Fungi are organisms such as yeasts, moulds, mildews and rusts, smuts or sooty moulds, puff balls, mushrooms, and bracket fungi. They may be microscopic in size or up to more than a foot in diameter. Unlike other plants, fungi possess none of the green pigment chlorophyll, necessary for the utilisation of CO2 from the air to form carbohydrates. Instead, they are dependent upon the substrate on which they grow to provide those food substances so essential for their growth and development. They live either saprophytically on dead organic material or as parasites on living organisms belonging to the plant or animal kingdom. Unlike flowering plants they reproduce themselves by spores, not seeds. These spores are minute, often under a hundredth of a millimetre in diameter, and are borne on elaborate fruiting bodies or sporophores. It is the fruiting body which is usually the most conspicuous part of the fungus plant. It varies in size from something less than a millimetre in diameter to more than 20 cm; it may be an elaborate structure, varying from a more or less undifferentiated mass of mycelium to a small, black, globose body, or a mass of brightly coloured fleshy discs, a puff ball or a mushroom. Identification of fungi is based on the microscopic structure of these fruiting bodies, since the vegetative mycelium (hyphae) which ramifies throughout the growth medium is of a more uniform character. It must be remembered that there are as many, if not more, species of fungi than there are seed plants and that the humid mild climate experienced in New Zealand is ideal for fungal growth.
There are three main groups of fungi:
Phycomycetes (literally algal fungi) which include filamentous fungi resembling colourless algae. They are chiefly aquatic and contain many soil and water moulds, as well as downy mildews of plants and the common bread mould, Rhizopus.
Ascomycetes or sac fungi, where typically eight spores are borne within a saclike hypha called an ascus. Such structures are formed either singly (in a yeast) or are united on an elaborate fruiting body which may be an apothecia (a disc-like fruiting body in which the fertile part is exposed) (2) or a perithecia (a flask-shaped body in which the fertile region is covered, opening to the exterior by a pore) (1)
Basidiomycetes, in which four spores are borne superficially on a structure known as a basidia. They may be formed singly as in rusts (5) or united on a large elaborate fruiting body, such as a mushroom (9) or a polypore (11), a bracket fungus (10), or a puff ball (7).
There is a subsidiary group, known as the fungi imperfecti, which includes forms with asexual spores. In some genera within this group a complete life cycle is unknown or may not exist. It includes many important plant pathogens which are responsible for fruit rots as well as leaf spots, stem or root rots of plants, and includes the common moulds, Aspergillus and Penicillium (4).
Yeasts are probably the oldest group of fungi to be domesticated because of the part they play in breadmaking and in brewing of alcoholic beverages. The common field mushroom has been cultivated for many years in Europe, and it is stated that an account of mushroom growing appeared in a French gardening book published in the mid-seventeenth century. Milk curd is inoculated with different species of Penicillium to give cheese characteristic flavours, e.g., Penicillium roqueforti is used to inoculate blue vein cheese. Within the last 20 years the cultivation of many mould species has become extremely important in the production of antibiotics, enzymes, and vitamins.
In nature, fungi play an important part in the decomposition of organic debris. Dead wood is quickly invaded by fungi and its hard texture is soon destroyed. Throughout the world there are fungi which live as saprophytes on organic matter in the soil and a more or less universal range of fungus species is always present. Not only do these fungi break down the organic material but they also help to maintain a soil texture. A special environment exists on or very near the surface of roots and the fungal flora of this “rhizosphere” differs from that in the rest of the soil. Specific fungi also grow in the association with specific plants of higher groups and often enter into the tissues of the living root without any noticeable pathogenic effects. The physiology of such a “mycorrhizal” relationship is not really clearly understood, but it is generally thought that under favourable conditions the other plant gains through the relationship with the fungus. In New Zealand only a few cases of mycorrhiza in our endemic plants have been investigated, but casual observations suggest that it is of common occurrence, especially in the Ericaceae plants (e.g., Pernettya and Gaultheria). In our exotic pine plantations fructifications of fungi associated with conifers of North America and Europe are extremely common, e.g., Amanita miscaria and Boletus granulatus, and it is apparent that these fungi have a mycorrhizal relationship with the pines.
Fungi are perhaps better known for the damage they do, rather than for their usefulness. They are responsible for the deterioration of textiles and food substances stored under damp conditions, as well as for the rot of harvested fruit and vegetables, sap stain in milled timber, and decay of timber in damp situations. Parasitic fungi are one of the principal agents of diseases in plants. In New Zealand in some seasons considerable losses are caused by diseases such as blight on potatoes and tomatoes, brown rot on stone fruit, and bitter rot on apples; rust and smut of grass and cereal crops are also common. Thus rigid spray programmes must be maintained to prevent serious crop losses, and resistant plant varieties be developed. Mushroom poisoning is not unknown in New Zealand, but in no case has the guilty species been identified. As little is known about mushrooms and toadstools common in our native forests, it is dangerous to eat fungi other than those known to be edible in European countries. The lethal Amanita phalloides has been collected in an Auckland park. Elsdon Best, in Forest lore of the Maori, notes that the Maori did eat some fungi, probably about 12 species, but only in times when food was scarce. They recognised that some species were poisonous. The common Jew's-ear fungus (Auricularia polytricha), which was at one time exported in quantity to the east, was eaten but not really liked, and was usually cooked with a green vegetable.
A cattle disease known as “staggers”, due to ergot poisoning, is not uncommon in North Auckland and is caused by seed heads of the grass Paspalum becoming heavily infected with the ergot fungus Claviceps paspali. “Facial eczema” in sheep and cattle has been shown to be due to a toxin in a mould Pithomyces chartarum, which grows on debris in pasture during humid conditions.
Studies in geographic distribution of fungi show that many species, especially among saprophytes, are common throughout the world. Fungal spores are so small that they are easily distributed by wind and in rain droplets. Natural transport, such as prevailing air currents, play an important part in spreading some crop disease epidemics. The most important factors are temperature and a suitable substrate. Pithomyces chartarum, the black mould fungus responsible for “facial eczema” in Australia, occurs in most warm temperate countries and only in the north of New Zealand. In this case temperature limits its distribution. Many species which parasitise leaves of seed plants are specific to a single host species, so that distribution is limited by the spread of the host. For example, 77 per cent of the rust fungi are found only in New Zealand. Cordyceps robertsii, the vegetable caterpillar parasitising a moth larva belonging to Oxycanus, occurs only in Australia and New Zealand. High mountain ranges and oceans also makes natural barriers to distribution, and even among saprophytic species there are in New Zealand a number which are endemic, e.g., the small spiney puff ball, Lycoperdon compactum, occurs only in forests in New Zealand. Similarly, the purple Secotium porphyreum occurs only in New Zealand Nothofagus forests.
Since the publication of a list of fungi in Hooker'sFlora novae-zealandiae (1855) and Hooker's Handbook (1867), where some 200 species were described, no catalogue of New Zealand fungi has been made. In Cooke's Australian fungi (1892) New Zealand species are referred to only when they occur in both countries. Records and observations on New Zealand fungi have, however, been published in periodicals, both in New Zealand and overseas, and the number of fungi reported to be present must now be well over 1,200 species belonging to approximately 240 genera. As fungi play an important role in the diseases of plants, studies have been directed into these groups and some 700 pathogenic species have been described. Few have been listed among the saprophytic species, and in large groups, such as mushrooms and toadstools, few species have been described, while for most groups of smaller fungi there are, as yet, no records.
by Joan Marjorie Dingley, M.SC., Plant Diseases Division, Department of Scientific and Industrial Research, Auckland.