Apr. 26, 1924 
Leather Rot of Strawberries 
365 
lowed to stand for an hour, with the berries exposed to the light; that is, for 
the length of time, and under the conditions, which make possible the discharge 
and germination of zoospores. The healthy berries were then removed, placed 
on clean moist newspaper in a sterilized pan and covered with another pan. 
Within three days the few that were taken out and cut showed softening and 
vascular browning; after one or two days more the remaining berries were 
covered with a scant growth of white mold and plantings from them yielded only 
Phytophthora. 
In other words, the berries became infected under conditions in which infection 
by zoospores was not only possible but actually much more probable than infec¬ 
tion, for example, by floating bits of mycelium. It is true, as noted earlier, that 
no zoospores were seen in any of the mounts made from Arkansas material. Yet, 
in the absence of proof to the contrary, this failure to find zoospores must be 
ascribed to a merely accidental failure to find conidia that were ripe for discharge. 
From these experiments (second method) and from control experiments 
conducted in the same way, except for the diseased berries, it was necessary 
at the end of 24 hours to remove a few fruits that showed signs of leather rot, 
the result of having to use berries from a section of the country in which the 
rot was so common that it was likely to occur in incipient stages even in fruit 
selected with the utmost care. The remaining control fruits and controls 
wounded but not inoculated with mycelium (Chicago experiments) failed to 
give Phytophthora at any time, though by the end of five or six days 75 to 90 
per cent of them were plainly diseased. Plantings from these diseased control 
fruits gave Pezizella, Sphaeronemella, an unidentified Rhizoctonia, and Botrytis. 
In experiments conducted in the field laboratory, Rhizopus gave very little 
trouble, probably because the berries came direct from the field and had been 
bruised only slightly or not at all. 
Attempts to inoculate strawberries with Phytophthora by laying bits of an 
agar culture of the fungus on the surface of uninjured fruits were always un- 
flnpPDOQTnl 
INFECTION IN THE FIELD 
Nothing definite is known about how infection takes place in the field. It 
may be that under field conditions the mycelium of Phytophthora is better 
able to enter uninjured fruits than it has appeared to be in the laboratory. It 
is certain that except after severe storms or general insect attack very few 
berries in the field have skin breaks of any sort, not to mention such wounds 
as were made in berries used for inoculation experiments. But conditions in the 
field which favor leather rot are precisely those which in the laboratory favor 
the discharge, and germination of zoospores. It seems likely therefore that 
most of the field infection is caused by zoospores; whether all of it is so caused 
is matter for further investigation. Berries which touch the ground are always 
first affected, or show the disease first, on the lower side; it is not known, how¬ 
ever, whether they become infected by zoospores or by direct growth of mycelium 
from the soil. This statement, in turn, raises the question whether the Phy¬ 
tophthora dealt with in this paper is a true soil fungus, in strawberry fields, or 
whether it lives on debris on the soil surface. Berries which hang free in the 
air and which may show the disease either at the tip or anywhere on the sides, 
could have become infected by zoospores or mycelium spattered onto them 
during rains; they might equally as well have become infected by means of 
zoospores which moved from the soil along the fruit stem to the fruit through 
the surface film of water which, during wet weather, covers all parts of the plant 
for hours at a time. More investigation is needed on all of these points. 
Investigation is also needed on the relation of the calyx to rot of the fruit. 
Even under conditions of moderate rainfall and temperature there are always 
