152 Journal of Agricultural Research voi. vi. No. 4 



Taubenhaus, as a result of his inoculations upon sweet potato (Ipomoea 

 batatas) with Diplodia tubericola E- and E-, Diplodia gossypii Zim., 

 Diplodia natalensis Pole Evans, and Lasiodiplodia theobromae (Pat.) 

 Griff, and Maubl., suggests that the characteristics of the genus Diplodia 

 be so extended that it may include all of the five genera. 



This genus, although it is not thought to include forms which are 

 absolute parasites, is nevertheless a source of serious trouble among some 

 of our cultivated plants. The injury is usually confined to a fruit rot 

 or to a dieback of the younger branches or shoots as in the Citrus disease 

 prevalent in Florida and the Isle of Pines.^ In both cases the fungus 

 has been described as following an injury which has been previously 

 inflicted either by mechanical means or as the result of the action of some 

 other fungus. In the United States the more important crops which 

 hitherto have been known to be affected are sweet potato, Citrus fruits, 

 corn (Zea mays), and cotton (Gossypium spp.) In our Southern States 

 the Diplodia injury is of considerable consequence in connection with 

 these products. As one enters the Tropics the number of plants which 

 are attacked increases. Among the list of hosts found here are Citrus 

 spp., Hevea spp., Theobroma cacao, and Thea spp. In certain cases where 

 the growing plant is attacked, the injury produced is sufficient to cause 

 the death of the host, as is the case with Diplodia vasinfecta Petch, 

 which causes an internal rootrot of tea. 



Since the cotton, sweet-potato, and watermelon fields of the South are 

 not widely separated, it is of some interest from the economic standpoint 

 to know whether a species found on one host will grow equally well upon 

 another. Plate XVII, figure 2, shows a watermelon nine days after it 

 had been inoculated with a culture of Diplodia tubericola E. and E. 

 obtained from Mr. L. L. Harter, of the Bureau of Plant Industry. The 

 decay took the same course in this melon as has been described for the 

 other inoculated material, which is shown in Plate XVII, figure i. The 

 pycnidia which were produced, however, retained the paraphyses. 



While the Diplodia injury is apparently the cause of serious loss in the 

 watermelon industry, there are other ways in which the crop suffers. Dr. 

 W. A. Orton, Pathologist in Charge of Cotton and Truck Disease Investi- 

 gations, Bureau of Plant Industry, who has made a careful study of ship- 

 ping conditions, is inclined to believe that the injury is confined to 

 certain districts. In other sections, anthracnose, due to Colletotrichum 

 lagenarium, is the source of considerable trouble. To the losses thus 

 caused by fungi must be added a small percentage of melons which have 

 been damaged by rough treatment and by the use of cars which have 

 been employed for the transportation of fertilizer or chemicals to the 

 fields. 



' Earle, F. S., and Rogers, J. M. Citrus pests and diseases at San Pedro in 1915. In San Pedro Citrus 

 Path. I,ab. ist Ann. Rpt. 1915, p. 5-41, 19 fig. [1915.] 



