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.

Ergotism was common in Europe in the Middle Ages. Known then as St. Anthony's Fire, it killed 40,000 people in an epidemic in a.d. 994. In 1722, the cavalry of Czar Peter the Great was felled by ergotism just as the czar was about to conquer Turkey, and the conquest never took place. Some historians have implicated ergotism in violent social upheavals such as the French Revolution and the Salem Witchcraft Trials. In 1951, an outbreak hospitalized 150 victims in a French village. Five persons died and 30 became temporarily insane, imagining they were being chased by snakes and demons.

In small, controlled doses, ergot drugs are medically useful. They stimulate contraction of the uterus to initiate childbirth and have been used in abortions and in the treatment of migraine headaches. Ergot is also an initial source for the manufacture of the hallucinogenic drug lysergic acid diethylamide, popularly known as LSD.

Fungi in this phylum play a basic role in the preparation of baked goods and alcohol. Enzymes produced by yeast aid in fermentation, producing ethyl alcohol and carbon dioxide in the process. The carbon dioxide produced in bread dough forms bubbles of gas, which are trapped, causing the dough to rise and giving bread its porous texture. Part of the flavor of individual wines, beers, ciders, sake, and other alcoholic beverages is imparted by the species, or strain, of yeast used to ferment the fruits or grains.

Yeasts are at least indirectly involved in the manufacture of a number of other important products. Ephedrine, a drug also produced by mormon tea, a leafless western desert

Kingdom Fungi 363

Kingdom Fungi 363

Ascoma Sac Fungus
Figure 1Q.8 An ascoma of a sac fungus.

Figure 1Q.Q Closed ascomata (cleistothecia) of a powdery mildew on an oak leaf, x 200.

shrub, is obtained commercially from certain yeasts. The drug is used in nose drops and in the treatment of asthma. Yeasts are also a rich source of B vitamins and are used in the production of glycerol for explosives. Ethyl alcohol is used in industry as a solvent and in the manufacture of synthetic rubber, acetic acid, and vitamin D. Yeast contains about 50% protein and makes a nourishing feed for livestock. Its enzyme, invertase, catalyzes the conversion of sucrose into glucose and fructose and is used to soften the centers of chocolate candies after the chocolate coating has been applied.

Several very important plant diseases are found in this phylum of fungi. Dutch elm disease (caused by Ophiostoma ulmi or O. nova-ulmi), a disease originally described in Holland, has devastated the once numerous and stately American elm trees in many towns and cities in the midwestern and eastern United States and has spread to the West and South. When Dutch elm disease was first discovered, limited control of the disease was achieved by spraying the trees with DDT to kill the elm bark beetles that spread the disease from tree to tree. DDT killed many useful organisms as well, however, and its use for such purposes was eventually banned.

Other sprays have since been used, again with limited success, and biological controls are now being sought. One such control was reported in 1980 by Gary Strobel of Montana State University. He injected Pseudomonas bacteria into 20 diseased trees and saved 7 of them when the bacteria multiplied and killed the Dutch elm disease fungus. In 1987, Dr. Strobel injected a genetically altered strain of Pseudomonas bacteria with more powerful toxins against

364 Chapter 19

Ergot Fungus Lsd
Figure 1Q.11 Ergotized rye. The prominent darker objects scattered throughout the rye are kernels infected with ergot fungus. (Copyright © Loran Anderson)

Dutch elm disease into 15 elm trees but then cut the trees down in protest to the red tape involved in not previously obtaining permission from the Environmental Protection Agency for his experiment. Whether or not this control technique will meet with widespread success remains to be seen, but it is the type of control that is much to be preferred to poisonous sprays that upset delicate ecological balances (see Appendix 2, which deals with biological controls).

Chestnut blight has virtually eliminated the once numerous American chestnut trees from the eastern deciduous forests. Attempts to control the disease have met with very limited success thus far. Much better success has been obtained in controlling peach leaf curl, a disease that attacks the leaves of some stone fruits, especially peach trees (Fig. 19.12). Sprays that contain copper or zinc salts apparently inhibit the germination of spores of peach leaf curl and have been effective in preventing serious damage when applied to trees before the dormant buds swell and open in the spring.

Ophiostoma Nova Ulmi

Figure 1Q.12 A peach leaf infected with peach leaf curl.

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    How is ophiostoma ulmi phylum?
    8 years ago

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