EXPERIMENTS WITH CLEAN SEED POTATOES ON NEW 

 LAND IN SOUTHERN IDAHO 



[preliminary paper] 



By O. A. Pratt, 



Assistant Pathologist, Cotton and Truck Crop Disease Investigations, 



Bureau of Plant Industry 



It has generally been assumed by plant pathologists that if disease- 

 free potatoes (Solatium tuberosum) were planted on new land the result- 

 ing product would be free from disease. For the past three years the 

 writer has been engaged in investigations of potato diseases in southern 

 Idaho, where this crop is grown under irrigation. As these irrigated 

 tracts have but recently been opened up, there are many acres of land 

 which may be classed as new in every sense of the word, since no agri- 

 cultural crops have ever been grown upon them. Pathologists and 

 potato growers alike believed that in these new lands just reclaimed 

 from the desert lay a wonderful opportunity for the production of disease- 

 free potatoes. However, from the beginning of the potato-growing 

 industry in the irrigated portion of southern Idaho potato diseases have 

 appeared each year. It is known that the first seed planted by the 

 potato growers of these irrigated tracts was far from being free from 

 disease, and it was naturally assumed that the diseases which appeared 

 in the product had been introduced with the seed planted. The dis- 

 eases most prevalent are wilt (Fusarium oxysporum Schlect.), blackrot 

 (F. radicicola Wollenw.), jelly-end rot (Fusarium sp.), Rhizoctonia or 

 russet scab, powdery dryrot (F. trichothecioides Wollenw.), and common 

 scab. 1 



During the first two years of the author's investigations of potato 

 diseases in southern Idaho, he observed that when potatoes were planted 

 on virgin land just reclaimed from the desert many diseases usually 

 appeared. Often the product from potatoes planted on such land 

 appeared to be more diseased than that from potatoes planted on 

 land which had been reclaimed from the desert for several years 

 and which had been planted with other crops, such as alfalfa or grain. 

 Frequently when such a diseased crop was observed, the grower would 

 insist that the seed potatoes he had planted had been practically free 

 from disease. Since certain of the diseases found, such as common scab 

 and blackrot, are easily detected on the seed, the writer was forced to 

 admit that in many such cases the grower might be right. Therefore, 



1 No attempt has been made to isolate an organism from the common scab found in this region, but since 

 its appearance is identical with that found in the East it is assumed that the causal organism is the same — 

 namely, Actinomyces chromogenus Gasperini. 



Journal of Agricultural Research, Vol. VI, No. 15 



Dept. of Agriculture, Washington, D. C July 10, 1916 



ei ( S73 ) G-86 



