Gau sun: A cultivated host-parasite combination from china

Abstract

The structure that is called "gau sun" in Cantonese and "jiao sun" in standard modern Chinese (Mandarin) is probably the only product of a plant host and a fungal parasite that is systematically cultivated and eaten as a vegetable. It consists of the swollen flowering culm of the grass Zizania caduciflora Turcz. and a comparatively small amount of the mycelium of the smut fungus Ustilago esculenta P. Henn., which is responsible for the swelling of the culm. Brief descriptions of gau sun, in English, have been given by Fischer and Holton (1957) and Herklots (1972). However, so far as we are aware, there is no comprehensive account of the economic botany of gau sun, and a survey of the literature suggests that the nature of gau sun is not well understood in the West. The earliest account of the formation of gau sun known to us is in An Outline of Materia Medica by Li Shih-Chen and published in 1578, indicating that the Chinese people have been cultivating and eating gau sun for at least 400 years. The origin of the association between Z. caduciflora and U. esculenta was discussed by Li (1966), who remarked that cultivation of Z. caduciflora first took place in the northern region of China-presumably north of the Yellow River. Later, the area of cultivation was extended southward, where infection occurred. He did not speculate on the possible host of U. esculenta before Z. caduciflora became available. Hance (1872) described gau sun as a "Chinese culinary vegetable," consisting of the shoot of a grass, but did not recognise that a smut fungus was associated with it. Later authors interpreted incorrectly the relationship between U. esculenta and the part of the plant that it affected: for example, Hennings (1895) described the fungus as affecting the inflorescence, and Zillig (1932) described gau sun as an hypertrophied inflorescence. However, Roger (1951) correctly stated that infection caused hypertrophy of the culm and that no trace of floral organization could be detected. Roger noted further that the parasitized plants did not flower, and that plants which flowered did not produce gau sun. The sterility of infected plants has been noted by several authors in China and by ourselves. Some Japanese authors have taken the view that the fungus is the main component of gau sun. For example, Hori (1907) mentioned that the Taiwanese "consume unripe Zizania smut as a delicacy," and Kawagoe (1925) described gau sun as the "hypertrophied sprout of Z. latifolia filled with the mass of the sporogenous hyphae of a smut fungus." In fact, the greater part of gau sun is composed of host tissue.