822 Journal of Agricultural Research vol. vi.No.21 



e. The leaves of ten apparently healthy Idaho Rural plants were 

 sprayed with a spore suspension of the fungus. As a check, the leaves of 

 ten apparently healthy plants were sprayed with sterile water. This 

 experiment was duplicated with Netted Gems. 



In the fall a careful examination was made of each plant and tuber. 

 Not the slightest trace of infection that could be ascribed to F. tricho- 

 thecioides could be found, though cultures were made from suspicious- 

 looking stem lesions and tuber discolorations. The punctures in the 

 tubers and stolons had healed over, leaving only the slightest scars as 

 evidence. The punctures in the stems could be found by very careful 

 scrutiny, but were entirely healed over. There was neither internal nor 

 external evidence of disease in the neighborhood of the punctures, whether 

 in stems, tubers, or tuber stolons. No disease appeared in the foliage 

 or stems as a result of spraying with the spore suspension. 



The results of the attempts to induce infection in growing potato 

 plants were such as might have been expected after several years' 

 search in commercial fields for evidence of disease which could be attrib- 

 uted to this organism. Several hundred cultures have been made from 

 diseased parts of growing potato plants. Out of these attempts, F. tri- 

 chothecioides has been obtained but 1 3 times, twice from Netted Gem tubers 

 infected with jelly-end rot and 1 1 times from potato stems infected with 

 footrot. In the footrot cultures, F. trichothecioides was associated with 

 other species of Fusarium, including F. radicicola and F. oxysporum, as 

 well as other fungi. It is not likely that F. trichothecioides attacked the 

 growing stem, but rather it is probable that it entered as a secondary 

 organism after the attacks of other fungi or bacteria. The writer has 

 shown in another paper 1 that jelly-end rot does not develop at temper- 

 atures below io° C. ; therefore F. trichothecioides is eliminated as one of 

 the contributing causes of this fieldrot, since, if F. trichothecioides were 

 generally present in tubers infected with jelly-end rot, such tubers when 

 placed in storage would continue to decay at temperatures as low as 

 4 (see pages 825 to 827). F. trichothecioides has never been obtained 

 from any other fieldrot. In commercial storage cellars, unbruised tubers 

 have never been found infected by F. trichothecioides; on the other hand, 

 the majority of bruised tubers in storage show more or less decay from 

 this cause. 



EFFECT OF PLANTING SEED INFECTED BY DRYROT 



Poor stands of potatoes have been observed from year to year in many 

 potato fields in southern Idaho. In many cases it was impossible to say 

 whether the poor stand was due to irregularity in planting or to poor 

 seed. In some cases, however, the only explanation that could be made 



1 Pratt, O. A. A western fieldrot of the Irish potato tuber caused by Fusarium radicicola. In Jour. 

 Agr. Research, v. 6, no. 9, p. 297-310, pi. 34-37. 1916. 



