Florida Agricultural Experiment Station


Because of its nature and manner of spread, most of the early
investigators were led to consider this disease to be of para-
sitic origin, but no specific organism was definitely proved to be
the cause until a few years ago.
 In 1914 a fungus was isolated from a foot rot lesion on a
 grapefruit tree at Palmetto, Florida, by Fawcett. This fungus,
 which later was identified as Phytophthora terrestria by Sherb-
 akoff, was recognized at the time as similar to the one causing
 brown-rot gummosis in California. Fawcett had previously
 isolated the same organism from gummosis lesions at the junc-
 tion of the root and trunk of an orange tree in California in 1912.
 He later states that foot rot, under California conditions, can
 not be distinguished from certain phases of brown-rot gummosis,
 except by means of culture tests for the isolation of the causal
 organisms.
 In 1916, the same fungus was isolated from an active case of
foot rot by Stevens, who was then with this Experiment Station,
and, a little later, he isolated it from other cases of foot rot in
other localities. A rather extended survey was then made of
the foot rot groves throughout the state and the same fungus
was repeatedly isolated from active cases of foot rot, from trees
in widely separated localities, covering the principal part of the
citrus belt. This fungus was inoculated into the bark of healthy
citrus trees and, in several cases, diseased areas developed that
were typical of foot rot lesions found under natural conditions.
Although this fungus was identified as Phytophthora terrestria
Sherb., it is now considered by most authorities, including Sherb-
akoff, to be a form of the species, Phytophthora parasitica Das-
tur. This fungus belongs to a group which contains some of
our most destructive plant parasites and attacks a number of dif-
ferent plants in Florida and the tropics. It may be properly con-
sidered a soil fungus since it can grow and perpetuate itself in
the soil for a long period. It is most active and develops most
rapidly in low-lying soils and in moist, shady situations.
 By no means all the trouble ascribed to foot rot in Florida,
however, is due to that specific trouble. Recent investigations
by the senior author have demonstrated that a very similar
trouble heretofore undistinguished from foot rot is due to Clito-
cybe mushroom root rot (see page 56).