Fig. 7. Camera-lucida drawings of germinating: chla- 

 mydospores of Ustilago maydis, showing diverse types of 

 germination (Kernkamp and Petty, 182). 



about 10 C for a year or two without losing its 

 viability. 



Chlamydospores lose their viability in silage after 

 a few weeks (260). This may also happen when they 

 are mixed with manure, especially if fermentation or 

 heating takes place; or if the spores come in contact 

 with destructive agents such as acids, alkalies, and 

 antibiotics. It is generally assumed that sporidia mul- 

 tiply and persist in nature in soil, especially in soils 

 rich in organic material; but this is not supported by 

 experimental evidence. In fact, Jackson (167) has 

 shown that soil prevents chlamydospores from ger- 

 minating. The writer has obtained similar results with 

 many types of unsterilized soil. 



Germination of spores. — The nature of chlamydo- 

 spore germination depends on environmental conditions 

 and the genetic makeup of the race of smut. Usually, 

 when a chlamydospore germinates on a solid nutrient 

 medium, it produces a basidium called a promycelium. 

 During the growth of the promycelium. meiosis occurs: 

 and then. 3 cell walls are laid down, so the promy- 

 celium eventually contains 4 cells. Each of the 4 

 promycelial cells usually contains a single haploid 

 nucleus and each cell gives rise to at least 1 sporidium. 



1) Types. — Although a 4-celled promycelium with a 

 sporidium at each cell is usually illustrated in most 

 textbooks in mycology, it is not necessarily the most 

 common type. Kernkamp and Petty (182) germinated 

 chlamydospores from 8 field collections. 4 crosses be- 

 tween monosporidial lines, and 2 diploid lines. Twenty- 



five different types of germination were observed 

 ( Fig. 7 ). Some of the more common types were promy- 

 celia with 1-8 cells, promycelia bearing 1 or more 

 hyphal branches instead of sporidia, and the chlamydo- 

 spore functioning as a basal promycelial cell. In 

 general, the type of germination was associated with 

 the specific collection of smut or cross indicating ge- 

 netic factors were involved. Environment also affects 

 type of germination; thus, Walter (350. 351) concluded 

 that, on the corn plant, chlamydospores usually ger- 

 minated directly and penetrated the host without the 

 formation of sporidia. 



2 ) Germination in water. — In most cases, chlamydo- 

 spores of U. maydis germinate poorly or not at all in 

 pure water. In this respect, they differ sharply from 

 other cereal smuts. Sometimes, after a rest period, 

 they germinate fairly well in water (34, 305). 



Stakman ( 305 ) found that the promycelia formed 

 in water were rather slender and secondary sporidia 

 rarely developed. In water, the promycelia often gave 

 rise to germ tubes. Sporidia. too, tended to produce 

 germ tubes on a non-nutrient substrate or when the 

 nutrient in the medium approached exhaustion. Platz. 

 Durrell, and Howe (264) obtained good germination of 

 chlamydospores on silicate gel and collodion; both are 

 non-nutrient materials. Clinton (60) also obtained 

 excellent germination in water, although the time re- 

 quired for germination was longer than in a nutrient 

 solution. Chlamydospores that failed to germinate in 

 distilled water germinated readily when a trace of 

 sugar or a small bit of host tissue was added to the 

 water. Apparently, only a very minute quantity of 

 nutrient material is essential for germination; and this 

 may account for some of the inconsistencies obtained 

 in germination of chlamydospores. 



3) Germination in nutrient solution. — Brefeld (34), 

 in 1883, was the first to discover that chlamydospores 

 germinate exceptionally well on nutrient substrates. His 

 work has been verified many times. Without difficulty 

 the writer has germinated, on nutrient media, chlamydo- 

 spores taken from immature galls. In nutrient media, 

 including manure decoction. Brefeld (34. 35) found that 

 secondary sporidia were produced in great abundance 

 and continued to multiply until the nutrient material 

 was exhausted. Brefeld's work indicated that chlamydo- 

 spores germinate readily in the sterilized soil, especially 

 in that containing manure; and that such a substrate 

 was conducive to growth of secondary sporidia. Since 

 then, many control measures have been recommended 

 on the basis of his pioneer work. There is, however, no 

 adequate experimental evidence that chlamydospores 

 germinate readily or that the sporidia bud extensively 

 in soil or manure in the field. Mrs. Edith Jones (175). 

 in 1923. found that chlamydospores in most cases ger- 

 minated rarely in unsterile soil, particularly those con- 

 taining barnyard manure. This is also in accord with 

 the writer's findings. In nature, there are many physical, 

 chemical, and biological factors that may inhibit spore 

 germination and sporidial multiplication. Many of these 

 inhibitors are apparently removed, at least in part, 

 when the material is sterilized. 



4 ) Effect of temperature. — Temperature has a tre- 

 mendous effect on the percentage, rapidity, and type 

 of germination of chlamydospores. Maire (209) indi- 



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