Angular Leafspot (Pseudomonas syringae pv. lachrymans)
Pseudomonas syringae pv. lachrymans (Smith and Bryan) Carsner.
On tetrazolium chloride agar (TZC) magenta bacterial colonies are formed.
Gram negative, non-spore forming rods (0.8 x 1-2 microns); motile with 1-5 polar flagella.
P. H. Williams; Plant Pathology Department; University of Wisconsin; 1630 Linden Drive; Madison, WI 53706.
No reports of change in pathogenicity. No races known.
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.
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.
Make a 1:19 dilution of the bacterial suspension in 0.01 M phosphate buffer.
Optical density at 625 nm is approximately 0.1.
Inoculum Distribution and Delivery:
Dip a gloved fingertip into the inoculum and spread the inoculum on the lower surface of the cotyledon. Repeat for each cotyledon inoculated.
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.
Inoculate cotyledons 3-4 days after emergence when cotyledons are expanded.
Incubate in the dark for 48 hr at 20 C and 100% relative humidity. Subsequently place plants in greenhouse 24-32°C.
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.
Simultaneous inoculation with anthracnose, downy mildew or bacterial wilt. Subsequent inoculation with cucumber mosaic virus (CMV) and powdery mildew.
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
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).