Apr. 8, 1918 Relation of Soil Fungi to Potato Diseases 97 



VERTICILLIUM 



Five species of the genus Verticillium were isolated, referred to in 

 Table III by No. 419, 477, 603, 771, and 825. No. 419 was isolated 

 twice from sample i ; No. 477 once each from samples i and 3; No. 603 

 once from sample 5; No. 771 once from group C; and No. 825 once each 

 from sample i and groups A and C. No. 771 proved interesting in that 

 it was once isolated from the discolored vascular bundles of a potato 

 tuber grown in plot 11 (191 6) on virgin desert soil, near Aberdeen, 

 Idaho. This species is briefly described as follows: Conidia oval to 

 elliptical, 2.5 to 8 by i to 3 n, in chains on branches in verticillate whorls; 

 mycelium and spores, in mass, from brick-red to dark reddish brown, 

 on such media as steamed-potato plugs, steamed rice, and agars con- 

 taining glucose. 



STERILE MYCELIA 



A sterile mycelium, reddish brown in color, was once isolated from 

 sample 5, a sterile white form, apparently the same in each case was 20 

 times isolated, 8 times from sample i, 4 times from sample 2, once from 

 sample 3, 5 times from group A, and once each from each of groups C 

 and D. A pink form was isolated once from sample 2 and twice from 

 group A. At first it was thought that this pink form might be a species 

 of Fusarium, which for some reason was slow in fruiting; but after 

 nearly a year's growth in culture, no fruiting bodies were produced. A 

 buff-colored form producing brownish to pinkish brown sclerotia-like 

 bodies was once isolated from group A, and a yellowish form isolated 

 once from sample 5. 



SIGNIFICANCE OF THE INVESTIGATIONS 



The special significance of these investigations lies in the finding of 

 parasitic fungi in desert soils, on wild plants growing in the desert, and 

 on cultivated plants in arid regions, where it is probable that the infec- 

 tion proceeded from the soil. These desert soils have commonly been 

 supposed to support only a scant fungus flora and to be free from organ- 

 isms of a parasitic nature. Their known presence in the soil, it is believed, 

 explains the appearance of disease in the product of disease-free seed 

 potatoes planted on new land and suggests that whenever it is attempted 

 to grow disease-free potatoes, the role played by soil fungi must be taken 

 into consideration. 



SUMMARY 



(i) Fungus forms were found to be abundant in desert soils. 



(2) Three fungi, Fusarium radicicola Wollenw., Fusarium trichothe- 

 cioidcs Wollenw., and Rhizoctonia solani Kiihn., known to be parasitic 

 on the Irish potato were isolated from Idaho soils never cropped with 

 potatoes. 



