May 17,1924 
A Fusarium Bulb Rot of Onion 
685 
On hard oat agar, culture 130 days old, chlamydospores (in conidia): 0-septate, 
range 6 to 10.5X5.5 to 8.9/*, average 8.3X8/*. 
On onion agar, culture 275 days old, chlamydospores (in conidia): 0-septate, 
range 6.7 to 9.6X6 to 9.2/*, average 7.9X8.4/*. 
On malt agar, culture 80 days old, chlamydospores, terminal and intercalary, 
very variable in size and shape from spherical to ovoid, mostly 1-celled, occa¬ 
sionally 2-celled; 1-celled range, 5.7 to 9X5.7 to 9/*, average 7.5X7.5/*; 2-celled, 
range, 7.5 to 10X12 to 13.5/*, average 8.0X12.5/*. 
After comparison with the descriptions by Wollenweber (10) and Sherbakoff 
(9) it is evident that this form belongs to the section Elegans of the genus Fusarium 
and within that group lies very close to Fusarium redolens Woll., FI hyperoxy- 
sporum Woll. ( F . lutulatum Sherb.) and F. oxysporum Schlecht. It differs from 
the first of these chiefly in the type of spore curvature. Its macroconidia are 
uniformly curved throughout (fig. 1), while a distinguishing character of F. redolens 
Fig. 1.—Camera lucida outlines of conidia of Fusarium cepae A. Sporodochial conidia from 24-day-old 
culture on red raspberry cane plug. B. Pionnotal conidia from 10-day-old culture on hard lima bean 
agar 
is that the conidia are typically broader toward, more curved near, and sometimes 
suddenly constricted at the apex. The strain here discussed never showed this 
last character. It agrees closely with F. hyper oxysporum as to size and shape of 
conidia, but differs decidedly in its general appearance on various media. It 
differs from F. oxysporum in having slightly larger spores and in the total absence 
of sclerotia. It agrees with Hanzawa’s description (4) of Fusarium cepae as to 
septation, curvature, and length of conidia, but differs slightly as to width of 
conidia and size of chlamydospores. Its measurements of 3-septate conidia 
average 3 to 5/*; he records 4.5 to 6.3/*. In his figures he has illustrated the swollen 
conidia; and if we assume that he also measured the maximum width of the 
swollen conidia, rather than the width at the septa, the discrepancy is probably 
accounted for. Wollen weber (If, p. 173) mentions the importance of considering 
this point in comparing the descriptions of Fusaria. 
TEMPERATURE RELATIONS 
Petri dishes of equal size containing equivalent amounts of hard potato agar 
(2 per cent glucose) were inoculated in the center with the organism and placed 
in duplicate in a series of incubators ranging from 4° to 35° C. Growth occurred 
over the entire range, but very slowly at the extremes. The diameter of the 
colonies after five days was taken as a criterion of comparison, the results being 
represented graphically in Figure 2. There is a gradual increase in the rate of 
growth up to 25°, with a distinct optimum at about 25° to 28°, and a rapid drop 
beyond 30° C. 
