July 10, 1916 Storage-Rots of Economic Avoids 557 



becomes gradually darker and eventually turns brown, particularly just 

 below the surface. Softening accompanied by stringiness of the tissue 

 begins in 48 hours and extends to a depth of X to yi inch in one week. 

 After a week or 10 days the surface becomes somewhat slimy and glisten- 

 ing from the production of pionnotes composed of numerous typical 

 spores of the causal fungus. Upon drying, the specimen takes on a 

 putty-like texture, shrinks perceptibly, and finally becomes dry and 

 powdery and of a dark-grayish color. Plate LXXXII, figures 1 and 2, 

 shows typical specimens of Colocasia esculenta and Xanthosoma sagitti- 

 folium, respectively, partially decayed by the powdery-grayrot fungus. 



An examination of rotted material shows that the fungus first destroys 

 the middle lamella and later to some extent invades the cells themselves, 

 the tissue finally becoming a disorganized mass of separated cells. 



CAUSE OF POWDERY GRAYROT 



For a period of three years Fusarium solani (Mart.) Sacc. has been 

 repeatedly isolated in pure culture from decayed tubers and corms and 

 has reproduced the characteristic rot when inoculated into dasheens. 

 From such inoculated tubers the organism has been recovered and again 

 made to produce the disease and subsequently recovered. The causal 

 organism has been found to agree with F. solani as laid down by Appel 

 and Wollenweber (1 ) both culturally and in size and septation (fig. 1 , F) of 

 spores, as shown by the following measurements : Tri-septateconidia taken 

 from pionnotes of a 16-day-old culture on cooked Irish potato vary from 

 27 to 41 by 5.0 to 6.2/jand average 5.7 by 37.0^. Four-septate conidia, 34.4 

 to 51.6 by 5.2 to 6.2/i, average 5.7 by 41.6/1. Five-septate conidia, 5.4 to 

 5.9 by 41.3 to 51.6/1, average 5.6 by 47.4/1. In this connection it should 

 be stated also that F. solani from Irish potato, isolated and identified by 

 Wollenweber at Dahlem, near Berlin, Germany, produced a similar rot 

 of dasheens. No difference between the two organisms could be detected 

 either culturally or in their parasitic habits. 



INOCULATION EXPERIMENTS 



A few preliminary experiments demonstrated that no decay would 

 result when this fungus was spread on an unbroken surface. On the 

 other hand, if placed on a freshly wounded surface, decay started in 24 to 

 48 hours, provided sufficient moisture was present to enable the fungus 

 to get a start. These results seem to indicate that the fungus gains access 

 to the tubers through wounds made by separating the tubers and corms 

 or through wounds made by other means. The results of our experi- 

 ments showed that two reliable methods of inoculation could be trusted; 

 (1) Inoculation of the tuber by wounds made by pricking with a sterile 

 needle or scalpel or (2) by splitting a corm or tuber in two and smear- 

 ing spores on the cut surface. If the latter method was employed, a 



