SWEET-POTATO STORAGE-ROTS 



By L. L. HarTER, Pathologist; J. L. Weimer, Assistant Pathologist; and J. M. R. 

 Adams, Laboratory Aid, Cotton, Truck, and Forage Crop Disease Investigations, 

 Bureau of Plant Industry, United States Department of Agriculture 



INTRODUCTION 



The production of sweet potatoes (Ipomoea batatas) in the United 

 States in 1917 was estimated to be a little over 87,000,000 bushels, 

 valued at more than $95,000,000 (Monthly Crop Report, December, 191 7). 

 Of this quantity probably about 50,000,000 to 55,000,000 bushels were 

 placed in storage either to be put on the market or to be used for home 

 consumption throughout the winter months. While no accurate data 

 can be given, it is estimated that only about 33,000,000 to 38,000,000 

 bushels of the stored crop were actually consumed ; the remainder were 

 destroyed by storage-rot organisms before they reached the market. 

 Based on the estimated average price of $1.10 per bushel for December, 

 19 1 7, the loss would be approximately $18,000,000. 



■ This article deals with the rots caused by 17 fungi responsible for the 

 loss of sweet potatoes in storage. Several of these organisms are of minor 

 importance, the largest percentage of decay being caused by only -a few 

 very destructive forms. In view of the fact that we are dealing with the 

 underground parts of the plant and the method of storing the roots, it 

 is only natural that a large number of fungi could be isolated. Many of 

 these proved to be only saprophytes; others were able to cause decay 

 only imder especially favorable conditions. 



The first phase of the problem consisted in making a collection of 

 the organisms found in the decayed roots or in the lesions of stored pota- 

 toes. Accordingly about 40 different fungi and several species of bac- 

 teria were isolated. Twenty-five of these fujngi were tested out to deter- 

 mine whether they were secondary invaders, saprophytes, or weak para- 

 sites capable of causing decay under certain conditions. Of this number 

 17 were found to exhibit varying degrees of parasitism, the remaining 

 8 being regarded as secondary invaders or as saprophytes. Some of the 

 forms most frequently isolated, in fact, almost always present, were 

 found to be weak parasites or strictly saprophytes. It was soon dis- 

 covered that two and often more forms could be isolated from the same 

 rotted root. Which of these was the primary cause of the decay could 

 only be determined by inoculation with pure cultures. The isolation of 



Journal of Agricultural Research, (33?) ^°^' ^^' ^°- ^ 



Washington, D. C. Nov. ii, 1918 



q{ Key No. G-161 



83815°— 18 2 



