636 Journal of Agricultural Research vol. vi, no. 17 



sorted out and sacked separately, and all the potatoes were stored in 

 sacks in a warehouse under about the usual commercial conditions. The 

 potatoes were sorted four days later and 65 diseased tubers were found, 

 all of which had been wounded. They were sorted a second time eight 

 days after digging and 52 more rotten tubers were found. None of the 

 unwounded potatoes showed evidences of the disease at any time, and no 

 more of the wounded tubers were rotten when they were sorted for the 

 last time 15 days after harvesting. Transfers were made from some of 

 these rotten tubers to corn-meal agar slants and P. debaryanum was 

 obtained in all these cultures. It is evident that this fungus is generally 

 present in these peat soils, that inoculations may be made by inserting 

 some of the soil in wounds in the tubers, and that potatoes wounded in 

 digging frequently become infected. Unwounded tubers are apparently 

 not affected with this disease. It would seem probable from these 

 experiments that more care in harvesting and sorting out of potatoes 

 injured in digging would decrease the losses from this disease. 



OTHER ROTS SOMETIMES MISTAKEN FOR LEAK 



It is quite possible that tuber-rots produced by other fungi may be 

 mistaken for potato leak. Two species of Fusarium, F. radicicola Wol- 

 lenw. and F. oxysporum Schlecht., which produce tuber-rots of the 

 potato are quite common in the San Joaquin potato region. Carpenter 

 (5) has shown that either one or the other of these fungi is usually present 

 in the jelly-end rot of potato tubers. He has also obtained F. radicicola 

 from specimens of rotten potatoes from San Joaquin County, California, 

 which were supposed to be affected with leak. The present writer has 

 found rotten tubers in consignments of potatoes from California which 

 had stood in the laboratory for a few weeks. These potatoes were 

 apparently sound upon arrival, with the exception of a few. which had 

 small rotten spots in the stem end. At the end of a few weeks some of 

 the tubers were entirely rotten and very much resembled those in the 

 advanced stages of leak. F. radicicola was obtained from several such 

 specimens. Neither Pythium debaryanum nor Rhizopus nigricans was 

 ever obtained. Potato dealers at Stockton and potato growers say that 

 the leak may develop after the potatoes have been in storage for a time 

 and sometimes after they have been sorted. Under such conditions the 

 rot is apparently not due to P. debaryanum nor R. nigricans, but to some 

 other organism, probably a species of Fusarium in many instances, as 

 in these experiments rots caused by P." debaryanum or R. nigricans were 

 usually evident in three or four days. If an inoculated potato was sound 

 at the end of a week it was not infected and the potato would remain 

 sound indefinitely. The experiments in which potatoes were kept at 

 low temperatures are, of course, excepted. It seems quite probable 

 then that potatoes affected with rots caused by Fusarium spp. are 

 sometimes confused with those affected with leak. 



