XIII, A, 4 Reinking : Philippme Economic-Plant Diseases 



215 



Causal organism. — The minute black bodies are pycnidia. 

 Upon crushing the pycnidia, a mass of small, one-celled, some- 

 what elongated, slightly olivaceous spores is expelled. The fun- 

 gus grows well in pure culture, producing at first a growth of 

 white mycelium, which later becomes studded with black 

 pycnidia. 



Control. — All diseased stems should be collected and burned. 

 Crop rotation should be practiced. 



IPOMOEA BATATAS POIR. SWEET POTATO 



STORAGE ROT: LASIODIPLODIA THEOBROMAE (PAT.) GRIFFON ET MAUBLANC 



Symptoms. — A common dry- 

 storage rot, which is character- 

 ized by the production of a sooty 

 mass of spores on the outside of 

 infected potatoes. This disease 

 is the same as that found upon the 

 cacao fruit and other root crops 

 and fruits (Plate XIX, fig. 5) . 



Causal organism. — The organ- 

 ism causing the disease is iden- 

 tical with that described under 

 cacao. Cross inoculations from 

 the fungus on cacao fruit to the 

 sweet potato or vice versa can 

 be easily carried out. The my- 

 celium penetrates throughout the 

 root and accumulates under the 

 surface to produce a series of 

 pycnidia, from which the mass 

 of black spores arises (fig, 20). 

 The organism is more fully dis- 

 cussed under cacao. 



Control. — Care should be used in digging the potatoes, so as 

 to avoid injuries. The surface of the potatoes should be allowed 

 to dry before storage. Storage should be in a well-ventilated 

 place. All infected potatoes should be taken out and burned. 

 Cacao fruits and root crops diseased with Lasiodiplodia must 

 be kept away from stored sweet potatoes, 



STORAGE ROT: RHIZOPUS 



Symptoms. — A soft rot is frequently produced by this fungus. 



Diseased roots are soft and are covered with a black felty mold. 



Caudal organism. — This felty mass is made up of large num- 



FiG. 20. Lasiodiplodia theobromae (Pat.) 

 Griff, et Maubl. Section 

 through diseased sweet potato, 

 showing pycnidium, ostiolum, 

 paraphyses, and immature 

 .spores (X 270). 



