Spring Onion (Allium fistulosum L.) Breeding Strategies

Abstract

Spring onion (Allium fistulosum L.) belongs to subgenus Cepa, genus Allium and family Liliaceae and popularly known as scallion, Welsh onion and Japanese bunching onion. Cultivation of spring onion dates back to 200 BC in China and reached Japan before 500 AD which later spread to Southeast Asia. Spring onion is grown worldwide, however the main area of cultivation remains in East Asia from Siberia to tropical Asia including China, Taiwan, Japan, the Philippines, Malaysia and Indonesia. The plant is a perennial herb, does not produce bulbs, and possesses hollow leaves and has traditionally been used in Chinese folk medicine to treat common cold, influenza, abdominal pain, headache and cardiovascular disease as well as having antifungal and antibacterial effects. Spring onion is known for its flavor and aroma and is a rich source of vitamin C, A and B₆, thiamine, folate, rhamnose, galactose, glucose, arabinose and xylose. Production of F₁ hybrids is considered as one of the main goals in crop breeding. The length of time taken is the main restriction in breeding programs as eight or more generations of inbreeding are needed to establish homozygous lines that can be applied in hybrid production. This process can be enhanced by using doubled haploid (DH) lines as components of hybrid cultivars. In this chapter, we give an overview of the origin, botanical classification, distribution, reported health benefits, genetic resource and conservation, crop cultivation practices and recent advances on biotechnology, and molecular biology and their application for crop improvement in connection with traditional breeding methods of spring onion. In this aspect, mutational breeding and somatic hybridization are the potential approaches for the development of new high-yielding and disease-resistant cultivars.

1 Introduction

Spring onion (Allium fistulosum L.) belongs to the Liliaceae family and in some countries is known as scallion , green onion, Welsh onion, salad onion, Japanese bunching onion, Spanish onion, two-bladed onion and green trail (Fig. 4.1). Other local names include cong in China; ciboule, oignon de Strasburg in France; rohtenlauch, winter zwiebel in Germany; negi in Japan; pa in Korea; pijplook, bieslook and indischeprei in The Netherlands, cebolla, ceboletta in Spain and chung in Taiwan (Inden and Asahira 1990; Sang et al. 2002). Allium fistulosum is a perennial, herbaceous plant which is usually grown for its edible tops, long leaf bases or young shoots. It does not develop bulbs, and possesses hollow leaves (fistulosum means hollow) which differ from leek, where their leaves are flat. A large number of A. fistulosum varieties resemble the leek, such as the Japanese negi, while smaller varieties resemble chives. Leaves of A. fistulosum are somewhat rounder in cross-section, not flattened adaxially.

Fig. 4.1

Spring onion sold at West End Market, Brisbane, Australia

1.1 Botanical Classification and Distribution

The inflorescence of spring onion lacks bracteoles and the size of the flower is about twice of Allium cepa. The scape is round, hollow, 40–75 cm tall, and does not have the typical bulge of onion scapes. Diameter of the umbel ranges from 3 to 7 cm and is not spherical. The order of opening of the pale yellow flowers begins at the top of the umbel and proceeds toward the base and becomes a distinguishing feature in contrast to most other alliums except chives (Rubatzky and Yamaguchi 1997). The filaments of the stamens are more protruded, they lack basal teeth and are not broadened at the base. This type of onion is harvested at an immature stage before the bulb has fully developed. Some useful characteristics in identifying different Allium vegetables are shown in Table 4.1. Their flavor and aroma much milder than red onion; they are eaten raw in salads and sandwiches. The green tops are used as a garnish or sliced in salads or stir-fries. It has been a common food to humans since the earliest times, along with garlic, leek, chive, bulb onion and shallot.

Table 4.1 Useful characteristic in identifying Allium vegetables

Spring onion belongs to subgenus Cepa, genus Allium and family Liliaceae; the basic chromosome number of A. fistulosum is 8; (2n = 2x = 16). The size of spring onion, A. fistulosum genome is estimated to be 11.7 pg/1C or 1.2 × 10⁴ Mbp (Ricroch et al. 2005). It is self-compatible with a high degree of cross-pollination. Self-pollination may occur in some plants and show inbreeding depression and poor growth. Landraces and open pollinated varieties exhibit high levels of heterozygosity and heterogeneity (Tsukazaki et al. 2006; Wako 2016).

1.2 Origin and Domestication

Traces of alliums have been found in the remains of Bronze Age settlements. Seven major edible Allium species from 500 to 650 varieties of Allium worldwide are among of the earliest domesticated crops for its flavor, medicinal and nutritional properties (Shigyo et al. 2018). Plants with the largest and quickest-growing bulbs were selected by early farmers which probably originated in northwestern China (Sang et al. 2002; Tsukazaki et al. 2010). Cultivation of spring onion dates back to 200 BC in China and reached Japan before 500 AD and later spread to Southeast Asia (Fig. 4.2). The earliest description of the crop and its cultivation is found in a Chinese book of 100 BC and mentioned the first time in Japanese literature in 720 AD (Inden and Asahira 1990).

Fig. 4.2

Map of origin and distribution of spring onion. Yellow dots indicate production sites

2 Health and Economic Importance

2.1 Health Benefits

Allium fistulosum has traditionally been used in Chinese medicine to treat the common cold, influenza, abdominal pain, headache and cardiovascular disease. According to a dictionary of Chinese drugs, the bulbs and roots are used for treatment of febrile disease, headache, abdominal pain (Yamazaki et al. 2016), diarrhea, snakebite, ocular disorders, habitual abortion, as well as having antifungal and antibacterial effects (Sang et al. 2002; Ueda et al. 2013). Extracts from spring onion are a potential source of natural antioxidants (Aoyama and Yamamoto 2007; Wang et al. 2006) and antimicrobial agents (Chang et al. 2013). It is also reputed to improve eyesight, help in digestion, perspiration, recovery from wounds and festering sores. It was traditionally served to sick people as a preservative against evil spirits. Kang et al. (2010) suggested that their fibrous roots have potential for as a hypoglycemic agent in controlling blood glucose.

Several studies indicate that Allium fistulosum is a rich source of vitamin C, A and B₆, thiamine, folate, potassium, copper, manganese, iron and chromium (Table 4.2). Leaf blades are rich in rhamnose, galactose, glucose, arabinose and xylose (Inden and Asahira 1990). The organoleptic quality of leaf-bunching onions improves under low temperature, which increases well-hydrated gels of cellulose, hemicellulose, protopection and water-soluble pectin, which embed free sugars carbohydrates storage in the leaf (Hang et al. 2004; Inden and Asahira 1990). Flavor is attributed to the enzyme allinase which acts on sulfur compounds when the tissues are disrupted. The strength of flavor increases with plant age (Peffley 1992). Spring onion is known to contain amino acids and peptides such as cysteine, and glutathione which act as a redox agent in dough, improving bread making properties (Seguchi and Abe 2003)

Table 4.2 Nutritional value of spring onion, Allium fistulosum per 100 g

Flavonoids, carotenoids and some sulfur compounds are phytonutrients found in spring onion. They are packed with highly effective flavonoids known for their health-promoting effects. Aoyama and Yamamoto (2007) studied the effect of thermal treatment on antioxidant activity and flavonoid content, and observed an increase in antioxidant activity and decrease in flavonoids of green spring onion compared to three other vegetables (yellow and red onion varieties and white-sheath spring onion) during the boiling procedure. The study suggested that green Welsh onion, but not the white one, is a potent antioxidant food comparable to yellow onion, and is a good source of kaempferol. It possesses anti-platelet, antioxidative, anti-hypertensive and anti-hyperlipidemic properties (Sung et al. 2015), and may lower cholesterol level and decrease the risk of heart attack and stroke. Several studies indicate that spring onion has excellent antibacterial and antifungal properties. Sung et al. (2018) suggested that Allium fistulosum extracts could be used as functional food materials for weight control in obesity. The roots contain allicin and diallyl disulfide and have the potential to reduce the body fat mass.

2.2 Economic Importance

Spring onion is grown throughout the world, but the main area of cultivation remains in East Asia from Siberia to tropical Asia including China, Taiwan, Japan, the Philippines, Malaysia and Indonesia (Inden and Asahira 1990). It is an important ingredient in Asian cuisine particularly in China, Japan, Korea and Southeast Asia. In Japan, it is the second most important ingredient after Allium cepa but it stands first in China, where it is used in different dishes. Shredded green onions often make up the green part of the five colors in a traditional Korean and Japanese meal. It is used as flavoring marinade in bulgogi (Korean grilled beef) and to flavor kimchi. Negi, which is also known as Welsh or spring onion, is among the most important ingredient in Japanese cuisine. It is usually served with soba noodles and tofu and always found in miso soup, negimaki and widely used as a garnish in noodles or stir-fried. In Southeast Asia it is mainly grown for salads, or as an herb to flavor soups and other dishes. Dehydrated spring onion is used as an additive to pre-processed food such as instant noodles, potato chips and others. The young inflorescence is sometimes deep-fried and consumed as a snack. Fried Allium oil is widely used in traditional Chinese cooking and has recently grown in popularity in the food manufacturing industry (Zhang et al. 2019).

Statistical analysis spring onion production is often combined with other Allium spp. Allium vegetables gross production in 2014 were valued at USD 61,348 million with 4% of it is contributed by green onions and shallots (Galmarini 2018). The main world production of this vegetable is in Japan, South Korea, China, and Taiwan ranking in their top ten vegetable crops. Bunching onion has the highest annual output of Allium crops in Japan in 2014 (Tsukazaki et al. 2017). The annual production in Japan is about 500,000 mt from 23,000 ha, whereas in South Korea, around 27,000 ha produces 723,000 mt, and in China, 20,754,000 mt from 545,000 ha. The main production areas are distributed in the southern parts of these countries (Galmarini 2018). Data on annual consumption per person shows their consumption is 6.6 kg/capita/year in Korea, 1.7 kg/capita/year in Japan and 5.1 kg/capita/year in China (Galmarini 2018). Meanwhile, the annual production in Indonesia in 1988 amounted to 163,000 mt from 24,500 ha. In the USA, they are grown mainly in Monterey, Riverside, and Ventura counties in California and in Arizona, Georgia, Idaho, New Mexico, Oregon, Texas and Washington. In South America, Colombia has a considerable production of Japanese bunching onion for domestic consumption (Galmarini 2018). It is the second largest vegetable crop produced in Colombia, with 327,000 mt from 17,000 ha.

Given the enormous area of cultivation, great adaptability to climate and varied uses, a very large number of cultivars exist. Each cultivar has a characteristic commercial value due to the proportion of green leaves and white sheathes (Yamazaki et al. 2016). The Kumazawa system, based on utilization and ecological characteristic, is widely accepted as a method to classify spring onion in Japan. The system divides the Japanese bunching onion into four groups. Kaga which show little tillering and is dormant in winter, has dark green thick leaves and is grown for the pseudostems. Kujyo which remains green during winter; its cold tolerance is generally low and it has tender, green leaves of excellent eating quality ; they tiller profusely and are mostly grown for their green tops. Senju which continues to grow during winter, although at a reduced rate, is intermediate between the former two and is mainly grown for the pseudostem. Meanwhile, Yaguranegi produces numerous tillers in spring and summer but its growth stops in winter, produces no flowers but only bulbils; it is propagated by division of the basal cluster or bulbils (Inden and Asahira 1990).

Spring onion is among the 15 most important crops in China. It is widely cultivated in Shandong, Henan, Hebei and Shaanxi provinces (Wang et al. 2018). It is preferred compared to bulb onion as it has a stronger flavor to enhance Chinese cuisine. There are more than 200 cultivars of Chinese spring onion which are classified as long pseudostem type, LP (long pseudostem, soft leaves, low soluble solids concentration and mild flavor), fleshy root types, FR (fleshy roots, high soluble solids concentration, stronger pungency and larger sheath diameter) and short pseudostem type, SP (intermediate between the other two types) (Liu et al. 2009).

On the island of Java, Indonesia, the three types of spring onion planted are bawang bakung which is grown for the pseudostem; bawang cina for the leaves and bawang daun which is the intermediate between the two. Among the popular Indonesian cvs. are Plumpung, Mambo, Nyonya, Siih Kecil and Tosari. Mixed cropping with white cabbage, carrot and potato is common in the highlands (Sulistriarini et al. 2016).

The main varieties of spring onion grown in Australia are Straight Leaf, Dynasty Winter King and Summer King. The immature bulb of bulb onion (Allium cepa) varieties such as early Lockyer White, South Australian White, Savages White and Gladalan White are sold as spring onion if harvested early with leaves intact. It is estimated that about 3 million bunches, or 1000 mt, of spring onion are produced from the Swan Coastal Plain, mainly between Wanneroo and Baldivis, in Western Australia (Burt 2007).

3 Current Cultivation Practices

Spring onion is easy to grow. It maintains vegetative growth all year round except in winter. Propagation is generally by seed and/or transplanted as seedlings in early spring, summer or autumn (Zhu et al. 2019). The crop produces tillers and can be propagated by seed or division. Division is preferred by most growers as it ensures that they have the chosen clone , especially where winter hardiness is an important requirement. Although it grows throughout the year, the best quality and highest yields are produced in late spring. Żurawik et al. (2013) showed that the highest marketable yield obtained from seeds sown at the end of April compare to early April in cv. Sprint. In temperate areas, propagation is mainly by seed , sown directly in the field or in nurseries before being transplanted into the field. Seed requirements are 8–16 kg/ha for direct seeding while 2–4 kg/ha for transplanting. In nursery beds, seeds are either broadcast or sown in rows or in 5–6 cm wide bands. Seedlings are ready for transplanting at about 15 cm height when it has pencil-thick base.

In Southeast Asia the crop is propagated mainly using basal tillers and can be planted the whole year round. Plants are rarely raised from seed as imported cultivars are more difficult to sow under tropical conditions and more time-consuming. In Indonesia, spring onion is planted in uplands as well as on dry paddy fields. In Java, it grows well above 200 m elevation, but it is more common above 500 m. Tillers are transplanted into raised beds or ridges, which are alternated with furrows for irrigation and drainage. There are many local selections and commercial cultivars, reflecting the adaptation to a wide range of climatic conditions. Most spring onion cultivars are well adapted to variations in rainfall and more tolerant of heavy rainfall than other Allium spp.

In Poland, spring onion is grown on a small scale (Majkowska et al. 2014) and mostly cultivated as a perennial crop out of rotation for the period of 3–4 years. Cultivars with a short pseudostem, strong tendency to tillering, abundant foliage production and fast regrowth after harvest like Siedmiolatka Czerwona, Kroll, Vita or Flamenco, are usually recommended beside other high yielding cultivars including Parade, Sprintesa, Performer, Ishikura Long White and Totem (Adamczewska-Sowinska and Kolota 2014). In Brazil, spring onion is grown throughout the year in highland regions and during autumn-winter in lower regions. Cultivars grown include Todo Ano, Nebuka, Evergreen, Natsu Hosonegui, Futonegui and Ibirité (Marcuzzo and Carvalho 2014).

The main advantage of growing from transplants is the possibility of obtaining earlier yields (Tendaj and Mysiak 2011). Seedlings are planted in furrows, and roots and bases are lightly covered by soil. The depth of the furrow is about 15 cm for pseudostem production and 5 cm for green top production. Distance between rows and within rows are 55–85 cm and 3–15 cm, respectively, depending upon tillering tendency (Warade and Kadam 1998). Single plants are grown in a square spacing 20 × 20 cm or 25 × 25 cm depending on the vigor of the clone . Seedlings are planted in groups of 3 or 4 approximately 20 cm each way when using seed (George 2011). Highest yield was obtained in cv. Sprint at a sowing rate of 8 kg/ha⁻¹ and grown in rows 20 cm apart (Żurawik et al. 2013). Spring onion can be produced in most types of soil such as sandy loam, loam and clay loams with an optimum soil pH of 5.3–5.8. However, it is more successful at higher elevations (>1000 m) than lower. Ideally, it will grow efficiently in well-drained good fertile soil with good potential moisture retention as it has a sparse, shallow root system, and is easily rooted in waterlogged soil. Sprinklers are typically used, while drip irrigation is uncommon because of close row spacing. Typically, 25–38 cm of water is needed to meet evapotranspiration requirements (Smith et al. 2011).

Recommended rates of fertilizers in cultivation for branched pseudostems on soil with high organic matter is 200–300 kg of nitrogen, 100–200 kg of P₂O₅, and 150–200 kg of K₂O per ha (Kolota et al. 2013). In greenhouse studies spring onion performed best when nitrogen was supplied as nitrate , NO₃⁻. Complete fertilizer is usually used during planting time followed by two or three additional applications of nitrogen fertilizer. The use of high N rates to increase large onion bulbs and excessive nutrient supply is common in intensive farms to maximize marketable yield . Due to spring onion’s poor root system, this practice may cause the risk of nitrate leaching. Therefore, the application of N fertilizer at the optimum recommended rate is essential in spring onion production (Liu et al. 2009).

A power tiller and a fertilizer applicator-ditcher was developed to reduce labor and cultivation costs, as the task can be completed so much faster than by the conventional way (Katahira et al. 2006). Growth, yield , flavor intensity and nutritional value of spring onion can be highly influenced by genotype, sulfur nutrition, soil type, climatic conditions, edaphic factors and management practices (Abbey et al. 2015). Sulfur fertilization reduces the total soluble solid content by 30% in spring onion cvs. Sydney Bunching as compared to Paris Silverskin. It also reduced the bulb diameters of Allium fistulosum cvs. Fragrant and Sydney Bunching, while increasing the bulb diameters in A. cepa cvs. Winter White Bunching, Egyptian Bunching, Winter Over and Paris Silverskin (Abbey et al. 2002).

Kołota et al. (2012) found that similar yields can be produced by spring onion cv. Performer harvested in early June to September. Meanwhile, lower yields with a gradual decrease of dry matter, carotenoids, sugars, volatile oils and nitrates have been produced from those harvested in October. Delay in harvesting at 60–120 days after planting results in a substantial yield increment with a simultaneous depletion of vitamin C, carotenoids, chlorophyll a and b, sugars, volatile oils, nitrates, total N, K and Ca content. Dry matter content in spring onion cv. Sprint yield depends significantly on the sowing date with seed sown in May having higher dry content than those sown in April (Żurawik et al. 2013). Tendaj and Mysiak (2011) showed that spring onion grown from transplants produce longer and wider diameter pseudostems compared to seeds sown directly in the field.

Allium fistulosum usually depends on arbuscular mycorrhizal (AM) fungi for P uptake, as the adventitious root system is shallow, especially in soils with a low to medium P level. Tawaraya et al. (1996) suggested that selection of suitable fungal species and optimal phosphate application is important for spring onion growth. High dependency on mycorrhizal colonization has been observed in cvs. Sydney Bunching, Winter Over, Vilr-Moscow, Ciboule 9379 and Kagoshimahanegi (Tawaraya et al. 2001). Perner et al. (2007) suggested that AM colonization may support the production of organosulfur compounds by compensating growth depression caused by changes in N-form ratios in field conditions.

Suggested field planting density is 400,000–500,000 plants per ha, depending on the production of green leaf or pseudostem, respectively. Green leaves can be harvested 2–3 month after transplanting. However, it will take about 6–9 months to harvest for blanching (Rubatzky and Yamaguchi 1997). Plants are ready to harvest in 8–10 weeks in summer and 12–14 weeks in winter (Burt 2007). Spring onion competes poorly with weeds as they initially grow slowly. Hand weeding is required but it is costly. Harvesting can be coupled with replanting, separating plantlets at intervals to ensure continuity of supply. The production requires a lot of manual labor as each onion must be lifted by hand, trimmed, cleaned and packed into bundles. Several efforts have been made by a number of researchers to develop customized machinery to enhance farm production. Mechanized lifters and trimmers have been developed to speed the harvesting process.

Spring onion varies according to the cultivar in both juvenile age and cold requirement. Su et al. (2007) studied genotypic differences in the interaction between low temperature and photoperiod of spring onion cvs. Chunwei, Changbao and Zhanqiu, and found that each suffered from stress at low temperatures during winter, but differed in their response; Chunwei is the most tolerant, followed by Changbao, while Zhangqiu is the least cold tolerant. Greenhouse culture and plug seedling transplanting of spring onion are common in Japan. It is usually cultivated continuously with other crops without rotation in Hokkaido. Seedlings are raised in the greenhouse for up to 2 months before being transplanted into open fields from late April to mid-June and being harvested 4 months later (August to October). Leaf sheaths of the plants are covered with soil three times by hilling every month to promote etiolated growth. Some farmers cultivate the plants in greenhouses from autumn to the following spring (Misawa et al. 2017).

Vernalization is important in spring onion in order to prevent bolting as it may lower the yield while seed producers prefer to induce flowering to speed up the seed production. Flower induction is controlled by temperature and day length. Low temperatures (generally less than 13 °C) and short days induce flowering when a seedling has more than 11 leaves or is more than 5–7 mm in pseudostem diameter. Specific seedling characteristics and sufficient time at low temperature are required for bolting. The temperature and time for vernalization may vary with cultivar. Plants are not vernalized when they are grown at more than 20 °C (Inden and Asahira 1990) and under a photoperiod of 16 h. With certain Taiwanese cvs. like Pei Chung, 5 days at 5 °C or 20 days at 10 °C are sufficient for vernalization. Dong et al. (2013) showed that cultivar, sowing date, transplant location and their interactions could influence bolting in spring onion. Bolting-susceptible cultivars are sown in late September to avoid vernalization temperature during winter while bolting-resistant cultivars can be sown earlier. They suggested that sowing around October and transplantation into the open field could delay bolting in cv. Xia Hei, while sowing in late August and transplantation to a plastic tunnel could accelerate flower bud development for seed production. Two mid-season flowering cvs., Kincho and Asagi-kujo, exhibited similar responses to temperature in flower initiation and bolting. However, after flowering was initiated, the early stage of flower development is day-neutral while a long-day photoperiod promotes flower development after the floret formation stage, followed by elongation of the seed-stalk (Yamasaki et al. 2011).

4 Pest and Disease Management

Although spring onion is generally a healthy crop, there are several bacterial and fungal diseases common to most Allium crops. Several problems regarding yield have occurred due to purple blotch (Alternaria porri), which causes concentric spots on the leaves, and downy mildew (Peronospora destructor). Most commercial growers follow guidelines for sanitation, crop rotation, use of resistant varieties and frequent monitoring to avoid severe disease outbreaks.

Successive cropping results in white rot (Sclerotium cepivorum) infestation as the pathogen is very persistent in the soil. Poor nutrition and heavy rains also can stimulate the disease development. In Victoria, Australia, vegetable growers report that this disease has progressively increased over the years due to frequent use of spring onion monocultures in short rotations with other non-host crops (radish, endive, parsley). Drastic increases of pathogen (sclerotia) populations in the soil lead to high disease levels and considerable yield losses which limit spring onion production. Rot commonly range from 5% to 50%, but in some seasons when soil conditions are favorable for disease development over 80% of plants may be killed (Villalta 2005).

Onion yellow-dwarf virus (OYSV), cycas necrotic stunt virus (CNSV) and tomato spotted wilt virus (TSWV) are pathogenic to Japanese bunching onion (Inden and Asahira 1990). The most important virus disease caused by the onion yellow dwarf virus is transmitted by various aphid species causing mosaic-type symptoms, including chlorotic mottling, streaking and stunting, and distorted flattening of the leaves. The Kujyo group of cultivars was found to be tolerant to this disease. The most serious pests are beet army worm (Spodoptera exigua) and the American bollworm (Heliothis armigera). They are difficult to control due to the waxy layer on the leaves and that the larvae hide inside the hollow leaves (Sulistriarini et al. 2016).

Onion thrips (Thrips tabaci L.) is one of the most important pests in spring onion causing both direct and indirect damage by feeding and ovipositing on leaves that may cause green onions (scallions) to be unmarketable and dry bulb onion size to be reduced. Rust (Puccinia allii) causes serious damage to the leaves. Purple blotch or alternaria leaf spot (Alternaria porri) causes heavy losses under moist conditions. Phytophthora blight (Phytophthora nicotianae var. parasitica) leaf spot (Pleospora herbarum), black spotted leaf blight (Septoria alliacea), botrytis leaf spot (Botrytis cinerea) and fusarium wilt (Fusarium oxysporum ) are fungal diseases which may affect the crop. Although a parental line with rust resistance has been successfully developed (Wako et al. 2012; Yamashita et al. 2005), it shows only a moderate level of field resistance to rust and does not completely control the disease. Li et al. (2018) reported that cultivation of cucumber with Welsh onion as a companion plant reduces root knots and egg masses of root-knot nematodes (Meloidogyne spp.) by 77%.

5 Germplasm Resources

Crop wild relatives (CWR) provide breeders with useful traits for crop improvement in a wide range of crops. Collection of germplasm of landraces and wild relatives creates a broad pool of potential genetic resources for breeding and innovative research (Hajjar and Hodgkin 2007). Improvement in gene bank information systems has allowed for better storage and management of a large quantity of data. The genus Allium is widely distributed over different regions from the dry subtropics to the boreal zone. Evolution of the genus coevolved with ecological diversification (Fritsch and Friesen 2002). Major efforts to collect source material of spring onion for evaluation and selection , and several trials have resulted in the economically-valuable Premyera variety of Welsh onion in southwestern Siberia (Shishkina et al. 2019).

Spring onion has resistance to several diseases that affect common onion as well, and it exhibits broad adaptability to a wide range of climatic conditions, winter-hardiness and early flowering. Cultivated germplasm forms the primary gene pool of the crop. This clearly indicates the potential for conserving genetic variation in landraces of the species (Ford-Lloyd and Armstrong 1993). Collections of Allium fistulosum exist in The Netherlands, Japan, UK, USA, Germany and the former USSR. A total of 975 accessions of A. fistulosum are conserved in botanical gardens and gene banks from 18,539 accessions of cultivated Allium genetic resources held worldwide (Table 4.3). About 89% of the Allium genetic resources are cultivated species (Keller and Kik 2018) with many economically-important species belonging to subgenus Cepa, e.g. A. cepa (onion, shallot), A. fistulosum (bunching onion) and A. schoenoprasum (chives).

Table 4.3 Number of accessions of cultivated Allium species (sensu Fritsch and Friesen 2002) conserved per subgenus and in botanical gardens and gene banks

Knowledge of genetic diversity aids in efficient management of germplasm and selection of parents for crossbreeding. Protein electrophoresis provides a source of marker genes for systematic studies within and between populations. Utilization of genes and their products such as isozymes and allozymes have been used to address issues dealing with local mating patterns, fine-scale structure within populations and broad-scale variation across species (Parker et al. 1998). Several studies using isozymes in Allium fistulosum are shown in Table 4.4. Most allozymes represent codominant Mendelian loci. However, their number is limited, and different taxonomic groups may exhibit variation and lack of polymorphism. It may also differ in metabolic function, and gene product could be exposed to selective processes in nature (Parker et al. 1998).

Table 4.4 Isozymes used in Allium fistulosum

Phylogenetic relationships and evolution within Allium species have been investigated by several researchers. Molecular marker technology is been widely used for diversity analysis, varietal identification and facilitates selection of certain agronomic traits for crop improvement such as their polymorphic nature, natural behavior, easy and fast assay preparation, high reproducibility and easy exchange of data between laboratories (Chinnappareddy et al. 2013). Restriction fragment length polymorphism (RFLP), random-amplified polymorphic DNA (RAPD), sequence characterized amplified region (SCAR), simple sequence repeat (SSR) and inter-simple sequence repeat (ISSR ) markers are widely used for diversity analysis, varietal identification and study of DNA transfer within species in Allium (Table 4.5). Wilkie et al. (1993) reported the use of RAPD for diversity analysis of seven cultivars of onion and a single cultivar each of spring onion, chive, leek and A. roylei (a wild relative of onion). Application and impact of molecular markers on evolutionary and diversity studies in the genus Allium was reported by Klaas (1998) and Klaas and Friesen (2002).

Table 4.5 Molecular markers used for diversity analysis and fingerprinting in A. fistulosum

Chloroplast and mitochondrial DNA are useful for the study of hybridization and introgression as they are inherited in a non-Mendelian, cytoplasmic fashion which usually relates to maternal transmission (Parker et al. 1998). Bark et al. (1994) demonstrated the use of RFLP in the chloroplast and nuclear genomes to assess DNA transfer from spring onion to bulb onion. Bradeen and Havey (1995) reported maternal phylogenetic relationship for Allium altaicum, A. fistulosum , A. cepa and A. vavilovii using RFLP of the chloroplast DNA. Use of mitochondrial DNA to distinguish cytoplasm of cultivated and wild Allium in subgenus Cepa was reported by Yamashita et al. (2000). RFLP analysis of mtDNA and cpDNA of two cultivated species of A. fistulosum and A. cepa along with four wild species in subgenus Cepa by Yamashita et al. (2001) demonstrated that phylogenetic relationships among the species closely correspond to the crossing ability test reported by Van Raamsdonk and Vries (1992). Yusupov et al. (2019) published a complete chloroplast of A. fistulosum consisting of 82,237 bp long single copy and 17,907 bp small single copy regions separated by 26,510 bp inverted repeat regions which could later be used for population genomic studies, phylogenetic analysis and genetic engineering studies of the genus Allium.

Nuclear DNA contains both unique single copy regions which generally code for a gene product and nonunique repetitive regions which consist of core sequences repeated in varying degree. Phylogenetic reconstruction based on nuclear DNA of Allium in subgenus Cepa was presented by Van Raamsdonk et al. (1997). A study using RAPD and RFLP by Friesen et al. (1999) showed that A. fistulosum originates from an A. altaicum progenitor. This result is contradictory to results published by Bradeen and Havey (1995) suggesting that phylogenetic hypotheses partly depend on the marker systems used. Development of RAPD marker for phylogenetic study in Allium subgenus Cepa has been reported by Shigyo et al. (2002). A study by Ricroch et al. (2005) revealed a significant interspecific variation in the amount of nuclear DNA and GC content of different onions and their wild allies. A phylogeny was constructed using internal transcribe spacer (ITS ) sequences of 43 accessions representing 30 Allium species belonging to 3 major subgenera and 14 sections showed a tendency towards a decrease in genome size within the genus. Friesen et al. (2006) divide Allium into 15 subgenera and 56 sections based on internal transcribed spacer region (ITS ) of nuclear ribosomal DNA with an estimation of 780 Allium species currently being recognized. Phylogenic analysis of Allium subgenus Cepa by Gurushidze et al. (2007) using sequences of the nuclear ribosomal DNA internal transcribed spacer (ITS) region showed that the subgenus is monophyletic with three species group consisting (a) A. altaicum/A. fistulosum , (b) A. farctum/A. roylei/A. asarense/A. cepa/A. vavilovii and (c) A. galanthum/A. oschaninii/A. praemixtum/A. pskemense.

Tandem repeats are usually associated with chromosomal landmarks such as centromeres, telomeres, subtelomeric and other heterochromatic regions can be used for chromosome identification and to study plant chromosome evolution in many crops. Son et al. (2012) used ISSR analysis to study the relationships among Allium species. A comparative genomic database for genetic mapping and marker data from Allium species and population reported by McCallum et al. (2012) provide a valuable resource for genetic and genomic studies of Allium genome including A. fistulosum . Kirov et al. (2017) reported two cytogenetic markers, HAT58 and Cat36 for identification of individual chromosomes in A. fistulosum . Development of SSR markers for identifying intraspecific F₁ hybrids and interspecific taxonomic analysis in Allium subgenus Cepa are reported by Araki et al. (2009).

6 Breeding Strategies

6.1 Traditional Breeding

Most cultivated alliums including spring onion are seed propagated (Havey 2002). Traditionally farmers raise their own seed or planting material. Breeders aim to improve cultivar homogeneity and adaptation to specific ecological conditions. High consumer and farmer preferences of low pungency, high sugar content, disease resistance, high yield, delayed bolting and suitability for mechanization are among the main important trait in spring onion breeding (Tsukazaki et al. 2017). Miyagi et al. (2011) showed that general consumers prefer strong flavor and sweetness of fresh and heated (boiled or grilled), besides soft texture of grilled bunching onion. Preferences on pungency, stickiness and texture for fresh, boiled and grilled spring onion vary depending on the consumer. Japanese food restaurants tend to value taste and flavor, while other types of restaurants tend to consider price and spring onion size.

Interspecies hybridization plays an important role in onion breeding as it allows introgression of valuable traits with improved characteristics. Among the interspecific crosses in Allium, those between A. fistulosum and A. cepa have been studied extensively because the former represents a rich source of several agronomic traits including resistance to diseases and pests (Budylin et al. 2014; Kik 2002) lacking in bulb onion. Breeders have used introgression of resistant genes from A. fistulosum into A. cepa for decades with many crosses between these species achieved (Table 4.6). Some commercial interspecific hybrids obtained are Beltsville Bunching which is an amphidiploid species of A. cepa and A. fistulosum , Delta Giant (backcross of A. cepa var. ascalonicum with an amphidiploid of shallot × A. fistulosum ), Top Onion which is a diploid interspecific between A. cepa × A. fistulosum and Wakegi Onion which is a diploid interspecific between shallot × A. fistulosum (Kik 2002).

Table 4.6 Interspecific crosses involving A. fistulosum

Studies on interspecific hybridization between Allium cepa and A. fistulosum , and research has continued over the years (Chuda and Adamus 2012). However, low fertility of the interspecific F₁ hybrid between these two species has made progress rather slow. Van der Valk et al. (1991) suggested that strong pre-fertilization and post-fertilization barriers limit the recombination between the chromosomes of bulb and bunching onions. Ulloa et al. (1994), showed that the number of bridges and fragments varied between the F₁ hybrid of A. fistulosum × A. cepa and BC₁ progenies (A. fistulosum × A. cepa) × (A. cepa). The F₁ hybrid and all BC₁ progenies were either sterile or very low seed set. Development of addition lines (Peffley et al. 1985) and the use of A. roylei as a bridging species (Khrustaleva and Kik 1998) was proposed to increase the possibility of genetic introgression from A. fistulosum into A. cepa (Martinez et al. 2005).

Since the 1980s, F₁ hybrids cultivars have been released in Japan with 80% new cultivars released per year. There are over 120 registered cultivars of spring onion in Japan with some developed using male sterility. Shigyo et al. (1996) established a series of alien addition lines, representing the 8 different chromosomes of shallot (Allium cepa Aggregatum group) in an A. fistulosum background. Yamashita et al. (1999) suggested that a male sterile line of A. fistulosum developed by continuous backcrossing with A. galanthum could be useful for spring onion breeding to eliminate the emasculation process and to produce large numbers of F₁ seeds. In Japanese bunching onion, male sterility is controlled by the interaction between a cytoplasmic factor S, and two nuclear genes Ms₁ and Ms₂ (Moue and Uehara 1985) with male sterility occurring when it is homozygous recessive (Havey 2002). The genotype of the male sterile plants and their maintainer are Sms₁ms₁ms₂ms₂ and Nms₁ms₁ms₂ms₂, respectively (Inden and Asahira 1990). Cytoplasmic male sterility (CMS) is important in spring onion breeding as it allows easy propagation of male sterile plants using an appropriate maintainer line (Havey 2004; Yamashita et al. 2009). However, the CMS expression depends on the genetic relationship between the cytoplasm donor species and bunching onion. Yamashita et al. (2009) reported that the frequency of male sterile plants in 8 of 135 spring onion accessions from Japan, China, Mongolia, Korea and Taiwan varied from 1.7% to 24.5%.

Kudryavtseva et al. (2019) revealed that spontaneous chromosome duplication produced allotetraploids from interspecific hybrids between Allium cepa and A. fistulosum by using GISH analyses. Interspecific hybrids between spring onion (A. fistulosum ) and chive (A. schoenoprasum) by reciprocal crossing through ovary culture producing vigorous growth and higher edible parts than their parents when using A. fistulosum as the seed plant (Umehara et al. 2006b). Yamasaki et al. (2011) reported that 24 h photoperiod treatment increased plant height and leaf number in both Kincho and Choetsu cvs. However, 16 h photoperiod only increased the plant height and leaf sheath diameter of cv. Choetsu but did affect cv. Kincho. Meanwhile, 16% of treated plants bolted under 24 h, 54% under 16 h and 77% under 8 h in cv. Kincho for 30 days of treatment. More than 30 days of treatment increased the percentage of bolting plants for 16 h and 24 h photoperiods. However, no differences in percentage of bolting were observed in the 60-day treatment for the 3 photoperiods (8, 16, 24 h) tested. Long-day photoperiod delayed bolting and increased the number of leaves in both cultivars. They suggested that spring onion requires facultative short-day during flower initiation process and that the inhibition of flower initiation by a long photoperiod can be overcome at low temperature.

6.2 Molecular Breeding

Spring onion is second most important species in the genus Allium because of its disease resistance, ecological adaptability and close relationship to A. cepa. Alien chromosome addition lines from A. fistulosum could enhance the possibility of breeding for selective chemical components in A. cepa (Yaguchi et al. 2009). Breeding of spring onion is time-consuming and requires a large area. It takes many years, usually 1–2 years per generation, because of slow plant growth. Development of molecular markers is important in facilitating the establishment of a genetic basis for plant breeding. Quantitative trait loci (QTL) analysis based on genetic linkage maps is required to reveal the mode of inheritance of selective agronomic traits targeted for crop improvement. Several studies on the use of molecular markers for the development of linkage map and QTL analysis are reported (Table 4.7). Yamashita et al. (1999) published the use of isozymes and RAPD analysis to develop genetic markers linked to the fertility restoring gene (Rf) for cytoplasmic male sterility (CMS) in backcross progenies between A. galanthum and A. fistulosum . Sequence characterized amplified region (SCAR) markers linked to fertility restoring gene for CMS were reported by Yamashita et al. (2002) and could be applied for marker associated selection (MAS ).

Table 4.7 Molecular markers used for the development of linkage map and QTL analysis in Allium fistulosum

Organization of a 378-bp satellite repeat in terminal heterochromatin of Allium fistulosum was reported by Fesenko et al. (2002). Isolation and development of SSR markers in spring onion as a primary basis for breeding was described by Song et al. (2004) and Yang et al. (2015). A total of 1796 SSR clones from SSR-enriched DNA libraries of spring onion were identified by (Tsukazaki et al. 2007) which are applicable for phylogenic analysis and construction of genetic linkage maps. Ohara et al. (2005b) used AFLP markers to study the relationship between heterosis and genetic distance in intervarietal F₁ hybrids of A. fistulosum . Tsukazaki et al. (2008) isolated 1940 SSR clones from size-fractionated genomic DNA libraries with potential use for cultivar identification and hybrid purity identification. A genetic map based on single nucleotide polymorphisms (SNPs) markers was assembled by using interspecific F₁ hybrid between A. roylei × A. fistulosum (Scholten et al. 2017).

The first linkage map of spring onion with AFLPs was constructed by Ohara et al. (2005a) using reciprocally backcrossed progenies of two inbred lines of Japanese bunching onion (A. fistulosum ) based on 149 AFLP markers, 1 cleaved amplified polymorphic sequence (CAPS) and 13 SSRs using reciprocally backcrossed progenies. Tsukazaki et al. (2008) constructed a detailed linkage map consisting of 17 linkage groups with 212 bunching onion SSR markers and 42 bulb onion (A. cepa) SSR , InDel, CAPS or dCAPS markers, covering 2069 cM. Ohara et al. (2009) added 24 SSRs and 1 CAPS to the previous map developed by Ohara et al. (2005a) on reciprocally backcrossed progenies resulting into 16 linkage group for the J map and 15 linkage groups for the D map. QTL analyses conducted showed that the seedling growth is controlled by many QTLs that exhibit various modes of gene actions, additive, dominant and overdominant.

Classification and identification of 30 bunching onion varieties based on simple sequence repeat (SSR) markers was reported by (Tsukazaki et al. 2010). Numerous DNA markers based on SSRs, SNPs and InDels were developed (Tsukazaki et al. 2015). Identification of restorer genes involved in the restoration of fertility in CMS is essential for the establishment of molecular breeding system. RAPD and SCAR marker distinguishing between N and S cytoplasm in several spring onion cultivars were reported by Gai and Meng (2010) and Gao et al. (2013, 2015). SCAR marker developed from AFLP marker distinguishing between CMS and fertile lines could be used by breeder to extract maintainer lines from open-pollinated spring onion (Wang et al. 2013). Gao et al. (2018) reported a competitive allele-specific PCR (KASP) marker developed from SNP detected in the atp6 gene could discriminate between male-sterile and normal cytoplasmic types.

Sequencing a huge genome by the high-throughput method has been initiated, as well as the development of molecular markers and linkage mapping. Allium Map for cultivated Allium vegetable including spring onion was developed by McCallum et al. (2012) and provides a genetic map and marker data from multiple Allium species. High throughput SNP genotyping, functional genomics using RNAi and transcriptome mapping can be exploited to understand the function of genes in the genome . Transcriptome sequencing utilizing next-generation sequencing (NGS ) has become an effective tool to discover novel genes in several crops. A total of 798 genes, representing 1.86% of total putative unigenes, were differentially expressed between waxy spring onion and non-waxy mutant spring onion varieties (Liu et al. 2014). More than 50,000 unigenes were obtained from transcriptome shotgun assembly (TSA) of next-generation sequencing (NGS ) data.

Genomic SSRs from bunching onion and EST-SSRs from bulb onion were used by Wako (2016) to study the genetic basis of bolting time in bunching onion. They reported that 2 QTLs associated with bolting time were detected on the linkage groups of chromosomes 1 (Chr. 1a) and chromosome 2 (Chr. 2a). However, the QTL on Chr. 1a was not detected in the KiC population (inbred line from ever-flowering, Kitanegi and late-bolting, Cho-etsu) grown in a heated greenhouse under unvernalized conditions. A single QTL with major effect was identified exclusively on the linkage group Chr. 2a in the SaT03 population (cross between early-bolting line, Chuukanbohon Nou 1 and late-bolting, Fuyuwarabe) were evaluated under field conditions. Tsukazaki et al. (2017) reported 27 QTLs for the 6 morphological traits (plant height, leaf length, pseudostem length, leaf width, pseudostem width, number of leaf sheath) in 16 regions of 11 linkage groups, with a major QTL for the number of leaf sheaths repeatedly detected on Chr. 8. They discovered 2 QTLs associated with pseudostem pigmentation on linkage groups Chr. 4a and Chr. 5a-2. Tsukazaki et al. (2012) revealed a major QTL for pseudostem pungency located within a 24.2 cM interval on Chr. 2a of spring onion.

A SSR-tagged breeding scheme to enhance the rapidity, ease and accuracy of variety identification and F₁ purity test was suggested by Tsukazaki et al. (2006). Tsukazaki et al. (2009) later proposed to protect breeders’ rights and confer traceability in allogamous crops. The scheme consists of three steps (Fig. 4.3):

• (a) Selection of a small number of highly polymorphic SSR loci that are not tightly linked to each other. Selection of prevailing allele at each locus, since the parental lines of the F₁ hybrids must carry different alleles at each selected locus.

• (b) Selection of plants in a foundation seed field that are homozygous for the prevailing allele at all the SSR loci selected.

• (c) Harvest of foundation seed from the plants selected. For F₁ breeding, one parental line should be homozygous at each selected SSR locus and the other should be homozygous for another allele.

Fig. 4.3

The SSR-tagged breeding scheme for conferring variety traceability

Production of stock seed normally will be followed by marketing of seed . Open-pollinated varieties should be homozygous and uniform at the selected SSR loci while the F₁ varieties should be uniformly heterozygous. Open-pollinated varieties and the parental lines of the F₁ varieties should not exhibit inbreeding depression since most of the loci can maintain their original heterogeneity.

6.3 Tissue Culture Applications

Micropropagation of Allium fistulosum can avoid the maintenance of male sterile lines by a non-restorer fertility line. A large number of identical offspring from a limited amount of parent material could be obtained to increase the number of female plants for the production of F₁ hybrid seed . Song and Peffley (1994) reported on in vitro culture of A. fistulosum and A. cepa interspecific derivatives (Table 4.8). Furthermore, the high proliferation of adventitious shoots were obtained from shoot tip culture of spring onion using MS medium (Murashige and Skoog 1962) supplemented with 2 mg/l 6-furfurylaminopurine (kinetin) and 0.5 mg/l 1-naphthylacetic acid (NAA) at 20 °C. Fujieda et al. (1977) found that in the presence of cytokine it stimulated the multiplication of adventitious shoots, but completely inhibited adventitious roots.

Table 4.8 Summary of tissue culture studies on Allium fistulosum , A. fistulosum × A. cepa and A. cepa × A. fistulosum.

Organ culture such as embryo and ovary can facilitate the recovery of progeny from high sterile interspecific F₁ hybrids and backcross progeny to overcome incompatibility in interspecific hybrids. Regeneration into haploid plantlets has been achieved in spring onion using flower and ovary culture (Ibrahim et al. 2016). Hybrid plants were obtained from embryo cultured on B5 medium (Gamborg et al. 1968) without growth regulators (Peffley 1992). Gonzales and Ford-Lloyd (1987) demonstrated successful embryo rescue of hybrids from crosses between Allium cepa and A. fistulosum using B5 medium. Umehara et al. (2006b) reported the production of interspecific hybrids between A. fistulosom × A. macrostemon through ovary culture using B5 medium modified by Dunstan and Short (BDS) containing 30 g l^–1 sucrose. Hybrids produce from germinated embryos transferred to BDS medium containing 1 mg l^–1 6-benzylaminopurine and 15 g l^–1 sucrose followed by subculturing on phytohormone-free B5 medium showed intermediate traits of both parents.

Somatic embryogenesis can provide regeneration of a large number of individuals from a single progenitor. However, the occurrence of somaclonal variation can be an issue in determining desired clones. Mutations and polyploidization are quite frequent in callus culture and thus enables their possible use in breeding program using somaclonal variation (Inden and Asahira 1990). Plant regeneration from callus culture is well established in Allium fistulosum and interspecific hybrids between alliums. Phillips and Hubstenberger (1987) developed procedures for micropropagation and plant regeneration from callus for A. fistulosum , A. altaicum, A. galanthum, A. roylei and selected progeny of interspecific crosses of A. cepa × A. fistulosum , A. cepa × A. galanthum and A. cepa × A. oschaninii. Lu et al. (1989) reported high frequency somatic embryo production from callus culture using BDS media supplemented with moderate to high auxin level and 2.5 g l⁻¹ proline and Shahin’s vitamins. A reproducible protoplast culture system using BDS basal medium supplemented with 5mM potassium nitrate , 2 μM 2,4,dichlorophenoxyacetic acid (2,4,-D) and 0.2 or 1 μM 6-benzylaminopurine (BAP) and a combination of 0.2 M sucrose and 0.2 M glucose has been established by Shimonaka et al. (2001). Plantlet regeneration was achieved 2–3 months after inoculating protoplast-derived calli to a half N MS medium. This finding enables the introduction of targeted genes such as disease resistance or male sterile genes from Allium species into spring onion using cell fusion or electroporation. Interspecific somatic hybrids between A. fistulosum and A. cepa are reported by Shimonaka et al. (2002) using protoplast electrofusion. Several amphidiploids and alloplasmic plants which are valuable for spring onion breeding have been produced.

The term haploid refers to a plant which possesses the gametophytic number of chromosomes in their sporophytes. Monoploids contain a single genome from diploid species while polyhaploids containing two or more genomes are derived from polyploid species. Haploid plants will become doubled-haploids (DHs) following chromosome doubling. This doubled-haploid methodology offers several advantages to plant improvement programs as it provide a rapid approach to achieve homozygosity. Since haploid plants carry only one set of alleles at each locus, upon doubling, homozygous and homogeneous lines are available. This allows identification of superior parental combinations, evaluation of environment × genotype interactions, avoids masking of recessive genes, and evaluation of qualitative and quantitative traits (Snape 1988).

Ibrahim et al. (2016) developed frequency of embryogenesis in spring onion using flower and ovary culture using cultured in BDS medium supplemented with 2 mg l⁻¹ 2,4-D and 2 mg l⁻¹ BAP fortified with 100 g/l sucrose, 200 mg l⁻¹ proline and 500 mg l⁻¹ myo-inisitol. Calli were recorded around 90 days after ovary inoculation and shoot induction was observed after 60 days of callus induction in BDS media (Dunstan and Short 1977). The cultures were green in color during the first 3 months and gradually turned yellowish as the culture progressed. Calli from the ovule were easily recognized with ovary burst after 4–5 months of inoculation (Fig. 4.4).

Fig. 4.4

(a) Shoot formation has been observed from callus inoculated from the ovary culture in BDS media, (b) Shoot regeneration has been observed after 150 days of culture. (Source: Ibrahim et al. 2016)

7 Conclusions and Prospects

There are seven major edible species among the hundreds of Allium varieties available worldwide. Great adaptability to varied climatic conditions has created many different varieties of the crop. Each cultivar has a commercial characteristic value due to usage including in food and Chinese medicine. Different studies show spring onion has excellent antibacterial and antifungal properties. Some species also purportedly show anti-platelet, antioxidative, anti-hypertensive, and anti-hyperlipidemic properties, and reduction of cholesterol level which may decrease the risk of heart attack. The plants are rich source of vitamin C, A and B₆, thiamine, folate and minerals.

Spring onion can be grown in most types of soil but in recent years several countries have reported different diseases on spring onion due to continuous cultivation. Japan and Taiwan are good examples for great adaptability of the crop, where intense cultivation is combined with selection , breeding and the development of a good marketing network which has led to greatly increased production; this indicates that there is great scope for the development of better cultivars and increased commercialization and intensification of production in Southeast Asia.

Several new methods developed to achieve high yields and disease resistance in spring onion; organ culture and somatic embryogenesis will help to retain the F₁ progeny and produce large single progenitor respectively. Recent efforts in developing high yielding cultivars with specific and broad adaptability, precocity, resistance to various pest and diseases, and good marketing quality have been initiated, and there is a great need to use biotechnological approaches for the development of new cultivars with high yield and better disease resistant characteristics.

Appendix I: Research Institutes Relevant to Spring Onion

Institution name	Specialization and research activities	Address	Contact information and website
Institute for Horticultural Development, Agriculture Victoria	Study on growth and dry matter production of spring onion, white rot disease management	Private Bag 15, Ferntree Gully Delivery Centre, Victoria 3156, Australia	daryl.joyce@nrevic.gov.au; https://www.ausvegvic.com.au/pdf/r%26d_VG01096_white_rot_onion_integrated_control_strategy_booklet.pdf
University of Queensland	Disease forecasting system in spring onion	Queensland 4343, Australia	v.galea@uq.edu.au https://researchers.uq.edu.au/researcher/200
Department of Genetics and Plant Breeding, Bangladesh Agricultural University	SNP markers, molecular breeding	Mymensingh 2202, Bangladesh	sathisbioinfo@gmail.com https://www.mdpi.com/2073-4395/8/9/179
Center of Medical Genetics, Ghent University	Cytogenetics, molecular markers, spring onion breeding	Ghent, Belgium	kirovez@gmail.com https://pubmed.ncbi.nlm.nih.gov/28150039/
Instituto Federal Catarinense	Crop improvement	C. Postal 441, 89163-356 Rio do Sul-SC, Brazil	marcuzzo@ifc-riodosul.edu.br; https://www.scielo.br/scielo.php?script=sci_arttext&pid=S0102-05362014000300363
University of Saskatchewan	Phylogenetics and taxonomy of Allium	Saskatoon, Canada	hugo.cota@usask.ca https://www.researchgate.net/publication/263500245_A_taxonomic_revision_of_Allium_Alliaceae_in_the_Canadian_prairie_provinces
Kunming Institute of Botany, Chinese Academy of Sciences	Study of chloroplast genome of A. fistulosum	Kunming, China	sunhang@mail.kib.ac.cn; https://www.tandfonline.com/doi/pdf/10.1080/23802359.2018.1545532
Beijing Technology and Business University (BTBU)	Nutritional value of A. fistulosum	Beijing 100048, China	chenht@th.btbu.edu.cn https://europepmc.org/article/med/31108752
Beijing Academy of Agriculture and Forestry Science (North China)	Genetics and breeding of spring onion, transcriptome sequencing	Beijing 100097, China	wangyongqin@nercv.org; https://web.b.ebscohost.com/abstract?direct=true&profile=ehost&scope=site&authtype=crawler&jrnl=16616596&AN=117067465&h=rpJH2%2fnRPYhGXzYAIQ5jM6HOBvVg%2fFbcqJHYXlaSayCx34ik0ZiFQYjpy2GM%2fi%2bbH0nL%2fuL%2bpCRml%2bFebRMIQA%3d%3d&crl=c&resultNs=AdminWebAuth&resultLocal=ErrCrlNotAuth&crlhashurl=login.aspx%3fdirect%3dtrue%26profile%3dehost%26scope%3dsite%26authtype%3dcrawler%26jrnl%3d16616596%26AN%3d117067465
University of Chinese Academy of Science	Genomic study of A. fistulosum	Beijing, China	sunhang@mail.kib.ac.cn https://search.proquest.com/openview/03b13ee11d15e8b54850a2f6dd17e8b8/1?pq-origsite=gscholar&cbl=3933403
College of Horticulture and Gardening, Yangtze University	SSR markers, RNA sequencing, molecular markers	Jingzhou, China	lchliu18@yangtzeu.edu.cn https://pdfs.semanticscholar.org/b581/67fcada93d4f194e6f5a0d8a834632f038ff.pdf
College of Horticulture, Northwest A&F University	Physiology of A. fistulosum	Yangling, Shaanxi 712100, People’s Republic of China	chengzh@nwsuaf.edu.cn https://pubmed.ncbi.nlm.nih.gov/24199907/
College of Resources and Environmental Sciences, China Agricultural University	Effect of mycorrhizal colonization on pungency	Beijing, China 100094	junlingz@cau.edu.cn https://pureadmin.qub.ac.uk/ws/files/452805/GuoT%20et%20al%202007.pdf
College of Horticulture, Shandong Agricultural University	SSR markers, transcriptome, molecular markers, molecular breeding, cytoplasmic male sterility	Tai’an 271018, P.R. China	sqliu@sdu.edu.cn https://www.mdpi.com/journal/ijms/special_issues/plant-molecular-biology?view=abstract&listby=type
Institute of Medical Plant Development, Chinese Academy of Medical Sciences and Peking Union Medical College	Physiology of spring onion	Beijing 100193, China	qianwangcau@126.com https://www.cabdirect.org/cabdirect/abstract/20143400467
Yantai Agricultural Science Academy of Shandong Province	Effect of spring onion root against root knot nematodes	Yantai, Shandong, P.R.China	ytnkyscs@163.com https://journals.plos.org/plosone/article/authors?id=10.1371/journal.pone.0201471
The First Hospital of China Medical University	Medicinal value of Allium	Shenyang 110001, China	zli@cmu.edu.cn; https://onlinelibrary.wiley.com/doi/abs/10.1111/ajco.13133
Shanghai Jiao Tong University	Supply and demand of spring onion	Shanghai, People’s Republic of China	gengna@sjtu.edu.cn;
Dept of Food Science and Technology, Chia Nan University of Pharmacy and Science	Nutritional and medicinal value of spring onion	60 Erh-Jen Road, Section 1, Pao-An, Jen-te Hsiang, Tainan Hsien, Taiwan	ipdduh@mail.chna.edu.tw
Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Ministry of Agriculture	SSR markers, RNA sequencing, molecular breeding	Beijing 100097, China	wangyongqin@nercv.org
Beijing Academy of Agriculture and Forestry Science	Effect on nitrogen and sulfur on the growth of spring onion	Beijing, China	wangyongqin@nercv.org https://www.researchgate.net/publication/269356745_Effect_of_Nitrogen_and_Sulphur_on_the_Growth_and_Qualities_of_Bunching_Onion
Yantai Agricultural Science Academy of Shandong Province	Nematodes control in spring onion	Yantai, Shandong, P.R.China	ytnkyscs@163.com https://www.researchgate.net/publication/326703074_Inhibitory_effects_of_components_from_root_exudates_of_Welsh_onion_against_root_knot_nematodes
Shanghai Jiao Tong University	Seed demand forecasting of spring onion	China	gengna@sjtu.edu.cn; https://journals.plos.org/plosone/article/authors?id=10.1371/journal.pone.0219889
Colombian Corporation for Agricultural Research (Corpoica)	Agronomic Evaluation of Bunching Onion in the Colombian Cundiboyacense High Plateau	CI Palmira, Colombia and CI Tibaitatá, Mosquera, Colombia	galeanomendoza@gmail.com https://core.ac.uk/download/pdf/205389639.pdf
Department of Food Science, Yuanpei University	Nutritional and medicinal value of Allium	Hsinchu, Chinese Taipei	hungder@mail.ypu.edu.tw, https://www.scirp.org/html/22-2700684_35298.htm
Department of Plant Medicine, National Chiayi University	Molecular breeding, crop improvement	60004, Taiwan	chienjui.huang@mail.ncyu.edu.tw; https://web.b.ebscohost.com/abstract?direct=true&profile=ehost&scope=site&authtype=crawler&jrnl=11254653&AN=130550885&h=v9HLDeIM%2fFJLxFvToiyvNQAzGyQbJykSwJ%2btnfTxbaKX7SScpNpWq0Un7BNWHLaetSGxWGqKfHD5CtN2Utoy6A%3d%3d&crl=c&resultNs=AdminWebAuth&resultLocal=ErrCrlNotAuth&crlhashurl=login.aspx%3fdirect%3dtrue%26profile%3dehost%26scope%3dsite%26authtype%3dcrawler%26jrnl%3d11254653%26AN%3d130550885
Université Paris-Sud	Allium genomic study	CNRS UMR 8079, Bâtiment 360, 91405 Orsay, France	agnes.richroch@esv.u-psud.fr https://www.sciencedirect.com/science/article/abs/pii/S0378111997003958
Botanical Garden of the University of Osnabrück	Phylogenetics, molecular markers	Albrechtstr 29, 49076 Osnabrück, Germany	nfriesen@uni-osnabrueck.de https://pubmed.ncbi.nlm.nih.gov/26639102/
Leibniz Institute of Vegetable and Ornamental Crops	Physiology of spring onion	Theodor-Echtermeyer-Weg 1, 14979 Großbeeren, Germany	perner@igzev.de https://pubmed.ncbi.nlm.nih.gov/18457399/
Institute of Plant Genetics and Crop Plant Research (IPK)	RAPD and non-coding chloroplast DNA study, cytogenetics, molecular markers	Corrensstr 3, 06466 Gatersleben, Germany	rutten@ipk-gatersleben.de
Dept. of Horticulture, University of Georgia	Physiology of onion	1111 Miller Plant Science Bldg., Athens, GA 30602	gboyhan@uga.edu
Indian Institute of Horticultural Research	Molecular markers, Allium genome and breeding	Bangalore, India	dclreddy@gmail.com
University of Bari ‘Aldo Moro’	Physiology of spring onion	Valenzano, Bari, Italy	mariano.fracchiolla@uniba.it
National Institute of Vegetable and Tea Science (NIVTS), National Agriculture and Food Research Organization (NARO)	Microsatellite , SSR , AFLP and molecular markers, genetic mapping, QTL study, molecular breeding	360 Ano-Kusawa, Tsu, Mie 514-2392, Japan	tsuka@affrc.go.jp
National Agricultural Research Center for Tohoku Region (NARCT)	SSR markers, molecular breeding, crop improvement	4 Akahira, Shimo-kuriyagawa, Morioka, Iwate 020-0198, Japan	amhonjo@affrc.go.jp
Institute of the Society for Techno-innovation of Agriculture, Forestry and Fisheries (STAFF)	SSR markers, molecular breeding	446-1 Ippaizuka, Kamiyokoba, Tsukuba, Ibaraki 305-0854, Japan	kan@staff.or.jp
Tohoku Agricultural Research Center, National Agriculture and Food Research Organization (NARO)	QTL study, molecular breeding	92 Nabeyashiki, Shimo-kugiyagawa, Morioka, Iwate 020-0123, Japan	tsuka@affrc.go.jp
National Research Institute of Vegetables, Ornamental Plants and Tea	Physiology of A. fistulosum , molecular markers, QTL mapping, molecular breeding	Kurume, Fukuoka 839-8503, Japan	yamasaki@narc.affrc.go.jp
Western Region Agricultural Center NARO	QTL analysis, molecular breeding	1-3-1 Senyu-cho, Zentsuji, Kagawa 765-8508, Japan	kenyamas@affrc.go.jp
Osaka City University	Study on antioxidant activity and flavonoid content	Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan	yamamoto@life.osaka-cu.ac.jp
Institute of Plant Genetics and Crop Plant Research (IPK)	Phylogenetics, molecular markers, molecular breeding	Corrensstr 3, 06466 Gatersleben, Germany	blattner@ipk-gatersleben.de
Botanical Garden of the University of Osnabrück	Phylogenetics, molecular markers	Albrechtstr 29, 49076 Osnabrück, Germany	nfriesen@uni-osnabrueck.de
Plant Nutrition, Institute of Crop Science, Humboldt University Berlin	Effect of fertilizer on yield of spring onion	nvalidenstr. 42, 10115 Berlin, Germany	george@igzev.de
Leibniz Institute of Vegetable and Ornamental Crops	Physiology of spring onion	Theodor-Echtermeyer-Weg 1, 14979 Großbeeren, Germany	perner@igzev.de
Institute of Plant Genetics and Crop Plant Research (IPK)	RAPD and non-coding chloroplast DNA study, cytogenetics, molecular markers	Corrensstr 3, 06466 Gatersleben, Germany	rutten@ipk-gatersleben.de
Dept. of Horticulture, University of Georgia	Physiology of onion	1111 Miller Plant Science Bldg., Athens, GA 30602	gboyhan@uga.edu
Indian Institute of Horticultural Research	Molecular markers, Allium genome and breeding	Bangalore, India	dclreddy@gmail.com
University of Bari ‘Aldo Moro’	Physiology of spring onion	Valenzano, Bari, Italy	mariano.fracchiolla@uniba.it
National Agricultural Research Center for Tohoku Region (NARCT)	SSR markers, molecular breeding, crop improvement	4 Akahira, Shimo-kuriyagawa, Morioka, Iwate 020-0198, Japan	amhonjo@affrc.go.jp
Institute of the Society for Techno-innovation of Agriculture, Forestry and Fisheries (STAFF)	SSR markers, molecular breeding	446-1 Ippaizuka, Kamiyokoba, Tsukuba, Ibaraki 305-0854, Japan	kan@staff.or.jp; i-kono@staff.or.jp
Tohoku Agricultural Research Center, National Agriculture and Food Research Organization (NARO)	QTL study, molecular breeding	92 Nabeyashiki, Shimo-kugiyagawa, Morioka, Iwate 020-0123, Japan	tsuka@affrc.go.jp
National Research Institute of Vegetables, Ornamental Plants and Tea	Physiology of A. fistulosum , molecular markers, QTL mapping, molecular breeding	Kurume, Fukuoka 839-8503, Japan	yamasaki@narc.affrc.go.jp
Western Region Agricultural Center, NARO	QTL analysis, molecular breeding	1-3-1 Senyu-cho, Zentsuji, Kagawa 765-8508, Japan	kenyamas@affrc.go.jp
Osaka City University	Study on antioxidant activity and flavonoid content	Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan	yamamoto@life.osaka-cu.ac.jp
Tohuku University	Biochemical characterization in A. fistulosum	Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan	koji.muramoto.d5@tohoku.ac.jp
Faculty of Agriculture, Tottori University	Micropropagation of spring onion, cytogenetics, microsatellite markers in Allium	4-101 Koyama-Minami, Tottori 680-8553, Japan	itai@muses.tottori-u.ac.jp
Faculty of Agriculture, Saga University	Isozymes markers, molecular markers in Allium, onion breeding	Saga 840-8502, Japan	tashiroy@cc.saga-u.ac.jp
Faculty of Agriculture, Yamagata University	Mycorrhizal colonization in A. fistulosum	Tsuruoka 997-8555, Japan	tawaraya@tds1.tr.yamagata-u.ac.jp
Faculty of Agriculture, Hokkaido University	Mycorrhizal colonization in A. fistulosum	Sapporo, 060-8589, Japan	tatsu@agr.nagoya-u.ac.jp
Faculty of Agriculture, Kyushu University	Biological control, pest management	46-01, Fukuoka 812, Japan	ueno@grt.kyushu-u.ac.jp
Faculty of Agriculture, Yamaguchi University	Molecular markers in Allium, QTL mapping, Allium genome study, molecular breeding	1677-1 Yoshida, Yamaguchi 753-8515, Japan	shigyo@yamaguchi-u.ac.jp
Faculty of Agriculture, Kyoto Prefectural University,	Biodiversity of Allium	Shimogamo, Sakyo, Kyoto, Japan 606-8522	yfujime@rio.odn.ne.jp.
Faculty of Life and Environmental Science, Shimane University	Micropropagation, physiology of spring onion	Matsue, Shimane 690-8504	yano@life.shimane-u.ac.jp
University of Toyama	Medicinal value of A. fistulosum	2630 Sugitani, Toyama, 930-0194, Japan	lee@pha.u-toyama.ac.jp
Faculty of Pharmaceutical Sciences, Sojo University	Medicinal value of A. fistulosum	22-1, 4-Chome, Nishi-ku, Ikeda, Kumamoto, 860-0082, Japan	none@ph.sojo-u.ac.jp.
Kansai University of Welfare Sciences	Molecular cytogenetic , molecular breeding	Kashiwara, Osaka 582-0026, Japan	myamamoto@tamateyama.ac.jp
Department of Biotechnology , Maebashi Institute of Technology	Micropropagation of spring onion	Maebashi 371-0816, Japan	ihonda@maebashi-it.ac.jp
Kobe Women’s University	Food science	Suma-Ku, Kobe City, Japan 654-8585	seguchi@kobe-wu.ac.jp
Gakushuin Women’s College	Food Science	Tokyo, Japan 162-8650.
Department of Pharmacognosy, Kyoto Pharmaceutical University	Food chemistry of A. fistulosum	Misasagi, Yamashina-ku, Kyoto 607-8412, Japan	matsuda@mb.kyoto-phu.ac.jp
Department of Pharmacognosy, Kyoto Pharmaceutical University	Nutritional and medicinal value of spring onion	Misasagi, Yamashina-ku, Kyoto 607-8412, Japan	matsuda@mb.kyoto-phu.ac.jp
Kazusa DNA Research Institute	RNA sequencing, biochemical analysis and molecular breeding	2-6-7 Kazusa-kamatari, Kisarazu, Chiba 292-0818, Japan	hh@kazusa.or.jp
Tottori Horticultural Experiment Station	Micropropagation and physiology of spring onion, rust resistance	Kurakoshi, Tottori 682-0948	shiraiwah@pref.tottori.jp
Fukuoka Agricultural Research Center	Molecular marker, ovary culture	Yoshiki 587, Chikushino, Fukuoka 818-8549, Japan	umehara@farc.pref.fukuoka.jp
Mibyeong Research Center, Korea Institute of Oriental Medicine	Nutritional and medicinal value of spring onion	1672 Yuseong-daero, Yuseong-gu, Daejeon 305-811, Korea	hkkim@kiom.re.kr
Suchon National University	SNP markers, molecular breeding	Suncheon 57922, Korea	my-656@hanmail.net; nis@sunchon.ac.kr
Sungkyunkwan University, Suwon	Development of spring onion harvester	Kyeonggi, Republic of Korea	seung@skku.edu
Institute of Traditional Medicine and Bioscience, Daejeon University	Nutritional value of A. fistulosum	Daejeon 300-716, Republic of Korea	sksh518@dju.kr
Institute for Food Sciences, Inje University	Nutritional and medicinal value of A. fistulosum	607 Obang-dong, Gimhae, 621-749 Korea	fdsnkiji@inje.ac.kr
Hankyong National University, Anseong	Nutritional and medicinal value of A. fistulosum	Kyeonggi, Republic of Korea	wypark@hknu.ac.kr
National Academy of Agricultural Science, Rural Development Administration, Suwon	Nutritional value of A. fistulosum	Suwon 441-707, Korea	wgkim@rda.go.kr
Mibyeong Research Center, Korea Institute of Oriental Medicine	Nutritional value of A. fistulosum	1672 Yuseong-daero, Yuseong-gu, Daejeon 305-811, Korea	dskim@kiom.re.kr; yysung@kiom.re.kr
National Academy of Agricultural Science, Rural Development Administration, Wanju	Nutritional value of A. fistulosum	Wanju, Korea	hgjaz@korea.kr
Center for Horticultural Seed Development of GSP	SNP markers, molecular breeding	Jeonnam, Suncheon 57922, Korea	jihee0830@cnu.ac.kr
Biotechnology Institute, Nongwoo Bio Co. Ltd	Molecular markers, linkage map, molecular breeding	Yeoju, South Korea	bk54@snu.ac.kr
Institute of JinAn Red Ginseng, Jinan-Eup	Nutritional and medicinal value of spring onion	Jinan-Gun, Chonbuk 567-801, Republic of Korea.	e-yoo0612@hanmail.net
Mokpo Experiment Station, National Institute of Crop Science	Mapping of AFLP markers	293-5 Cheongcheon, Cheonggye, Muan, Jeonnam 534-833, Korea	yssong25@rda.go.kr
Wageningen University and Research Centre	Allium genomic study, molecular marker	Postbus 16, 6700 AA, Wageningen Netherlands	sjaak.vanheusden@wur.nl
Wageningen UR Plant Breeding, Wageningen University and Research Centre	SNP markers, molecular markers, molecular breeding	The Netherlands	olga.scholten@wur.nl
Laboratory of Genetics, Wageningen University	Spring onion breeding	Wageningen (The Netherlands)	hans.dejong@wur.nl
DLO-Centre for Plant Breeding and Reproduction Research CPRO-DLO, Department of Vegetable and Fruit Crops	Cytogenetics, DNA-based phylogenies in Allium subgenus Cepa, spring onion breeding	PO Box 16, 6700 AA Wageningen, The Netherlands	c.kik@cpro.dlo.nl
The New Zealand Institute for Plant & Food Research Ltd	Allium genomic study, molecular marker	Private Bag 4704, Christchurch, New Zealand	john.mccallum@plantandfood.co.nz
Faculty of Environment, Society and Design, Lincoln University	Allium genomic study, molecular marker	PO Box 84, Lincoln 7647, New Zealand.	yanbo.deng@gmail.com
University of Agriculture in Cracow	GISH study, molecular markers, molecular breeding	29 Listopada 54, 31-425 Cracow, Poland	a.chuda@org.ur.krakow.pl
Department of Horticulture, Wroclaw University of Environmental and Life Sciences	Physiology of spring onion	PI, Grunwaldzki 24a, 50-363 Wrolaw, Poland	katarzyna.a-sowinska@up.wroc.pl
Department of Vegetable Crops and Medicinal Plants University of Life Sciences in Lublin	Physiology of spring onion	Leszczyńskiego 58, 20-068 Lublin, Poland	maria.tendaj@up.lublin.pl
West Pomeranian University of Technology	Agronomy of spring onion	P.Pawla VI 1, 71-459 Szczecin, Poland	azurawik@zut.edu.pl
Department of Plant Cytology and Embryology, Institute of Botany, Jagiellonian University	Molecular markers, micropropagation, cytogenetics of spring onion	Gronostajowa 9, 30-387 Cracow, Poland	patryk.mizia@uj.edu.pl; a.joachimiak@uj.edu.pl
University of Warmia and Mazury in Olsztyn	Physiology of spring onion	Olsztyn, Poland	majkowska-gadomska@uwm.edu.pl
Center of Molecular Biotechnology , Russian State Agrarian University-Moscow Timiryazev Agricultural Academy (RGAU-MTAA)	GISH study, cytogenetics, spring onion breeding	49, Timiryazevskaya Str., 127550 Moscow, Russia;	khrustaleva@timacad.ru
All-Russia Research Institute of Vegetable Breeding and Seed Production	GISH study, cytogenetics, spring onion breeding	Moscow oblast, p/o Lesnoy Gorodok, 143080 Russia	mail@vniissok.ru
NakhonPhanom Agricultural Research & Development Center	Integrated cultivation of spring onion with other vegetables	Thailand	niyom_sp@hotmail.co.th
Institute of Biocience and Technology, Cranfield University	Study on growth and dry matter production of spring onion, water deficit stress and soil type	Silsoe, Bedfordshire MK45 4DT, UK	l.abbey.s99@cranfield ac.uk
University of Warwick	Physiology of spring onion	Coventry, UK	dezer@turing.ac.uk
Horticulture Research International	Study on growth and dry matter production of spring onion	Wellesbourne, Warwick CV35 9EF, UK	l.abbey.s99@cranfield ac.uk
University of New Hampshire	Physiology of Allium fistulosum	38 Academic Way, Durham, NH 03824	becky.sideman@unh.edu; http://www.colsa.unh.edu/aes/
US Department of Agriculture, Agricultural Research Service, South Central Agricultural Research laboratory	Physiology of Allium fistulosum	911 Highway 3 W, Lane, OK 74555, USA	russo_vincent@hotmail.com
Department of Plant Science, Rutgers University	Food chemistry, antifungal constituents in A. fistulosum	65 Dudley Road, New Brunswick, New Jersey 08901-8520	ssang@rci.rutgers.edu
Department of Plant and Soil Science, Texas Tech University	Somatic embryogenesis and micropropagation and cytogenetics of A. fistulosum , spring onion breeding, isozyme markers	Lubbock TX 79409-4169,USA794	epeffley@ttacs.ttu.edu
Plant Sciences Department, The University of Tennessee	Physiology of spring onion	252 Ellington Plant Sciences, 2431 Joa Johnson Drive, Knoxville, TN 37996-4561	dkopsell@utk.edu
USDA-ARS and Department of Horticulture, University of Wisconsin	Molecular markers, molecular breeding	Madison, WI 53706, USA	michael.havey@ars.usda.gov
Seminis Vegetable Seeds, DeForest	Cytogenetics, spring onion breeding	WI 53532, USA	llblacktw@netscape.net
Institute of Botany, Academy Sciences of Uzbekistan	Genomic study of A. fistulosum	Tashkent, Uzbekistan	ktojibaev@mail.ru