2 CIRCULAR 27, U. S. DEPARTMENT OF AGRICULTURE 



"BUBBLES" DISEASE 



Probably the most serious disease of the cultivated mushroom in 

 this country is that commonly called " bubbles," due to a parasitic 

 fungus of the genus Mycogone. Specimens of mushrooms with this 

 disease were first received by the United States Department of Agri- 

 culture in 1909. Microscopic examination revealed the presence of 

 Mycogone, the disease known in France as "la mole." The occur- 

 rence of this mushroom disease is now quite common in North Amer- 

 ica. This trouble has been recognized abroad as a serious disease for 

 more than 40 years. It has caused extensive losses in England, 

 France, and Germany and in severe cases has caused the abandon- 

 ment of the business for a period of years or in extreme cases 

 indefinitely. 



Mushrooms affected with bubbles are deformed from the begin- 

 ning of their growth. They are covered at first with a white cottony 

 growth which later somewhat disappears, and the mushrooms become 

 soft and rotten. The diseased mushrooms become greatly distorted, 

 as is shown in the illustration on the title-page. Often the stem 

 becomes swollen or bulbous or the entire mushroom presents a shape- 

 less mass showing no differentiation of cap, gills, or stem. "Where 

 a cluster of mushrooms is attacked the entire cluster grows together 

 into a misshapen mass. As the disease progresses, drops of a brown- 

 ish fluid are exuded and the diseased mushrooms emit a very l dis- 

 agreeable odor. 



It is generally believed that this disease was introduced with im- 

 ported spawn. Certain phases of the disease in the beds are 

 unknown. The mycelium is known to live in the wood of beds, 

 especially when the wood is somewhat softened or beginning to 

 rot, and particularly when the houses have not been fumigated 

 thoroughly. Experiments in this office have shown that the fungous 

 threads of the parasite Mycogone are present in the rotten wood and 

 may retain their vitality for more than three years, showing that 

 abandonment of a house for one year will not make it safe for 

 growing a crop. The relation of Mycogone to the spawn is not 

 exactly known. From the experiments and observations made, the 

 presence of Mycogone does not prevent running of the spawn; the 

 earliest evidence of the disease appears at the time the mushrooms 

 begin to show. 



Observations on the Mycogone disease in North America show it 

 to be exceedingly variable as to its time of appearance and the 

 severity of its attack. It may be noticed when the first mushrooms 

 appear in a bed, or it may not develop until the season is about over. 

 These two extremes are often seen, but ordinarily the disease is most 

 destructive during the middle of the productive period. 



The disease does not start at a single place in a bed. Diseased 

 plants occur scattered among healthy plants, especially when the 

 disease appears late. 



In order to understand clearly how the disease is spread it is 

 necessary to know the way in which the fungus causing the disease 

 grows. 



The usual method of plant propagation is by seeds. However, in 

 iungi no true seeds are produced, but there are other bodies which 



