juiyio, 1916 Storage-Rots of Economic Avoids 551 



Plate LXXXI, figures 1 and 2, shows the typical rots of C. esculcnta 

 and Alocasia sp., respectively, produced by the Java blackrot fungus. 



The rot progresses slowly. About seven days elapse after inoculation 

 before any noticeable softening of the tuber occurs under optimum con- 

 ditions and about four to eight weeks are required for complete destruc- 

 tion of the tuber and blackening of the tissue. Finally both the tubers 

 and corms become very dry and hard and are cut by a knife with diffi- 

 culty. The middle lamella is first dissolved, the hyphse later penetrat- 

 ing the cell walls and burying themselves among the starch grains. The 

 tissue finally becomes a disorganized mass and powdery when com- 

 pletely dried. Under normal conditions the rot does not produce any, 

 or, at most, only slight shrinking or malformation of the tuber. In 

 fact, a whole tuber may be completely destroyed internally and become 

 black throughout without much external evidence of it. Fruiting bodies 

 later develop, but they are mostly covered by the epidermis and can 

 scarcely be detected without rupturing the surface. 



Under natural conditions the corms decay more readily than the 

 tubers, although the latter are frequently met with in storage and suc- 

 cumb easily to artificial inoculation. It is evident from a careful study 

 of material that natural infection originates in the wounds made by 

 breaking the tubers from the corms and at points where the roots are 

 broken off. After becoming established the fungus may spread in all 

 directions without penetrating deeply until the surface of the corm is 

 well covered, and then it may penetrate farther in; or it may cover an 

 area 1 or 2 inches in diameter and push inward to the center in the 

 form of a cylinder. 



CAUSE OP BIvACKROT 



The writer has isolated and successfully inoculated into the dasheen 

 species of Diplodia from five different hosts, as follows: D. tubericola 

 (E. and E.) Taub. from sweet potato; D. gossypina Cke. from a dead 

 limb of cotton; D. machirae Speg. from a dead branch of Toxylon pomi- 

 ferum Raf. from New Jersey; Diplodia sp. from a limb of Mangifeva 

 indica from Cuba, furnished by Dr. J. R. Johnston, pathologist of the 

 Cuban Experiment Station, and a species of Diplodia from dasheen 

 which, because of its great similarity to D. tubevicola, is referred to that 

 species. The type of decay produced by these different species is macro- 

 scopically the same. It is a well-known fact that there are a great number 

 of different species of Diplodia described in the literature, many of which 

 may prove to be identical. No attempt has been made to go into the 

 taxonomy of this group, but it may be of interest to note the points of 

 similarity and difference between the species here studied. The organ- 

 ism isolated from dasheen can not be distinguished in culture from D. 

 tubericola from sweet potato. Both develop into stroma in culture and 

 on the host, and the spores differ but little in shape (fig. 1, A, B) and 

 size. 



