May 17,1924 
A Fusarium Bulb Rot of Onion 
693 
when the plants were not -wounded. As high as 22 per cent infection was se¬ 
cured in plants grown out of doors, from sets and from seed, on previously inocu¬ 
lated soil. Bulbs inoculated through wounds and kept under ordinary labora¬ 
tory conditions very seldom became infected. Exposure in a moist chamber 
for 48 hours after inoculation followed by removal to laboratory conditions re¬ 
sulted usually in 100 per cent infection. 
In controlled soil-temperature experiments the disease developed within the 
limits of 15° to 32° C. Most rapid development occurred at 28° to 32°. 
Progress was much slower as the temperature decreased. The disease did not 
develop at 12°. 
Variation in soil moisture had little or no effect upon the progress of the dis¬ 
ease after initial infection had taken place. 
The results of soil-temperature experiments coincide with the occurrence of 
the disease in the field. In southeastern Wisconsin the soil temperature mean 
at 1 to 2 inches does not ordinarily reach 15° C. until May 15 or later while 
the optimum temperature for the disease is not reached until July 1 or later. 
The disease in this section does not appear until after the latter date. The most 
serious outbreaks of Fusarium bulb rot in the United States are in the Walla 
Walla section of Washington and the Uncompahgre section of Colorado; in 
Europe, the Valencian district of Spain suffers most. All three sections are 
subject to extremely hot weather during the latter part of the onion-growing 
season. 
As a storage disease the bulb rot is most active at or above room temperature. 
At about 30° C. the tissues decay and desiccate rapidly. At 20° the decay is 
rapid but the tissue remains watery for a longer time. At about 15° the decay 
is very slow but premature sprouting is evident. At around 8° the rot is very 
slight indeed, but the promotion of premature sprouting in inoculated bulbs 
is very marked. Thus at this low temperature the indirect effect of the disease 
may cause heavy losses in storage or transit. 
LITERATURE CITED 
(1) Clinton, G. P. 
1915. notes on plant diseases of Connecticut. Conn. Agr. Exp. Sta. 
Ann. Rpt. 1915 (6), 421-451, pi. 17-24. 
(2) - 
1920. NEW OR UNUSUAL PLANT INJURIES AND DISEASES FOUND IN CON¬ 
NECTICUT 1916-1919. Conn. Agr. Exp. Sta. Bui. 222: 396-482, 
pi. 33-56. 
(3) Edgerton, C. W. 
1921. ONION DISEASES AND ONION SEED PRODUCTION. La. Agr. Exp. 
Sta. Bui. 182, 20 p., 9 fig. 
(4) Hanzawa, Jun. 
1914. FUSARIUM CEPAE, EIN NEUER ZWIEBELPILZ JAPANS, SOWIE EINIGE 
ANDERE PILZE AN ZWIEBELPFLANZEN. MyCOl. Centbl. 5: 4-13, 
1 col. pi. 
(5) Karrer, J. L., and Webb, R. W. 
1920. TITRATION CURVES OF CERTAIN LIQUID CULTURE MEDIA. Ann. Mo. 
Bot. Gard., 7: 299-305, illus. Literature cited, p. 305. 
(6) Link, G. K. K., and Gardner, Max W. 
1919. MARKET PATHOLOGY AND MARKET DISEASES OF VEGETABLES. 
Phytopathology 9: 497-520. Literature cited, p. 519-520. 
(7) Ridgway, Robert 
1912. COLOR STANDARDS AND COLOR NOMENCLATURE. 43 p., 53 COl. pi. 
Washington, D. C. 
