Eutrema japonicum Seeds | Wasabi
Plant Profile
A second, longer isothiocyanate is far less volatile than the pungent one. Known in the literature as 6-methylsulfinylhexyl isothiocyanate, it survives cooking and has been the focus of work on inflammation and on the broader family of isothiocyanates from brassica vegetables. It is part of the reason wasabi is studied as more than a condiment.
Japanese growers recognise two cultivation systems. Sawa wasabi is planted in terraced beds along a cold, running stream, with the rhizomes sitting in gravel under moving water. Oka wasabi is grown in shaded field beds under trees or shade cloth, watered by overhead mist. The water-grown crop produces the larger, more expensive rhizome.
The species spent most of its botanical life as Wasabia japonica, a name still printed on packets and menus everywhere. Molecular work moved it into an expanded Eutrema, the genus that also holds Asian relatives used as substitutes, and the accepted combination is now Eutrema japonicum. Growers ignore the change; herbaria do not.
Science & Biotechnology
The rhizome stores sinigrin, a glucosinolate, in one set of cells and the enzyme myrosinase in another. Nothing happens while the tissue is intact. Grate it and the two meet, and allyl isothiocyanate is released as a volatile, water-soluble irritant that drifts away in minutes. Soy sauce and citrus speed the loss, which is why both are kept off the paste.
Uses & Benefits
The rhizome is not the only edible part. Leaf stalks and leaves are chopped and packed with sake lees to make a lightly fermented pickle that is a speciality of Shizuoka, and the young leaves go into salads, rice dishes and dressings. The stalks keep a mild version of the signature heat, which makes them useful where a full grating would overwhelm a dish.
Growing from Seed
Azumino, in Nagano Prefecture, is the district most often associated with the terraced, stream-fed version of the crop, and its spring-fed farms are a working illustration of the method: narrow beds, water in from above, water out below, and shade for most of the day. The Izu peninsula in Shizuoka runs the same system on a different geology.
Wasabi wants cool, oxygen-rich water moving past its roots. Streams fed by snowmelt at around eight to eighteen degrees suit it, while warm, stagnant water invites rot. Combined with the need for deep shade and constant humidity, that requirement explains why the crop is confined to mountain valleys, and why field-grown plants under mist are so much easier to manage.
Commercial planting stock is raised largely in the laboratory. Meristem culture takes a tiny dome of dividing tissue from a healthy plant and grows it out free of the viruses that accumulate in field stands, and the resulting clones are then bulked in trays. The method gives growers uniform rhizomes of known quality instead of variable divisions.
The serious disease is a soft rot of the rhizome, caused by pectolytic bacteria in the same group as the organisms behind potato blackleg. It moves fastest when the water or the medium runs warm and the plants are crowded. There is no cure once the tissue collapses, so clean stock, cool water and prompt removal of affected plants carry the whole programme.
Most of the green paste sold with supermarket sushi is horseradish, mustard flour and colouring, and no part of it came from a mountain valley in Japan. Real wasabi commands a price that reflects two or three growing seasons in running water. Telling them apart is simple: only the true rhizome produces heat that appears and disappears within a quarter of an hour.
Use a loose mix of loam, leafmould and coarse grit that holds moisture without packing, and sow shallow, covering the seed lightly. Keep the trays cool and shaded, and water from below with cool water. Plant out when seedlings show four to six true leaves, spacing them twenty-five to thirty centimetres apart on a slight slope, so water moves past the crowns instead of settling.
Our Take
Wasabi is a cool-climate plant, and in a hot garden the honest advice is to grow it in a shaded pot or a north-facing seep rather than a sunny bed. Never let the crown sit under water in summer. If your conditions are marginal, the related Asian crop usually sold as Eutrema yunnanense is more forgiving, while the trade form of the true species is listed under Wasabia japonica in many catalogues. For the same pungent chemistry on easier ground, grow arugula, and consider brown mustard if you want the heat in seed form.
Related Reading
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