Fig. 4. Ears and tassel of corn affected with smut. V 



apparently because of infection by bacteria and certain 

 fungi. Further, species of Rhizopus, Mucor, Aspergillus. 

 Penicillium, and other genera are not uncommon in 

 corn smut galls. 



Smut galls may develop on any part of the plant 

 above ground, wherever the pathogen encounters 

 meristematic tissue. Galls are usually most prevalent 

 on ears, tassels, stems, and nodal shoots. On certain 

 varieties, leaf infection is also very common, especially 

 on or near the midrib, at the junction of the leaf- 

 sheath and the blade. Galls may occasionally occur on 

 brace roots, but they have never been reported on 

 underground roots. 



The galls vary from minute sizes to several cm 

 diam. occasionally reaching the size of a man's head. 

 The size, the shape, and the degree of proliferation 

 depend to a considerable extent on the location of the 

 gall on the plant and the susceptibility of the host and 

 also on the virulence of the culture of smut (Fig. 5). 



Leaf galls differ greatly in size and texture. The 

 large ones occur most frequently on the leaf sheath, 

 while on the blade they are most numerous. Although 

 the galls on the blade are usually small, they may be 

 large and extend many cm along the midrib, sometimes 

 more than half the length of the leaf. Many of the 

 very small leaf galls remain firm and frequently con- 

 tain few. if any. spores. Adjacent tissue often becomes 

 chlorotic and develops anthocyanin. the extent depend- 



stilago maydis (Stakman, 310). 



ing on the race of smut and on the variety or line of 

 corn ( 54. 59. 311). 



The smut galls on the main stalk occur most com- 

 monly just above the nodes, but they may arise on any 

 portion of the stalk. Although galls located on the 

 stalks may be rather large. 20-30 cm diam. they are 

 usually attached to stems for only a relatively short 

 distance. 2-5 cm. They vary greatly in size and shape; 

 sometimes, they are distinctly Iobed or convoluted. 



At every node of the stem, there is the bud of a 

 potential shoot ("ear). These frequently become in- 

 fected and often give the appearance that infection 

 actually arose from the stem. Sometimes, on certain 

 varieties, these shoot-galls are completely enclosed by 

 the leaf sheath and may then only be observed by 

 stripping back the leaves. 



In the ears, the ovaries and glumes are normally 

 smutted as is the husk sometimes; but apparently, the 

 cob proper and the silk are seldom, if ever, involved. 

 Sometimes, the entire pistillate inflorescence may be 

 converted into a huge smut gall. The husks in many 

 cases are pushed apart or broken through, exposing the 

 black smut mass (Fig. 1. 4). 



When tassel flowers are smutted, usually each floral 

 organ forms a small gall and the tassel retains its 

 shape. Sometimes, virtually the whole tassel and stalk 

 below the tassel are converted into a large mass of 

 smut. When the first joint below the tassel "neck" 



10 



