J01t >] PARASITIC Kumx TON IAS IN A.MKKICA 



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and income cases a curling of the leaves or resetting results. When 

 the main stem is attacked below the surface of the soil and the stolons 

 are cut off, the condition known as "little potatoes" is produced; in 

 such cases a cluster of small, short-stemmed tubers is formed above 

 the wound. The production of aerial potatoes, rosette, and leaf curl- 

 ing also occurs when the stolons are attacked and the young tubers are 

 cut off. 



These abnormal developments of the potato are usually associated, 

 and are secondary physiological effects due to disturbances of the 

 nutrition of the plant. They occur most frequently on poorly drained 

 land and especially on heavy soils. 



Rolfs 92 attributed the potato failure of 1902-03 in Colorado to 

 little potato. Selby 103 in Ohio, in his studies of the Rhizoctonia dis- 

 ease on potato, gave particular attention to rosette. In 1914 Morse 

 and Shapovalov 09 concluded that the Rhizoctonia disease of potato is 

 of a more serious nature than is generally considered. In one field 

 which they had under observation for several seasons, they attributed 

 the poor and uneven stands, unexpected low yields, early ripening, 

 and death of the tops to Rhizoctonia. In most cases they confirmed 

 the observations made by Rolfs. Recently investigators all over the 

 country have been emphasizing the serious nature of the disease. 



In January, 1915, material of Rhizoctonia Crocorum on potato 

 tubers was received from Mr. F. D. Bailey of the Oregon Agricultural 

 Experiment Station. On comparing it with Rhizoctonia Solani, it was 

 found to be entirely different in all respects. However, this fungus is 

 identical with the fungus on alfalfa reported by a number of observers 

 (Webber, Heald, and Freeman) as R. Crocorum. Thus it appears 

 that R. Crocorum is present in this country on alfalfa and on potato 

 tubers. 



Bailey 8 describes the Rhizoctonia disease of potato as follows : 



"The surface was almost entirely covered with a dense, felt-like mat of a 

 chocolate color when dry, violet -brown when moist. This mat was found to be 

 composed of mycelium which had long narrow cells and a branching habit char- 

 acteristic of Rhizoctonia. The greater part of this mycelial mat could be easily 

 removed, and beneath this the surface of the tuber was covered with very small 

 dark spots. These spots appeared to the unaided eye as minute eruptions of the 

 skin. Under the microscope one can see the mycelial threads attached at these 

 points, and a freehand section thru such a spot shows it to be a structure com- 

 posed entirely of interwoven fungus threads forming a sclerotium. No evidence of 

 differentiation or any type of spore formation within this body could be found 

 on examination of many sections. The portion of the sclerotium near the sur- 

 face is composed of cells that are very deeply colored, giving the black appear- 

 ance. The outer surface of the sclerotium is seen to project above the surface, 

 while the lower or underlying portion is embedded in the outer cortical layers 

 of cells of the tuber. Furthermore, there is a strand of fungus tissue extending 

 deeper than the sclerotium, which connects it with a layer of the same type of 

 fungus tissue spreading between the cortex and parenchyma from the poini where 

 this strand reaches the parenchyma. 



"Attempts to grow this fungus in culture failed. This has boon the experience 

 reported in attempts to grow Ehizoctonia violacea Tul." 



