[ 16;:! ] 



No. 20. 



ON THE CAUSE OP ROLLING IN POTATO FOLIAGE ; AND ON SOME 

 FURTHER INSECT CARRIERS OF THE LEAF-ROLL DISEASE. 



By PAUL A. MURPHY, Sc.D., A.R.C.Sc.L, 



Seeds and Plant Disease Division, Department of Agriculture and 



Technical Instruction for Ireland. 



(Plate VI.) 



[Read Februaey 27. Printed May 15, 1923.] 



Within comparatively recent years the designation "leaf -roll" has, by general 

 agreement among phytopathologists, become restricted to a single specific 

 disease of the potato plant. It is not necessary to discuss here the tangled 

 history of the varying connotations of the term as used by different investigators 

 since 1905. At the present time this name is the one applied by almost all plant 

 pathologists exclusively to that very widely distributed disease of the potato 

 plant which has as its most constant external symptom a distinctive thickening 

 and upward marginal rolling of the leaflets of the lower leaves in the first 

 instance, and which is accompanied by a more or less pronounced diminution 

 in yield of new tubers — features which are persistent and not merely of seasonal 

 or shorter duration.' As thus defined, the disease corresponds to the secondary 

 leaf -roll of Quanjer." 



No general account of the disease need be given, here except in so far as the 

 results obtained by previous iiivestigators have a direct bearing on the work 

 now to be described. This deals mainly with some features of the physiology 

 and histology of affected plants and with the transmission of the disease by 

 certain classes of insects. The work was carried out principally at the Albert 

 Agricultural College, Glasnevin, Dublin, in a laboratory and special plots pro- 

 vided for the purpose. Acknowledgments are due to Mr. R. McKay, A.R.C.Sc.L, 

 who acted as Outdoor Assistant during the season of 1922, for the care of the 

 plots and for carrying out some of the exiaerimental details. 



I. — Previous worlc on the Translocation of Food Materials in Diseased Plants.- 



It had already been surmised by a number of workers, including Sorauer, 

 Spieekermann, Kock and Kornouth, Doby and Quanjer, that some disturbance 

 in the mechanism of food transference in the plant underlay the disease described 

 by them as ' ' leaf -roll. ' ' Unfortunately it is difficult in many cases to establish 

 with certainty the identity of the malady under discussion. The majority of 



'It is .desirable that tiie more indeterminate name "leaf-curl," which is still unfortu- 

 nately retained in the official publications of the English Ministry of Agriculture, should 

 not be used for this disease. 



' Comparatively little attention was paid during- the course of this work to primary leaf- 

 roll, but it may be mentioned in anticipation that starch was found to accumulate to an 

 abnormal extent in the upper leaves, which are the ones tliat first become rolled in this 

 stage of the disease. : 



3CIENT. PKOC. R.D.S., VOL. XVII, NO. 20. 2 H 



