1920.] The White Rot Disease of Ox\ion Bulbs. 1093 



THE WHITE ROT DISEASE OF 

 ONION BULBS. 



A. D. Cotton, 



Mycologist to the Ministry of Agriculture and Fisheries, 



AND 



M. N. Owen, 



Botany School, University of Cambridge. 



The disease here described causes considerable damage to 

 the onion crop, especially in market gardens and allotments. 

 Until recently, however, it has not attracted serious attention, 

 and, except in one isolated instance, it has never been the 

 subject of scientific investigation. During the past two years 

 the disease has been studied at the Ministry's Pathological 

 Laboratory at Kew, and experimental work has been carried 

 out in gardens and market gardens in that neighbourhood 

 in which it had been found to occur. The fungus causing the 

 disease has been isolated, grown artificially in pure culture, 

 and the nature of its life-cycle determined. As a result of 

 these studies the White Rot of onions has been clearly differen- 

 tiated from certain diseases with which it has hitherto been 

 confused by almost all writers. Furthermore, the fungus 

 itself has been found to be quite distinct from two fungi 

 (namely, Sclerotinia hulhonim and Botrytis cinerea) both of which 

 have, at one time or another, been regarded as the cause of the 

 trouble in question, and to be identical with another parasite 

 detected and described many years ago, but in more recent 

 times almost entirely overlooked. 



Now that the life-history of the causative organism is pro- 

 perly known it is possible to suggest methods for controlling 

 the spread of the White Rot disease, although there is still 

 room for further investigation in this direction, especialh^ with 

 regard to soil fungicides and trials as to the susceptibihty and 

 resistance of different varieties of onions. 



The only previous account which deals in any way clearly 

 with the White Rot disease is that* by the Italian botanist 

 Voglino, who records its occurrence on garlic in various parts 

 of Italy, and gives a description of the microscopic characters 

 of the fungus. This being the case a fairly full general account 

 of the disease and the fungus causing it is given below, though 



* Le Stazioni sperimcntati agrarieitaliane, 1902. Vol. XXXVI. fasc.II., 



pp. 89-106. 



