oct.i.i93i A Dryrot Canker of Sugar Beets 49 



the drying out and final cracking of this outer covering the fungus, 

 possibly because of a better oxygen relation, eats radially into the beet, 

 producing deep cankers (PI. 5 and 6). The decaying tissues rapidly 

 dry out as the fungus advances inward, leaving the cavity partially 

 filled with a dry, pithy residue. Frequently the content of the canker 

 appears as a definite plug, which, upon wetting, may be removed intact 

 from the cavity of the canker (PI. 9, D). 



Except for slight cracking, the outer layer of dead cells remains entire 

 and furnishes a definite covering until the lesion has reached approxi- 

 mately its limit of tangential spread. As the cells of this outer covering 

 finally dry out the central perforation enlarges and ultimately gives rise 

 to a definite crack which may extend the entire diameter of the lesion 

 (PI. 4; 8, D; 5). Frequently adjacent cracks become confluent, 

 resulting in large characteristic fissures, which in severe cases of the 

 disease may obtain from 2>^ to 3 inches in length and from % to 1% 

 inches in depth (PI. 5, 6). With numerous points of attack the beet by 

 harvest time is converted into a dry, brittle shell filled with a pithy mass 

 of host and fungous debris (PI. 6). 



During the season careful study was made of a large number of the 

 beets taken from each of the different fields in which the dryrot had 

 been found. In all cases the characteristic cankers exhibited the pres- 

 ence of the sterile stage of Corticium vagum. This fungus, it was found, 

 may be obtained regularly in a pure form from any part of the typical 

 canker, provided the outer covering of the lesion is not previously de- 

 stroyed. The brown layer separating the normal from the diseased 

 tissue (PI. 8, A-C) has never failed to yield the fungus free from other 

 organisms, and even from the open lesions cultures have been obtained 

 with remarkable ease and regularity. The degree to which other organ- 

 isms are found to be excluded is phenomenal. 



To determine the etiological relation of the fungus, inoculations were 

 made September 3 on partially grown beets. In the process of inocula- 

 tion the soil was removed to a depth of approximately 4 inches from 2 1 

 beets in each of five rows. Each of the 2 1 beets in the first row was 

 punctured a number of times with a sterile needle, and the inoculum, 

 consisting of the beet fungus, grown for several days on potato agar, was 

 then scattered throughout the soil as the latter was replaced about the 

 beet. Row 2 was inoculated exactly as row i except that in place of 

 needle punctures slight incisions were made in the beet by the use of a 

 sterile scalpel. The beets in rows 3 and 4 were wounded as in row i, 

 and the soil was inoculated with two different "strains" of Corticium 

 vagum,} Row 5 was left uninoculated, and the beets after wounding as 

 in rows i and 2 were covered and grown as controls. All the wounded 



1 These "strains" were obtained from the surface of a potato tuber in 1918 and have proved virulent 

 on potato stems in both sterilized and unsterilized soil. 



