Stemphylium botryosum Wallr.
RoseMary Salter and Kenneth Leath                                      PDF Version

THIS TEST IS IN THE DEVELOPMENTAL STAGE AND SHOULD BE USED CAUTIOUSLY

Greenhouse
Container ......Flats or moveable carts
Medium .........Greenhouse planting mix
Temp/Light .....21 to 30°C; 16+ hour daylength
No. of Plants ..30 to 40 per rep; 1 to 2 rows of plants per entry per flat
No. of Reps ....3 minimum
Other ..........Promote good growth

 INOCULUM CULTURE

 Source .........Infected leaf tissue

 Storage.........Sealed cultures for several months or silica gel crystals for longer periods

Temp/Light .....Culture 21+1°C, 12 hour daylength; storage 4°C

Storage Life ...At least 4 years

Incubation .....Cultured on V-8 plates under cool white fluorescent lights at 20Mm -2sec-1 for approx. 10 days

 INOCULATION PROCEDURE

Age of Plant....4 to 6 weeks (4 to 6 trifoliates); or on regrowth

Plant Counts....Prior to inoculation

Type of Inoc .... Conidial suspension with 50 to 100 ppm Tween 20 or 1 small drop per liter

Concentration .. lx10⁴ to 5x10⁴ spores per mL

Method .........Foliar spray until runoff

INCUBATION

Location .......Moist chamber for 48 hours

Temperature.....20 to 23°C

Lighting .......Darkness is satisfactory for the initial 48 hours, then 16 hr daylength

Humidity .......100% R.H. for initial 48 hours

Age at Rating .... 5 to 8 weeks (about 10 days after inoculation)

Class descriptions are subjective and may be adjusted. Fewer classes may be used and still meet the objectives of many experiments.

1 Resistant ....Healthy, symptom-free top growth

2 Resistant ....Small (<lmm) brown or black lesions orpepper spots; no defoliation

3 Susceptible ..Larger (I to 3mm), discreet lesions with necrotic centers; usually no chlorosis or defoliation

4 Susceptible ..Large (>3mm), target-type lesions or necrotic areas; may have petiole lesions

5 Susceptible ..Lesions >3mm, chlorosis, defoliation

CHECK CULTIVARS

No checks are available for the Eastern (warm-temperature) biotype. However, Apalachee has been reported to have some resistance (3).

DISTRIBUTION AND SEVERITY OF STEMPHYLIUM LEAF SPOT

Stemphylium leaf spot; Stemphylium botryosum Wallr.
Click on the map above for a larger version. See also the KEY

 Name .....K.T. Leath

Address...USDA-ARS
U.S. Regional Pasture Res. Lab.
University Park, PA 16802

 Phone.....814-863-0945

CORRELATION TO FIELD REACTION

Greenhouse and field test results have been similar.

RACES

No races are known to exist, but two biotypes of S. botryosum have been reported; the warm-temperature (Eastern) biotype, and the cool-temperature (California) biotype.

CULTURE OPTIONS AND RANGE OF CONDITIONS

Stemphylium can appear variable in culture. Keep refrigerated for storage. The cool temperature biotype has shown variability for virulence among single spore subcultures.

PLANT GROWTH OPTIONS AND RANGE OF CONDITIONS

Plants may be started in the greenhouse or growth room. Four-week old regrowth has been inoculated successfully.

INOCULATION AND INCUBATION CONDITIONS

After inoculation, keep plants moist for a full 48 hours. Incubation can range from 1 to 2 weeks after inoculation.

HELPFUL INFORMATION

Dry plants slowly after humidity treatment. Air-dry away from direct sunlight. Selections may be reinoculated to test for escapes.

ALTERNATIVE METHODS

Selection may be possible under field conditions. Field inoculations have been done.

 1. Cowling, W.A., D.G. Gilchrist, and J.H. Graham. 1981. Biotypes of Stemphylium botryosum on alfalfa in North America. Phytopathology 71:679-684.

2. Hill, R.R., Jr., K.T. Leath, and K.E. Zeiders. 1972. Combining ability among four-clone alfalfa synthetics. Crop Sci. 12:627-630.

3. Lucas, L.T., T.H. Busbice, and D.S. Chamblee. 1973. Resistance to Stemphylium leafspot in new alfalfa variety. Plant Dis. Rep. 57 (11):946-948