TECHIN^ICAL BULLETK^ ^V 4. 



DEPARTMENT OF BOTANY. 



DEVELOPMENT AND PATHOGENESIS OF THE 

 ONION SMUT FUNGUS/ 



BY P. J. ANDERSON. 



I. Introduction. 



Onion smut is the most destructive of all onion diseases in New Eng- 

 land. In the Connecticut Valley it is probably responsible for more loss 

 to the growers than all the other diseases of this crop combined. Despite 

 the fact that a m.ethod of control by the use of formaldehyde has been 

 developed, many fields are now planted to other less profitable crops on 

 account of the ravages of smut; every year sees fields plowed up because 

 smut has so reduced the stand that it is not worth while to tend them; 

 more important in the aggregate, perhaps, is the smaller toll which the 

 disease exacts from each onion grov/er throughout considerable sections 

 of the vaUey. 



Investigation of the disease with the primary object of finding better 

 methods of control was begun by the Department of Botan}^ of the Massa- 

 chusetts Agricultural Experiment Station in 1918, and has been continued 

 to date. Smce control measures are necessarily conditioned by the nor- 

 mal life history of the pathogene, and since a review of the publislied re- 

 search of other investigators showed that the development of the fungus 

 had been inadequateh^ studied, this phase of the problem has been made 

 the subject of no inconsiderable part of the ^\Titer's study. Results of the 

 work which deals directlj^ with control are to be presented in another 

 publication. The present papei concerns certain phases of the life cycle 

 of the causal organism {Urocydis ccpulae Frost) in which it seemed to tlie 

 writer that further investigation v/as desirable. Beginning with germina- 

 tion of the spores, the development of the fungus will be followed through 

 its saprophytic stage, infection of the host, distributive stage within the 

 host and final sporogenesis. 



» This paper embodies the results of prehminary and fundamental work on a project having 

 for its chief aim the control of onion smut. A report on the more practical phases of this project 

 is to be published shortly. 



