Nov. 



Sweet-Potato Storage-Rots 347 



JAVA BLACKROT 



Java blackrot, a disease caused by Diplodia tubericola (E. and E.) 

 Taub., is probably as widely distributed as the sweet-potato crop itself, 

 and the total loss from this disease is large. It has been collected from 

 every part of the United States, and specimens have been sent to the 

 writers from Cuba, Isle of Pines, Philippine Islands, Japan, Porto Rico, 

 South America, and elsewhere. It can be found in practically every 

 sweet-potato storage house and also in the banks. This disease causes 

 a greater loss in the Tropics and the southern part of the United States 

 than in the northern sweet-potato belt. 



Java blackrot was first reported on sweet potatoes in 1 896 by Clendenin 

 (7). The specimens on which she observed the disease were sent from 

 Java to the Louisiana Experiment Station in 1894. From what we 

 know at the present time, however, it is likely that this disease had been 

 common in this country long before then, probably ever since sweet 

 potatoes have been cultivated. The fact that it was first reported on 

 sweet potatoes imported from Java is no evidence that it was introduced 

 at that time. We now know that species of Diplodia occurring on 

 various hosts will also infect sweet potatoes. Investigations have shown 

 (j6) that D. gossypina Cke., D. natalensis Ev., and Lasiodiplodia nigra 

 Appel and Laub., will all cause a rot of sweet potatoes similar to the rot 

 caused by D. tubericola. Furthermore, it has been shown by the senior 

 author {18) that D. tubericola from dasheen {Colocasia esculenta), D. 

 gossypina, D. maclurae Speg. and Diplodia sp. from mango {Mangijera 

 indica) will produce a rot of sweet potatoes identical with the rot pro- 

 duced by D. tubericola isolated from sweet potatoes. Further evidence 

 of the cosmopolitan nature of these organisms has been submitted by 

 Meier (27), who found that D. tubericola from sweet potato would cause 

 the stem-endrot of the watermelon (Citrullus vulgaris). 



It is therefore probable that species of Diplodia from other hosts, if 

 inoculated into sweet potatoes, dasheens, or watermelons, would cause 

 similar rots. 



DESCRIPTION OF JAVA BLACKROT 



Diplodia tubericola rots sweet potatoes very slowly. Under laboratory 

 conditions there is little or no evidence of decay for a week or 10 days, 

 and usually 4 to 8 weeks are required to entirely destroy a potato. The 

 pycnidia, which ordinarily develop in great abundance, generally appear 

 at the end of one month on the part of the potato first decayed. They are 

 externally coal black, crowded closely together or confluent, and micro- 

 scopically suggest minute domelike elevations on the surface. Unlike 

 some of the fungi of this group, many pycnidia are completely buried, 

 the spores escaping only after maceration or disintergation of the host. 

 The tissue is first rendered brown in color, but later becomes coal black 

 and hard. Concomitant with the loss of \vater, the root shrinks, eventu- 



