376 J.L. BECKERMAN AND G.W. SUNDIN
Fig. 8.2. Signs and symptoms of fire blight disease on apple. (a) Ooze production from an
overwintered canker on the trunk of a “Gala” apple tree. The arrow denotes a fly that has
been attracted to the ooze. Flies play an important role in the transfer ofE. amylovoracells
from ooze to flower stigmas. (b) Early blossom blight symptoms on “Jonathan” apple; ooze
emergence from the flower pedicel is denoted by the arrows. (c) Shoot blight symptoms
on “Fuji” apple. (d) Shoot blight symptoms on young “Gala” apple trees. Trees grafted
onto fire blight susceptible rootstocks are at risk of being killed by rootstock blight.
surface of apple flowers, and in particular to the stigma surface
(Thomson 2000). The surface of the tips of stigmas particularly favors
exponential growth ofE. amylovorain the intercellular spaces between
papillae cells. Under conducive weather conditions, populations can
double every 35 min, and populations of 10^5 to 10^6 E. amylovoracells
per flower are common (Thomson 2000). The availability of free mois-
ture through rain or heavy dew is required to enableE. amylovoracells
to migrate down the style where these cells infect flowers through natu-
ral openings present in the nectaries. Flower infection leads to blossom
blight symptoms (flower death) and initiates further internal systemic
migration of theE. amylovoracells within the tree (Fig. 8.2b). Blossom
blight infections can significantly reduce current season yields, even
if the epidemic stops at that stage. A portion of the population can