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1.1 Introduction

The word “Allium” comes from the Greek word “aloe,” which means to avoid, and was given to the genus because of the characteristic offensive smell of its members. The genus Allium is one of the largest plant genera and includes about 780 species. Cultivation of Allium species is reportedly very old and as extensive as civilization itself (Block 2010). The wealth of Allium species was mentioned in the ancient civilizations both as flavorful foods and healing herbs.

Allium is a genus within the family Alliaceae and belongs to the order Asparagales of the monocot division. Asparagales and the Poales (which includes the grasses) are two well-supported monophyletic orders within the monocots (Rudall et al. 1997). The genus Allium is mainly restricted to the regions that are seasonally dry, with centers of diversity in Soutwest/Central Asia, eastern Asia, and in North America. Members of the genus Allium include many economically important crops such as onions (Allium cepa), shallots (Allium oschaninii), leeks (Allium ampeloprasum var. porrum), scallions (Allium ascalonicum), garlic (Allium sativum), chives (Allium schoenoprasum), Japanese bunching onions (A. fistulosum), rakkyo (A. chinense) and Chinese chives (A. tuberosum). Others such as A. karataviense and A. christophii are cultivated as ornamentals (Huxley et al. 1992).

Different communities use several wild Allium species for different purposes while breeders use them as sources of economically important traits for improving the cultivated species. Many wild Allium species are believed to have significant potential contribution to the Allium breeding community and to the global food and health needs. Despite the importance of these species, there are very few studies and research investments on them. The taxonomy is not extensive and conservation efforts have been limited. The limited extent of genomic tools within the genus as a whole has further limited research focus to cultivated species. We provide here a brief review on wild Allium species including basic botany, conservation initiatives, contribution toward the development of cytogenetic stocks, genetic tools, and improvement of the cultivated species. The potential for more domestication and commercialization of wild Allium species as a source of income, nutrition, and medicinal remedy are also mentioned.

1.2 Basic Botany of the Species

The taxonomy of Allium has been described as complicated with a great number of synonyms and intrageneric groupings (Klaas 1998). The genus comprises either short- or long-lived perennials (Brewster 1998) with characteristic storage organs (Fritsch and Friesen 2002). The typical storage organs are rhizomes, roots, or bulbs.

The bulbs are generally enclosed in membranous tunics, free or almost free tepals, and often in a subgynobasic style (Friesen et al. 2006). The bulbs can be large and single, or small, forming clusters (Le Guen-Le Saos et al. 2002) and range in size from 2–3 mm to 8–10 cm in diameter.

The leaves are tubular (as in onions) or flat arising from the underground stem with long sheathing base, which can give the appearance of a stem (Block 2010). Many Allium species have basal leaves that wither away from the tips downward before or while the plant is flowering (http://www.absoluteastronomy.com/topics/Allium). The inflorescence can be fasciculate, umbel or head like, few to many, and loose to dense flowers have been reported (Fritsch and Friesen 2002). Flowering time varies with various Allium species. Flowering has been recorded in spring, summer, or autumn (Brewster 1998). A majority of Allium species are outbreeders, but the occurrence of both outbreeding and inbreeding forms in the same species has been reported (Brat 1965).

Allium species contain nectaries, which are located between the base of the ovary and the flattened widened base of the inner whorl of stamen and filaments (Peumans et al. 1997). The ovaries are largely trilocular and the styles are single and slender (Fritsch and Friesen 2002). The seeds can be angular or globular (Fritsch and Friesen 2002). Polyembryony (the development of multiple seedlings from a single seed) has been observed in several Allium species within the subgenus Rhizirideum (Specht et al. 2001).

1.3 Conservation Initiatives

As in many other crop species, there is evidence of genetic erosion in Allium species (Mingochi and Swai 1994). Goodding’s onion (Allium gooddingii), a delicate perennial with reddish-purple flowers and a pungent onion aroma, was listed as a candidate for federal endangered/threatened status (http://www.fws.gov/southwest/es/Arizona/Goodings.htm ). Allium roseum var. odoratissimum, which is harvested from roadsides during spring in Tunisia, is marketed very cheaply creating the risk of genetic erosion. Allium roylei, one of the most important sources of disease resistance genes in the genus Allium (Kofoet et al. 1990), is also a threatened species (Araki et al. 2010) and an urgent plea for its conservation has been made (Kohli and Gohil 2009). The need for protection of A. gooddingii was recognized in 1998 by the Forest Service and the Environmental Protection Agency of the United States of America, which helped considerably toward the protection of this species against erosion (USFWS 2000). Ghrabi (2010) describes the need to protect and domesticate A. roseum as an urgent necessity.

Global networks have, therefore, been formed to coordinate the collection, conservation, and utilization of the genetic resources within the genus Allium. Examples include the European Cooperative Program for Plant Genetic Resources (ECPGR) Allium Working Group, the United Kingdom Natural Resources Institute Onion Newsletter for the Tropics network, and the Allium Improvement Newsletter (Astley 1994). The Allium working group (http://www.ecpgr.cgiar.org/Workgroups/Allium/Allium.htm) established in 1982 in Europe is one of the original six working groups constituted during the first phase of ECPGR. The work of the ECPGR Allium working group benefited significantly from the work program of the European Genetic Resources Allium project (ended 31 Mar 2000), and the research projects FAIR (1996–2001) and “Garlic and Health” (1998–2003). In the framework of the European Genetic Resources 20 Project, over 200 accessions of wild taxa belonging to 35 species were collected and preserved in Greek gene Bank, Greece (Samaras 2001).

In India, the National Bureau of Plant Genetic Resources (NBPGR) conducted extensive plant exploration in different Allium-growing states resulting in the collection of over 2,200 accessions of Allium species including wild relatives such as A. ampeloprasum, A. auriculatum, A. ascalonicum, A. carolinianum, A. chinensis, A. wallachi, A. tuberosum, and A. rubellum (Singh and Rana 1994). NBPGR also introduced over 1,100 accessions of Allium germplasm from over 40 countries (Singh and Rana 1994). In Tunisia, the Medenine Institut des Regions Arides has recently developed a research program to protect, conserve, and domesticate A. roseum (http://www.uicnmed.org/nabp/database/HTM/PDF/p5.pdf).

Given the outbreeding nature of most Allium species, cryopreservation has been suggested as a viable method of conservation (Volk et al. 2004) but this will need to be combined with traditional field maintenance, pollen storage, and in vitro culture (Working Group on Allium 2009). Cryopreservation should be done carefully due to the high risk of contamination and virus infection.

1.4 Role in Elucidation of Origin and Evolution of Cultivated Allium Species

The genus Allium is one of the largest genera of perennial bulbous plants on earth. The use of internal transcribed spacer (ITS) region of ribosomal DNA recently classified the genus into 780 species, 56 sections, and 15 subgenera (Friesen et al. 2006). Earlier molecular comparisons recognized 67 sections and 14 subgenera (Fritsch and Friesen 2002). The fact that so many species exist suggests that a lot of evolutionary differentiation has occurred (Stevenson et al. 1999).

Both morphological and molecular data have been used to study evolution of the genus Allium. Wendelbo (1969) initially suggested that all other groups in Allium might be derived from rhizomatous species without bulbs. Rhizomes are a distinct feature within the subgenus Rhizirideum. More recent reports indicate that rhizomes have evolved from an ancestral bulbous life form that was subsequently lost at least twice independently (Ricroch et al. 2005). Other Allium species (A. caeruleum, A. proliferium, A. vineale, A. carinatum, and A. scorodoprasum) have been grouped as viviparous due to the development of topsets instead of flowers or intermingle with flowers in the florescence (Kamenetsky and Rabinowitch 2001).

More molecular studies of the genus have given insight into evolution of the cultivated Allium species. Amplified fragment length polymorphism (AFLP) studies in garlic clustered garlic clones very closely with A. longicuspis suggesting that the two species are not genetically distinct (Ipek and Simon 2001). A. longicuspis and A. tuncelianum are genetically identical to garlic and therefore, were earlier suggested as possible ancestors of garlic (Block 2010). However, DNA analysis indicated that neither A. longicuspis nor A. tuncelianum are ancestor species of garlic (Block 2010).

In the subgenus Cepa, section Cepa, the closest wild relative of A. cepa and A. fistulosum has been identified as A. vavilovii and A. attaicium, respectively (Klaas and Friesen 2002). A. oschaninii, on the other hand, appears to be a sister group to A. cepa/A. vavilovii evolutionary line (Friesen and Klaas 1998). A. ampeloprasum is thought to be the ancestor species of leek and kurrat (A. ampeloprasum var. kurrat) (Block 2010).

The use of nuclear ribosomal DNA [ITS and external transcribed spacer (ETS)] has been suggested to provide sufficient resolution for investigating evolutionary relationships within Allium (Nguyen et al. 2008). Nguyen et al. (2008) used combined sequences from 39 native Californian Allium species with 154 ITS sequences available on GenBank to develop a global Allium phylogeny with the simultaneous goals of investigating the evolutionary history of Allium in the Californian center of diversity and exploring patterns of adaptation to serpentine soils (Nguyen et al. 2008). The ITS region alone was sufficient to resolve the deeper relationships in North American species.

1.5 Role in Development of Cytogenetic Stocks and Their Utility

Allium species show variation in several cytogenetic characters such as basic chromosome number, ploidy level, and genome size. Allium species are identified by their symmetrical and uniform karyotypes, which can often make chromosome identification difficult (Stevenson et al. 1999). The somatic chromosome number ranges from 2n = 16–40 with basic chromosome numbers of x = 7, 8, and 9 (Karpaviciene 2007).

The ploidy level varies from 2x to 16x (De Sarker et al. 1997; Klaas 1998; Bennett et al. 2000) while the 2C DNA amounts per genome ranges from 16.93 to 63.57 pg (Ricrocha and Brown 1997). In a study of 25 Allium species, Jones and Rees (1968) found considerable differences among 2C-values measured by Feulgen densitometry. Ohri et al. (1998) confirmed this in a survey of 86 Allium species (representing all six subgenera), measured in 4C nuclei by Feulgen densitometry. The same conclusions were drawn from the study of genome size in 28 Allium species (Baranyi and Greilhuber 1999).

To study chromosome organization within Allium species, an integrated map of Allium cepa × (A. roylei × A. fistulosum) was used (Khrustaleva et al. 2005), which showed that Allium species recombination predominantly occurs in the proximal half of chromosome arms. Cytological analysis in populations of A. roylei has reportedly revealed presence of complex chromosomal configurations during male meiosis and chromosomal heteromorphicity in somatic metaphase spreads (Kohli and Gohil 2009). Unstable B-chromosomes have also been reported in some European populations of A. schoenoprasum (Stevens and Bougourd 1994).

Overall, very little cytogenetic work has been done in wild Allium species. The most notable is the use of A. galanthum cytoplasm to develop cytoplasmic male sterile (CMS) substitution lines of cultivated Allium species (Yamashita 2005). More studies are required in this area to improve our understanding of these complex genomes. Significant utilization of wild Allium cytogenetic stocks in the breeding of cultivated species will depend a lot on our deep understanding of the specific genomes involved.

1.6 Role in Classical and Molecular Genetics

Allium genetics is poorly understood mainly due to the large genomes of the Allium species. There have been almost no classical genetic studies and the use of molecular tools has only been recently initiated. The few genetic studies in Allium species have focused on specific traits of economic importance such as bulb color, flavor, and disease and pest resistance.

Lack of genetic variability within some cultivated Allium species necessitates the use of closely related germplasm for the development of linkage maps. In the section Cepa, for example, A. roylei has been crossed with A. cepa and A. fistulosum to develop a linkage map. A. roylei shows a unique position in the taxonomy of the genus Allium (Fritsch and Friesen 2002). The nuclear DNA profile of A. roylei is related to the species of Cepa and Phyllodolon though its chloroplast DNA profile is related to the section Schoenoprasum (van Raamsdonk et al. 2000). A. roylei crosses easily with A. cepa and A. fistulosum. Crosses between A. roylei and A. cepa yield fertile hybrids.

The first Allium linkage map based on an F2 population of an interspecific cross between A. cepa and A. roylei used AFLP markers (van Heusden et al. 2000a). This map was later used to locate a resistance locus for downy mildew (Peronospora destructor) to the distal end of chromosome 3 (van Heusden et al. 2000b). Downy mildew is a common and serious disease in onions, which results in major yield losses. Kofoet et al. (1990) reported that resistance to downy mildew in A. roylei was controlled by a single dominant gene named Pd1. The location of the resistance gene was confirmed using genomic in situ hybridization (GISH) and this resistance was successfully introduced into a bulb onion cultivar by the use of conventional backcrossing (Scholten et al. 2007).

Studies of resistance to anthracnose (Colletotrichum gloesporioides Penz) among A. cepa and A. roylei (Galvan et al. 1997) revealed that the resistance of A. roylei to the Brazilian anthracnose isolate is dominantly inherited. The same study also suggested that the resistance was most likely determined by more than one gene (Galvan et al. 1997).

Another important trait in Allium species is bulb color, which has been widely studied. The pigments responsible for bulb color are flavonoids. Flavonoids are common plant secondary metabolites that have been shown to function as antioxidant agents (Sengupta et al. 2004). Flavonoids are involved in UV protection, plant–microbe interactions, fertility, and pigmentation (Shirley 1996). Inheritance of bulb color has been shown to be very complex (Masuzaki et al. 2006), involving five major genes (Davis and El-Shafie 1967). I and C are the genes concerned with the expression of the pigmentation. C of the basic color factor is likely a regulatory gene controlling chalcone synthase (CHS) gene transcription (Kim et al. 2005). I is also presumed to be a regulatory gene as it inhibits pigment formation regardless of the other dominant genes (Kim et al. 2004). CHS is presumably located on chromosome 5A (Masuzaki et al. 2006) of A. cepa.

Although these genes have been studied in cultivated Allium species, it is expected that the flavonoid synthesis pathway in wild Allium species would contain similar genes making such reports applicable in the wild species.

1.7 Role of Wild Allium Species in Crop Improvement

Wild Allium species act as a reservoir of important traits that can be used to broaden the genetic base of the cultivated Allium species. However, the relatively long juvenile phase in most cultivated species and severe inbreeding depression have further hindered the use of wild Allium species for the improvement of cultivated Allium species. There are a few reports of interspecific gene introgression through classical breeding most of which have been done within the section Cepa.

Genes for resistance to downy mildew and Botrytis leaf blight (Botrytis squamosa) have been transferred from A. roylei (Kofoet et al. 1990; de Vries and Wietsma 1992) to A. cepa. A. roylei has also been used as a bridging species to stably introgress disease resistance genes from A. fistulosum into A. cepa. A. fistulosum harbors a number of genes for resistance to diseases and pests (Rabinowitch 1997). Although A. fistulosum and A. cepa are grouped under the same section, Cepa, the genome of A. cepa has a 28% higher DNA content than A. fistulosum (Labani and Elkington 1987) making crosses between the two species non-viable. Using the bridge-cross approach, A. fistulosum was stably integrated into A. cepa genome and unique populations were developed in which the important resistance genes segregated (Khrustaleva and Kik 2000).

Breeding for increased flavonoid content has become a major objective within Allium as people pay more attention to health-promoting compounds. In onions, flavonoid content has been the subject of many studies (Masuzaki et al. 2006; Kim et al. 2009a). Given the importance of flavonoids for human consumption, it is important to find ways of developing Allium cultivars that accumulate flavonoids to a larger extent (Masuzaki et al. 2006) and the wild germplasm presents a viable option. Allium ursinum (wild garlic) and A. victorialis have been reported to contain novel flavonoids (Andersen and Fossen 1995; Wu et al. 2009) that could be introgressed into garlic (A. sativum). Although garlic breeding in the past was limited to clonal selection of wild varieties or spontaneous mutants, routine seed production has been developed (Simon and Jenderek 2004) making it possible to introgress genes from closely related species using conventional means.

Higher fructan content is another trait of interest in Allium that could be improved using wild species. Fructans are a significant source of soluble dietary fiber (Kleessen et al. 1997). Fructan consumption has been correlated with lower rates of colorectal cancers (Roberfroid and Delzenne 1998). Analyses have reported that accumulation of fructans is associated with greater thiosulfinate concentrations (Havey et al. 2004). Thiosulfinates have incredible health benefits and have been shown to be abundant especially in A. tuberosum L. (Kim et al. 2008). More screening of the wild germplasm using traditional and molecular means could reveal more novel sources for the improvement of fructan content in the cultivated species.

Wild Allium species have played a role in creating and restoring CMS in cultivated Allium species. CMS is a maternally inherited condition in which a plant is unable to produce functional pollen (Schnable and Wise 1998). Male sterile plants are essential to exempt breeders from the difficulty of emasculation and results in the production of large numbers of F1 seeds. Compared with genic male sterility, which is controlled only by nuclear genes, the CMS system allows easy propagation by using the appropriate maintainer line (Yamashita et al. 2010). The cytoplasm of A. galanthum Kar. et Kir., a wild species in section Cepa, has been used to develop a male sterile line for shallot and bunching onion (Yamashita et al. 1999) thus making it possible to produce hybrid seeds in these species at a commercial scale. A. roylei restores CMS (type T) in A. cepa (de Vries and Wietsma 1992).

Embryo rescue has been employed where distant crosses do not result in viable offspring. The procedure of embryo culture defines the techniques used to promote development of an immature or weak embryo into a viable plant. Depending on the organ used, embryo rescue is referred to as embryo, ovule, or ovary culture. Interspecific hybrids between A. fistulosum L. and A. macrostemon Bunge have been developed through ovary culture (Umehara et al. 2006a). A. macrostemon is a perennial herb with medicinal properties that propagates vegetatively and grows wild in China, Korea, and Japan (Fritsch and Friesen 2002). Embryo rescue has also been done to improve the aroma profile of onions (Keusgen et al. 2002). Embryo rescue of Allium species is usually done on a phytohormone-free medium (Umehara et al. 2006b).

Tsukazaki et al. (2006) proposed a “simple sequence repeats (SSR)-tagged breeding” scheme to enhance the rapidity, ease, and accuracy of variety identification and F1 purity test in bunching onion. Their breeding scheme could be extended to other Allium species and utilized in backcrossing programs. With the current progress in Allium transformation (Eady et al. 2005; Kenel et al. 2010), it will be possible to transfer genes of interest from distant wild relatives into cultivated Allium species. Despite the few successes in introgression of resistance genes within the section Cepa, there are many diseases and pests such as neck rot (Botrytis allii Munn.), basal rot (Fusarium spp.), black mold (Aspergillus niger Tiegheim) for which sources of resistance are yet to be identified (Singh and Rana 1994). There is potential in identifying these genes from the wild germplasm. As domestication of more Allium species is still going on, future research will need to focus on optimization of screening, transformation protocols, and development of more molecular markers for the newly domesticated species.

1.8 Genomics Resources

Molecular tools for the improvement of Allium species have been lacking and the huge nuclear genomes are the major constraint. The first isolation of SSRs in the genus Allium was from bulb onion (A. cepa) (Fischer and Bachman 2000) only recently. In wild Allium species, the AFLP linkage map developed using F2 population of an interspecific cross between A. roylei and A. cepa was the first Allium genetic map based on an interspecific cross (van Heusden et al. 2000a, b). However, this effort resulted in two maps; one map based on A. cepa markers and the second map based on A. roylei markers. The two maps were not integrated and 25% of the markers remained unlinked (van Heusden et al. 2000a, b). More recently, SSR markers have been developed and evaluated in both cultivated (A. fistulosum, A. cepa) and wild Allium species (A. roylei, A. vavilovii, A. galanthum, A. altaicum) (Araki et al. 2010).

A number of expressed sequence tags (ESTs) have been developed for cultivated Allium species (Kuhl et al. 2004; Kim et al. 2009b), even though none was detected from the National Center for Biotechnology Information (NCBI) database for wild Allium species. ESTs are a useful resource for identifying full-length genes and could be used in wild Allium species to identify novel genes. SSRs and single nucleotide polymorphisms (SNPs) derived from ESTs are likely to be transferred to the wild species as they are derived from less variable regions of the genome. There are currently EST-derived SSRs developed from an analysis of a bulb onion cDNA library (Kuhl et al. 2004) that could be tested for transferability in wild Allium species of interest. A garlic EST database (Kim et al. 2009b) is also available for the development and testing of more markers in interesting closely related wild species.

There are no known reports of bacterial artificial chromosomes (BACs) developed for the wild Allium species but those developed for onion (Suzuki et al. 2002) and garlic (Lee et al. 2003) will be a starting point toward the identification of candidate genes in wild Allium species. Given the close phylogenetic relationship between the Poales (includes the grasses) and Asparagales (Chase et al. 2000), it is highly expected that the advanced genomic resources available within the Poales (complete genomic sequence in Oryza sativa L., assembled BAC contigs, comprehensive EST databases) could be used for genetic improvement of Asparagales. However, only scant colinearity has been observed so far at the recombinational level between onion and rice (O. sativa L.) (Martin et al. 2005). More analysis within the wild Allium species may reveal more significant colinearity and provide insights into the evolution of the Allium species.

With the advances recently made in sequencing technologies, more genomic resources will be developed at a faster and cheaper rate than was possible a decade ago. These resources will make it possible to exploit the useful genetic variation available within the wild Allium species.

1.9 Scope for Domestication and Commercialization

The genus Allium comprises about 700 species of which less than 10% are cultivated but reports show evidence that domestication is still going on (Fritsch and Friesen 2002). There are several species of minor importance grown as semi-domesticated types or as wild economic species (Pandey et al. 2005) in India and other parts of the world. Domestication has therefore been done for different purposes.

A. komarovianum Vved was recently introduced into cultivation in North Korea as a vegetable (Hanelt 2001). Other wild Allium species used as vegetable in different parts of the world include A. fasciculatum in Bhutan (Pandey et al. 2008) and A. roylei in India (Kohli and Gohil 2009). Najjah et al. (2009) demonstrated the potential of A. roseum as an antimicrobial agent against food poisoning bacteria. A. oschaninii, A. pskemense, and A. praemixtum are used in Tajikistan and Uzbekistan as spices. In the western Himalayas, dried leaves of A. stracheyi are used for seasoning vegetable curries (Negi and Gaur 1991). Allium vineale, a perennial from bulblets emits a strong garlic or onion smell when crushed and has potential for use as spice.

The use of curative members of the genus Allium has a long tradition in several Asian populations with deep historical roots (Keusgen et al. 2006). A. pskemense and A. praemixtum are used in Tajikistan and Uzbekistan for medicinal purposes. In India, A. wallichii, A. ampeloprasum, A. griffithianum, and A. tuberosum are used as medicine (Pandey et al. 2008). A. roylei is used in India to relieve headache and fed to horses to relieve colic (Kohli and Gohil 2009).

The potential of domestication of A. mongolicum in China has been explored for its high nutritious, medicinal, and ecological value (Zi-Zhu et al. 2006). Wild Allium species have also received attention as ornamentals due to a wide range of attractive colors and persistence of floral or long vegetative cycle (Pandey et al. 2008). Allium species are used in rock gardens, herbaceous beds, perennial borders, as pot plants, as decorative items, and in dry arrangements (Kamenetsky and Fritsch 2002). Processed products of wild species of A. auriculatum, A. carolinianum, A. griffithianum, A. humile, A. roylei, and A. wallichii are reportedly in great demand (Pandey et al. 2008).

Wild garlic capable of producing seed has played a major role in generation of sexually producing garlic enabling commercial seed production in garlic. As important traits continue to be selected by end users of various wild Allium species, more domestication of these important species will need to be done in order to protect them from overexploitation.

1.10 Some Dark Sides and Recommendations for Future Actions

The major problem faced with some wild Allium species is their weediness. The most studied weedy Allium is A. vineale (wild garlic), a perennial bulb flower, native to Europe, North Africa, and western Asia. A. vineale has a highly developed system of reproduction (Ronsheim and Bever 2000), which allows it to survive a wide range of environmental conditions as well as various chemical and control measures (Leys and Slife 1986). This species was introduced in Australia and North America, where it has become an invasive species. A. vineale is especially a problem among cultivated grasses (Ferguson et al. 1992). Wild garlic is resistant to herbicides due to the structure of its leaves, being vertical, smooth, and waxy (Davies 1992; Block 2010). The use of herbicides is not effective especially because unsprouted underground bulbs may remain dormant and gradually sprout over a 4–5 year period. More knowledge of this species at DNA level would benefit the development of novel control approaches.

The other problem is the strong odor of most species within the genus Allium normally produced upon damage of vegetative parts. Although evidence shows that the substances responsible for the odor have health benefits (Rose et al. 2005), stronger and more offensive odors reduce their successful utilization in breeding and consumption. Allelopathic effects have been reported in several Allium species both cultivated and wild (Djurdjevic et al. 2003). These plants release allelochemicals by exudation, decomposition, leaching, and vaporization. Such chemicals may be toxic within the rhizosphere (Yu 1999) and have been reported to inhibit germination of some plant species (Djurdjevic et al. 2003).

The ongoing activities relating to collection and conservation of genetic resources of Allium will require much more support in the future, if exhaustive collection of all species is to be achieved and genetic erosion avoided. The use of more modern techniques in germplasm enhancement through characterization and conservation will be needed. More genomic resources such as ESTs and molecular markers, as well as transcriptome and/or genome sequence data will be necessary in these species for more efficient utilization of their resources. Breeders will also need to come up with more long-term pre-breeding programs that will be necessary for the transfer of useful traits from the wild to the domesticated species. More investment in biotechnology-related research projects in future will go along way toward the improvement of these species.