History
Wasabia japonica, known as Japanese Horseradish (Wasabia japonica) is a native condiment crop of Japan. It is not known when Wasabia japonica was first brought into cultivation but Japanese historical records indicate that Wasabia japonica, known originally as wild ginger, was introduced as a medicinal plant by Sukahito Fukae. The first Japanese medical encyclopaedia called “Honzo-wamyo” was published in A.D. 918 and it states that “wild ginger” (Wasabia japonica) had been grown in Japan for at least a thousand years (1). During 1596-1615 A.D. Wasabia japonica cultivation began on the upper reaches of the Abe River in Shizuoka prefecture. Its use, however, was restricted to the ruling class by order of the Shogun Iieyasu Tokugawa (2). At present, the natural distribution of Wasabia japonica in Japan ranges from Russia’s Sakhalin island, north of Hokkaido (the most northern Japanese island) to Kyushu (the southernmost major Japanese island) (3).However, the Shimane region is the largest area of Wasabia japonica production and breeding research in Japan at present.
Wasabia japonica is now being grown in many countries in the world including New Zealand, Taiwan, Korea, Israel, Brazil, Thailand, Canada and USA. In New Zealand, the Ministry of Agriculture and Fisheries introduced Wasabia japonica for experimental cultivation in 1982 The majority of their products are used in Nutraceutical products due to its high level of active constituents. Preliminary assessment of the growth and plant yield of soil-grown Wasabi japonica was carried out at Lincoln in 1995 (7). Yields of flavour compounds, as affected by fertilizer treatment, were carried out in 1997 (8, 9). Further research has been performed at Lincoln University to develop an understanding of Wasabia japonica growing in New Zealand, especially the agronomy, cultivation methods, ITC variation and stability (10).
Botany of wasabi
Wasabia japonica is a member of the Cruciferae family which also includes cabbage, cauliflower, broccoli, sprouts, water cress, radish, mustard and horseradish. The European horseradish (Armoracia rusticana) is a distant cousin of Wasabia japonica and is often coloured and mixed with mustard and other ingredients to produce a “faux” wasabi . The genus Wasabia consists of two species, Wasabia tenuis (an uncultivated species) and Wasabia japonica (the cultivated species). These two species are distinguished primarily by their cytology, stem size, colour, leaf size and shape.
Wasabia japonica is a glabrous, perennial herb that grows about 450 mm high, producing leaves on long petioles from the crown of the plant. As the plant ages the rhizomes start to form and, at maturity after 18 months, the Wasabia japonica plant has a distinctive thickened stem (or rhizome) connected to the heart shaped leaves by long, thin petioles.
Rhizomes are the most favoured plant part of Wasabia japonica. Dependent upon the variety, the plants have one or more main rhizomes and can have a number of secondary stems.
The lengths and weights of rhizomes vary widely between variety e.g. for Daruma – the single rhizome length ranges from 50 to 200 mm long and weighs 4 to 120gm. Wasabia japonica leaves are simple, cordate-reniform, undulate-toothed and 80-250 mm in diameter. Petioles are vertical to oblique, 300–500 mm long, basally flattened and surround the rhizome. Whole fresh plants can weigh up to 3.4 kg.
Wasabia japonica flowers are white, bracteate, arranged on racemes, with ascending sepal, cruciform and obovate petals, perfect septum, elongate styles and simple stigma. Fertilisation is mainly by cross pollination, and insects. Seeds must be stored in a cool moist environment, since dry storage will result in desiccation and loss of viability of the seed. Fresh seed is naturally dormant until it is vernalised by storing at a low temperature. Fresh seed is notoriously difficult to germinate, and methods are closely guarded by growers.