1909.] Report on "Sprain" in Potato Tubers. 647 



Owing to the very diverse symptoms presented by the 

 material submitted to Kew for examination, under the name 

 of "sprain," it has been found impos- 

 Report on "Sprain" sible to formulate a diagnosis of the 



in Potato Tubers. disease. 



Perhaps the most constant symptom 

 is the presence of small, rust-coloured spots, scattered in 

 greater or less abundance throughout the flesh. This appear- 

 ance agrees with what is known as "internal disease" in the 

 South of England, which, again, possesses many points in 

 common with the disease of apples called "bitter pit," the 

 precise nature of which is still obscure. 



In some examples mycelium is present in the tissue of the 

 brown spots, and in such instances, under proper treatment, 

 " winter-rot," caused by Nectria solani (Reinke), always 

 develops. On the other hand, in some examples no mycelium 

 can be detected, and however long such specimens are kept 

 under favourable conditions, no fungus appears. 



Five tubers said to show "sprain" were planted in the 

 experimental ground at Kew. Each tuber was cut in two, 

 and each one showed rusty patches in the flesh. Three 

 months after planting two of the hills showed no haulms 

 above ground, and, on digging down, the "sets " were found 

 to be almost destroyed by winter-rot. On lifting the re- 

 mainder at the end of September, the crop produced by four 

 of the "sets" was found to be infected with "sprain" — i.e., 

 the flesh showed small spots of a brown colour. Every 

 tuber was cut and examined, and there was not a single one 

 exempt. The old "sets" of these four roots were in a 

 deliquescent condition, and teeming with the conidial form 

 of winter-rot. The four remaining "sets" produced a per- 

 fectly clean crop. The "sets" were shrivelled, but showed 

 no signs of winter-rot. 



The above account agrees with what had previously been 

 observed at Kew, namely, that the brown spotting of potato 

 tubers is in some instances an incipient stage in the develop- 

 ment of winter-rot, and as it is not at all probable that two 

 distinct diseases presenting similar symptoms — rust-coloured 

 spots — are present in potato tubers, it must be assumed that 



