CONTROL OF THE POWDERY DRYROT OF WESTERN 

 POTATOES CAUSED BY FUSARIUM TRICHOTHE- 

 CIOIDES 



By O. A. Pratt, 



Assistant Pathologist, Office of Cotton and Truck Disease Investigations, 

 Bureau of Plant Industry 



INTRODUCTION 



Wherever potatoes {Solarium tuberosum) are grown, storage-rots occur. 

 These rots are in the majority of cases caused by wound parasites which 

 attack the potato tubers through bruises in the skin occasioned by the 

 handling of the potato crop in harvesting. A type of storage dryrot 

 known as "powdery dryrot" and ascribed to the parasite Fusarium tri- 

 chothecioides Wollenw. is apparently restricted to the arid and semiarid 

 sections of the western part of the United States. Undoubtedly rots due 

 to other causes also occur, but powdery dryrot is the only storage-rot 

 causing enough damage to be of any great economic importance in the 

 irrigated West. It would be difficult to arrive at any definite statement 

 of the losses entailed by this disease, but it is known that they have been 

 enormous. In several cellars visited, the writer estimated the losses 

 caused by partial and total decay of the tubers to be from 30 to 50 per 

 cent. Reports from farmers show that in some cases the losses have been 

 much greater. This storage dryrot may be described as an external dry- 

 rot proceeding from bruises in the skin of the tuber. The decayed portion 

 usually presents a wrinkled, sunken appearance, and in advanced stages 

 may show a pinkish white growth of the fungus (PI. CVIII, fig. 1, 2). 

 The decayed tissue presents various shades of color from nearly black to 

 light brown, the most characteristic color being sepia brown. Internal 

 cavities partially filled with the mycelium and spores of the fungus 

 are frequently found in decayed tubers (PI. CVIII, fig. 3). 



The first description of this disease was made in 191 2 by Jamieson and 

 Wollenweber, 1 who demonstrated that the rot was caused by a species of 

 Fusarium which they called "Fusarium trichothecioides Wollenw." One 

 year later Wilcox, Link, and Pool 2 described a dryrot of potato tubers in 

 Nebraska, ascribing it to a species of Fusarium which they called " Fusa- 

 rium tuberivorum." This fungus has since been demonstrated by Wollen- 



1 Jamieson, Clara O., and Yv'bllenweber, H. W. An external dry rot of potato tubers caused by Fusarium 

 trichothecioides Wollenw. In Jour. Wash. Acad. Sci., v. 2, no. 6, p. 146-152, 1 fig. 1912. 



2 Wilcox, E. M., Link, G. K. K., and Pool, Venus W. A dry rot of the Irish potato tuber. Nebr. Agr. 

 Exp. Sta. Research Bui. i, 88 p., 15 fig., 28 pi. (1 col.). 1913- Bibliography, p. 85-88. 



Journal of Agricultural Research, Vol. VI, No. 21 



Dept. of Agriculture, Washington, D. C. Aug. 21, 1916 



fb G— 92 



(817) 



