Acta agriculturae Slovenica, 121/2, 1–8, Ljubljana 2025 doi:10.14720/aas.2025.121.2.19925 Review article / pregledni znanstveni članek Brassica oilseed crops in Japan: cultivation, consumption, and cultivars Shinya NAKUI 1, Tetsuo MIKAMI 2, 3 Received October 08, 2024; accepted April 18, 2025 Delo je prispelo 8. oktober 2024, sprejeto 18. april 2025 1 LLC OMEGA Farmers, Butoku-cho, Shibetsu, 095-0062, Japan 2 HAL GREEN Co., Ltd., 193-6 Toiso, Eniwa, 061-1405, Japan 3 Corresponding author, e-mail: tm-mars@fgbb.jp Brassica oilseed crops in Japan: cultivation, consumption, and cultivars Abstract: Brassica oilseed crops are the third most impor- tant source of edible vegetative oils in the world. Among these crops, the cultivation history of B. rapa goes back to very an- cient times in Japan. Its cultivation area expanded substantially in the 17th century and Brassica oil was used as fuel for lamps and cooking oil. Brassica napus L. ssp. napus was introduced into Japan mainly as an oil crop in the late 19th century, after which it gradually replaced the heirloom B. rapa L. ssp. oleif- era (DC.) Metzg. cultivars used in the production of edible oil. The rapeseed (B. rapa and B. napus) cultivation area in Japan reached its peak in the 1950s and then decreased rapidly due to increase of imports of inexpensive oilseed crops. In recent years, however, domestic cultivation of B. napus has started to increase again. Japanese people consume rapeseed oil well and consider it to be a healthy oil with low levels of saturated fatty acids. This article aims to provide the information about the history, current state, problems, and prospects of rapeseed cultivation in Japan. The paper also describes an overview of agronomic characteristics of representative Japanese cultivars as well as cultural practices. Key words: Brassica napus; Brassica rapa; breeding; culti- vation history; cultural practices; vegetative oil Oljarice iz rodu Brassica na Japonskem: gojenje, uporaba in sorte Izvleček: Oljarice iz rodu Brassica so tretji najpomembnejši vir jedilnega rastlinskega olja v svetovnem merilu. Med njimi se je gojenje oljne repice (B. rapa) na Japponskem pričelo že v pra- davnini. Površine njenega gojenja so se močno povečale v 17. stoletju, ko se je njeno olje uporabljalo kot gorivo za svetiljke in kuhanje. Oljna ogrščica (Brassica napus L. ssp. napus) je bila uvedena na Japonsko pretežno kot oljarica v poznem 19. stoletju in je nadomestila sorte oljne repice (B. rapa L.ssp. ole- ifera (DC.) Metzg.), ki so se uporabljale za pridelavo jedilnega olja. Površina gojenja obeh vrst je na Japonskem dosegla višek v petdesetih letih prejšnega stoletja in potem hitro upadla zaradi povečanega uvoza poceni jedilnega olja iz teh vrst. V zadnjih letih se domača pridelava oljne ogrščice spet povečuje, ker ga prebivalstvo rado uporablja kot zdravo jedilno olje z majhno vsebnostjo nasičenih maščobnih kislin. Namen članka je po- dati informacije o zgodovini, sedanjem stanju, problemih in bodočem gojenju oljne ogrščice na Japonskem. Članek daje tudi pregled agronomskih lastnosti japonskih sort kot tudi o načinih gojenja. Ključne besede: Brassica napus, Brassica rapa, žlahtnjenje, zgodovina gojenja, tehnike gojenja, rastlinsko olje Acta agriculturae Slovenica, 121/2 – 20252 S. NAKUI et al. 1 INTRODUCTION Brassica crop species are of particular importance in agricultural production within the Brassicaceae family and have undergone extensive domestication (Gulden et al., 2008; OECD, 2016; McAlvay et al., 2021). Among these, B. napus L. ssp. napus (oilseed rape), B. rapa L. (syn. B. campestris L., turnip rape), B. juncea (L.) Czern. et Coss. (Indian mustard), and B. carinata Braun (Ethi- opian mustard) form the oilseed group, and in Japan, rapeseed chiefly refers to B. napus and B. rapa (MRC In- stitute for Environment & Health, 1997; Zając et al., 2016; Kawasaki et al., 2022). As a side note, B. juncea is grown as an oilseed crop mainly in India as well as in some re- gions of China, and the cultivation of B. carinata is basi- cally limited to Northeast Africa (Zając et al., 2016). In this paper, “rapeseed” is used to collectively designate B. napus and B. rapa. Brassica rapa was one of the first Brassica species to be domesticated (Guo et al., 2014). Mizushima and Tsu- noda (1969) hypothesized that B. rapa originated in cold uplands near Turkey from where it migrated into the flat- lands of Europe and Siberia. However, the exact center of origin of B. rapa has been debated; proposed centers of origin include Europe (Zhao et al., 2005), Central Asia (Ignatov et al., 2008; Qi et al., 2017), and East Asia (Song et al., 1988; Zhao et al., 2005). Brassica napus (2n = 38) is an amphidiploid with an AACC genome, and evolved through the spontaneous hybridization between B. rapa L. (2n = 20) with an AA genome and B. oleracea L. (cab- bage/kale; 2n = 18) with a CC genome (OECD, 2016; Quezada-Martinez et al., 2021). It seems likely that the southwest European Mediterranean region, where the wild forms of the two parental species exist, is one of the places where this hybridization event occurred (Prakash and Hinata, 1980; Rahman, 2013). Rapeseed oil, which is low in saturated fatty acids (e.g., less than 4 % palmitic acid), with relatively high levels of oleic acid (55-68 %) and linolenic acid (7-10 %), is thought to offer health benefits (MRC Institute for Environment & Health, 1997; Fujimura-Ito et al., 2011; Huang et al., 2015). Linolenic acid has valuable nutrition- al functions in humans (Nakui and Mikami, 2024), and oleic acid provides thermal stability, making rapeseed oil desirable for cooking oil. High oleic-acid oil also tastes better (Cartea et al., 2019). Nevertheless, Brassica seeds generally contain more than 40 % erucic acid in oil, and more than 100 µmoles of glucosinolates per gram of the oil-free meal (Rahman, 2013). Oil with high erucic acid content has anti-nutritional properties and is considered unsuitable as a source of food for humans (Rahman, 2013; Cartea et al., 2019). Additionally, glucosinolates are considered nutritionally undesirable since the pres- ence of glucosinolates limits the use of this protein-rich meal in animal feed (Rahman, 2013). Intensive breeding efforts have been made to develop elite cultivars with low erucic acid, low glucosinolate content, and increased yields. The resulting improved crop is called “double-low” rapeseed or “canola” and has become one of the most im- portant oilseed crops in the world (Quezada-Martinez et al., 2021). Recently, rapeseed oil has drawn Japanese consumers’ attention because of its healthful properties (Japan Oilseed Processors Association, 2024). Among vegetable oils, the food-use consumption of rapeseed oil is the highest in Japan, followed by palm oil and soybean oil (Yagi et al., 2023). In the present article, we review literature to provide an up-to-date summary in relation to the history, current state, problems, and perspectives of rapeseed cultivation in Japan. The paper also focuses on the agronomic char- acteristics of representative Japanese cultivars and cul- tural practices. 2 HISTORY OF RAPESEED CULTIVATION IN JAPAN 2.1 Brassica rapa L. Brassica rapa exists in various forms such as oilseed, leafy (e.g., Chinese cabbage, mizuna) and root (e.g., tur- nip) type vegetables, and feed for livestock (e.g., fodder turnip) (Guo et al., 2014). The history of B. rapa cultiva- tion goes back to very ancient times in Japan (Nishizawa et al., 2010). The initial use of the B. rapa crops intro- duced into Japan seems to have been as leafy vegetables rather than as an oilseed crop (Nishizawa et al., 2010). It remains unclear as to when oil production from B. rapa seeds began in Japan, but Brassica oil is believed to have been already utilized as lamp fuel in the end of the 16th century (Japan Oilseed Processors Association, 2015; Tokyo Oil Inquiry House Market, 2016). In those days, the oil market was monopolized by a group of merchants and the oil extracted from oil perilla (Perilla frutescens (L.) Britt. var. frutescens) was the major source of lamp fuel in the country (Japan Oilseed Processors Associa- tion, 2015; Nakui and Mikami, 2023). Perilla seed oil was also widely used as drying oil for waterproofing paper umbrellas, polishing or coating wood, and in the man- ufacture of lacquer wares (Nitta et al., 2003; Yamanaka Aburaten, 2023). After the 17th century, rapeseed was recognized to have high economic value; B. rapa seeds were crushed more readily for oil in comparison with oil perilla seeds, and the light produced by burning rapeseed oil was Acta agriculturae Slovenica, 121/2 – 2025 3 Brassica oilseed crops in Japan: cultivation, consumption, and cultivars brighter than that of perilla oil (Yamanaka Aburaten, 2023). Rapeseed oil production was officially encouraged and the cultivation areas of B. rapa then expanded sub- stantially (Tokyo Oil Inquiry House Market, 2016). We would like to add that B. rapa was also grown for cooking oil alongside sesame, as western-influenced fried foods including tempura (deep-fried fish and vegetables) and hiryouzu (deep-fried tofu fritter) became popular from the 17th to the 19th centuries (Ohashi, 2007). 2.2 Brassica napus L. ssp. napus Unlike B. rapa, the cultivation of B. napus in Japan is fairly recent, with a European cultivar being first in- troduced into the southwestern area of the country in 1878 (Nishizawa et al., 2010; Kawasaki et al., 2022). This cultivar was known as the name of ‘Daichosen’ and was characterized by late maturity and high plant height. Af- terwards, ‘Hamburg’ was introduced from Germany into the northernmost island, Hokkaido in 1886 (Nishizawa et al., 2010). ‘Hamburg’ was a very late maturing cultivar that was well adapted to a cold climate (Nishizawa et al., 2010). At the beginning of the 20th century, two Brassica oilseed crops, viz., B. napus and heirloom B. rapa were cultivated throughout the country, but the acreage of B. napus culti- vars gradually increased because these cultivars exhibited higher seed and oil yield as well as resistance to a major disease, Sclerotinia stem rot (Shiga, 1970). In a 5-year av- erage from 1926 to 1930, rapeseed (B. napus and B. rapa) was harvested from ca. 72,000 ha with a total yield of ca. 73,000 metric tons annually in Japan (Fig. 1). Planned rapeseed improvement by Japanese public research institutions commenced in the 1930s (Chen et al., 2017). The methods of breeding rapeseed were actual- ly pure line selection and interspecific hybridization. The interspecific crossing was aimed at introducing early ma- turity from B. rapa into B. napus cultivars. Public breed- ing program also included the introgression of moisture resistance from B. rapa into B. napus (Shiga, 1970). This was because a number of farmers in southwestern Japan grew rapeseed after the rice harvest in the paddy fields with the purpose of raising farm incomes (Nishizawa et al., 2010). Breeding and intensive selection for desirable agronomic traits led to the generation of various B. napus cultivars, some of which gained wide acceptance com- mercially. Consequently, B. napus cultivars replaced con- ventional B. rapa (Nishizawa et al., 2010). Domestic rapeseed production ranged between ca. 77,000 tons and 132,000 tons in the 1930s, but produc- tion decreased sharply during World War II (Fig. 1). Fol- lowing the war, the rapeseed acreage increased again and the largest total production of 320,000 tons was achieved in 1956. Thereafter, the cultivation areas and production of rapeseed decreased rapidly (Fig. 1). There are several reasons for this, of which the most important one must be that the import volume of inexpensive oilseed crops including rapeseed and soybean jumped sharply due to the import liberalization (Kawasaki et al., 2021). 3 CURRENT STATE OF DOMESTIC OIL- SEED RAPE CULTIVATION 3.1 PRODUCTION Japan’s oilseed rape production nearly disappeared from the 1980s to the 2000s. In the 2000s, the average annual consumption of oilseed rape in Japan was ca. 2.2 million tons (Saiwai Shobo, 2011), and the domestic de- mand was almost entirely met by imports mostly from Canada and Australia (MAFF, 2024a). Apart from being used as edible oil, rapeseed oil has been utilized for sev- eral purposes in industry, including chemical manufac- turing, paint, cosmetics, and pharmaceuticals (USDA, 2023). Almost all the rapeseed imported as edible oil material was of canola quality [low erucic acid (less than 2 % in the oil), low glucosinolate content (less than 30 µmoles per gram in the oil-free meal)] (CODEX, 2001; OECD, 2001). In recent years, however, oilseed rape acreage and production in Japan have started to increase again. As shown in Table 1, average production per year from 2018 to 2023 inclusive was ca. 3,600 tons. The limited recov- ery in oilseed rape production is undoubtedly due to the subsidies granted by the Japanese government to farmers who grow oilseed rape and other crops (e.g., wheat, bar- ley, soybean), with the aim of encouraging stable farm management (Kawasaki et al., 2022). Moreover, this ten- Figure 1: Production and cultivation area of rapeseed (B. napus and B. rapa) from 1926 to 1987 in Japan. Source: MAFF (1963, 2024a) Acta agriculturae Slovenica, 121/2 – 20254 S. NAKUI et al. dency is partly owing to the choice of health-conscious people to use more domestic produces, in order to ensure safety of the foods they consume on a daily basis. 3.2 CULTIVAR DEVELOPMENT Since the 1980s, oilseed-rape breeding programs in Japan have focused on the development of cultivars with low erucic acid, low glucosinolate content, and increased yields, because there were no domestic cultivars which did meet the canola standards (Kawasaki et al., 2022). At- tempts have also been made to breed the genotypes with improved winter hardiness and high resistance to diseas- es, and a number of cultivars have been released. Agro- nomic characteristics of representative Japanese cultivars are described below. 3.2.1 ‘Kizakinonatane’ ‘Kizakinonatane’ was produced by crossing ‘To- hoku 72’ as the seed parent with ‘Rapora’ as the pollen parent , and registered as an erucic acid-free cultivar in 1992 (Okuyama et al., 1994). This cross was made with the aim of combining the high yield potential of ‘Tohoku 72’ and the zero-erucic acid trait of ‘Rapora’, and ‘Kizak- inonatane’ was developed using pedigree method. It is a high-yielding and medium-maturing cultivar with re- sistance to lodging and Sclerotinia stem rot. The cultivar also exhibits tolerance to cold and snow damage, and is recommended for northern Japan where the climate has long, cold winter. 3.2.2 ‘Nanashikibu’ This cultivar was derived from a cross of ‘Morishi 148’ x ‘Oominatane’, and registered as ‘Nanashikibu’ in 2002 (Kato et al., 2005). It is characterized by high seed- yield potential, zero erucic acid content, good lodging re- sistance, and moderate resistance to Sclerotinia stem rot. ‘Nanashikibu’ is a relatively early-flowering cultivar and its seeds can be harvested before the rainy season (com- monly from beginning of June to mid-July in Japan with the exception of Hokkaido where there is no rainy sea- son) begins; this cultivar has been predominantly grown in temperate central and southwestern Japan. 3.2.3 ‘Kirariboshi’ ‘Kirariboshi’ originated from a cross between ‘Morikei 188’ and ‘Karat’, and in 2004, it was registered as the first Japanese high-yielding, double-low cultivar (Ishida et al., 2007). This cultivar is medium-maturing, and resistant to lodging and Sclerotinia stem rot. Toler- ance to cold and snow damage is relatively high. 3.2.4 ‘Kirakiraginga’ ‘Kirakiraginga’ is a high-yielding cultivar free of erucic acid and with low glucosinolate content (Honda et al., 2017). It resulted from hybridization of ‘CASCADE’ with ‘Kirariboshi’, and was released in 2014. The culti- var is useful both for the edible oil and livestock feed markets. ‘Kirakiraginga’ has resistance to lodging and is tolerant to cold and snow damage; it grows well in cold northern climates. 3.2.5 ‘CR Nanashikibu’ This clubroot resistant (CR) cultivar was produced by introducing two CR loci, Crr1 and Crr2, from Chinese cabbage (B. rapa) into ‘Nanashikibu’ via DNA marker- assisted selection and backcrossing (Kawasaki et al., 2021, 2022). It was registered in 2022. ‘CR Nanashikibu’ has desirable characteristics similar to those of ‘Nanashi- kibu’, e.g., zero erucic acid content, lodging resistance, and moderate resistance to Sclerotinia stem rot. 3.2.6 ‘Penokanoshizuku’ The cultivar originated from a cross between ‘OZ028-2’ and ‘Kizakinonatane’ (Kawasaki et al., 2022). The release of ‘Penokanoshizuku’ in 2019 provided the industry and growers with high-yielding and double-low rapeseed. This cultivar exhibits resistance to Sclerotinia 2018 2019 2020 2021 2022 2023 Harvest area (ha) Total yield (t) Import volume (t) 1,920 3,120 2,337,350 1,900 4,130 2,359,212 1,830 3,580 2,252,378 1,640 3,230 2,342,162 1,740 3,680 2,100,818 1,740 3,680 2,021,557 Table 1: Production and import of oilseed rape from 2018 to 2023 in Japan Source: MAFF (2024a), Statistics Bureau of Japan (2024) Acta agriculturae Slovenica, 121/2 – 2025 5 Brassica oilseed crops in Japan: cultivation, consumption, and cultivars Japan, oilseed rape is commonly rotated with soybean, wheat, common buckwheat, and sugar beet (Mori, 2009). 5 DISEASE AND PEST PROBLEMS Sclerotinia stem rot has been the most widespread and serious disease of rapeseed in Japan. It is caused by the soil-borne fungus Sclerotinia sclerotiorum (Libert) de Bary and has resulted in considerable yield losses. In the fields having a history of Sclerotinia infestations, crop ro- tation and selection of resistant cultivars (see preceding section) should be followed. Other major diseases that can cause crop losses include clubroot (caused by Plas- modiophora brassicae Woronin) and root knot [caused by Meloidogyne arenaria (Neal, 1889) Chitwood]. Clubroot has a wide host range and can attack almost all Brassica crops. The disease is difficult to manage by disease con- trol practices such as crop rotation, increasing soil pH, and use of agricultural chemicals (Kawasaki et al., 2021). Thus, the most effective way to control this disease is by sowing resistant cultivars; as mentioned above, Japanese breeders released a promising clubroot-resistant cultivar ‘CR Nanashikibu’ carrying two resistant genes, Crr1 and Crr2 (Kawasaki et al., 2021). Rapeseed insect pests include cabbage armyworm (Mamestra brassicae (L., 1758), small cabbage white (Pi- eris rapae crucivora Boisduval, 1836), and cabbage aphid (Brevicoryne brassicae (L., 1758)). It is important to pro- tect the plants via insecticide application or other inte- grated pest management strategies. In addition, timely scouting is recommended for early detection and best management of insect pests. 6 CONCLUDING REMARKS In the early 2010s, the Japanese government decided to promote the cultivation of oilseed rape by allocating subsidies, and then the rapeseed production area has in- creased gradually (Kawasaki et al., 2022). However, Ja- pan still only produces ca. 0.2 % of what it consumes (see Table 1), and hence it is becoming essential to make the country self-sufficient even a little by increasing oilseed rape yields via the development of high-yielding culti- vars. According to the statistics available (MAFF, 2024a; USDA, 2024), the rapeseed yield (2,110 kg ha-1 in 2023) in Japan is considerably lower than that (3,310 kg ha-1 in 2023) in the European Union where hybrid cultivars pre- dominate. Hybrids seem likely to be the best method of enhancing yields (Ma et al., 2000; Gehringer et al., 2007). Lefort-Buson et al., (1987) previously reported that the stem rot. It is also tolerant to cold and snow damage, and adapted to cold northern climates. 4 CULTURAL PRACTICES Oilseed rape requires well-drained, loose fertile soil with a pH of 5.8-6.5 (Mori, 2009). In Japan, feral rapeseed populations are found throughout the country (Nishizawa et al., 2010; Chen et al., 2020). Oilseed rape can outcross to the feral rapeseed if they are in close proximity and there is synchrony of flowering. In order to ensure the seed purity, the commercial seeds should be multiplied not by growers themselves but by certi- fied seed-production agencies. Time of seeding plays an important role for successful harvest and good yield of the crop. In northern Japan, the optimum time of sow- ing is between mid-August and mid-September, while in warmer central and southwestern Japan, sowing normal- ly occurs from late September through early November (MAFF, 2024b). The seed sowing depth should be around 2-3 cm for best germination. Seeding rates vary by seed- ing methods, genotypes, seeding date and moisture sta- tus of the soil. Seeding is mostly done using drill seeder at 300-600 g per 10 a in the country. Oilseed rape com- petes poorly with weeds during the early stage of growth, making early weed control essential. An effective weed control program includes both cultural and herbicidal approaches. Post emergence herbicides can be used to control grassy weeds such as annual bluegrass, leading to minimizing yield decreases. In Japan, oilseed rape is cultivated as an autumn- planted winter crop that needs vernalization (winter chilling) to flower. Flowering usually begins around late February (southwestern Japan) or late April (northern Japan) of the second growing season and continues for three to four weeks. Oilseed rape is ready to harvest when the plant is well dried and there are no more green pods (Mori, 2009). Harvesting too early results in too many immature seeds and low-quality seed oil, whereas late harvesting can cause excessive shattering and yield loss. Traditional mechanical pressing method is commonly applied to edible-oil extraction from rapeseed in Japan (MAFF, 2024b). Pressing oil retains the nutritional value, natural golden color, and inherent flavor of the oil. Addi- tionally, mechanical pressing does not need solvents and chemicals, making it a simple and safe process. However, this method usually results in low oil yield. For optimum crop yields and disease control, grow- ers should not plant oilseed rape in the same field more often than once in three years. It is also important to avoid planting oilseed rape after cruciferous crops. In Acta agriculturae Slovenica, 121/2 – 20256 S. NAKUI et al. F1 hybrids between Japanese and European winter-type rapeseed cultivars exhibited high levels of yield hetero- sis. Meanwhile, all Japanese rapeseed cultivars cur- rently grown are derived from pedigree selection (Ka- wasaki et al., 2022). In the country, therefore, oilseed rape has yet to benefit from enhanced yield through hy- brid breeding. Cytoplasmic male sterility (CMS) among cruciferous crops has been broadly investigated to im- plement it as a low-cost, efficient and reliable system for the production of F1 rapeseed hybrids (Kamiński, 2013; Yamagishi and Bhat, 2014). Several hybrid breed- ing systems are available at present, of which the Ogu- INRA CMS system is widely used in Europe and North America, and the Pol CMS system is preferentially uti- lized in China (Li et al., 2022). Dominant genic male sterility may be also usable for hybrid breeding in the crop (Li et al., 2022). Efforts are required to establish hybrid breeding program of oilseed rape using appro- priate male sterility systems in Japan. Moreover, winter damage remains a significant barrier for oilseed rape cultivation in the main produc- ing area, Hokkaido where the crop is usually grown un- der thick snow cover from winter to spring. Thick snow cover acts as a heat insulator between the atmosphere and the soil, suppressing soil freezing; snow cover pro- tects the plants from low temperature stress in winter (Shimoda et al., 2023). During recent years, oilseed rape has often suffered from a severe freezing injury in east- ern Hokkaido, due to the late onset of snow cover and less snow fall. Because of that, some farmers are reduc- ing rapeseed plantings and diverting more land under other crops which give them better return. There is an urgent need to identify cold-resistant germplasm and to develop oilseed rape cultivars with robust cold hardi- ness. In Japan, more than 600 rapeseed germplasm ac- cessions, including Japanese landraces and cultivars as well as overseas accessions, are maintained at the Ge- netic Resources Center of the National Agriculture and Food Research Organization (Chen et al., 2017). This collection is expected to harbor huge genetic variation and provide opportunities for trait improvement. Now- adays, genomics takes an important position in genetics and plant breeding. Through the use of whole-genome sequencing technology and diverse molecular markers, the genomics studies in B. napus have achieved great progress (Quezada-Martinez et al., 2021; Gu et al., 2024). The availability of various genomic resources al- lows the breeders to better understand agronomic traits at the genetic level, which will facilitate the generation of novel oilseed rape cultivars with improved traits. 7 ACKNOWLEDGEMENTS We are grateful to Mr. Hidetoshi Nakajima (LLC OMEGA Farmers) for support throughout this work. Conflicts of interest The authors declare no conflict of interest. Data availability Original data are available from the corresponding author upon reasonable request. 8 REFERENCES Cartea, E., Haro-Bailón, A.D., Padilla, G., Obregón-Cano, S., del Rio-Celestino, M., Ordás, A. (2019). Seed oil quality of Brassica napus and Brassica rapa germplasm from north- western Spain. Foods, 8(8), 292. https://doi.org/10.3390/ foods8080292 Chen, R., Hara, T., Ohsawa, R., Yoshioka, Y. (2017). Analysis of genetic diversity of rapeseed genetic resources in Japan and core collection construction. Breeding Science, 67(3), 239- 247. https://doi.org/10.1270/jsbbs.16192 Chen, R., Shimono, A., Aono, M., Nakajima, N., Ohsawa, R., Yoshioka, Y. (2020). Genetic diversity and population structure of feral rapeseed (Brassica napus L.) in Japan. PLoS ONE, 15(1), e0227990. https://doi.org/10.1371/jour- nal.pone.0227990 CODEX. (2001). Codex standard for named vegetable oils. CX- STAN 210-1999. Codex Alimentarius, 8, 11-25. Fujimura-Ito, T., Ando, M., Otsuka, K., Mukai-Kubo, K., Ko- bayashi, A., Tsuyuguchi, S., … Nishiike-Wada, T. (2011). Cooking characteristics of domestic rapeseed oil: Compari- son with canola oil. Journal of the Japanese Society for Food Science and Technology, 58(7), 309-317. (in Japanese) Gehringer, A., Snowdon, R., Spiller, T., Basunanda, P., Friedt, W. (2007). New oilseed rape (Brassica napus) hybrids with high levels of heterosis for seed yield under nutrient-poor conditions. Breeding Science, 57(4), 315-320. https://doi. org/10.1270/jsbbs.57.315 Gu, J., Guan, Z., Jiao, Y., Liu, K., Hong, D. (2024). The story of a decade: Genomics, functional genomics, and molecular breeding in Brassica napus. Plant Communications, 5(4), 10084. https://doi.org/101016/j.xplc.2024.10084 Gulden, R.H., Warwick, S.I., Thomas, A.G. (2008). The biology of Canadian weeds. 137. Brassica napus L. and B. rapa L. Canadian Journal of Plant Science, 88(5), 951-996. Guo, Y., Chen, S., Li, Z., Cowling, W.A. (2014). Center of origin and centers of diversity in an ancient crop, Brassica rapa (turnip rape). Journal of Heredity, 105(4), 555-565. https:// doi.org/10.1093/jhered/esu021 Honda, Y., Kawasaki, M., Yamamori, M., Kato., M. (2017). A new winter double low rapeseed (Brassica napus L.) culti- var, ‘Kirakiraginga’, that offers high oil yield and multi-use of seeds. Bulletin of the NARO Agricultural Research for To- hoku Region, 119, 1-16. (in Japanese) Acta agriculturae Slovenica, 121/2 – 2025 7 Brassica oilseed crops in Japan: cultivation, consumption, and cultivars Huang, Z., Suzuki, K., Ikemoto, A. (2015). Evaluation of safety and quality of rapeseed oil made in China and Japan. Mem- oirs of the Faculty of Education and Human Studies, Akita University (Natural Science), 70, 99-110. (in Japanese) Ignatov, A.N., Artemyeva., A.M., Hida, K. (2008). Origin and expansion of cultivated Brassica rapa in Eurasia: linguistic facts. ISHS Acta Horticulturae, 867, 81-88. Ishida, M., Yamamori, M., Kato, M., Yui, M. (2007). A new double low cultivar of winter rapeseed, ‘Kirariboshi’. Bul- letin of the National Agricultural Research Center for Tohoku Region, 107, 53-62. (in Japanese) Japan Oilseed Processors Association. (2015). Origin of veg- etative oil production. Vegetative Oil Information, 96. (in Japanese) Japan Oilseed Processors Association. (2024). Recent trends in vegetative oils in Japan. Retrieved from https://www.oil. or.jp>trends>pdf>oilreef (in Japanese) Kamiński, P. (2013). Development of male sterile broccoli lines with Raphanus sativus cytoplasm and assessment of their value for breeding purposes. Journal of Horticultural Re- search, 21(2), 101-107. https://doi.org/10.2478.johr-2013- 0028 Kato, M., Yamamori, M., Yui, M., Ishida, M., Chiba, I., Okuyama, Y., … Sugawara, S. (2005). Breeding of a new zero-erucic acid rape cultivar, ‘Nanashikibu’ adaptable to temperate climate. Bulletin of the National Agricultural Re- search Center for Tohoku Region, 103, 1-11. (in Japanese) Kawasaki, M., Ohara, T., Ishida, M., Takahata, Y., Hatakeyama, K. (2021). Development of novel clubroot resistant rape- seed lines (Brassica napus L.) effective against Japanese field isolates by marker assisted selection. Breeding Science, 71(5), 528-537. https://doi.org/10.1270/jsbbs.21014 Kawasaki, M., Ishiguro, K., Nemoto, E. (2022). Oilseed rape breeding in Japan: its history and future prospects. Toku- sanshubyou, 35, 2-5. (in Japanese) Lefort-Buson, M., Dattee, Y., Guillot-Lemoine, B. (1987). Het- erosis and genetic distance in rapeseed (Brassica napus L.): use of kinship coefficient. Genome, 29(1), 11-18. https://doi. org/10.1139/g87-003 Li, Z., Yuan, R., Wang, M., Hong, M., Zhu, L., Li, X., … Zeng, X. (2022). Development of the PARMS marker of the dom- inant genic male sterility (DGMS) line and its utilization in rapeseed (Brassica napus L.) breeding. Plants, 11, 421. https://doi.org/10.3390/plants11030421 Ma, C., Kimura, Y., Fujimoto, H., Sakai, T., Imamura, J., Fu, T. (2000). Genetic diversity of Chinese and Japanese rapeseed (Brassica napus L.) varieties detected by RAPD markers. Breeding Science, 50(4), 257-265. https://doi.org/10.1270/ jsbbs.50.257 MAFF (Ministry of Agriculture, Forestry and Fisheries, Japan). (1963). The document about rapeseed in Japan. Tokyo, Ja- pan: Ministry of Agriculture, Forestry and Fisheries (in Japanese) MAFF (Ministry of Agriculture, Forestry and Fisheries, Japan). (2024a). Statistics on crops. Retrieved from https://www. maff.go.jp>sakumotu>sakkyou_kome (in Japanese) MAFF (Ministry of Agriculture, Forestry and Fisheries, Japan). (2024b). Oilseed rape in Japan. Retrieved from https://www. maff.go.jp>pdf>soba.natane-2.pdf (in Japanese) McAlvay, A.C., Ragsdale, A.P., Mabry, M.E., Qi, X., Bird, K.A., Velasco, P., Emshwiller, E. (2021). Brassica rapa domestica- tion: untangling wild and feral forms and convergence of crop morphotypes. Molecular Biology and Evolution, 38(8), 3358-3372. https://doi.org/10.1093/molbev/msab108 Mizushima, U., Tsunoda, S. (1969). Origin of Brassica crops. Agriculture and Horticulture, 44, 1347-1352. (in Japanese) Mori, T. (2009). Oilseed rape cultivation in Takikawa city, Ja- pan. Tokusanshubyou, 5, 44-49. (in Japanese) MRC Institute for Environment & Health. (1997). Oilseed rape: Allergenicity and Irritancy. Southampton, UK: MRC Insti- tute for Environment & Health Nakui, S., Mikami, T. (2023). Production, uses, and ancestry of an oilseed crop, Perilla frutescens (L.) Britton var. frutescens in Japan: An overview. Agriculturae Conspectus Scientificus, 88(2), 93-97. Nakui, S., Mikami, T. (2024). The history and current state of flax (Linum usitatissimum L.) cultivation and use in Ja- pan. Acta Agriculturae Slovenica, 120(1), 1-7. https://doi. org/10.14720/aas.2024.120.1.15093 Nishizawa, T., Tamaoki, M., Aono, M., Kubo, A., Saji, H., Na- kajima, N. (2010). Rapeseed species and environmental concerns related to loss of seeds of genetically modified oilseed rape in Japan. GM Crops, 1(3), 143-156. https://doi. org/10.4161/gmcr/1.3.12761 Nitta, M., Lee, J.K., Ohnishi, O. (2003). Asian Perilla crops and their weedy forms: Their cultivation, utilization and genetic relationships. Economic Botany, 57(2), 245-253. https:// doi.org/10.1663/0013-0001(2003)057[0245:APCATW]2.0 .CO;2 OECD. (2001). Consensus document on key nutrients and key toxicants in low erucic acid rapeseed (canola). Report No. ENV/JM/MOND (2001) 13. OECD. (2016). Brassica crops (Brassica species). In: Safety as- sessment of transgenic organisms in the environment, volume 5: OECD consensus documents (pp. 151-289), Paris, France: OECD Publishing Ohashi, K. (2007). Cooking oil & fat and their use seen in pub- lications during the Meiji period – Centering on a novel Shokudoraku. Bulletin of the Institute of Modern Culture, Showa Women’s University, 803, 84-93. (in Japanese) Okuyama, Y., Shibata, M., Endo, T., Sugawara, S., Hiraiwa, S., Kaneko, I. (1994). A new zero-erucic rape variety ‘Kiza- kinonatane’. Bulletin of the National Agricultural Research Center for Tohoku Region, 88, 1-13. (in Japanese) Prakash, S., Hinata, K. (1980). Taxonomy, cytogenetics and ori- gin of crop Brassicas, a review. Opera Botanica, 55, 1-57. Qi, X., Au, H., Ragsdale, A.P., Hall, T.E., Gutenkunst, R.N., Chris Pires, J., Barker, M.S. (2017). Genomic inferences of domestication events are corroborated by written records in Brassica rapa. Molecular Ecology, 26(13), 3373-3388. https://doi.org/10.1111/mec.14131 Quezada-Martinez, D., Addo Nyarko, C.P., Schiessl, S.V., Mason, A.S. (2021). Using wild relatives and related spe- cies to build climate resilience in Brassica crops. Theoreti- cal and Applied Genetics, 134(6), 1711-1728. https://doi. org/10.1007/s00122-021-03793-3 Rahman, H. (2013). Review: Breeding spring canola (Brassica napus L.) by the use of exotic germplasm. Canadian Journal Acta agriculturae Slovenica, 121/2 – 20258 S. NAKUI et al. of Plant Science, 93(3), 363-373. https://doi.org/10.4141/ cjps2012-074 Saiwai Shobo. (2011). The latest information about oils and fats in Japan. Retrieved from https://www.saiwaishobo. co.jp>yushi (in Japanese) Shiga, T. (1970). Rape breeding by interspecific crossing be- tween Brassica napus and Brassica campestris in Japan. Ja- pan Agricultural Research Quarterly, 5(4), 5-10. Shimoda, S., Terasawa, Y., Kanaya, M. (2023). Control of snow mold damage of winter wheat by snow compaction (Yuki- fumi). Soil & Tillage Research, 225, 105554. https://doi. org/10.1016/j.still.2022.105554 Song, K.M., Osborn, T.C., Williams, P.H. (1988). Brassica tax- onomy based on nuclear restriction fragment length poly- morphisms (RFLPs). Theoretical and Applied Genetics, 75(5), 784-794. https://doi.org/10.1007/BF00265606 Statistics Bureau of Japan. (2024). Trade statistics of Japan: Ag- riculture, forestry and fisheries products. Retrieved from https://www.e-stat.go.jp>stat-search>files (in Japanese) Tokyo Oil Inquiry House Market. (2016). A group of oil sellers provided light in a million city, Edo. Tokyo, Japan: Saiwai Shobo USDA. (2023). Japan: Oilseeds and Products Annual. Retrieved from https://www.fas.usda.gov/data/japan-oilseeds-and- products-annual-8 USDA. (2024). European Union: Oilseeds and Products Annual. Retrieved from https://www.fas.usda.gov/data/european- union-oilseeds-and-products-annual-4 Yagi, K., Takada, S., Funatsu, T., Matsubara, T. (2023). Struc- tural analysis of the food system of imported rapeseed: To- ward stable oilseeds procurement in Japan. Journal of Food System Research, 30(3), 163-177. https://doi.org/10.5874/ jfsr.23.30.3_8 (in Japanese) Yamagishi, H., Bhat, S.R. (2014). Cytoplasmic male sterility in Brassicaceae crops. Breeding Science, 64(1), 38-47. https:// doi.org/10.1270/jsbbs.64.38 Yamanaka Aburaten. (2023). About the oils: Japanese oils. Re- trieved from https://www.yoil.co.jp/en/colum-cat/wa Zając, T., Klimek-Kopyra, A., Oleksy, A., Lorenc-Kozik, A., Ratajczak, K. (2016). Analysis of yield and plant traits of oilseed rape (Brassica napus L.) cultivated in temperate re- gion in light of the possibilities of sowing in arid areas. Acta Agrobotanica, 69(4), 1696. https://doi.org/10.5586/aa.1696 Zhao, J., Wang, X., Deng, B., Lou, P., Wu, J., Sun, R., … Bonne- ma, G. (2005). Genetic relationships within Brassica rapa as inferred from AFLP fingerprints. Theoretical and Ap- plied Genetics, 110(7), 1301-1314. https://doi.org/10.1007/ s00122-005-1967-y