July 15, 1924 
Botrytis Rot of the Globe Artichoke 
87 
becoming gray to grayish-brown with 
age. Conidia are produced in rather 
loose clusters on the rounded to 
slightly inflated ends of the tips and 
lateral branches of the upright sporo- 
phores. In old cultures sclerotia are 
present, which on germination give rise 
either to vegetative mycelium or to 
short, rather compact tufts of conidio- 
phores with grayish-brown conidia. 
With the possible exception of cul¬ 
ture No. 255, whose spores are usually 
slightly smaller than those of the others, 
there is very little variation in size of 
the conidia of the various cultures. In 
the seven cultures used in most of the 
studies, the spores ranged from 8.2 to 
10.5m in width and from 11.3 to 14.4m in 
length, averaging 9.4 by 13.1m. 
The growth characteristics and spore 
measurements of these fungi are well 
within the range and description of 
the fungus usually designated B. cinerea 
Pers. In view of the existing confu¬ 
sion regarding species within the genus 
Botrytis, it has been thought best to 
refer to the organism or organisms 
under consideration as the B. cinerea 
type, since, as stated in the beginning 
of this article, practically all Botrytis 
strains occurring on vegetables are 
identical and can be grouped as the B. 
cinerea type (with the possible excep¬ 
tion of culture No. 255). 
TEMPERATURE RELATIONS 
In temperature experiments on plates 
and tubes of potato-dextrose agar, it 
was found that one culture, No. 1610, 
just isolated from an artichoke bud, 
was able to make radial growth rang¬ 
ing from 1 to 7 mm. within seven days 
at —*2° C. None of the other strains 
which had been cultured on artificial 
media for some time were able to grow 
under the above conditions, although 
in other respects the strains appear 
very similar. This suggests that a 
difference in pathogenicity may be 
expected in cultures, due to loss of 
vigor in growing on artificial media. 
All other strains grew from 0.5 to 2 
mm. in radius at —1.5° to — 1° in seven 
days. During the seven-day period at 
0° these strains grew 7 to 14 mm. in 
radius while the newly isolated strain 
No. 1610 under parallel conditions 
grew but slightly faster. At higher 
temperatures growth becomes more 
rapid until at 20° to 22° an average 
daily radial growth of 5 to 7 mm. is 
made. From experiments conducted 
at still higher temperatures it appears 
that the optimum for growth on potato- 
dextrose agar lies between 22° and 25°. 
These observations agree well with the 
results of Brooks and Cooley 4 for B. 
cinerea. 
The reactions to temperatures above 
31° are approximately alike for the 
various strains in plate cultures. Usu¬ 
ally very little growth is made. An 
increase of 1 to 2 mm. observed in 
some cases was mostly a very fine aerial 
mycelium arising from the inoculum. 
A few sporophores bearing conidia were 
also noted developing from the inocu¬ 
lum of one strain. But their vitality 
is so reduced at the above temperature 
that the organisms are not likely to 
produce appreciable decay. 
SPORE GERMINATION 
The spores of all strains germinate 
readily in hanging drops of sterile 
water and on the surface of nutrient 
agar plates. The majority germinate 
within 24 hours at room temperature 
and above, while a smaller percentage 
form germ tubes at temperatures 
around 0° C. The extreme range is 
wide, as successful germination has 
been obtained at temperatures as low 
as —2° and as high as 32° C. 
An experiment in which the tempera¬ 
tures ranged between —2° C. and 
— 1.5° with a mean of —1.75° showed 
good germination in the three strains 
tested. In a similar experiment in 
which spore dilutions of four different 
strains were poured upon plates of 
potato dextrose agar and placed where 
the temperature varied between — 1° 
and —3°, good germination was ob¬ 
tained within 48 hours. From 50 to 
75 per cent of these spores germinated, 
and their germ tubes ranged from 20 
to 90 m in length. It appears from 
these and other tests that mature 
conidia falling upon a suitable nutrient 
medium can germinate and make slow 
growth at temperatures below 0°. In 
sterile water at the above tempera¬ 
tures, however, germination seldom oc¬ 
curs, or is at most rather feeble com¬ 
pared with growth on a nutrient me¬ 
dium. 
Spore dilutions on potato-dextrose 
agar plates held at 31° to 32° C. give 
50 to 90 per cent germination within 
24 hours. Growth of the germ tubes 
continues 4 or 5 days, then usually 
stops when they reach 100 to 200m in 
length. This would seem to indicate 
a temperature of 32° as the maximum 
for growth from conidia in the strains 
under observation. 
* Brooks, C., and Cooley, J. S. temperature relations of apple rot fungi. Jour. Agr. Re¬ 
search 8: 139-163, illus. 1917. 
