FLOWER BULBS: A REVIEW. 13 1. BULBS : INTRODUCTION AND IMPORTANCE IN CUT FLOWER TRADE. Bulbs have been of vital interest ever since they made their first appearance on earth 35 million years ago (Binney, 1998). Flower bulbs often referred to as ornamental geophytes constitute a diverse group of varied morphological, developmental and physiological growth forms among the plant kingdom (Raunkiaer, 1934; Rees, 1989; Halevy, 1990; De Hertogh and Le Nard, 1993b). Horticulturally, today world wide bulb production and utilization have increased about three fold over the last 20 years; besides the spectrum of bulbs being researched and commercially grown is expanding greatly (De Hertogh and Le Nard, 1992). Extensive literature pertaining to bulbs has appeared in scientific journals and in trade publications. The fact that about nine International flower bulb symposia have been conducted under the auspices of International Society for Horticultural Science (ISHS), highlights the increasing importance of bulbs in world floriculture (Schenk, 1971; Rees and van der Borg, 1975; Rasmussen, 1980; Bogers and Bergman, 1986; Doss et al., 1990; Saniewski et al., 1992; Lilien-Kipnis et al., 1997; Littlejohn et al., 2002; Okubo et al., 2005). A bulb in common usage may mean a tuber, corm or a true bulb (Trivedi, 1987). The word "bulb" is used as a general term by gardeners for any of the flowers planted at the fall and may even include some corms (crocus), tubers (anemones) or tuberous roots (ranunculus); but actually in spring, the most spectacular flowers are produced by the true bulbs. In horticultural sense, a bulbous plant is a herbaceous or perennial ornamental species that produces fleshly storage organs which may be a true bulbs, corms, tubers, rhizomes or tuberous roots. To a botanist a bulb is an underground storage organ with a vertical stem axis surrounded by 14 swollen leaf bases. In strict botanical terms the word “bulb” is used for an underground vertical shoot bearing modified leaves that are used as food storage organs by a dormant plant. A baby bud surrounded by the scales is located at the basal central portion of the bulb. In true bulbs, the scales contain all the food required by the bulb to flower and thrive. Anchoring the scales and the floral stalk also holding the bud is the basal plate which sustains the roots of the plant. The entire package is protected by a thin outer skin called the tunic; however some families such as Liliacaea possess “non-tunicate" bulbs. True bulbs are mostly found among the monocotyledonous species particularly in members belonging to Liliaceae and Amaryllidaceae. The cultivation of flower bulbs for commercial purposes started in Haarlem, Holland about 400 years ago. Later the cultivation spread to the north and then more especially to the south. The area between Haarlem and Leiden eventually became known as 'De bollenstreek' - the bulb district. For many years a large part of the population earned their living from bulbs whether in nurseries, export or in industries that supplied the sector. The town of Lisse regarded itself as the centre of the bulb-growing area and boasted a postmark that declared: "Lisse, the centre of the bulb district". Alongside this bulb-growing district, a second one developed during World War I in the most northern area of the province of North- Holland, the Anna Paulowna Polder and after World War II there was a massive expansion in the cultivation of flower bulbs there. After 1945 a new centre emerged in the Noordoostpolder (the North-East Polder); where mainly tulips, lilies and gladioli were cultivated. Today the Dutch flower bulb industry is a highly dynamic enterprise. Importance of bulbs: The cultivation of bulbs have surpassed the other flower sources; as the bulb are easy to store, require minimal attention and respond to varied soil conditions. Also bulbous plants are sought after for 15 varied natural compounds obtained from them. Large number South African traditional healers over many centuries have increasingly used bulbous plants mainly belonging to the Amaryllidaceae and Hyacinthaceae families. A number of such plants have particular uses as disinfectants and anti-inflammatory agents (Louw et al., 2002). Bulbous plants of family Amaryllidaceae particularly those belonging to genus Narcissus have been reported to contain up to 0.1% of galanthamine used in the treatment of Alzheimer’s disease (Lopez et al., 2002). Besides Narcissus, rich contents of galanthamine have also been extracted form the bulbs of Galanthus and Leucojum (Sener et al., 1999). Status of bulbs in cut flower trade: Bulb flowers occupy a significant position in world-wide production and trade in cut flowers. The total acreage of flower bulbs have been reported to be about 32,153 hectares world wide. Out of this about 22.987 hectare has been reported to be under bulb cultivation in Netherlands alone which was about 14.265 hectares in 1980. The top five types of bulbs which are sold world over are: tulips, lilies, narcissi, hyacinth and gladioli. The Netherlands accounts for about 65% of the total production area for flower bulbs in the world and therefore remains the leader in this sector. The export value of Dutch bulbs has doubled in the past 25 years while the total export value of ornamental produce is five times bigger. Many types of bulb flowers particularly tulips and lilies are exported from the Netherlands. The major markets being Germany, United Kingdom, France and United States. Costa Rica exports lilies to the value of about 5.5 million euros to the US. In addition countries such as Chile (2.4 million euros) and Mexico (0.8 million euros) export lilies to US market. Tulips are undoubtedly the largest cultivated bulbs. Production of tulips takes place in some 15 countries world-wide, with the 16 largest production area in the Netherlands with 10,800 hectares (88%). The other five main countries are Japan 300 hectares, 2.5%; France 293 hectares, 2.4% ; Poland 200 hectares, 1.6% ; Germany 155 hectares, 1.3% and New Zealand 122 hectares, 1% (Buschman, 2005). 2. BULBS : EVOLUTION, GEOGRAPHICAL EXPANSES AND CONDUCIVE CONDITIONS FOR GROWTH. Evolution of bulbous habit of growth: Originally the evolution of geophytic or bulbous lifestyle developed as a protective mechanism to allow plants to get through hard times especially drought and cold. Accordingly bulbs fall into two groups: spring-flowering (which are planted in the fall) and summer-flowering (which are planted in the spring). Spring-flowering bulbs such as tulips, crocuses, hyacinths, daffodils, and irises are the universal symbols of spring. Their vibrant and colorful flowers are the first to bring life back to a barren winter landscape. Summer-flowering bulbs (dahlias, begonias and anemones) bring variety, texture, unique color and long flowering times to summer gardens. A more accurate grouping however divides bulbs into hardy and tender varieties. As a rule spring- flowering bulbs are hardy bulbs. These bulbs are planted in the fall generally before the first frost and can survive the cold winter months. Many hardy bulbs such as daffodils perennialize well and can be left in the ground to flower year after year. Most summer- flowering bulbs such as Dahlia, Hippeastrum, Hymenocallis, Gladiolus, Polianthes, Zantedeschia are tender bulbs. These bulbs cannot survive harsh winter conditions and must be planted in spring after the last frost of the season. To enjoy these bulbs year after year they must be dug up in fall and stored indoors over the winter. Geographical expanses of bulbous habit: Subtropical zone has been 17 primarily represented to be the main evolutionary line of bulbous habit, later the bulbous habit has been shown to have branched naturally to varied ecological regions in both temperate and arid regions (Khokhryakov, 1975; Merrow, 2002). Geographically the bulbous habit of growth occurs almost exclusively in temperate parts of the world i.e. beyond 30 degrees north and south latitude. The common natural habitats of bulbous plants are the Mediterranean; South Africa; West Asia especially Turkey and Iran, Central Asia and Afghanistan; the areas around the Black Sea and the Caucasus besides the Pacific coast of North and South America. Fewer bulbous genera have been shown to be indigenous to Japan, Great Britain, North East America, tropical and North Africa (Bryan, 2002). The evolution of geophytes in climatic areas with marked seasonal changes has led to their adaptation to periods of high and low temperatures, drought and to significant changes in the plant’s morphological structure as also the annual developmental cycles of growth and dormancy. Not surprisingly most bulbous species are native to either grassland habitats or mountainous regions. There have been reports about the suitability of mountainous condition for the bulb development in lilies (Xia et al., 2005). In grasslands, bulbs are usually spring-blooming with foliage dying down by early summer. In mountainous areas the bulbs flower quickly during spring mature their foliage during the short summer and then disappear below ground during the long cold winter. Most common bulbs which grow and flower well in the hills include Agapanthus, Anemone, Cylamen, Eurycles, Fritillaria, Iris, Ixia, Hyacinth, Moraea, Montbretia, Nerine, Paeonia, Kniphofia, Ornithogalum, Ranunculus, Tulip, Watsonia, Sparaxis, Zantedeschia and Begonia etc. Although some hardy types of Freesia, Narcissus, Gloxinia and Lilium may flower in plains but they do not show very attractive display of colour and often fail to flower in the 18 second year. Conducive conditions for bulb growth: The optimum conditions for most bulbs are a cold dry winter often covered with snow, water ready rains in spring followed by a dry summer with cool or dry autumn (Furse, 1971). Mediterranean region is the suitable location for this type of climate and as such Holland appears to lead the world bulb production.