Japanese Bulb Onion: Production, Consumption, and Cultivars

In a 5-year average from 2014 to 2018, bulb onion was harvested from 25,720 ha with a total yield of 1,212,000 tons annually in Japan (Table 1). The top three bulb onion-producing areas are Hokkaido (the northernmost island), Hyogo (a district of west central Japan), and Saga (a district in southwestern Japan). In 2018, bulb onion production in Hokkaido accounted for 62.1% of national output, followed by Saga (10.2%) and Hyogo (8.3%) (MAFF 2019a). Bulb onion is the second most consumed vegetable in Japan, behind cabbage (ALIC 2019). The annual per capita consumption of bulb onion was 5,375 g in 2018 (ALIC 2019). Insufficient quantities of bulb onion are grown domestically, so approximately 20% of the supply is imported from China, the United States, and New Zealand; for example, in 2018, 301,700 tons were imported to supplement domestic production (ALIC 2019).

Domestically grown bulb onion is primarily used to enhance the flavor of other foods, and both mild and pungent onions are in demand for both, as ingredients of popular Japanese dishes and in the manufacture of sauces, paste, canned soups, pickles, extracts, and dehydrated products. Onion bulbs come in three different colors: yellow, white, and red. Although yellow onion cultivars are most commonly grown in Japan, there is an increasing demand for mild-flavored, white or red onions suitable for serving raw. It is also worth mentioning that red onions with high quercetin-glycoside content have recently attracted the attention of consumers (Muro et al. 2015).

In Japan, bunching onion (Allium fistulosum L.), a close relative of bulb onion, is one of the most popular flavoring vegetables and economically important; approximately 22,400 ha of bunching onion were harvested in 2018 with a total yield of 452,900 tons (MAFF 2019a). This crop presumably has its origin in north-western China and had been introduced into Japan by the 7th century (Tsukazaki et al. 2010; Fujime 2012).

On the contrary, the cultivation of bulb onion in this country is fairly recent, with the first attempt to grow it being in Hokkaido in 1871 (Abe et al. 1955; Satoh et al. 1993). The commercial production commenced in the end of the 19th century, after the successful growing of a well-known ancient cultivar ‘Yellow Globe Danvers’ introduced from the United States (Satoh et al. 1993; Kojima 2010). An open-pollinated cultivar ‘Sapporo-ki’, a selection from ‘Yellow Globe Danvers’, dominated almost all bulb onion-growing areas in Hokkaido until the beginning of 1970s (Komochi 2015). Likewise, in Osaka district of west central Japan, a local cultivar ‘Senshu-ki’ was selected from a US introduction ‘Yellow Danvers’ in the late 19th century and later became the progenitor of modern cultivars grown in western Japan (Kojima 2010).

In 1973, a serious onion disease Fusarium basal rot, caused by the soil-borne fungus Fusarium oxysporum f. sp. cepae, broke out in Hokkaido (Komochi 2015). The epidemic caused substantial losses in bulb yield and quality. Unfortunately, ‘Sapporo-ki’ lacked resistance against the disease. Thereupon, efforts were concentrated on developing F1 hybrid onion cultivars with resistance to Fusarium basal rot in Hokkaido (Kojima 2010).

Now, F1 cultivars characterized with hybrid vigor for various traits of economic importance as well as uniformity in agronomic characteristics, including maturity, and color, shape and size of bulbs are preferred (Khosa et al. 2016; Colombo & Galmarini 2017). Although bulb onion is considered an outcrossing crop, it is self-fertile (Currah & Ockendon 1978). The onion umbel consists of hundreds of small, perfect flowers, making emasculation impractical (Currah & Ockendon 1978). The production of hybrid onion seed became economically feasible with the discovery of cytoplasmic male sterility by Jones and Clarke (1943).

A Fusarium basal rot-resistant cultivar ‘Furanui’ was produced by crossing cytoplasmic male sterile line ‘W202A’ with a pollen parent line ‘F316’ originated from ‘Sapporo-ki’, and approved for release in 1979 (Komochi 2015). The line ‘W202A’, which exhibited resistance to the disease in question, was bred in the University of Wisconsin, USA (Komochi 2015). What is important, in this context, is that onion hybrid cultivars offer a great benefit to private seed companies, because the identity of the parental inbred lines utilized to develop the hybrid is protected. The hybrid cannot be reproduced without the original inbred parents. Nowadays, F1 hybrid cultivars developed by private seed companies occupy large onion-growing areas in Japan, though the accurate numerical data for acreage and production under hybrid bulb onions are not available (Komochi 2015).

Bulb onion may be direct-seeded or transplanted. In Japan, bulb onion is commonly grown in nursery beds and 1- to 2-month-old seedlings are then transplanted into the production field, which ensures earlier maturity, higher yield, and better control of weeds.

The onion plant forms bulb in response to the amount of daylength in the region where it is being grown. Japanese bulb onion cultivars are typically classified into long-day (14 or more h long), short-day (11–12 h daylengths), and intermediate-day types (Kojima 2010).

For bulb production, long-day genotypes are mostly cultivated in a high-latitude region, Hokkaido (41°N – 46°N) where seeds are sown on the nursery beds from mid-February to early March, and the resultant seedlings usually become ready for transplanting to the ground in about 60 days after sowing. Harvesting takes place from early August to September. Most of the Hokkaido bulb onions are relatively pungent, with hard bulbs that store well.

On the other hand, the cultivars grown in low-latitude regions such as Saga (33°N – 34°N) and Hyogo (34°N – 36°N) are short-day or intermediate-day type. In these regions, seeds are generally sown during mid-September through early October, and the onion crop is harvested during late March through mid-June. Bulb onions from Saga and Hyogo are mainly marketed from April through August, whereas Hokkaido bulb onions are sold from late August to May of the following year. Although more than 100 bulb onion cultivars are available for cultivation in Japan, commercial onion production is currently dominated by a small number of cultivars. The agronomic characteristics of major bulb onion cultivars are given in Table 2. The average bulb weight indicated is from Nakayama (2009).

Bulb onion is subject to a wide range of diseases and pests in Japan. Among the diseases, downy mildew caused by the oomycete Peronospora destructor is of great concern. This soil-borne disease inflicts substantial damage when relatively cool moist weather prevails (Scholten et al. 2007). In 2016, severe epidemic of downy mildew occurred in Saga and Hyogo districts (Zen & Shobu 2017), which caused a reduction in bulb growth and quality, with yield losses of 20–40% being reported (Saga Prefecture 2019).

Several cultural and chemical methods are recommended for the control of downy mildew: soil solarization of the nursery beds as a means of reducing the population size of the pathogen in question; removal of all infected plants from the field; good soil drainage; and timely application of fungicides (e.g., at the first sign of the disease or when conditions become favorable for disease development) (Saga Prefecture 2019). Other bulb onion diseases include Fusarium basal rot, bacterial soft rot (caused by Pectobacterium carotovorum), gray-mold neck rot (caused by Botrytis aclada), gray mold (caused by Botrytis cinerea), onion rust (caused by Puccinia allii), and pink root rot (caused by Pyrenochaeta terrestris) (Kodama et al. 1976; Kodama & Saito 1981; Tanaka 1983; Akutsu 1995; Iketani-Saito et al. 2016). Potential diseases of concern during storage of onion bulbs are gray-mold neck rot and bacterial soft rot.

Onion thrips (Thrips tabaci) is a widespread pest of bulb onion in Japan. Thrips feeding impacts photosynthetic potential, resulting in bulb yield reduction (Hamasaki 1999). Other insect pests which may infest the bulb onion plants include onion fly (Delia antiqua) and Liriomyza chinensis. In recent years, the bulb onion fields attacked by L. chinensis have gradually increased in Hokkaido (Hokkaido Plant Protection Office 2019). This pest does damage to onion bulbs as well as leaves, which reduces the eventual marketable yield. Pesticide use is the primary method to control the pests in bulb onion, though the chemical control is, for most situations, neither economically sustainable nor environmentally suitable and leads to pesticide resistance (Hamasaki 1999).

With regard to agricultural produce, Japanese consumers tend to be highly demanding, laying great emphasis upon its quality and safety. To meet such demands, major Japanese retailers are now focusing their attention on customer satisfaction as well as providing competitive price. In particular, retailers need significant effort to attract consumers by quality and safety assurance from on-farm production to consumption: the production and selling of safe food are essential for protecting consumers from the hazards such as microbial contamination and pesticide residues. Japanese supermarket chains are increasingly requiring their fresh-produce suppliers (including bulb onion growers) to provide evidence of compliance with on-farm food safety standards, known as Good Agricultural Practices (GAPs).

Global GAP is a pioneering private food safety standard established by a consortium of European retailers (Amekawa 2009; Tallontire et al. 2011). It sets stringent criteria for compliance with a set of control points relating to food safety, hygiene, labor conditions, animal welfare, and environmental management on the farmland (Amekawa 2009). Global GAP seeks to ensure transparency, accountability, and social trust by means of an elaborate traceability system and third-party certification (Amekawa 2009).

In Japan, a private voluntary standard named JGAP was developed in 2007 by the Japan GAP Foundation (a non-profit organization) with due regard to the specific features of Japan's agriculture, in terms of the scale of farming, environmental and legal issues, and institutions (Nabeshima et al. 2015; Japan GAP Foundation 2019). ASIAGAP was subsequently created based on the JGAP standard. This certification program was recognized to conform to the benchmarks of Global Food Safety Initiative (GFSI) and became GFSI approved in 2018 (Japan GAP Foundation 2019). As shown in Table 3, GAP-certified farms increased in number from 1,891 in 2013 to 4,845 in 2018. However, the dissemination of GAP approaches in Japan is still limited to a fraction of growers. Actually, only 2% of onion bulbs marketed had the GAP certification in 2018 (MAFF 2019b). The same holds true for other representative vegetables such as cabbage, lettuce, and tomato (MAFF 2019b).

One of the reasons having direct implication in the limited dissemination is that stringent compliance with GAP standards demands costly investments for growers. These investments relate to various inputs, including safer yet more costly pesticides, structures such as pesticide storage units and packhouse, and periodical certification and accreditation (Amekawa 2009). Another reason is that Japanese consumers generally regard domestically grown agricultural produce as safe and quality (Jonker 2000; Nabeshima et al. 2015). Hence, awareness of the significance of GAP approaches seemingly remains insufficient among growers in Japan. In addition, a lot of farmers think that GAP certification does not lead to an increase in their income (Japan Finance Corporation 2018), which may prevent the dissemination of GAP approaches. Meanwhile, an increase in the acquisition of GAP certification is important for strengthening the competitiveness of Japan's agriculture via the export expansion of Japanese agricultural produce (MAFF 2019c). Importers and retailers in overseas markets increasingly demand certification of compliance with Global GAP standard or an equivalent standard. Nevertheless, the amount of export of most vegetable crops harvested in the country still remains small; for instance, Japan exported 11,465 tons (only ca. 1% of national output) of bulb onion, primarily to South Korea and Taiwan in 2015 (Hakodate Customs 2016).