JOMAL OF AGRKMTDRAL RESEARCH 



Vol. XIII Washington, D. C, May 27, 1918 No. 9 



POX, OR PIT (SOIL ROT), OF THE SWEET POTATO 



By J- J- Tauben'haus 

 Plant Pathologist and Physiologist in Charge, Texas Agricultural Experiment Station 



INTRODUCTION 



Next to the blackrot [cause: Sphaeronema fimbriatum (E. and H.) 

 Sacc] and stemrot (causes : Fusarium batatatis Wollenw. and F. hyper- 

 oxysporum Wollenw.), pox, or pit, may be considered as the most im- 

 portant and serious disease of the sweet potato (Ipomoea batatas). Until 

 recently the trouble had been misunderstood, having been frequently 

 mistaken for blackrot. For this reason the exact distribution of this 

 disease and the money losses caused by it are not definitely known. 



HISTORICAL REVIEW 



Pox, or pit, of the sweet potato was first described in 1890 by Hal- 

 sted (5) * imder the name "soilrot," and was attributed by him to a 

 fungus of a new genus and species named " Acrocystis batatas E. and H." 

 Halsted's work was unchallenged for nearly 23 years. In 191 3 the 

 writer began the investigation of sweet-potato diseases at the Delaware 

 Experiment Station, first studying the pox of the sweet potato. During 

 the course of the investigation it became apparent that the fungus 

 Acroscystis batatas was not the cause of pox, and it further became 

 apparent that in reality the genus Acrocystis was nonexistent and that 

 A. batatas was mistaken for another organism. In 1914 the writer- (15) 

 was the first to call attention to these facts in print. In the summers 

 of 1 91 4 and 1 91 5 much time was spent in an infected field at Felton, 

 Delaware, and more than 1,000 plate cultures were made of the various 

 stages of the disease. At no time did the fungus A . batatas ever appear in 

 culture. On the other hand, the predominant flora which constantly ap- 

 peared were a species of Fusarium, an Actinomyces, bacteria, and a 

 Rhizoctonia. Numerous inoculations of healthy sweet-potato roots in 

 the field and in the greenhouse proved that the bacteria and the 

 species of Fusarium were saprophytic in nature. The species of Rhiz- 

 octonia reproduced lesions that were very unilke the atypical pox. 



> Reference is made by number (italic) to "Literature cited." p. 449-450- 



Journal of Agricultural Research, Vol. XIII, No. 9 



Washington, D. C. M^V =^7. 1918 



am KLey No. Tex.-i 



(437) 



