Nov. II, i9i8 Sweet-Potato Storage-Rots 349 



On March i, 191 5, six sweet potatoes were inoculated with Diplodia 

 tubericola from dasheen and kept in an open receptacle. One potato was 

 decayed by Rhizopus nigricans. By June i two v.ere entirely decayed, 

 and D. tubericola was isolated from them. Three remained sound. 



The question has frequently been raised whether or not Diplodia 

 tubericola attacked the plants in the field and was carried on the infected 

 roots to the storage house where it further developed. A number of 

 half-grown plants were inoculated in the field by inserting spores and 

 hyphse of D. tubericola from sweet potatoes into the stem near the hill. 

 When the potatoes v/ere dug, none of the plants showed any evidence of 

 disease. The potatoes from all the inoculated plants were stored together, 

 but none of them were decayed by D. tubericola. From these results and 

 numerous field observations it is concluded that this organism does not 

 attack the plants in the field, and consequently could not transmit the 

 disease to the roots. 



DRYROT 



Diaporthe batatatis (E. and H.) Harter and Field causes what is com- 

 monly known as the dryrot of sweet potatoes. It was first reported by 

 Halsted {12) in 1890, who attributed the disease to Phoma batatae E. 

 and H. Later the disease v/as more exhaustively studied by Harter and 

 Field {21), who obtained in pure culture the perfect stage of the causal 

 organism to which the name ''Diaporthe batatatis" was given. The 

 imperfect stage of the fungus is the only one found on the potatoes from 

 the storage houses or field material. They reported the occurrence of 

 the disease in the States of North Carolina, Texas, New Jersey, Virginia, 

 Mississippi, Alabama, and Indiana. Since then it has been collected 

 in many other States, or diseased specimens have been received from 

 them, so that it can be safely said to have a wde distribution. In 191 7 

 D. batatatis was isolated from material from the Isle of Pines and when 

 inoculated into healthy plants on the Potomac flats near Washington 

 D. C, produced characteristic symptoms of the disease. This strain, 

 while identical morphologically, is a more vigorous parasite than any 

 isolated from material collected in the United States. 



Although this organism is quite prevalent, the total loss from the dis- 

 ease it produces is relatively small, the loss being more in storage than 

 in the field, though it is occasionally found on the slips in the hotbed. 

 Like many other fungi, it will grow as a saprophyte and is for this reason 

 found also as a secondary invader. Inoculation experiments have 

 shown that it is quite capable of causing decay. 



Diaporthe batatatis usually enters the potato from the stem end and 

 progresses slowly downward. It grows very slowly, requiring 4 to 8 

 weeks to entirely destroy a potato. In this respect it resembles D. 

 tubericola. Infected potatoes become much shrunken and wrinkled and 

 finally mummified (PI. 25, B). The surface, beneath which the tissue 



