Introduction

Zizania latifolia Turcz., which belongs to the tribe Oryzeae within Gramineae, is a perennial aquatic plant grown in lakes, ponds or wetlands (Fig. 1), and is an important crop that has been grown in China since ancient times (Chen 1991; Zhai et al. 2001; E Natural Health Center 2006). It is recorded in the book ‘Li Ji’, written in the Zhou Dynasty (from 771 to 221 B.C.), that the seed was used as one of six main crops. The subsequent book ‘Er Ya’ (about 202 B.C.) recorded that the flowering stem in some individuals became infected by an unknown epiphyte or bacterium and could not flower again; this infection was accompanied with a swollen stem and the formation of spindly, though still edible, shoots. Much more recent research has shown that the swollen flowering stem is a direct result of infection by Ustilago esculenta P. Henn. and that the spindly shoots are a result of the stimulation of indole-3-acetic acid secreted by the epiphyte (Yu 1962; Chan and Thrower 1980; Thrower and Chan 1980).

Fig. 1
figure 1

Zizania latifolia grows in lakes, ponds, wetlands and water fields (from the E Natural Health Center 2006)

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In ancient China the wild plant was mainly distributed along the Changjiang River, from upriver locations in Sichuan Province to the more downriver sites in Jiangsu and Zhejiang Provinces. However, the edible seed of this plant disappeared during the Tang Dynasty (618–907) due to mass migration to this region and the filling in of the lakes, and the plant became scarce during the Ming Dynasty (1368–1644) (You 2006). However, based on a study carried out between 1991 and 2001, Zhai et al. (2001) reported that there were wild fertile plants distributed throughout five lakes in eastern China. The article by these researchers would appear to represent one of the few reports currently available on the distribution of this wild species in present-day China, the scarcity of which may be attributable to a strong shattering trait and varying weather patterns in the autumn (You 2006). As a result, it has not been possible to domesticate this plant species throughout China and other countries, even though its grain has high nutritional value in comparison to American wild rice (Z. aquatica) (Zhai et al. 2001). It is notable that infected individuals are still maintained, with the underlying reason possibly being that the spores of the epiphyte can remain hidden in the underground creeping stem, consequently surviving the winter and maintaining the infection cycle year after year; clonal propagation with one genotype confirms a relatively coincident autumn.

Distribution

Cultivars of Z. latifolia can be found mainly in regions of southeastern Asia, including Russia (from eastern Siberia to the far eastern area), Japan, Korea and China. It is cultivated at scattered locations throughout Korea and Japan, and in China it is widely cultivated from northern Beijing to southern Guangdong province and Taiwan, and from eastern Sichuan province to Shanghai. The largest area under Z. latifolia cultivation area in China is found in the region surrounding Tai Lake, Jiangsu and Zhejiang provinces. It is estimated that more than 20,000 ha are under cultivation with this crop plant in Zhejiang province alone and that 500,000 tons of fresh product are harvested from this plant species each year (Yu et al. 2003).

Cultivation

There are two main types of cultivars cultivated in China at present. One is a single-season crop plant that only can be harvested once each year, in the fall (from August to November) (Table 1); the other is two-season plant which is planted in the spring and then can be harvested twice in the fall and once the summer thereafter (Table 2). The first type, a strictly short-day plant, can develop shoots only when the days become shorter in the fall. This kind of plant, which is taller and has fewer underground creeping stems, has fewer cultivars, a lower yield and a wider distribution, ranging from northern Beijing to southern Guangdong province, when compared with the other type. The second type is insensitive to sunlight and endemic to the South, with Changjiang River as a divide.

Table 1 Agricultural characteristics and original places of the main cultivars of Zizania latifolia harvested only once in the fall (from Yu et al. 2003)
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Table 2 Agricultural characteristics and original places of the main cultivars of Z. latifolia harvested twice in the fall and once the following summer (from Yu et al. 2003)
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The present-day crop of Z. latifolia differs from that of its ancestor, mainly in that present-day plants infected by U. esculenta do not flower and they form swollen shoots. Common practice is that either the healthy individuals with flowers or those with black spots in the shoots will be removed from the field when harvesting. Under natural conditions it is very difficult for the healthy plant to form seed set due to unequal breakaway of chromosomes in metaphase I of the meiotic cycle (E Natural Health Center 2006). Therefore, the selection of good-quality individual plants from the field to be used for clonal propagation is the most usual method of plant propagation. Although healthy plants not forming shoots as well as infected plants are removed after harvest each year, there are always some such individuals that develop in the fields, which may correlate with the infectivity of the epiphyte under the different micro-climates. (Fig. 2).

Fig. 2
figure 2

A Z. latifolia plant infected by Ustilago esculenta (left, from E Natural Health Center 2006) with the swollen shoot (right)

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Physiological and biochemical aspects

In addition to some research having been carried out on the ecology of the wild species (Omokawa et al. 2003; Wu and Yu 2004; Asada et al. 2005a, b), much attention has been given to the cultivated and infected species, which has been given another name, Z. caduciflora (Turcz.) Hand.-Mazz., by some researchers (Jiang et al. 1998, 2005a; Zheng et al. 1999; Qiu et al. 2002; Liang et al. 2004; Yu et al. 2005), although it is not yet officially recognized by taxonomists (Chen et al. 1990; Shu et al. 1990; Chen and Shu 1991; Chen and Xu 1994). Various physiological and biochemical aspects of Z. latifolia have been studied, including the differences between individuals with and without infection (Jiang et al. 1998), the difficulty in forming healthy individuals (Tan 1995; Yang 2003), biomass accumulation (Jiang et al. 2005a), the plant content of N, P and K ions and protein (Qiu et al. 2002; Jiang et al. 2003a), changes in dry weight, fresh weight and starch content (Jiang et al. 2001), the accumulation and allocation of carbohydrate (Jiang et al. 2003b) and the biochemical changes during stem gall formation (Cheng et al. 2004). In addition, the non-structural carbohydrates, enzymes and the content of endogenous hormones have been studied (Jiang et al. 2004, 2005b).

Future research and commercial aspects

The harvest shoot is a delicious aquatic vegetable which contains 1.5% protein, 0.1% fat and 4.0% sugar along with some inorganic salts (Xing 2002). It is considered to be one of the three most famous foods in Jiangsu and Zhejiang provinces. Although this plant is mainly used as aquatic vegetable in China, it is also a medicinal plant, according to the records maintained in the Chinese ancient books, which can reduce fever, inhibit thirst, prevent poisoning induced by alcohol, among others.

This plant has been widely introduced into many regions in China and beyond (Chen 2002), and the amount of surface area under cultivation has be expanded so that it is now only second to the lotus (Nelumbo nucifera Gaertn. ssp. nucifera) among all of the 12 aquatic vegetables cultivated in China for high nutritional value and price. Many studies have been carried out on its safe production, such as the good agricultural practices (Yu et al. 2003), planting on mountainous terrain at high altitudes (400 m) in order to harvest earlier and reduce disease and pest harm (Liu et al. 2001; Rao et al. 2004; Wu et al. 2005) and the tridimensional pattern with fish and ducks mixed with the plants in field (Deng et al. 2003). Given that Z. latifolia represents an intermediate form of rice and the cultural practices of rice and Z. latifolia are similar (similar characters, including morphology and growth environment), some research has been carried out on common pests and diseases (Zheng et al. 1999; Xu et al. 2001; Chen et al. 2003; Yu et al. 2002; Xiao et al. 2005). In order to estimate the genetic resources, many accessions have been evaluated and new cultivars selected (Kong et al. 1994; Ke et al. 1997, 2000a, b, 2003; Yu et al. 2005). Due to extensive cultivation of a single cultivar in some regions, the overstocking of fresh products often results in the crop decaying or being abandoned due to logistics problems in the same harvest period. Therefore, the packing, storing and processing of the product has attracted the interest of some researchers (Xi et al. 2001; Zhou et al. 2002; Chen et al. 2003a, b; Gao et al. 2003; Zhu and Gao 2005; Li 2005).

Although the ripened shoot is used as a delicacy, the other parts of this plant are little utilized in China, although leaves can be used as a culture substrate of edible fungi (Cai 2003) and the aboveground parts can be forage for cattle and fish due to the most coarse protein and nitrogen content in the plant within the genus Zizania (Pan et al. 1993). To date, ten patents in the Derwent Innovations Index have been found from the year 1998, among which six are from Korean and three from Japan, with one from the USA. These patents are for using the leaf of Z. latifolia as tea for treating various diseases and the extract of the plant as a component of food, pills or cosmetics. In addition, the plant is a potential bio-enhancement tool in the natural purification of water as it absorbs nitrogen and phosphate (Lee et al. 2004; Jiang et al. 2005c), although it has low rate of phosphorus removal (Liang et al., 2004) and its removal rates of nitrogen and phosphorus are lower than that of Phragmites communis (Cav.) Trin. ex Steud. (Zhang et al. 2003a, b).