Murphy — The Sources of Infection of Potato Tubers. 355 



Morse.i The results are summarized by Jones, Giddings, and Lutnian^ as 

 follows : — " . . . where the tops are attacked by the late blight the harvest- 

 ing of the tubers should be delayed until a week or more after the death of 

 the tops." In the results of two experiments quoted 55'3 per cent, and 18'4 

 per cent, of the potatoes rotted when they were dug early, while the 

 percentages of rot in similar potatoes dug from three to four weeks later were 

 7"3 and 6'0 respectively. The condition of the foliage as regards blight was 

 not stated. 



Jones and his co-workers did not go into the question of the source of 

 tuber infection after the foliage was practically or completely dead, although 

 they seemed to have assumed that such infection was possible. Jensen 

 proved that the spores remained viable for five days in soil, but his work 

 necessitates the assumption that tubers may contract the disease during more 

 than double that period after the foliage is dead. If this actually takes place, 

 it is necessary to assume an unsuspected amount of vitality in the spores of 

 Phytophthora infestans or the existence of some hitherto undiscovered phase 

 in the life-history of the fungus. 



II.— Phytophthoka Tuber-rot in Eastern Canada. 



The present author was led to a consideration of the question of the 

 sources of tuber infection by residence for some years in the Maritime 

 Provinces of Canada, where the ravages of blight developing in the tubers 

 after the crop is dug sometimes exceed the damage wrought by the disease 

 on the growing crop. A considerable number of blighted tubers are some- 

 times found when the ci'op is lifted, yet at other times such tubers may be 

 almost absent. When, however, the apparently healthy portion of the crop 

 is stored, in many cases an outbreak of Phytophthora rot sets in which may 

 destroy a large proportion of the tubers. In some cases the result is that 

 not the one-twentieth part (or thereabouts) of the normal crop required to 

 supply " seed " for the following year survives. The sale of tubers may be 

 almost entirely held up for a month or two in the autumn in bad years, 

 because buyers are afraid to touch any potatoes, no matter how sound they 

 look. After the latter part of October the danger is held to be over, as 

 the disease will by then have developed far enough to be recognized. 



' Jones, L, R., and W. J. Morse : " Potato Diseases and their Remedies. — Relation of 

 date of digging to development of rot." Vermont Agr. Experiment Station, Fifteenth 

 Annual Report (1901-2), pp. 219-223, 1902 ; Sixteenth Annual Report (1902-3), pp. 161- 

 162, 1903 ; Seventeenth Annual Report (1903-4), pp. 391-395, 1905. 



-Jones, L. R., N.J. Giddings, and B. F. Lutman : "Investigations of the Potato 

 Fungus, Phytophthora infestans." U.S. Dept. of Agriculture, Bureau of Plant. Industry, 

 Bull. 245. 1912. 



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