cates that optimum temperature for germination of 

 chlamydospores lies between 20' and 25 C. This was 

 also the most favorable temperature for sporidial and 

 mycelial development. 



Mrs. Jones (175) obtained somewhat different re- 

 sults: the optimum temperature was between 26" and 

 34 C. maximum between 56 : and 38°C, and spores 

 germinated to a slight extent at ST. which is not 

 necessarily the minimum. Hiittig (153) found the car- 

 dinal temperatures for germination to be: minimum 

 OC. optimum between 20 and 50 C, and maximum 

 just below 35°C. Temperature may also greatly modify 

 the type of germination. Thus, at about C. Hiittig 

 found that there was a tendency for chlamydospores to 

 bud off sporidia or hyphal segments rather than pro- 

 duce normal promycelia. At 50 C. the promycelia fre- 

 quently gave rise to hyphal branches instead of 

 sporidia. Mrs. Jones (175) also noted less sporidial 

 production at the higher temperatures. The length 

 of promycelia may also be materially influenced by 

 temperature. 



The rapidity of germination is of course closely asso- 

 ciated with temperature. Hiittig (153) found that the 

 most rapid germination occurred at the higher tem- 

 peratures. Thus. 96 c t of spores germinated at 50C in 

 12 hr and only 40% at 10 C in 16 hr. Mrs. Jones (175) 

 obtained somewhat similar results. Under favorable 

 conditions, the first crop of sporidia will be produced 

 in 12-16 hr; the second crop usually requires only 

 4-6 hr. 



In general, the most favorable temperatures for bud- 

 ding and growth of sporidia lie close to optimum 

 temperatures for chlamydospore germination. The max- 

 imum for budding of sporidia is about 40 C. but at 

 this temperature chlamydospores do not germinate. 



5 i Special stimulants. — Plazt. ct al. i 264 i concluded 

 that crushed plant tissue stimulated spore germination 

 because the material liberated carbon dioxide. They 

 indicated that an atmosphere with 15% C0 2 was opti- 

 mum for spore germination, whereas an amount above 

 this percentage was inhibitory. They also found the 

 optimum pH for germination to lie between 4.9 and 

 5.6. The minimum and maximum pH's for germination 

 have not been recorded. Itzerott (162 i reported a pH 

 of 4.4 as optimum for germination, minimum pH 2.2. 

 and maximum pH 8.5. 



Leszczenko i 197 i found that certain inorganic and 

 organic salts and alkalies could stimulate germination 

 of chlamydospores. He attributed this to an increase in 

 the permeability of the spore wall. 



Schmitt ( 290 1 states that ultraviolet irradiation of 

 chlamydospores retarded germination and the delay 

 increased with the dosage. Pichler and Wciber i 259 i 

 also reported an injurious effect of ultraviolet irradia- 

 tion, whereas Kommedahl (186) obtained only a little 

 effect from beta irradiation by the use of radiophos- 

 phorus in KTL.PO.,. Platz 1 262 i failed to germinate 

 chlamydospores when they were completely immersed 

 in media and kept in air-tight vials. 



Most of the studies made on effect of passing 

 chlamydospores through the alimentary tract of ani- 

 mals involved species of smuts other than U. maydis. 

 Cugini (68), in 1S91. found that spores of U. maydis 

 remained viable after passage through the alimentary 



■Am&*& *■>* 



**• 



Fig. 8. Reaction of a selfed line of corn to 2 physio- 

 logic races of I ' stilago maydis (Stakman and Christen- 

 sen, 311). 



tract of cows, whereas Arthur and Stuart ( 5 i claimed 

 they were not viable. Ficke and Melchers (94), in 

 1929. found that the passage of spores of U. maydis 

 through the digestive tract of horses and cattle rendered 

 almost all spores nonviable. Their work indicated that 

 most of the spores lost their viability because of acids 

 present in the stomach. They concluded that the num- 

 ber of spores that remained alive in the feces was too 

 small to be of any importance in the perpetuation and 

 spread of the pathogen. 



Methods of Inoculation. — A great many investi- 

 gators since Tillet have inoculated seed of corn with 

 chlamydospores of i'. maydis and obtained negative 

 results (5, 25. 143). Artificial inoculation of corn was 

 not successful until Brefeld < 1SS5-95 i sprayed the corn 

 plant with a suspension of sporidia produced in a nu- 

 trient culture (34. 55. 36). This spray method i which 

 now also involves chlamydospores I has been employed 

 subsequently by many workers (57. 105. 158). More 

 recently, dry chlamydospores also have been dusted on 

 plants. The two techniques have been used extensively 

 in the field for testing lines and varieties of corn for 

 smut resistance. 



Application oj manure and spores. — Because Brefeld 

 demonstrated that U. maydis srew readily on manure 

 decoction, it was generally accepted that the application 

 of manure to the soil would tend to increase the amount 

 of inoculum and thus increase smut infection (34, 36). 

 Therefore, to create an artificial epidemic of smut, it 

 became a fairly common practice in experimental work 

 to apply barnyard manure mixed with chlamydospores 

 to the test plots or corn rows (105. 158). The time 

 of the first application of manure varied from seedling 

 stage to plants about 1 m high. Sometimes, this treat- 

 ment was repeated 2 or 5 times at biweekly intervals. 

 In addition, some workers also sprayed the plants at 

 frequent intervals during the growing season with spo- 

 ridia or chlamydospores. 



There are no experimental data to indicate that the 

 application of manure or the frequent spraying and 

 dusting with inoculum actually increased the percent- 

 ages of smutty plants beyond natural infection. It 



15 



