Human and Ecological Relevance of the Sac Fungi

Morels, which some people have called the world's most delicious mushrooms, and truffles have been prized as food for centuries. Most mushrooms are, however, included in the club fungi discussed in the next section "Phylum Basidiomycota—The Basidiomycetes (Club Fungi)." Wealthy Romans and Greeks used to insist on preparing morels personally according to various recipes they had concocted, and they are still prized as gourmet food today. Prior to 1982, numerous unsuccessful attempts were made to cultivate them under controlled conditions, but morels now can be mass-produced commercially and are presently being marketed. Morels (Fig. 19.10) are tan in color and have a spongelike, somewhat cone-shaped top on a stalk that resembles a miniature tree trunk. The numerous depressions between the ridges each contain thousands of asci. Although well-cooked morels are perfectly edible by themselves, some persons have become ill after consuming undercooked specimens or consuming them with alcohol. Caution in this regard is advised.

A related mushroom called a false morel or beefsteak morel is considered a delicacy by many but has caused death in others. False morels contain a volatile toxin (monomethyl hydrazine) that may render them poisonous to humans if cooking has failed to eliminate all of the toxin.

When rye, and to a lesser extent other grains, comes into flower in a field, it may become infected with ergot fungus (Fig. 19.11). This fungus seldom causes serious damage to the crop, but as it develops in the maturing grain, it produces several powerful drugs. If the infected grain is harvested and milled, a disease called ergotism may occur in those who eat the contaminated bread. The disease can affect the central nervous system, often causing hysteria, convulsions, and sometimes death. Another form of ergotism causes gangrene of the limbs, which can result in loss of the affected limb. It can also be a serious problem for cattle grazing in infected fields. They frequently abort their fetal calves and may succumb themselves.

Stern-Jansky-Bidlack: Introductory Plant Biology, Ninth Edition

19. Kingdom Fungi

Text

© The McGraw-H Companies, 2003

Chapter 19

• Zygote nuclei, formed when two nuclei unite. They undergo meiosis prior to the development of I ascospores.

fertilization hymenium —

fertilization hymenium —

Ergot Fungus Life Cycle

sterile hyphae

•ascogenous hyphae spore ascogonium antheridium

Figure 1Q.7 Life cycle of a sac fungus. When hyphae of two different strains of a sac fungus become closely associated, male antheridia may be formed on one and female ascogonia on the other. Male nuclei migrate into an ascogonium and pair but do not fuse with the female nuclei present. Then new hyphae (ascogenous hyphae), whose cells each contain a pair of nuclei, grow from the ascogonium. In a process involving fusion of the pairs of nuclei (followed by meiosis), fingerlike asci, each containing four or eight haploid nuclei, are formed in a layer called a hymenium, which lines an ascoma. The haploid nuclei become ascospores, which are discharged into the air. They are potentially capable of initiating new mycelia and repeating the process.

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