Minnesota Plant Diseases. 



293 



Loose smut of oats [Ustilago avenae (Pers.) fens.]. This 

 exceedingly common and destructive disease is very well 

 known on account of the enormous damage which it yearly 



causes to oat crops. In the 

 United States alone, losses of 

 many millions of dollars year- 

 ly, by oat smut, have been re- 

 corded. The application of Jen- 

 sen's Hot Water Method and 

 the formalin treatments have 

 in recent years greatly de- 

 creased the loss by this disease. 

 When an oat plant is at- 

 tacked, usually all of the heads, 

 and all of the grains in each 

 head, become smutted. Very 

 few if any grains escape in a 

 smutted plant and those that 

 do are always stunted. The 

 stamens of the flowers as well 

 as the ovaries are attacked by 

 the fungus. The grain is con- 

 verted into a large sac with a 

 very thin membrane complete- 

 ly filled with the black spores 

 of the fungus. The smut 

 spores are blown about by the 

 wind before harvest time and 

 become attached to healthy 

 grains or fall on the ground. 

 In the following year when 

 the oat grain has commenced 

 to sprout, the fungus spores 

 also germinate. A spore in 

 germination first forms a very short chain of cells, which bud 

 off from their sides little secondary spores. These spores 

 sometimes fuse in twos, thus probably gaining in strength 

 by uniting forces. The spores either with or without fusion 

 may continue to bud off other spores when placed in favora- 

 ble nutritive conditions such as a culture medium. They 



FIG. 146. Loose smut of oats. Original. 



