1094 The White Rot Disease of Onion Bulbs, [feb.. 



technical details and other matter of purely scientific interest 

 are omitted from the present paper. 



Hl8toricar. — The destruction of onion bulbs by a fungus 

 producing a white mould was observed by Berkeley as long ago 

 as 1841. He described the fungus and gave it the name of 

 Sclerotium cepivorum.'^ He states that the fungus is " very 

 common on onions at the point from which the roots spring, 

 and often very destructive." His description is meagre, it is 

 true, but sufficient, nevertheless, to distinguish it from allied 

 fungi. Berkeley's specimens, moreover, are preserved in the 

 Herbarium at Kew ; and examination of these shows that they 

 are precisely identical with the White Rot fungus so prevalent 

 to-day. 



Since that date other forms of rotting in onion bulbs have 

 been described, and great confusion has arisen as to the various 

 diseases and also as to the fungi causing them. Much has been 

 written, both in Britain and on the Continent, but with the 

 exception of Voglino and a few quite recent writers, Berkeley's 

 5. cepivorum has been more or less confused with the onion 

 disease caused by Botrytis. No doubt the presence of the two 

 fungi on one and the same bulb (as sometimes occurs late in the 

 season) may partly account for this. 



As a specific disease, quite distinct from Botrytis, White Rot 

 was first correctly distinguished in this country in the Annual 

 Report of the Plant Disease Survey of the Ministry of Agricul- 

 ture for 1 91 7 (p. 20). The popular name there employed was 

 " Dry Rot," from the dry nature of the decay which the fungus 

 produces. Since the term dry rot is usually associated with 

 forms of decay occurring in storage, and as the present disease 

 attacks the growing crops and seldom, if ever, causes trouble 

 in storage, this term appears to be somewhat inappropriate. 

 For this reason, therefore, another popular name, viz., " White 

 Rot " (derived from the abundance of white mould at the base 

 of diseased bulbs in the early stages) has been adopted, and the 

 same name is employed in the Ministry's Plant Disease Survey 

 Report for 191 8. In Bedfordshire, where this disease is wide- 

 spread, it is termed " Mouldy Nose," and in the north it is 

 often, though erroneously, termed Mildew (see later, p. 1098). 



Description of the Disease. — Onions become attacked with 

 White Rot when the soil in which they are sown or planted is 

 contaminated with the fungus. They usually first show 

 symptoms of attack at the end of May or early in June. As 

 might be expected in the case of a disease contracted from the 



* Ann. andl^Mag. Nat. Hist., VI., January, 1841, p. 359. 



