Early Ideas On Plant Diseases

Although wheat rust was sometimes very destructive in Europe, the most generally prevalent disease of wheat was the bunt or the stinking smut (Figure 4.1). In 1750, the Academy of Arts offered a prize for the best dissertation on cause and cure of bunt. It was at that time variously ascribed as due to the use of pigeon droppings, sheep, or horse dung as manure. A French farmer named Matthieu Tillet (1714-1791) put most of these guesses to the test. He divided a piece of land crosswise into five equal parts. The first of these he manured with pigeon dropings, the second with sheep manure, the third with night-soil, the fourth with horse manure, and the fifth as control. Next, he divided the land lengthwise into four strips. In one he sowed seed deliberately blackened with dust from the bunt, in the second he used seed treated with sea salt and lime, in the third seed treated with lime or with lime and nitre, and the last, which served as control, received seed without any treatment. All the plots that had been sown with seed deliberately contaminated with bunt dust showed a predominance of bunted ears. The plots sown with seed that had been treated with lime, lime and salt, or lime and nitre, were practically free from bunted ears. This solved the riddle; the bunt was no doubt caused by infection of the seed by the black dust from bunt balls. Though Tillet linked the bunt dust with disease and won the prize, he did not realize that a pathogenic fungus causes the wheat bunt. He thought instead that the black dust contained a poisonous principle that could be partially antidoted by saltpeter and lime.

The development of the microscope destroyed the myth associated with plant diseases. In 1807, Benédict Prévost, Academician and Professor of Sciences at Montauban, began

Infected Wheat Plant From Smut
Figure 4.1 Bunt (smut) of wheat caused by Tilletia. (A) Healthy and infected spikes of wheat. (B) Enlarged view of diseased and healthy spikes. Smut spores (chlamydospores) formed in masses in spike of wheat. Photo: Department of Plant Pathology, Purdue University.
Chlamydospore

Figure 4.2 Germination of teliospore (chlamydospore) of wheat bunt, Tilletia. Haploid sporidia (basidiospores) are at the tip of the germ tube (promycelium). These fuse in pairs via conjugation tube to produce an infective dikaryotic mycelium. (From Burnett, Fungal Populations and Species (2003). Oxford University Press. With permission.)

Figure 4.2 Germination of teliospore (chlamydospore) of wheat bunt, Tilletia. Haploid sporidia (basidiospores) are at the tip of the germ tube (promycelium). These fuse in pairs via conjugation tube to produce an infective dikaryotic mycelium. (From Burnett, Fungal Populations and Species (2003). Oxford University Press. With permission.)

the study of the bunt. He put some particles (spores) from the bunted ears into water and examined them from time to time under the microscope. Within three days, the particles produced a short tube which had a bunch of small shoots at the top that resembled an onion bulb with long narrow leaves, and he called it hydre végétale because of its peculiar appearance (Figure 4.2). Prévost noticed that the bunt spores did not germinate in water taken from a copper vessel and thus discovered that traces of copper were toxic to bunt particles. Two brothers, Charles and Louis Tulasne, showed that the particles from the bunt were spores of a fungus. Working in Paris, the brothers studied various kinds of spores and published their microscope observations between 1861 and 1865. They described various kinds of spores produced either simultaneously or in succession by the same fungus.

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    What are the diseases of thermophilic fungus?
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