May 27, 1918 Pox of Sweet Potato 



449 



(6) Pox is caused by a myxomycete, Cystospara batata Elliott, and not 

 by the fungus Acrocystis batatas E. and H. 



(7) The disease may be reproduced at will artificially. Infection can 

 not take place by inserting bits of diseased tissue into healthy parts. 

 The contact of healthy roots with the active sHme is necessary for arti- 

 ficial infection. The organism may be grown artificially on culture 

 media. 



(8) Pox seems to be equally active in wet and in dry weather. The 

 greatest damage, however, occurs in dry weather, when the roots seem 

 to be more distorted. 



(9) In the field the disease does not seem to be disseminated by free- 

 wind-blown spores (cysts) of the causal organism; nor does it seem to be 

 carried over on infected roots kept in storage. It seems to spread v/ith 

 lumps of soil which may adhere to the working tools in wet weather. 

 Evidences also tend to show that the disease is disseminated in the 

 field by rain water. 



(10) Pox seems to be a field trouble only. 



(11) Pox also attacks the Irish potato and the turnip. The beet and 

 tomato are suspected of being susceptible hosts. There seems little 

 doubt that Morse and Ramsey, in attributing the "pit" disease of the 

 Irish potato to Rhizoctonia spp., were in reality dealing with pox, the 

 injury by Rhizoctonia spp. being merely secondary. 



(12) C. batata probably hibernates as cysts in the soil. 



(13) A new species of Actinomyces, A. poolensis Taubenhaus, is found 

 associated wdth the C. batata. The former acts only as a wound parasite 

 and secondary invader. 



(14) The genus Acrocystis, as originally described by Halsted, is not 

 valid and is nonexistent. The fungus Acrocystis batatas was mistaken by 

 Halsted for a myxomycete which Elliott has named "Cystospora 

 batata," the true cause of pox (soilrot). 



(15) The red varieties of the sweet potato seem to possess the great- 

 est resistance to pox. 



(16) Soil sterilization of the soil of the seed bed to control pox is not 

 recommended. Rotation of crops tends to decrease the disease in a sick 

 soil. The rotation remains to be worked out. 



LITERATURE CITED 

 (i) Barre, H. W. 



I910. REPORT OP BOTANIST AND PLANT PATHOLOGIST. In S. C. Agr. Exp. Sta. 



23d Ann. Rpt. [igogj/io, p. 23-39. 



(2) DUGG.^R, J. F. 



1897. SWEET POTATOES: CULTURE AND USES. U. S. Dept. Agr. Farmers' Bui. 

 26, 30 p., 4 fig. 



(3) Elliott, J. A. 



1916. THE SWEET POTATO "soiL ROT" OR "pox" ORGANISM. In Science, 

 n. s. V. 44, no. 1 142, p. 709-710. 



