eChapters

1. Introduction

The development of food products using composite flour has increased and is attracting much attention from researchers, especially in the production of bakery products and pastries. This article focuses on the use of composite flour to produce food products, namely bread, biscuits, and pasta, with looks at on its impact, following some improvements made, on the sensory quality, rheology characteristics, and nutritional values as well as its overall acceptance. The blending of wheat flour with various sources of tubers, legumes, cereals and fruit flour in different percentages to produce variety of food products are also reported. The positive effects of the use of composite flour can be seen in the final product related to the functional and physicochemical properties and health benefits of raw blended flour along with percentage blending. Overall, composite flour is a good new approach to utilizing uncommon food products as the application of composite flour produced products with different characteristics and quality, depending on the types and percentage of wheat flour used in the formulation.

Bread has been the staple food worldwide and habit of bread is derived in part due to the convenience and wholesomeness. Wheat is a commonly used cereal for making bread as it gives the desired texture due to the presence of gluten forming proteins like gliadins and glutenins (Decock & Cappelle, 2005). In earlier times idea of composite flour in developing countries originated in order to cut down on import of wheat (as it was not grown in many countries) but in recent past refined wheat flour consumption has lead to health issues and thus in order to improve nutritional and functional properties composite flour has been the norm. Composite flour is the one obtained by mixing wheat flour with cereal and legume flours for making bread and biscuits (Dendy, 1992). However, mixing of non-wheat flours, roots and tubers, legumes or other raw materials can also be regarded as composite flour.

Though the pesticide application represents viable solution to pest control, however indiscriminate use poses threat to target as well as non-target crops. The side effects of pesticides therefore have to be considered based on their use and on the agricultural system to which particular pesticide is used. Studies should be implied on effects and persistence of pesticides in crops and is consequent effects on soil microbial flora and associated nitrogen metabolism. Safe alternate methods like development of relatively cheaper biopesticide should be encouraged. More efficient methods have to be developed and validated for dissipation of pesticide residues in food grains. Human health and environment has gained great importance in the modern world. The widespread use of insecticides has resulted in problems caused by its interaction with the natural biological systems. Study showed that higher amounts of acetamiprid have some negative effects on corn plant physiology. Thus, the use of pesticide should be controlled following the standards of developed countries to protect health and the environment.

Partitioning of assimilated carbon among sink organs is a critical factor that controls the rate and pattern of plant growth. Environmental stress often restricts resource availability while successful acclimation sets in motion processes that restore the supply. A key mechanism contributing to regulation of carbon partitioning is an expression of genes that control activity of the enzymes which initiate sucrose metabolism at specific sites and stages of ontogeny. Drought stress not only limits the size of the source and sink tissues but the phloem loading, assimilate translocation and dry matter portioning are also impaired. However, the extent of effects varies with the plant species, stage, duration and severity of drought. Crop production faces many challenges, due to changing environmental conditions and evolving needs for new plant-derived materials. 
The extreme temperatures those are consequences of present-day global climate changes are considered as major abiotic stresses for crop plants. Temperatures exceeding the limits of adaptation substantially influence the metabolism, viability, physiology, and yield of many plants. Plants exposed to extreme temperatures often show a common response in the form of oxidative stress. However, the extent of damage caused by extreme temperatures depends greatly on the duration of the adverse temperature, the genotypes of the exposed plants, and their stage of growth. Numerous research findings support the notion that induction and regulation of antioxidant defenses are necessary for obtaining substantial tolerance against environmental stress. Plant adaptation to either high temperature or low temperature is a multigenic response which is very complex in nature. Plant response to continuous light depends on plant tolerance and can be modified by alteration in temperature, light intensity, CO2 level, and other environmental factors.

Plant–water relations concern how plants control the hydration of their cells, including the collection of water from the soil, its transport within the plant and its loss by evaporation from the leaves. Flow of water through plant and soil over macroscopic distances is driven by gradients in hydrostatic pressure. Over microscopic distances it is driven by gradients in water potential. Evaporation of water from leaves is primarily controlled by stomata, and if not made good by the flow of water from soil through the plant to the leaves, results in the plants wilting. Plant water deficit is initiated as the crop demand for water exceeds the supply. The capacity of plants to meet the demand and thus avoid water deficit depends on their “hydraulic machinery.” This machinery involves firstly the reduction of net radiation by canopy albedo, thus reflecting part of the energy load on the plant. Secondly, it determines the ability to transport sufficient amount of water from the soil to the atmosphere via the stomata in order to provide for transpiration, transpirational cooling and carbon assimilation. Water is transported by way the soil-plant-atmosphere continuum and it is largely controlled by the resistances in the continuum as determined by root, stem, leaf, stomata and cuticular hydraulic resistances. The gross effects of deficient and of excessive soil moisture on plant growth are well known, but controversy has existed for many years around the question whether the so-called “‘available moisture” is equally available for plant growth or available only with such increasing difficulty that plant growth functions are retarded before the wilting point is reached. Various measurable aspects of plant growth do not respond in the same manner to increasing moisture stress. Crops will respond to irrigations, although measured soil moisture stress is quite low. Problems of relating plant growth to soil moisture stress conditions varying with both time and soil depth are considered. Soil factors affecting density or depth are reviewed and several ways weather factors influence soil, -moisture-plant-growth relations summarized.

Marginal land areas will need to be used to meet the increasing requirement of future generations, especially in developing countries. These marginal areas commonly impose abiotic stresses on crops due to factors such as salinity, drought, flooding, low nutrients and aluminium or heavy metal toxicity. As a consequence, the growth and yield of crops from such areas is typically low and their quality in also poor. Endogenous plant growth regulators play an important role in regulating plant responses to abiotic stress by sensitizing growth and developmental processes. While the physiological and molecular mechanisms linked to the role of ABA and cytokinins in stress tolerance are well explained, there is growing interest to elucidate the associations of auxins, ethylene, gibberellins, brassinosteroids, and polyamines in stress tolerance mechanism and also on possible cross talk mechanism among different growth regulators during stress tolerance acquisition. Identification and characterization of the gene regulating synthesis of different endogenous growth regulators and recent progresses on hormonal signaling, mutant research, and physiological actions have provided scope for manipulating their biosynthetic pathways for developing transgenic crop plants with enhanced abiotic stress tolerance. Researches have also provided some leads in exploiting the potential of growth regulators in enhancing the resistance to abiotic stresses of crops. Plant growth-regulators (PGRs), are biochemical and chemical compounds stimulates plant growth and productivity when applied, even in small quantities at appropriate plant growth stages. These are being extensively used in agriculture to enhance the productivity in agricultural crops. Their central role in plant growth and development is through nutrient allocation and source-sink transitions while most of the plant bioregulators (PBRs) stimulate redox signaling under abiotic stress conditions.

We do not know when intercropping began nor why early civilizations fostered its use. Whether by design or accident, intercroppinq dominated early agriculture and is still practiced in many areas of the world. With the advent of “modern” agriculture, intercropping began disappearing from many areas. This shift was driven primarily by mechanization and specialization. Despite pressures to abandon intercropping, it has survived and flourished Inereasing interest in sustainability and environrnental concerns have drifted attention back to intercropping as a means of better utilization of resources while preserving the environment.
Through intercropping, farmers can achieve the full production of the main crop and also an additional yield (bonus) associated with an increased plant population of the second component. Hence, intercropping can increase incomes obtained by smallholder farmers in areas where labor is not shortage, through reduction of economic risk and market fluctuation resulting from growing a single crop which is more prone to natural hazards and helping the farmers in better utilization of land by having more than one crop produced per unit area. Though all intercrops produced higher productivity, the farmers could better use the appropriate population of component crops in intercropping systems in order to maximize yield of both crops as well as total productivity. It is, therefore, important to support intercropping systems with appropriate agronomic practices such as timely irrigation, pest protection and the likes to sustain the cropping system in the countries where labor is not problem for proper management in general even though sometimes sole cropping may became more productive.

Most food legumes have a long history of domestication almost as long as cereals, and during this time they have been subjected to conscious and unconscious selections for better adaptation to environmental condition as well as better seed yield. In general, crops during their ontogeny faces a number of abiotic stress viz., excessive and/or low soil water stress, soil salinity stress, high as well as low temperature stress. It has been well documented that crop yields would be greater in many cropping regions if more water were available. 
Availability of water for agriculture is being challenged increasingly because of growing demand for water from other sectors such as industry, urban use, and for social and environmental purposes. Water stress may conceivably arise either from an insufficient or from an excessive water activity in the plant’s environment. Many physiological characteristics are correlated with the water potential of mesophyll tissue but the correlations are species specific. There is a general hierarchy of sensitivities among general physiological activities. Most sensitive are cell expansion, cell wall synthesis, protochlorophyll formation, and nitrate reduction. Generally turgor pressure is still accepted as the best indicator of water stress in plants. The specific mechanism by which turgor regulate physiological function probably relate to cell walls and membranes. Cell membrane structure, and spatial arrangement of enzyme, transport channels, cellulose synthesis rosettes, and receptor proteins may be dependent on turgor pressure.

The extreme temperatures those are consequences of present-day global climate changes are considered as major abiotic stresses for crop plants. Different studies clearly show that temperatures exceeding the limits of adaptation substantially influence the metabolism, viability, physiology, and yield of many plants. Plants exposed to extreme temperatures often show a common response in the form of oxidative stress. However, the extent of damage caused by extreme temperatures depends greatly on the duration of the adverse temperature, the genotypes of the exposed plants, and their stage of growth. There is ample need to develop temperature tolerance in crop plants by exploring suitable strategies. Numerous research findings support the notion that induction and regulation of antioxidant defenses are necessary for obtaining substantial tolerance against environmental stress. The development of genetically engineered plants, by the introduction and/or overexpression of selected genes, would to be one feasible strategy. However, plant adaptation to either high temperature or low temperature is a multigenic response which is very complex in nature. Thus the task of identifying the traits those correlate with stress tolerance is incredibly difficult for researchers. Plant response to continuous light depends on plant tolerance and can be modified by alteration in temperature, light intensity, CO2 level, and other environmental factors.

The stresses, drought, salinity, chemicals, cold and hot temperatures, have interconnected effects on plants, resulting in the disruption of protein homeostasis. Maintenance of proteins in their functional native conformations and preventing aggregation of non-native proteins are important for cell survival under stress. The heat shock proteins buffer this environmental variation and are therefore important factors for the maintenance of homeostasis across environmental regimes. Heat shock proteins are known to be expressed in plants experiencing high-temperature stress. Heat shock proteins are important in relation to stress resistance and adaptation to the environment. Their molecular function might be membrane or protein stabilization, but, for now, for most heat shock proteins the molecular function remains to be elucidated. The general observation of the response and induction of heat shock proteins following heat stress suggests that they play a fundamental role in cellular homeostasis. It is possible that heat shock proteins may be involved with the phenomenon of acquired thermotolerance. Heat stress disturbs cellular homeostasis and can lead to severe retardation in growth and development, and even death. Temperature stress can have also a devastating effect on both the plant anabolism and catabolism, initially acting on protein complexes, being the quaternary structure the first folding that is lost during heat stress or heating. Understanding the role of HSPs in relation to stress resistance in a more applied perspective as a potential indicator of stress is important. New technological developments make it possible to investigate the role of genes coding for heat shock proteins in greater detail. A combination of genomics and proteonomics will further elucidate the effects of stress on expression patterns at the DNA, RNA and protein level.

Plants that are affected by various abiotic stresses react differently as a result such as the reduction in organ size or a change in the antioxidant enzyme system, and while drought and heat are often studied separately, in nature they often occur together, meaning it is essential to carry out joint studies. Furthermore, and related to the above when we consider high temperature stress, one must always consider the use of water and nutrients by the plant and other physiological functions. The effects of heat stress can also be analyzed by the technique that measures lipid peroxidation in polyunsaturated acids of the plasma membrane. The accumulation of metals in plants, affects the normal processes of plant metabolism. The study shows that there is a relationship between high metal contents in plants and their modified morphology: strong reduction of leaf thickness, modified parenchyma structure, and decreased mitochondria organization were ascertained, although toxic symptoms were apparently absent. Water-deficit stress has a significant effect on plants growth and development, with primary affects on plant structure, leaf morphology and cell ultrastructure. Physiological processes such as stomatal conductance, photosynthesis and respiration are consequently impaired with further implications on the metabolic functions such as carbohydrate and energy production as well as carbohydrate translocation and utilization.

Abiotic Stress in Plants
             
World population is growing at an alarming rate and may reach about 6 billion by the end of the year 2050. Though, the agricultural productivity is also being increased world over, yet it is not keeping pace to meet the demand of food availability. The main reasons for limiting the agricultural productivity are water shortage, depleting soil fertility and mainly various abiotic stresses and climatic change. Minimizing these loses is of primary concern for all nations to cope with the increasing food requirement. The abiotic stress is defined as the negative impact of non living factors on the living organism in a specific environment and abiotic stress is the most harm full factor concerning the growth and productivity of crops worldwide. Researches have shown that abiotic stressors are at their most harm full when they occur together in combination of abiotic stress factors (Mittler, 2006; Bianco and Defez, 2011). Numerous stresses caused by complex environmental conditions i.e. drought, too high and too low temperatures, freezing, salinity, UV light, heavy metals and recently through smog (air pollution) leading to substantial crop losses worldwide (Mahajan and Tuteja, 2005). The abiotic stresses might increase in the near future even because of global climatic change.

Climate change drastically influence water availability, salinity and several adverse soil conditions which will have direct bearing on original yields. Abiotic stress factors influence growth and secondary metabolite production in higher plants. The influences are well marked. In fact, productivities depend on the changed ecosystem also. Secondary metabolites play a major role in the adaptation of plants to the changing environment and in overcoming stress constraints. This flows from the large complexity of chemical types and interactions underlying various functions: structure stabilizing, determined by polymerisation and condensation of phenols and quinones, or by electrostatic interactions of polyamines with negatively charged loci in cell components, photoprotective, related to absorbance of visible light and UV radiation due to the presence of conjugated double bonds, antioxidant and antiradical, governed by the availability of –OH, –NH2, and –SH groupings, as well as aromatic nuclei and unsaturated aliphatic chains, signal transducing. Several plant-abiotic stress stimuli systems evidenced the multiplicity of biochemical mechanisms involved in the protective role of secondary metabolites:

Environmental stress can disrupt cellular structures and impair key physiological functions. Drought, salinity, and low temperature stress impose an osmotic stress that can lead to turgor loss. Membranes may become disorganized, proteins may undergo loss of activity or be denatured, and often excess levels of reactive oxygen species are produced leading to oxidative damage. As a consequence, inhibition of photosynthesis, metabolic dysfunction, and damage of cellular structures contribute to growth perturbances, reduced fertility, and premature senescence. Responses to environmental stresses occur at all levels of organization. Cellular responses to stress include adjustments of the membrane system, modifications of the cell wall architecture, and changes in cell cycle and cell division. In addition, plants alter metabolism in various ways, including production of compatible solutes that are able to stabilize proteins and cellular structures and/or to maintain cell turgor by osmotic adjustment, and redox metabolism to remove excess levels of ROS and re-establish the cellular redox balance. At the molecular level, gene expression is modified upon stress and epigenetic regulation plays an important role in the regulation of gene expression in response to environmental stress.

Sweet pea (Lathyrus odoratus) is the only species in the genus Lathyrus and family Fabaceae which is widely cultivated as an ornamental plant. Lathyrus comes from the Greek word “Lathyros” in which the prefix “la” means “very” and suffix “thyros” means “passionate”. The “Odoratus” is derived from Latin word which means “fragrant” (Fernald, 1950). It is mainly grown for its beautiful flower colour forms. It is an annual climbing plant growing to a height of 1-2 m with the support of a terminal tendril which twines around the plants and helps to climb. The illness caused by the ingestion of sweet pea is known as odoratism or sweet pea lathyrism. Sweet pea was used to verify Mendel’s work with the garden pea (Pisum sativum L.) in the early 1900s (Bateson, 1902). The genetical phenomenon of linkage was first demonstrated in the sweet pea. It is used prominently as a model organism to study flower development due to its large, colourful and fragrant flowers. The essential oils extracted from the sweet pea can be used in perfume blends.

ORIGIN AND DISTRIBUTION

Sweet pea (Lathyrus odoratus L.) was discovered in Sicily in 1695 (Rice, 2002). Its species are found both in the Old World and the New World. The main centres of diversity are the Mediterranean region, Asia Minor and North America as well as temperate South America and East Africa (Kupicha, 1977, Jackson and Yunus, 1984, Yamamoto et al., 1984 and Simola, 1986). It generally grows in temperate regions and has been found on all continents except Antarctica (Kenicer et al., 2009 and Kenicer et al., 2005). Its cultivation is popular not only in the United Kingdom and the United States but also in Europe, Russia, Egypt, New Zealand, Australia and Japan (Hambidge,

1996, Inoue, 1981, 2007 and Rice, 2002). There are some reports of commercial sweet pea cut flower production (Hammett, 2006, Inoue, 1981 and Parsons, 2004). A seed bank at the Chichester Collection was started in 1998 and stores around 900 cultivars and around 100 accessions of other species.

Clematis is member of the Ranunculaceae family which also known as buttercup family. This cosmopolitan genus comprises climbing lianas, small shrubs and erect sub-shrubs distributed predominantly in the temperate zone of both hemispheres but with some species distributed in tropical areas (Tamura, 1995, Johnson, 1997, Grey-Wilson, 2000 and Wang and Li, 2005). The word clematis is taken from Greek as in “klema” meaning “a vine branch”. Most species are known as Clematis in English while some are also known as Traveller’s joy, Leather flower, Vase vine and Virgin’s bower the last three being names used for North American species (Chawla et al., 2012). Most Clematis is climbers (Roh and Song, 1997), however; two notable exceptions are the species C. heracleifolia and C. integrifolia which are herbaceous and fit well in a perennial garden border. The vast majority of these are very hardy. Some species however, particularly the evergreens can only take a few degrees of frost. Most Clematis varieties produce single flowers. Some varieties produce double flowers; others produce both single and double flowers. Clematis blossoms often change colour, some very marked through the life of each flower particularly when grown in full sun. Pastel colours will hold their colour best if grown in some shade. Many Clematis species are scented, although none are strongly perfumed. The most-highly scented is the tender species C. armandii. Montana types can also be relatively aromatic often with a scent reminiscent of vanilla. Of the large flowering hybrids, Fair Rosamund is the only one with any noticeable scent.

Lotus belongs to the Nelumbonaceae family and the genus Nelumbo. There are two species in this genus; Nelumbo nucifera Gaertn. distributed in Asia and Oceania, and Nelumbo lutea distributed in North and South America (Qichao and Xingyan, 2005). Although, the species nucifera is the most important (commercially and culturally), it is critical to describe the American species, evaluate its horticultural value and its potential as a source of genetic diversity. The American species, represented by Nelumbo lutea (Syn. N. pentapetala or Nelumbium luteum) is known as American Lotus, Water-chinquapin and Yellow Lotus (Sayre, 2004) and is native to the eastern and central portions of the US ranging from Maine to Wisconsin and in the south from Florida to Texas. It is one of the most spectacular and graceful aquatics among all the native plants of India. N. indica are found all over India and extend as far as Kashmir to Kanyakumari exhibiting enormous thermoplasticity and phenotypic diversity with a large number of racial variants with different shapes, sizes and colours. First Indian fossilised record of N. nucifera has been reported from the Pleistocene epoch of Kashmir. The presence of Nelumbo in the Tertiary period of Assam is reported on the basis of impressions of leaves and rhizomes found in the collection from Eocene bed near Damalgiri. These records confirm the evidence in support of the view that N. nucifera is indigenous to India.

Lotus has good fragrance. About seventy compounds were identified with hydrocarbons representing > 75% of the extract. 1, 4 – Dimethoxy benzene, 10, 8 – Cineole, ferpinen – 4al and linalool were important constituents characterization of the scent of lotus flower (Omata et al., 1991).

Poinsettia (Euphorbia pulcherrima) is one of the most popular ornamental pot plants belonging to the family Euphorbiaceae. The botanical name Euphorbia pulcherrima means very beautiful. Euphorbia pulcherrima the name originally given by German botanist Karl Ludwig Wilenow was changed to “Poinsettia” in honour of “Mr. Poinsett” in 1836 by William Prescott. Poinsettia is a short-day, non-food and non-feed vegetatively propagated ornamental plant. Poinsettias are fascinating winter blooming small shrubs or trees which can grow anywhere from about 0.6 to 5 m tall. The coloured bracts of poinsettia plants are actually leaves. Colours of the bracts can be red, pink, orange, white or marbled. These coloured bracts are caused by photo-periodism. Poinsettias have also been called the lobster flower and the flame-leaf flower due to the red colour. California is the top U.S. Poinsettia-producing state.

ORIGIN AND DISTRIBUTION

The poinsettia (Euphorbia pulcherrima) is the world’s most economically important potted plant but despite its preeminence it is not clear which wild populations are ancestral to the varieties cultivated around the world. Tradition holds that the U.S. envoy to Mexico, J. R. Poinsett collected the progenitors of the over 300 varieties in global cultivation on an 1828 excursion to northern Guerrero State, Mexico. It is unknown whether the contemporary cultivars are descended from plants from Guerrero or whether germplasm from other parts of poinsettia’s 2000 km long distribution entered into cultivation during the nearly 200 years of subsequent poinsettia horticulture.

The combination of nuclear and plastid haplotypes characterizing cultivars was found only in northern Guerrero. Whereas, distribution modeling indicated that suitable habitat conditions for wild poinsettias are present in this area consistent with their likely wild status. Finding shows that the area of northern Guerrero as the cultivated poinsettia’s probable ancestral region congruent with the traditional account attributing the original collections to Poinsett (Trejo et al., 2012). Poinsettias are originally native to the central and southern parts of Mexico where they grow as a shrub up to 5 m. The poinsettia was introduced to the United States by Mr. Poinsett in 1828. It was introduced into North America in1838 from Mexico and since that time it has achieved considerable economic importance as a pot plant in the florist trade.

Orchids belong to family Orchidaceae, the largest family of the flowering plants. The term ‘orchid’ has its origin from the Greek word, “orchid” meaning “testicle”, referring to the paired underground tubers of terrestrial orchids. There are several generas in orchids, which are popular for their separate importance as cut flower, pot plant, medicinal properties, flavour extraction, etc. The fascinating flowers exhibit an incredible range of shape, size and colour, long life of flowers on plant and an amazingly long keeping quality, which no other plant can claim.

ORIGIN AND DISTRIBUTION

Majority of the cultivated orchids are native of tropical countries and occur widely in humid tropical forests of South and Central America, Mexico, India, Ceylon, Burma, South China, Thailand, Malaysia, Philippines, New Guinea and Australia. Brazilean cattleyas, Mexican laelias and Indian dendrobiums, cymbidiums and vandas have been extensively utilized for the development of modern orchid industry in the world.

Geranium (Pelargonium spp.) belongs to the family Geraniaceae. The name Pelargonium was introduced by Johannes Burman a Dutch Botanist in 1738, from the Greek word “Pelargos” means stork because the seed head looks like a stork’s beak. Due to their long and beak-shaped fruits, they are also known by the name of cranesbills. Geraniums are popular flowering plants and grown as decorative pot plants for indoor and outdoor. There is a world demand for the rose geranium essential oil of Pelargonium species which contains geraniol, linalool and citronellol, substitutes for the expensive attar of roses in the perfume trade. Pelargonium species was known for their medicinal value by the earliest indigenous people (Swanepoel, 2009).

ORIGIN AND DISTRIBUTION

The plants originated from South Africa (Swanepoel, 2009), as well as Reunion, Madagascar, Egypt and Morocco and were introduced to European countries such as Italy, Spain and France in the 17^th century. Geranium includes around 422 species of flowering annual, biennial and perennial plants. Both Geranium and Pelargonium are genera in the Family Geraniaceae. Linnaeus originally included all the species in one genus. Geranium, but they were later separated into two genera by Charles L’ Heritier in 1789. Although members of the Pelargonium genus are often referred to as ‘Pelargoniums’ to try to avoid confusion, many people still use the older common name of ‘Geranium’.

Most of the Pelargonium plants cultivated in Europe and North America have their origins in South Africa. Geranium robertianum is found throughout Europe, Asia and North Africa where it grows on a variety of soils, rocks, tree trunks and decaying organic matter such as logs. It is a component of virtually all forest types there. In the Pacific Northwest it is primarily found west of the Cascade crest although it extends along the Columbia River in Klickitat County. Ecological structure of Geranium robertianum L. populations under natural conditions and in the garden in Poland. Geranium farreri found in China, in south Gansu and north-west Sichuan.

Dahlia (Dahlia spp.) syn. Georgina belongs to family Compositae (Asteraceae). Dahlia was named after “Professor Andreas Dahl”, a Swedish pupil of Linnaeus and author of Observations Botanicae. In India, dahlia is grown as potted plant and landscape uses but it is a poor crop as commercial flower due to shorter commercial life and its potentialities have not been exploited so far. Therefore, there is need to originate more and more new quality cultivars. Dahlias are half-hardy perennials with tuberous roots. Stems are mostly erect, branched, glabrous or scabrous. The leaves 1-3 pinnate, with slightly serrated margin are produced opposite at each node on the stem. They bear flowers on a long, stiff stems well above the foliage. Ray florets are neutral or pinnate and disc florets perfect.

ORIGIN AND DISTRIBUTION

The wild species of Dahlia are natives of Mexico and Central America, where some hybridization and selection had probably already occurred prior to their introduction into Europe at the end of the 18^th century (Crane et al., 1947 and Sorensen, 1969). The dahlia has been in Europe for over 200 years. It came from Mexico to the Botanical Gardens in Madrid towards the end of the 18^th century and was named by Abbe Cavanille in honour of Andreas Dahl, Swedish scientist-cum-environmentalist. The dahlia was introduced into England in 1803, but from a few varieties it soon had more than 300 varieties within the first 15 years. The initial named species imported into Europe were D. pinnata, D. rosea and D. coccinea. The first dahlias grown outside of Madrid were single (open-centred) and multi-ray open centre flowered, but it was not long before the horticultural growers of the day discovered the dahlia was a natural hybrid and when grown from seed, it readily changed its form and colour, Thus it has a range of different types. Further introduction, accompanied by hybridization and selection, have resulted in the production of a wide range of flower, forms and colours. Most of the garden types have been developed from D. variabilis. The first double flowered varieties were called Show and Fancy types. The show were self-coloured, ball like flowers, while the Fancy ones were multi-coloured.

During the mid 1800’s, these Show and Fancy flowers attained cult status with gardeners and several thousand different varieties were recorded. Other forms followed, in 1829 the first Anemone flowered dahlia appeared and then in 1850 the first Pompon was raised in Germany and was named after the bobble on a French sailor’s hat. The origin of the cactus and Decorative type belongs to the arrival of ‘Juarrezii’. According to the written records it was important as a piece of tuber from Mexico in 1872 to Holland. M. Van de Berg of Uttrecht received this so called species from Mexico and released stock of the variety in 1874. Subsequently, ‘Juarrezii’, named after a President of Mexico, was introduced into the UK by W. Cullingford a Vice President of the NDS and distributed by H. Cannell after 1880. Collerettes are the last form of dahlia to have been raised, that has their origin in France and is due to sporting of dahlias at Jardin Botanique de Lyon at the end of the 19^th century.