Other fungi such as S. conigenus, F. cir-
cinatum, and D. pinea are seedborne
pathogens capable of causing other
diseases such as stem cankers and shoot
dieback. S. conigenus becomes established
in seedlots when older cones are
inadvertently included in the cone harvest.
The conditions that favor this pathogen’s
establishment in seeds include high humidity,
low light, and cool temperatures
ranging from 10 to 20 °C (50 to 68 ºF).
Seed contamination levels by Fusarium
species can vary by collection date and
by orchard. Fresh wounds are known to
provide infection courts for F. circinatum
and various agents can wound reproductive
structures, including insects, high
wind, hail, and cone handling practices.
Seed contamination by F. circinatum can
also vary greatly among clones in seed
orchards. Cones from clones that are
highly susceptible to pitch canker tend to
have greater levels of seed contamination.
These diseased cones can contaminate
the cones and seeds from less susceptible
clones when they are included in bulk
collections. Not all Fusarium species are
pathogenic to tree seeds and isolates of
some species (for example, F. oxysporum)
can vary greatly in pathogenicity.
moisture conditions that may affect seeds
during collection, extraction, and storage.