Jan. 22, 1917 
Temperature Relations of Apple-Rot Fungi 
145 
packages and in the crowding of some of it nearer to the top of the 
chamber. While the thermograph records did not indicate any error, 
it is probable that in the last experiment some of the fruit in the 5 0 
chamber was exposed to a temperature about i° warmer than indicated. 
The behavior of the more virulent rot fungi has been practically the 
same on one variety of apples as on another, but with the weaker or¬ 
ganisms the variety of apples has had an important modifying effect 
upon the temperature results. Cephalothecium roseum produced a small 
amount of rot 
on the Yellow 
Newtown at 5 0 , 
but was unable 
to attack the 
Winesap, York 
Imperial, and 
Ben Davis at 
this tempera¬ 
ture or to pro¬ 
duce any signifi¬ 
cant growth on 
these varieties at 
io°. Fusarium 
radicicola was 
able to rot New- 
towns at a lower 
temperature 
than Winesap. 
Trichoderma sp. 
rotted the York 
Imperial at 20° 
but did not rot 
the Ben Davis. 
The apparent 
difference in 
susceptibility of 
varieties may have been partly due to differences in ripeness of the fruit, 
as there seemed to be no satisfactory way of determining the compara¬ 
tive maturity of the different varieties. It was repeatedly observed that 
a slight increase in the ripeness of apples of a particular variety caused 
a definite increase in susceptibility to rot. This modifying effect of 
maturity of the fruit was particularly noticeable as the minimum tem¬ 
perature for the fungus was approached. In this connection it may be 
mentioned that in cases where fungi had apparently lost some of their 
rot-producing power as a result of long culturing in the laboratory this 
attenuation was particularly evident at the lower temperatures. 
Vol 
Olo 
0 ft. 10 
Temperature (^Centigrade) 
Fig. 2.—Graph showing the development of rot on Yellow Newtown apples. 
The curves show the average weekly increase in diameter. With Sclerotinia 
drierea, Spkaeropsis malorum, and Volutella fructi they are based on records 
made two weeks after inoculation; with the other fungi on records made three 
weeks after inoculation. 
