PCC MarchApril Final Draft

Pythium species
P. aphanidermatum
P. irregulare
P. mastophorum
P. polymastum
P. sulcatum
P. ultimum
P. uncinulatum
P. violae
Reported row crop hosts
bean, beet, cabbage, carrot, cauliflower, cucumber, eggplant, lettuce, melon, onion, parsley, pea, pepper,
potato, radish, spinach, sweet potato, tomato, watermelon
asparagus, basil, bean, beet, Brussels sprouts, cabbage, carrot, cauliflower, celery, cilantro, cucumber, eggplant,
endive, lettuce, melon, onion, parsley, pea, pepper, potato, radish, spinach, sweet potato, tomato, watermelon
celery, parsley
broccoli, cabbage, cauliflower
carrot( infects other crops but causes few symptoms)
bean, beet, Brussels sprouts, cabbage, carrot, cauliflower, celery, cilantro, cucumber, eggplant, endive, leek,
lettuce, melon, onion, pea, pepper, potato, radish, spinach, sweet potato, tomato, watermelon
lettuce
carrot( infects other crops but causes few symptoms)
Table 2. Examples of Pythium pathogens with broad vs. narrow host ranges
"Fertigation
delivers fertilizer
to active
roots. As long as
irrigation is
managed to deliver
only needed
water, fertigation
can be a
highly efficient
method of
fertilization."
Continued from Page 15
Disease Development
Development of Pythium diseases is
straightforward. Initial inoculum is
almost always linked with infested field
soils and associated soil water. Pythium
is a soilborne pathogen that resides in
the soil primarily as dormant resting
structures. Pythium inoculum is not
seedborne or airborne. For Pythium
to become active, grow, and produce
those swimming zoospores, the soil
must be wet for prolonged periods.
Once susceptible
seed, seedlings,
and other plant
parts are in
close contact
with Pythium
inoculum,
infection can take
place and disease
will be initiated.
If wet soil
conditions persist
and temperatures
are optimum
for the pathogen,
disease losses can
be significant.
Diagnostic Considerations
Pythium is not the only soilborne
pathogen that causes seedling damping-off
and root rots of row crops. On
spinach, damping-off and root rot can
be caused by both Pythium and Fusarium;
visually, one cannot distinguish
between the symptoms caused by these
two pathogens. Pythium and Phytophthora
pathogens both cause dark, discolored
roots of lettuce and cannot be
differentiated in the field. Cauliflower
transplants are susceptible to both Pythium
and Rhizoctonia pathogens, both
of which caused the roots to become
Pythium plant pathogens can grow very rapidly. Pictured here are
three-day-old cultures of Pythium, Phytophthora, Fusarium and
Verticillium. The diameter of the petri dish is 85 mm.
16 Progressive Crop Consultant March / April 2021