318 maine agricultural experiment station. i907. 



Internal Brown Spot of the Tuber. 



A peculiar spotting of the interior of potato tubers has been 

 observed for some time by Mr. Charles Fish of Brunswick. 

 Samples were sent to the Station and examination showed that 

 the appearance of the diseased potatoes agreed in every respect 

 with the published description of the "internal brown spot" 

 which is quite common in some parts Of Europe. So far as the 

 writer can learn the occurrence of the disease in America has 

 been recorded in the publications of but 2 of the Stations.* In 

 Scotland and England this disease is more commonly known 

 as "sprain." 



The surface of the tuber looks perfectly healthy and normal. 

 On cutting open the affected ones the flesh is found to be dotted 

 with rusty-brown spots as is illustrated in Fig. 48, which repre- 

 sents a series of consecutive slices through the same tuber. 

 These spots vary in size from minute dots to one-eighth of an 

 inch or even one-fourth of an inch in diameter. The diseased 

 areas are of various shapes but more often approach the spher- 

 ical in general outline. The affected portions are not confined 

 to any particular portion of the tuber, and where they are few 

 enough to be isolated from one another the spots are entirely 

 imbedded in what appeared to be healthy tissue. 



A larger supply of the affected tubers was secured to deter- 

 mine whether or not the disease was of parasitic origin. Care- 

 ful examination with the microscope failed to show the presence 

 of either fungi or bacteria. Neither could any such organisms 

 be isolated from the spots — the diseased areas appeared to be 

 sterile when cut out with a flamed knife and transferred with 

 proper precautions to tubes or plates of nutrient media. 

 ^ The variety examined was Burpee's Extra Early, grown on 

 rather dry, sandy loam. A special brand of commercial fer- 

 tilizer for potatoes was used but no stable dressing was applied. 

 Mr. Fish states that he finds considerable difference in the 

 resistance of various varieties to this disease. Green Mountain 

 is not very susceptible, while Early Prolific was badly affected 

 one season. The amount of spotting present varies also with 

 the season. 



* Minn. Exp. Sta. Bui. 39, pp. 212-213 (1894) ; Bui. 45, p. 310 (1895). 

 N. Y. (Geneva) Bui. ioi, pp. 78-83 (1896). 



