NC State and USDA Cucumber Disease Handbook
Angular Leafspot (Pseudomonas syringae pv. lachrymans)
Pathogen:
Pseudomonas syringae pv. lachrymans (Smith and
Bryan) Carsner.
Culture Description:
On tetrazolium chloride agar (TZC) magenta bacterial colonies
are formed.
Microscopic Description:
Gram negative, non-spore forming rods (0.8 x 1-2 microns); motile
with 1-5 polar flagella.
Source:
P. H. Williams; Plant Pathology Department; University of Wisconsin;
1630 Linden Drive; Madison, WI 53706.
Relative Stability:
No reports of change in pathogenicity. No races known.
Variants:
No information.
Storage and Retrieval:
On tetrazolium chloride agar (TZC) bacteria can be maintained
for 3 months at 4°C. In sterile distilled water bacteria
remain viable one year. To retrieve aseptically remove a single
colony from the agar or a loop full of bacteria from the water
and streak on TZC. Incubate at 20-24°C.
Inoculum Increase:
Aseptically put a single colony from TZC agar in a 125 ml Erlenmeyer
flask containing 50 ml Husain-Kelman (HK) broth. Place the flask
on a rotary shaker at 28°C for 20-24 hr.
Inoculum Preparation:
Make a 1:19 dilution of the bacterial suspension in 0.01 M phosphate
buffer.
Quantification:
Optical density at 625 nm is approximately 0.1.
Inoculum Distribution and Delivery:
Dip a fingertip in the inoculum and spread the inoculum on the
lower surface of the cotyledon. Repeat for each cotyledon inoculated.
Host:
Cucumis sativus L., cucumber.
Source of Resistance:
PIs reported to contain some resistance: 169400, 264664, 267086,
267745, 257486, and 137848.
Differentials - Controls:
Susceptible check Wisconsin SMR 18. Resistant check Gy 14.
Growth of Host:
Cucumber seeds are sown in steam sterilized coarse grade vermiculite
in wooden flats (52 x 36 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.
Tissue Age:
Inoculate cotyledons 3-4 days after emergence when cotyledons
are expanded.
Postinoculation Environment:
Incubate in the dark for 48 hr at 20 C and 100% relative humidity.
Subsequently place plants in greenhouse 24-32°C.
Disease Response:
Plants are rated as resistant, intermediate, or susceptible 6-8
days after inoculation. Resistant plants develop necrotic tan
lesions. Intermediate plants have tan lesions with a yellow green
border. Susceptible plants have elongate irregular lesions with
yellow margins.
Multiple Inoculation:
Simultaneous inoculation with anthracnose, downy mildew or bacterial
wilt. Subsequent inoculation with cucumber mosaic virus (CMV)
and powdery mildew.
Saving Host:
Resistant, intermediate, and susceptible plants can be transplanted
to steam sterilized soil.
Procedures Developed by:
Paul H. Williams and Mary J. Palmer
Department of Plant Pathology
University of Wisconsin
1630 Linden Drive
Madison, WI 53706 USA
10-07-82
Additional Tips:
For best results, test seedlings at 3-4 leaf stage. Inoculate
with mist sprayer under newer leaves. Incubate at 100% RH, 20-25°C
1 day (dark), then 100% RH, 14°C 4-6 days (lights on).
|
