Fig. 2. Diagram illustrating the life cycle of Vslilago 

 maydis. There are many types of deviation from the one 

 given, especially in germination of chlamydospores and mei- 

 osis (by C. M. Christensen). 



nothing about nuclear condition, mode of formation, 

 nature of germination, or function in the life cycle. 



The smutty overgrowth produced by U. maydis on 

 corn (Z. mays L.) and teosinte (E. mexicana Schrad.) 

 has been called by several common names: boil, blister, 

 excrescence, gall, pustule tumor, sorus. and swelling. 

 Until about 1900. the term pustule was not uncommon 

 in the U.S.A. and blister is still commonly used in 

 certain European countries (237). Although boil is 

 still used frequently, the term gall is used most com- 

 monly, particularly in the U.S.A. 



Life History. — The life cycle of U. maydis is com- 

 pleted in most cases every time it passes through the 

 host. Three distinct nuclear phases occur in the life 

 history of U. maydis: the diplophase. haplophase, and 

 dicaryophase. This involves karyogamy. meiosis, and 

 plasmogamy. Consequently, a collection of chlamydo- 

 spores does not represent a pure breeding population. 

 The diploid stage is normally restricted to the mature 

 chlamvdospore and ends when the spore germinates 

 (Fig. 2). 



Chlamydospores are produced in vast numbers in 

 smut galls on corn and teosinte. The spores overwinter 

 on the ground, especially in galls and in plant parts. 

 The smut galls are more or less repellent to water; 

 therefore, the chlamydospores may appear perfectly 

 dry in the spring although the gall may be lying on 

 wet ground. Of course, this may not necessarily occur 

 in moist and humid regions. The galls, at least the 

 greater portion of them, persist until the crop is 

 harvested. Some galls are broken off by mechanical 

 means and fall to the ground; and chlamydospores may 

 be washed off by rain, scattered by farm machinery. 

 perhaps by insects, and readily by wind. 



Usually, the diploid chlamvdospore germinates by 

 the formation of a promycelium on which haploid 



Fig. 3. Germinating chlamydospores of L'stilago maydis 

 producing secondarv sporidia in nutrient media (Brefeld, 

 34). 



sporidia are borne (Fig. 3). The sporidia germinate 

 and can be readily propagated on artificial substrates 

 and also in the moisture that collects in axils and in 

 whorls of corn leaves. U. maydis is heterothallic; the 

 parasitic stage, which is the dicaryophase, is initiated 

 by the fusion of sporidia or mycelia of opposite sexes, 

 usually in the host. Chlamydospores also may give rise 

 directly to germ tubes. The germ tube penetrates only 

 the tender tissues and infection is termed local. 



In the host, the dicaryophase usually persists until 

 the formation of chlamydospores. When young develop- 

 ing galls are subjected to very high humidities, how- 

 ever, the dicaryotic mycelium in the host may give rise 

 to chains of aerial haploid sporidia: and. if the vege- 

 tative mycelium is diploid, the sporidia are diploid. 

 These chains of aerial sporidia are readily disseminated 

 by air currents and driving rains and also may be an 

 important source of inoculum. In culture, dicaryons do 

 not persist because the nuclei usually dissociate, result- 

 ing again in the original haploid lines. M. 15. Moore 

 • unpublished data. University of Minnesota) appar- 

 ently isolated dicaryotic hyphae from a living corn 

 plant. At least the hyphae he isolated were stout, con- 

 torted, and grew slowly on potato-dextrose agar. 



Symptoms. — U. maydis may produce several morpho- 

 logical changes in plants of corn and teosinte. Smut 

 galls are semifleshy, consisting of the smut fungus 

 intermixed with enlarged cells of the affected organs 

 of the host. Young galls are at first firm and light in 

 color and covered with semiglossy peridium which 

 turns black as the gall matures. When the membrane 

 dies, it usually cracks open, exposing the dry powdery 

 spores (Fig. 4 I. 



The mature gall is rather spongy; but sometimes a 

 portion of the gall, or the entire gall, may become firm. 



