were frequently reported from individual states (341). 

 Until about 1940. losses in Minnesota ranged from 

 3 to 10% annually. Now. it is perhaps less than 1% 

 for field corn in Minnesota, but much more for sweet 

 corn and similar losses also occur elsewhere in the 

 U.S. (78, 109). 



In general, most estimates of smut losses have been 

 based on plainly visible infection. Less conspicuous 

 galls are frequently overlooked, although they may 

 often reduce yield of corn materially, especially if 

 multiple galls occur on the same plant (161, 170). 

 Therefore, many of the figures presented here and in 

 early publications are most likely underestimates of the 

 actual losses incurred. It is relatively easy to approx- 

 imate smut losses when seedlings are killed or when 

 stalks are so severely infected that ears are almost 

 destroyed, but not when the smut galls are small and 

 more or less hidden. 



A number of investigators (160. 161. 170. 176) have 

 found that yield of ear corn from infected plants 

 varied with the number, size, and location of the galls. 

 On the average, a single gall reduced ear yield about 

 25%. Multiple galls on the main stalk, including the 

 neck (peduncle), usually were more destructive than 

 galls of similar size and number located on shoots and 

 suckers (161, 170). A medium or large gall and mul- 

 tiple small galls located on a main stalk frequently 

 caused the plant to be barren (57, 105. 161. 176. 328). 

 whereas galls on shoots and suckers seldom did. Small 

 galls on the ear or tassel seldom reduced ear yield 

 significantly whereas large galls at the same locations 

 usually caused barren stalks or severe reduction in ear 

 yield. 



Some losses from smut infection may be indirect. 

 Ears produced from smutty plants usually have a 

 poorer luster and lower quality than those from smut- 

 free stalks (170, 328). Michaelson (227) found that 

 plants infected with U. maydis were more subject to 

 stalk rot caused by Diplodia zeae (Schw.) Lev. and 

 Gibberella zeae ( Schw. > Petch. than smut-free plants 

 and that ears of smutted plants were more likely to be 

 invaded with ear-rotting fungi than those from smut- 

 free plants. 



Terminology. — In 1847. the Tulasnes (337) called 

 the germ tube of the chlamydospore a "promycelium." 

 The primary, asexual spores borne on the promycelium 

 were designated as "sporidia," but sometimes they also 

 were referred to as "basidiospores." Brefeld (36) called 

 them "conidia" because they were able to bud like 

 yeast. Because of long and common usage, the term 

 sporidia is the one preferred today by most workers. 



The reduction division and segregation of factors 

 normally occur in the promycelium. Therefore, sporidia 

 are often spoken of as "segregates" (314). They are 

 really haploid and gametic in nature and are not exactly 

 comparable to segregates in higher plants. Occasionally, 

 meiosis does not occur; then, the sporidia are diploid. 

 These diploid lines, which can cause infection when 

 injected singly into corn plants, are designated as 

 "solopathogens" (54). 



The parasitic stage is usually a "dicaryon," i.e., the 

 2 compatible nuclei of opposite sex are associated to- 

 gether in a cell. Although the dicaryon behaves genet- 

 ically like an Fj hybrid, the nuclei are not fused; 



hence, it is a plasma-hybrid and not a zygote (55). The 

 zygote is actually restricted to the chlamydospore. In 

 a few cases, the terms "inbreeding" and "outbreeding" 

 have been used. By "inbreeding" is meant the mating 

 of sporidia from the same promycelium. By "outbreed- 

 ing" is meant the mating of sporidia from different 

 promycelia (55). This usage may not be exactly com- 

 parable to that used for higher plants and animals, 

 but indicates more clearly than any other terms what 

 actually has been done. 



The term chlamydospore deserves special considera- 

 tion because it has been used and defined differently 

 by mycologists and pathologists. The usage of chla- 

 mydospores in smut fungi is a well-established term and 

 has come to have definite meaning to scientists in 

 different fields of smut investigations (85, 106, 282, 

 317. 333. 361). Most writers on smuts from about 1900 

 to the present day use the term chlamydospore. During 

 this period, however, various other names have been 

 given to the smut spores produced in sori and galls. 

 These names are "gemmae." "resting spore," "brand- 

 spore." and "teleutospore" (now "teliospore"). 



According to Fischer and Holton (98), the use of 

 the term "chlamydospore" is fundamentally incorrect 

 because a chlamydospore is supposed to be an asexual 

 spore. This statement is questionable because certain 

 smuts produce sori or galls that contain both diploid 

 and haploid chlamydospores (146). In fact, Rowell 

 (280) obtained galls of U. maydis that consisted en- 

 tirely of haploid, asexually produced chlamydospores 

 that were morphologically identical to true diploid 

 chlamydospores of this species. In U. ischaemi Fckl., 

 also, apparently no nuclear fusion occurs (312). 



In nature, it is not uncommon for chlamydospores 

 of U. maydis and also of U. avenae (Pers.) Rostr. to 

 germinate directly and cause infection without the 

 formation of promycelia and sporidia (350, 354); and 

 thus germinate like chlamydospores of other fungi. 

 Further, similar types of germination may well occur 

 in other smut fungi. Moreover, the nuclear condition 

 of so-called chlamydospores that are produced in 

 culture may be either haploid or diploid; and it is 

 possible that some are even dicaryotic. Surely these are 

 not teliospores ! 



Finally, the terms chlamydospore and teliospore were 

 used long before their sexual function was ascertained. 

 These 2 terms were derived primarily on the basis of 

 spore formation. Even today, this is used as a cri- 

 terion for separating the rusts from smuts (1 ). Further, 

 no one has made a thorough study of nuclear condi- 

 tions or method of germination of chlamydospores in 

 the other fungi and the need for such a study should 

 be apparent. 



Because of the confusion that exists in regard to the 

 nuclear condition in chlamydospores and because of 

 the well-established usage of the term chlamydospore 

 in the smuts, the writer prefers to retain the usage of 

 chlamydospore in this paper. If a change in name is 

 really desirable, however, then the older name "brand- 

 spore" which is still in common use in Europe, includ- 

 ing Great Britain, would be a more appropriate one 

 than teliospore (144). "Brandspore" has the flawless 

 attributes of meaning a smut spore and implying 



S 



