1122 



Eeversion of Blackcurrants. 



[Mar., 



REVERSION OF BLACKCURRANTS: 



A METHOD OF IDENTIFICATION. 



A. H. Lees, M.A., 

 Plant Pathologist, Research Station, Long Ashton, Bristol. 



Mr. W. P. Searrooe recently stated that his experience in 

 inspecting growers' plantations is that not one grower in a 

 hundred really knows when a bush is reverted and when not. 

 With this dictum the present writer heartily agrees. It is, 

 of course, no discredit to the fruit grower that such is the case. 

 There is undoubtedly great difficulty in identifying slight cases, 

 as the disease is very insidious in nature. In most diseases, 

 there is a distinct and well-marked change in the appearance of 

 the plant which soon makes itself evident even to the 

 inexperienced eye. The case of reversion is otherwise. In its 

 initial stages there is no very obvious change in the colour or 

 shape of the leaf. It is only after the disease has advanced 

 somewhat that a change becomes noticeable to the unskilled 

 eye. Even then the colour change is but slight : the chief 

 difference is in the shape. 



These facts make identification of the disease, from the 

 grower's point of view, a very difficult one, and it is not 

 surprising, therefore, that most growers do not recognise 

 it until it has reached a comparatively advanced stage. 

 Nevertheless, it is obvious that it is extremely important 

 that some method be found to enable the inexperienced to decide 

 quickly whether or not any given bush in his plantation showed 

 signs of disease. The great loss of crops entailed by it are 

 well known, and in the present state of knowledge the only 

 methods open to the grower of curtailing its ravages are propa- 

 gation from sound stock and rogueing. In order to keep the 

 disease in check, the latter process must be done both in the 

 cutting beds and in the plantation. 



The method about to be described was tested during the 

 1920 season and found to be uniformly reliable. It enables 

 the observer to detect the disease in its earliest stages, and can 

 be used as a means of identification from about the middle of 

 May until the end of the season, when leaf fall begins. On 

 p. 1125 are shown seven leaves of the blackcurrant. Fig. 1 is 

 a normal leaf, while Fig. 2-7 represent various stages induced 

 by increasing amounts of reversion. There are two main points 

 to observe in Fig. 1: — 



