates have not been studied in detail. Some of the cultivated plants reported to yield less valuable products due to poor knowledge of proper agro-technology. However, recently detailed studies have been initiated on the cultivation of medicinal plants like safed musli (Chlorophytom borivilianum L.), rauwolfia (Rauwolfia serpentina Benth. Ex Kurz.), turmeric (Curcuma longa L.) (Mishra and Pandey, 1998; Prajapati et al., 2003; Singh and Chauhan, 2003 and Singh et al., 2004), Withania somnifera L. Dunal (Patra et al., 2004); Isabgol (Plantago ovata Forsk.), Papaver somniferum, Catheranthus roseus and Senna sp. (Gopinath and Pandey, 2002).
Growth and productivity of medicinal plants can be improved by application of nutrients and growth regulators (Mu et al., 1995; Deans et al., 1999; Tomar et al., 1999a and Kumar 2000). Different factors affecting seed germination and vigour index of seeds, Kattimani et al., 1999; Naidu et al., 2000; Gera et al., 2003; Khan et al., 2003; Yogeesha and Shivananda, 2003 and Sankhyan et al., 2004).
Application of fertilizers like Urea, Super phosphate and Muriate of potash singly or in combination, has improved the growth of Plantago ovata Forsk. (Sharma et al., 2003 and Yadav et al., 2003), Mentha arvensis L. (Rahman et al., 2003), Guava (Tomar et al., 1999), Lawsonia inermis L. (Khandelwal et al., 2003), Wheat (Seregina et al., 2004), Arachis hypogaea L. and Helianthus annus L. (Maity et al., 2003) and Phaseolus vulgaris L. (Olivera et al., 2004). In medicinal plant cultivation the plant part/ or parts used as source of drug, determine the value of the product and a combination of the treatment of nutrients with growth regulators have been determined to improve the growth potential in Euphorbia triculli, E. lathyrus and Pedillanthus (Kumar
et al., 1995). In recent years, the use of growth regulators in crop production has been given prominence throughout the world (Manikandan and Hakim, 1999). The use of growth regulators for obtaining increased yield for agriculture crops is routinely applied. The growth regulators have been found to improve growth and flowering in Dahlia variabilis L. (Hossain et al., 1999) and Chrysanthemum (Kumar and Godha, 2001) when applied singly or in various combinations. Application of Nitrogen and Potassium fertilizers has been reported to affect the vegetative growth and flowering in Ceratonia siliqua (Correia et al., 2004).
The increase in plant growth by application of growth regulators or fertilizers has not been one sided boon for cultivation of medicinal plants. The Chlorophytom collected from wild conditions has been reported to be of high value in comparison to the cultivated plants (Ramawat et al., 1998). Cultural practices, for raising medicinal plants are of a paramount importance, as period of sowing and harvesting will determine the quality of drug. The environmental factors like soil pH, soil EC, rainfall, and temperature during the growth period have been reported to influence the value of crude drug samples.
Asparagus racemosus Willd. is multiplied through vegetative propagation in nature. There is always problem of heterogeneity in obtaining uniform seed stock. Previous studies using seeds as means of propagation indicated that plants developed through seeds are poor in vigour. Seeds have been reported to have a low viability and they have a slow rate of growth (Gupta et al., 2002). The natural regeneration of this under shrub is through tuberous roots that have been scarce in nature because of indiscriminate collection of wild material. In vitro cultivation, cryopreservation and micropropagation through tissue culture may also aid the preservation of medicinal plants and provide the complimentary conservation option (Benson et al., 2000).
In vitro propagation of economical and medicinal plants offers not only means for the mass multiplication of existing stocks of germplasm for biomass energy production but also for the conservation of important elite or rare plant species those are threatened with danger of extinction. Clonal propagation of favourable lines through in vitro culture of explants would also facilitate breeding programme (Bajaj, 1986). According to Murashige (1974) there are four areas in which plant tissue culture can be applied possibly either presently or in near future viz., i) production of pharmaceutical and natural products,
ii) genetic improvement of plants, iii) recovery of disease free clones and preservation of valuable germplasm and iv) rapid clonal multiplication of selected varieties.
Tissue culture technique has been widely accepted as a tool of biotechnology for vegetative propagation of plants of agricultural, horticultural and forestry importance (Dave and Purohit, 2002). In vitro propagation enables a broad range of species to be cloned under highly controlled conditions (Hussey, 1986). Clonal propagation of plants via tissue culture can be carried out by : i) enhanced branching , ii) axillary branching , iii) somatic embryogenesis and iv) callus organogenesis (Thorpe and Harry,1990). The technique has been successfully used in propagation of wide range of herb and shrub species (Murashige, 1974). Extensive work has been done on several ornamental species of family Liliaceae (Krikorian and Kann, 1986) but very few medicinal plants of this family have been cultured in vitro (Jha et al., 1984).
Recently there has been an upsurge of micropropagation of several medicinal plants viz., Dioscorea zingiberensis (Chen et al., 2003), Artemisia petrosa spp. Eriantha (Pace et al., 2004), Albizia procera Benth. (Swamy et al., 2004), Azadirachta indica A. Juss. (Quraishi et al., 2004), Rosa damascena Mill. (Sharma et al., 2004), Achrus sapota L. (Liao et al., 2004), Hagenia abyssinica (Feyissa
et al., 2005) and Phellodendron amurense Rupa. (Azad et al., 2005) Micropropagation is being utilized commercially in the mass multiplication of ornamental plants worldwide (Huetteman and Preece, 1993). Nodal segment contain axillary buds, capable of producing a complete plant, have been employed for clonal propagation. With the use of tissue culture technique, rate of shoot multiplication can be increased manifold by culturing the nodal explant on a culture medium having an appropriate cytokinin and auxin-cytokinin. Large number of plants have been produced in diverse group of families using nodal segments as explant, Plumbago zeylanica L. (Rout et al., 1999 and Selvakumar et al., 2001), Centella asiatica L. (Tiwari et al., 2000), Holarrhena antidysenterica Wall. (Raha and Roy, 2001), Accacia catechu Willd. (Sahini and Gupta, 2002), Asparagus maritimus (Stajner et al., 2002a), Decalepis hemiltonii (Gururaj et al., 2004), and Ficus carica L. (Pasqual et al., 2004).
Many attempts in the clonal propagation of Asparagus genus have been made using shoot tip and lateral bud clusters (Yang and Clore, 1974). However, in vitro multiplied shoots of Asparagus often produce thin and weak roots or even no root formation at all and the plantlets thus obtained rarely survive when they are transferred to soil (Shigeta et al., 1996). Little work has been undertaken on in vitro culture in Asparagus racemosus as compared to that of A. officinalis, the horticultural variety extensively used for the preparation of soup and as a vegetable in European countries. A. racemosus is less known to world, but it has many uses in ayurvedic medicines. This has led to its increasing demand in the crude drug market.
A separate family Asparagaceae has now been created by removing the genus from Liliaceae family (Brumitt, 1992). The genus, Asparagus comprises 150 species (Drost, 1997) and consists of herbs, shrubs and vines which are widespread in the Old World. The genus is classified into three subgenera (Asparagus, Protasparagus and Myrsiphyllum) according to Clifford and Conran (1987). They are grown throughout the world but they originated mainly from Asia, Africa and Europe (Encke, 1958). The species of the first subgenus are dioecious, with unisexual flowers, while the second and the third subgenera include only hermaphrodite flowers. The genus Asparagus represents highly valuable plant species having therapeutical and nutraceutical importance in addition to being consumed as food (Shasnay et al., 2003). Genome size, rDNA ITS polymorphism, genetic variability and relationship of economically important Asparagus led to modification in its classification (Stajer et al., 2002b). The large genus Asparagus has a remarkably consistent basic chromosome number of x = 10, found in species of different ploidy levels, which is based on karyotype analysis (Kar and Sen, 1987; Sheidai and Inamdar, 1992 and Rudall et al., 1998). Geographic distribution, gender system, chromosome number of some important Asparagus species are presented in Table 1 .
Some of the important medicinal plants are Glycyrrhiza glabra L., Abrus precatorius L., Croton tiglium L. and Asparagus racemosus Willd.
Glycyrrhiza glabra L. (Liquorice), a dicotyledonous herb has been used in medicine for skin eruptions, including dermatitis, eczema pruitus and cyst. Liquorice extract is considered as an effective agent for treatment of atopic dermatitis (Saeed et al., 2003). It has tonic, alexipharmae, alternative and expectorant properties.