oct.i.igzx A Dryrot Canker of Sugar Beets 51 



when examined under the microscope is found to be composed of masses 

 of hyaline, vigorously growing young hyphae ramifying through and 

 between the rapidly decaying host cells. It is in this advance layer 

 that the major portion of the tissue destruction occurs. The brown 

 layer advances uniformly inward by additions from the normal host 

 tissue, while the outer surface of the layer rapidly dries out and con- 

 stantly contributes its substance to the pithy mass occupying the resulting 

 cavity of the canker. The thickness of the layer is dependent largely 

 upon the rate at which the moisture is lost from it outer surface as the 

 fungus eats its way radially into the normal tissue. No evidence of direct 

 penetration of tlie normal cells by the fungus has been found. On the 

 other hand, it appears that dissolving enzyms precede considerably the 

 advancing mass of young hyphae (PI. 8, C). 



This method of tissue destruction resembles in a very definite way that 

 described by Ramsey (5), by which Rhizoctonia solani Kiihn attacks 

 and produces a definite pitting of the mature potato tuber. A similar 

 process of decay is described by Atkinson (r) for the "sore shin" of 

 cotton. He states that — 



the fungus {Rhizoctonia solani) never seems to penetrate far into the living tissues, but 

 kills as it goes, and the tissues become brown, depressed, and present the appearance 

 of a plant having a deep and ugly ulcer at the surface of the ground. 



A type of decay most accurately resembling this particular beet rot is 

 described by Richards (7) for the potato stem-canker caused by Corticium 

 vagum. 



The early production of definite cankers by a slow corroding of the 

 normal tissue, finally resulting in a complete dryrot of the beet, suggests 

 a possible name "dryrot canker" for the disease here described. 



Various American workers. {2; 4, p. 243-^4; 3) have reported rootrots 

 of the sugar beet which they attribute to the work of Rhizoctonia solani 

 Kiihn. It appears difficult at this time, however, to determine the possible 

 relation of these to the particular type of dryrot described in this article. 

 The indefiniteness of the literature on the subject in fact does not justify 

 any general statement as to the possible distribution of the disease. 



During September and October of 1920 a preliminary survey ^ was 

 made of the beet-growing districts in four counties of Utah — Cache, 

 Davis, Utah, and Salt Lake. The disease was found in 18 fields of the 

 51 visited in Cache County and in 3 fields of the 20 surveyed in Davis 

 County. Very serious damage occurred in a number of these fields. 

 No indication of the trouble v/as found in either Utah or Salt Lake 

 Counties. 



The limited survey does not permit of an estimate of the loss to the 

 total sugar-beet crop of the State; nevertheless, the general prevalence 



1 This survey was conducted in cooperation with the Office of Plant Disease Survey, United States 

 Department of Agriculture. The author wishes to express his indebtedness to Dr. G. R. Lyman for this 

 support. 



