NC State and USDA Cucumber Disease Handbook
Bacterial Wilt (Erwinia tracheiphila)
Disease:
Bacterial wilt.
Pathogen:
Erwinia tracheiphila (E. F. Smith) Holland.
Culture Description:
On agar media grayish white to cream, circular, smooth and glistening
bacterial colonies. Infested stems exude sticky, stringy bacterial
slime when cut.
Microscopic Description:
Gram negative, non-sporeforming, capsulate rods (0.5-0.7 x 1.2-2.5
µm); motile with peritrichous flagella.
Source:
P. H. Williams; Plant Pathology Department; 1630 Linden Drive;
Madison, WI 53706.
Relative Stability:
Highly unstable in culture. Loses virulence and viability quickly.
No evidence of change in pathogenicity in nature.
Variants:
No information.
Storage and Retrieval:
The bacteria can be stored in excised, infected hypocotyls, petioles,
and stems at -17°C for 1 year. To retrieve, grind frozen
tissue and use for inoculum.
Inoculum Increase:
Bacteria are maintained in susceptible host tissue, fresh or
frozen. To increase inoculum, inoculate each leaf of a susceptible
plant as for routine inoculation (see inoculum preparation, quantification,
and inoculum distribution and delivery sections). Grow inoculated
plant in greenhouse 24-28°C. Fertilize once/week. When petioles
are drooping due to bacterial wilt, check a petiole for stringy,
sticky bacterial slime. When present, the petioles and stems can
be harvested for inoculum. Use tissue immediately or freeze.
Inoculum Preparation:
Infected hypocotyl, petiole, or stem tissue, fresh or frozen,
is ground using a mortar and pestle.
Quantification:
Check tissue for slime. If very slimy, a small amount of tap
water can be added to increase inoculum. Check again for slime.
If tissue is not slimy, discard.
Inoculum Distribution and Delivery:
Place some ground tissue in the needles of a flower frog, 1 cm
diameter, 20 needles arranged in concentric rings. Dip the needles
in inoculum. Puncture the cucumber cotyledon or leaf twice with
the flower frog needles to insure penetration of bacteria. Dip
the needles in inoculum before wounding each plant.
Host:
Cucumis sativus L., cucumber.
Source of Resistance:
PIs reported to contain some resistant plants are 200815, 200818,
and 222187.
Differentials - Controls:
Susceptible check Straight Eight. Resistant check WI 1589 from
Dr. C. E. Peterson.
Growth of Host:
Cucumber seeds are sown in steam sterilized coarse grade vermiculite
in wooden flats (52 x 26 x 7 cm). Each flat contains 10 rows,
25 seeds/row. Resistant and susceptible checks are sown in row
6. The flats are placed on a heated germination bench. Vermiculite
temperatures of 32°C insure rapid and uniform germination.
Newspaper on top of the flat prevents cooling by evaporation.
Newspaper is removed when seeds germinate. If inoculating plants
in the leaf stage, transplant 2 week old seedlings to steam sterilized
soil in 4" plastic pots. When plants are 4 weeks old, transplant
to 8" clay pots. Soil composed of sand:peat:field soil: field
compost:perlite (1:1:1:1:1). Fertilize plants in 4" and 8" pots
once/week.
Tissue Age:
Inoculate young tissue, either cotyledons or leaves, of any size
plant.
Postinoculation Environment:
Incubate in the greenhouse at 24-28°C. High humidity is
not required, but plants may be placed at 100% relative humidity
and 25°C for 48 hours.
Disease Response:
Plants are rated as susceptible or resistant 5-7 days after inoculation.
Susceptible plants wilt at point of inoculation. The wilt progresses
along the stem. Resistant plants do not wilt.
Multiple Inoculation:
Simultaneous inoculation in the cotyledon stage with scab, anthracnose,
angular leaf spot, or downy mildew. Subsequent inoculation with
cucumber mosaic virus (CMV) and powdery mildew.
Saving Host:
Resistant plants can be transplanted to steam sterilized soil.
Susceptible plants die. If a desirable plant is presumed to be
susceptible, a cutting can be inoculated to check disease reaction.
Susceptible plants inoculated at the leaf tip may usually be saved
by excising the inoculated leaf at the junction of the petiole
and stem as soon as wilting appears.
Paul H. Williams
Mary J. Palmer
Department of Plant Pathology
University of Wisconsin
10-07-82
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