150 



BULLETIN Vol. II, No. 2, APRIL, 1889. 



Diseases of the Irish potato, F. L. Scribxer, B. S. (pp. 27^3). 



Potato Rot [Phytophthora infestans) (pp. 27-37).^ — This contains 

 an account of the life history of the fungus which causes potato rot, 

 and advice regardino; the treatment of the disease. 



(1) The life iiistorv of the fungus, brie% stated, is as follows: 



The spores liijliting ui)oii the le.-ives of the potato germinate in drops of dew 

 or rain, and the prodnct of germination — tlie zoospores — jienetrate to the inte- 

 rior tissnes of the plant, and after growing for a time throngh these tissues, tho 

 mycelium sends out, chiefly from the under surface of the leaves, slender fruit- 

 ing branches whereon are produced a new crop of spores. These may carry the 

 disease to the other plants in the field, or to other parts of the same plant; that 

 is, they may serve to spread the disease in the tops, which we term blight, over 

 the entire field, or by being washed into the ground they may reach the tubers 

 and cause the rot. The fungus, once having gained entrance to the tubers, may 

 or may not vegetate rapidly. Its presence, however, is soon made evident by 

 a bro\\'ning of the flesh underlying the skin and by a more or less extensive 

 discoloration and de]>ression of the latter. Under certain conditions the disease 

 in the tubers may make no further progress throughout the winter, but the 

 mycelium of the fungus remains alive and ready to renew its activity upon the 

 first favoring circumstances. Such potatoes may often be found in the markets 

 and are used for food every daj', and it is too frequently the case that they are 

 preserved for seed. Used for this latter purpose the.v will hardly fail to affect 

 the ncAV crop and bring about a new development of spores. 



(2) Treatment: 



Select for planting a light, sandy loam or a soil which is well drained ; plant 

 onlj^ perfectly sound or disinfected seed; spraj' the tops with the Bordeaux 

 mixture, or some preparation containing suli>hate of copper; store in a cool, dry 

 place and keep dry. 



A netv disease of the Irish potato (pp. 37-43). — The foUoAving 

 abstract of this article was prepared by Mr. B. T. Gallowa}^, chief of 

 the Section of Vegetable Pathology of this Department, and has 

 already been published in the Journal of Mycology, Sept., 1889. 



The new disease was discovered among the potatoes obtained from the Uni- 

 versity farm, and is described as causing the tuber to wither, then dry up and 

 become hard. The skin is only partially discolored, but the surface is covered 

 with small pimples, each surrounded by a depression. Sections through a 

 diseased tuber revealed the fact that the flesh was apparently sound, but 

 slightly wilted. The only discoloration of the flesh was innuediately under the 

 pimples; here the tissues were brown. The microscope sliowed that the brown 

 areas were filled with numerous little worms of various sizes and development. 



" These little worms," says the writer, " were at once recognized as nematodes 

 or thread-worms, and were evidently the cause of the disease." 



" How did these worms get into the potatoes? Probably from the soil in 

 which they \^ere grown, for it is kno\\n that many of the parasitic nematodes 

 spend a certain period of their existence underground. It is very likely that 

 they were first introduced into the University farm through planting infected 

 seed. The potatoes planted were being saved for seed, and were these to be 

 planted they would certainly cari-y the worms to the new crop and thus per- 

 petuate the disease." 



Owing to the limited knowledge of the life history of the nematode the author 

 says it is impossible to indicate any definite course of treatment. 



