| Review of Literature
Isabgol (Plantago ovata) is an important medicinal crop commercially cultivated in India. The genus Plantago of family Plantaginaceae, includes some 200 species (Rahn, 1996). Although its centre of diversity is believed to lie in central Asia, some species have now become dispersed widely, with maximum concentration in the temperate regions (Dhar et al., 2005; Vahabi et al., 2008). In Romania and Bulgaria, leaves from Plantago major are used as a folk remedy to prevent infection on cuts and scratches because of its antiseptic properties (Cho et al., 2004; Dagar et al., 2006). Many works based on morphological characters, cytology and enzyme electrophoresis have been used to study the diversity and phylogeny of the Plantago ovata (Ronsted et al., 2002; Dhar et al., 2006; Bannayan et al., 2008; Vahabis et al., 2008).
Since prehistoric times, the species of the genus have been cultivated for their various medicinal uses. Phenylethanoid glycosides were isolated from aerial parts of Plantago herbs (Attau-r-Rahman, 2006) and therefore, known for various medicinal purposes (Blumenthal et al., 2000). P. lanceolata and P. major have been used as anti-inflammatory agents (Beara et al., 2010). P. major contains biologically active compounds such as polysaccharides, lipids, caffeic acid derivatives, flavonoids, iridoid glycosides and terpenoids (Samuelsen, 2000). P. major is known to possess hepatoprotective and anti-inflammatory (Turel et al., 2009) and hematopoietic activity (Velasco-Lezama et al., 2006). P. lanceolata is known to show antimicrobial and nematicidal activity (Biere et al., 2004; Blumenthal et al., 2000). Sorbitol (20) is the characteristic carbohydrate in Plantago (Ronsted et al., 2000, 2003). Research on different aspects of Plantago species is made by various workers (Hammad, 2002; Koocheki et al., 2007; Prakash et al., 2011; Rifat-uz-Zaman et al., 2006; Vahabi et al., 2008).
Isabgol husk, the seed epidermis having muco-polysaccharide layers, is widely used against constipation, diarrhoea and intestinal irritation. Isabgol is also an excellent source of dietary fibre and has hypocholaesterolemic activity (Kawatra et al., 1990) and is widely accepted as food additive in several processed materials like cookies, ice-cream, bread, etc. (Trautwein et al., 2000; Dhar et al., 2005; Vahabi et al., 2008; Manivel and Saravanan, 2010). It used in herbal medicine as a bulk-forming laxative (FDA, 1985; ESCOP, 2003; Williamson, 2003) promote(s) bowel movements by increasing bulk volume and water content (ESCOP, 2003; Sweetman, 2007; WHO, 2007) provide(s) gentle relief of constipation and/or irregularity (ESCOP, 2003; EMEA, 2006a; Pray, 2006). It is also useful against dysentery and intestinal irritation or inflammation. Isabgol husk can lower blood cholesterol level. It is exploited by being blended into confectionary and junk foods (Pflumer et al., 1990; Trautwein et al., 2000; Mandal et al., 2010). Hannan et al. (2006) reported that Plantago ovata Aqueous extracts of husks of Plantago absorption has been reported to reduce postprandial glucose concentrations in diabetic patients. P. ovata reduce hyperglycemia in type 1 and type 2 diabetes by inhibition of intestinal glucose.
This crop is mainly cultivated in arid and semi-arid regions of Gujarat, Rajasthan and some parts of Madhya Pradesh as rain-fed Rabi crop where intermittent drought limits Isabgol production. In general the crop matures in 110 - 120 days after sowing (DAS) and requires supplementary irrigation to increase the seed yield (Maiti and Mandal, 2000). Isabgol, generally flowers at about 60 DAS and seed maturation takes 7-8 weeks after flowering.
It is an export-oriented commodity primarily cultivated to cater the international demand. In fact, India is the sole exporter of Isabgol husk and seeds in the world market (Maiti and Mandal, 2001). India currently ranks first in production and trade of Plantago ovata in the world market. Every year, India produces about 13,000 metric tons of isabgol seeds and 3,200 metric tons of seed husk, with a majority of production in the states of Gujarat, Madhya Pradesh and part of Rajasthan (especially in Malwar and the northern belt). About 90% of the seeds and husks are exported, making isabgol a major foreign exchange earner for India. Although Plantago psyllium (cultivated earlier in France), Plantago major, Plantago lanceolata, Plantago pumilla, Plantago coronopus, Plantago argentia and Plantago lagopus are only of small importance in the pharmaceutical industry (Bhagat et al., 1978; Husain et al., 1994; Dala and Sriram, 1995; Lal et al., 1996; Lai et al., 2000). The annual export earnings from Isabgol husk and seed stands of US $ 400-600 million (Maiti and Mandal, 2000).
Mital and Bhagat (1979) studied the floral biology of Plantago ovata and other species of genus Plantago and reported that in Plantago ovata, long styled flowers were protogynous whereas in short styled flowers, the stigma receptivity synchronizes with the time of anther dehiscence. The other species viz., P. psyllium, P. coronopus, P. lagopus, P. lanceolata and P. albicans expressed protogyny.
Stigma-pollen maturation schedule and their interrelationship in diploid and tetraploid. P. ovata revealed that anthesis in maximum number of florets occurred during morning hours and stigma maturity was distributed to both morning and evening hours (Patel et al., 1980).
Atal and Kapur (1963) proposed new standards for quality of husk as foreign organic matter 2% ash, 2% acid, insoluble ash 0.2%, swelling factor 55, and non mobile gel volume 40 ml. The gel compared with those of sodium alginate, methyl cellulose, sodium carboxymethyl-cellulose and starch appears to be superior in spread ability, penetration, and washability (Mithal and Zacharias, 1971).
Sharma and Koul (1986) tabulated data on mucilage content, swelling factor, seed volume and weight of 100 dry seeds for 10 Plantago species and reported the largest amount of mucilage in P. ovata.
Plantago in spite of being an important medicinal crop, not much research work has been done for its improvement. Crop improvement relies on the ability to generate genetic variation and selection of individuals with improved characteristics. Modern crop improvement efforts have relied heavily on the intensive use of favorable alleles present in cultivated germplasm collection, thereby contributing to the narrow genetic base of elite germplasm (Matus and Hayes, 2002). Therefore, it is important that attempts be made to expand the genetic diversity by utilizing new and unrelated source of germplasm. The use of nuclear techniques and the radio activity in plant breeding is taken up for a long time and broadly known as induced mutation since the discovery of X- rays about a century ago, the use of ionization radiation, such as X-rays, gamma rays or neutrons for inducing variation has become established technology.
Pioneering work on induced mutagenesis was done by the American geneticist H.J. Muller, who published in 1927 a paper describing his discovery that mutation frequency is increased following irradiation of the fruit fly, Drosophila melanogaster with X-rays. He later received the Nobel Prize for this work. At almost the same time the induction of mutations was demonstrated in corn and barely by another American worker, L.J. Stadler.
These two discoveries initiated new field induced mutagenesis, which now became an important tool for developing new genotypes and high yielding varieties and also for locating gene on chromosome, exploring genomes, studying gene structure, expression and regulation. With this discovery, plant breeders and geneticist started investigating the use of radiation induced mutations for changing plant traits of beneficial use. Induced mutation in plant breeding is being used from last few decades for improvements in crop fruit and ornamentals (Donini and Sonnino, 1998; Predieri and Hale, 2001). Induced mutations have been successfully used in improvement of major crops such as wheat, rice, barely, cotton, peanuts, which are seed propagated (Ahloowalia and Mauszynski, 2001). In last seventy years, more than 2500 varieties derived from mutagenesis programmes have been released, as listed in the IAEA/FAO mutant variety database, including 534 rice lines, 205 wheat lines, and 71 maize lines of which 65% were released after 1985 (Parry et al., 2009). Most of mutant varieties were released in China (26.8%). India (11.5%), USSR and Russia (9.3%), Netherland (7.8%) USA (5.7%) Out of the 2252 accessions, 75% of the mutants were from crops and 25% was ornamental and decorative plants (Ahloowalia et al., 2004).
In last decade much work has been carried out in different crops by several workers on induced mutation, viz. Stojsin (1998) in soya bean, Sareen and Koul (1999) in Plantago ovata Forsk. Harer et al. (1999) in Chickpea (Cicer arietinum), Srivastava (1999) in Artemisia annua, Lal et al. (1999) in Isabgol (Plantago ovata), Buirchell (1999) in Lupinus atlanticus and Lupinus pilosus for low alkaloids. Huang et al. (1999) in rice, Henery (2001) in cowpea, Chowdhary and Das (2001) in hexaploid wheat, Reddy (2001) in hexaploid triticale, Waghmare (2001) in Lathyrus sativus, Bahl et al. (2002) in Lippia alba, Khudhaire et al. (2002) in Soya bean, Kumar and Ramesh (2004) in barely, Mishra and Momin (2004) in green gram, Kar and Swain (2005) in Sesame, Badere and Choudhary (2004a) in linseed (Linum usitatissimum L.), Mensah (2005) in cow pea (Vigna unguiculata), Khan et al. (2005) in Cicer arietinum, Floria and Ichim (2006) in Trigonella, Rafique et al. (2006) in Vigna radiata, Manjaya and Nandawar (2007) in Soya bean, Meenu and Chauhan (2008) in Brassica, Nirmilakumari et al. (2008) in Panicum sumatrense L., Khan et al. (2009) and Samiullah et al. (2009) in Vigna radiate, Singh et al. (2009) in Triticum aestivum. Laric et al. (2009) in Sorghum bichlor (L.), Khan et al. (2009) in Chicorium intibus studies various aspect of induced mutation. Nevertheless little attention has been paid towards medicinal plants. In Plantago limited research work has been carried out which are summarized below:-
Bhatti et al. (1970) studied variability of quantitative characters in gram as affected by gamma irradiation. Results obtained from the M2 generation indicated that, in irradiated populations, the variance for the number of pods & their cyto-morphological behavior was increased which could be exploited in the crop improvement programmes.
Dry seeds of Plantago ovata were subjected to different doses of gamma rays (Sareen, 1991). Apart from other variants, a translocation heterozygote was recovered in the irradiated progeny. To generate more variants, this individual was crossed in various directions.
The first consistent chromosome counts in Plantago were reported by McCullagh (1934). Other studies were made in connection with taxonomic studies in order to explain the relationships in particular groups of related species (Bocher et al., 1955; Rahn, 1957; Cartier, 1971, 1973; Zemskova, 1977). Studies also covered the cytology of Plantago species from different phytogeographic regions (Gregor, 1939; Runemark, 1969; Briggs, 1973).
Badr and EI-Kholy (1987) studied Plantago chromosomes in the Egyptian flora of the 10 studied species, five were found to have a basic numbers of n=6: P. Arabica, P. lagopus, P. lanceolata, P. major and P. notata. The study revealed that Plantago major was characterized by short chromosomes and a symmetric karyotype compared with other species.
The species Plantago ovata was first studied for karyotype by McCullagh (1934). She reported two terminal chromosomes in the somatic complement, but none was confirmed in subsequent studies (Fujiwara, 1956).
In general, the karyotype in Plantago consists of medium- sized chromosomes, mostly with meta and sub-metacentric constrictions, with no marked size difference between individuals in the total length of the chromosome complement. One or two pairs of chromosomes possessed secondary constrictions.
The chromosomes of Plantago could be classified as meta-centric, sub-metacentric, or sub-terminal. Pramanik and Sen Ray Chaudhuri (1997) studied the karyograms of some species of Plantago obtained from different parts of the world and revealed that karyograms had standard features. Despite homogeneity in total features, each species differed from the other in minor-karyotypic details indicating the role of structural changes of chromosomes in evolution. The basic chromosome number n = 6 is the most common among the species Plantago and may be considered the ancestral number in the genus (Badr et al., 1987; EI-Bakatoushi and Richards, 2005).
Contributions on cytology of Plantago species of different phytogeographic regions have been made by various workers from within India (Dhar et al., 2006; Singh et al., 2009) and outside (Mohsenzadeh et al., 2008).
Two new cytotypes (4x, 6x) for Plantago depressa are new reports to India and hexaploid cytotype with n = 18 for the species is reported for the first time from world with only earlier reports of n = 6 (Huss, 1981; Khatoon and Ali, 1993) and n = 12 (McCullagh, 1934).
Chromosome number n = 6 and 12 for P. major is in conformity with the previous report by Sharma et al. (1992). Besides the diploid cytotype, a tetraploid cytotype is also known to occur in nature (Sharma and Koul, 1995). The species reveals the polymorphic nature as has also been reported by Jain (1978b).
Van Dijk et al. (1988) reported the presence of distinct ecotypes in the species. Presently, cytomixis has been recorded in the species P. major which results in aneuploidy as reported by Sharma and Koul (1995) in Kashmir Himalayan populations. However, there is no previous report on chromosomal associations found in this species. Geographical and ecotypic variations have a significant effect on morphology of the plant. This is basically due to genetic changes influenced by change in environmental conditions (Bradshaw, 1984). Altitude variations differentially influence the morphological and biochemical responses of P. major (Prakash et al., 2011).
Bhagat and Hardas (1980) studied induced and natural polygenic variations in Plantago ovata. They found mutated diploid populations to be highly variable. The frequency of favorable genotypes for seed yield and other related traits was high in population derived from NMU treatment followed by EMS treatments. The increased genetic variation (induced) may provide much scope for selection and contributing towards high yield.
Padha et al. (1998) isolated an aneuploid offspring with 9 chromosomes in Plantago ovata (2n=8), by screening the progeny of a cross between translocation heterozygote mother plant (obtained by gamma irradiation) and a disomic pollen donor.
Plantago, represents an assemblage, individual species of which may vary from triploid to hexadecaploids (Sharma, 1984). Some of these polyploids are spontaneous and most of them are induced, mostly through the application of colchicines (Chandler, 1954, Zadoo and Farooqi, 1977, Mital et al., 1975, Koul and Sharma, 1986, Kumar and Srivastava, 1994).
Chandler (1954) reported that the induced tetraploids of Plantago ovata showed greater vigour, larger seed size but were less fertile than diploids. In the tetraploids of P. ovata induced by Zadoo and Farooqi (1977), the seeds were superior to diploids both in quality and quantity of mucilage.
Kumar and Srivastava (1994) reported that the seed treatment with 0.4% colchicine for 48 h could effectively induce tetraploidy in P. ovata. The tetraploids showed gigantism over their diploid prototypes. The tetraploid flowers stayed longer resulting in improvement in keeping quality and extension of blooming period to some extent.
Investigation of the genetic system of six species of Plantago has revealed striking differences in their breeding and meiotic systems. P. patagonica is an in breeder on account of pre anthesis cleistogamy, whereas P. lanceolata is an obligate out breeder as it is self incompatible. P. drummondii, P. lagopus, P. Ovata and P. major show mixed mating in various proportions (Sharma et al., 1992). Briggs (2008) performs chromosome identification in Plantago ovata Forsk through C-banding and FISH technique.
Shazia et al. (2008) carried out Structure characterization and carboxymethylation of arabinoxylan isolated from isabgol (Plantago ovata) seed husk.
Dangar et al. (2006) on the basis of his experiment on sodic land reported that isabgol can successfully be grown on moderately alkali soils up to pH 9·6 without the application of any amendment.