Common Leaf Spot Resistance
Pseudopeziza medicaginis (Lib.) Sacc.
Kenneth Leath

PLANT CULTURE Greenhouse Container ..............    Flats or tool carts, 31x62x7.5cm deep Media ................... Not critical Temp/Light ............ 18 to 24°C; daylength not critical No. of Plants ......... 20 to 25 per replication No. of Reps ........... 4 minimum Other .................... Inoculate with Rhizobium meliloti Dang and fertilize as needed. No insecticide within 1 week of inoculation    INOCULUM CULTURE    Source .................... Infected leaves Storage.................... 6 months at 4°C; longer on silica gel    INOCULATION PROCEDURE Age of plant ............. 6 to 8 weeks Type of inoc............. Sporulating oatmeal agar plate cultures;21 to 30 days old Temp/Light .............. 19 to 23°C; dark Method ................... Cultures inverted 30 to 60 cm above plants, approximately one culture per 900cm2 of plant material, in place until 10 spores per cm2 collected on trap slides, usually 15 to 24 hours; plates repositioned periodically to increase uniformity of deposition; plants are sprayed with water after plates are removed Time of Inoc............. Usually 24 to 48 hours Conditions ............... Saturated RH; 19 to 21°C; dark    INCUBATION    Duration .................. 72 hours at 100% RH in mist chamber Location................... After initial 72 hour period, move from moist conditions to greenhouse, allow leaves to dry slowly out of direct sunlight Measurement .......... Type and size of leaf spot, usually 14 days after inoculation    RATING    1 Resistant.............. No spots 2 Resistant ............. Barely visible pepper spots, 1 mm diam or less 3 Susceptible .......... Spots >1 mm, no chlorosis 4 Susceptible .......... Spots >2 mm, chlorosis or defoliation 5 Susceptible .......... Spots >3 mm, chlorosis, defoliation, with or without fruiting structure (apothecia) in center of lesion.    CHECK CULTIVARS      Approximate Expected Resistance (%) Acceptable Range of Reaction (%) Resistant     MSA-CW3An3** 60 40-70 Ramsey** 60 40-70 Susceptible     Ranger** 30 10-35 Moapa** 0-10 0-10 DISTRIBUTION AND SEVERITY OF COMMON LEAF SPOT Common Leafspot Pseudopeziza medicaginis Lib. Sacc.(Click on the map above for a larger version.  See also the KEY)   SOURCE OF INOCULUM AND SCIENTIST WITH EXPERTISE    Name ..................... K.T. Leath Address................... USDA-ARS U.S. Regional Pasture Research Lab University Park, PA 16802 Phone ..................... 814-863-0945    CORRELATION TO FIELD REACTION Correlation to field results is good; no exceptions reported.    RACES    No races are known. CULTURE OPTIONS AND RANGE OF CONDITIONS Cultures should be sealed to prevent drying. Considerable care should be taken to prevent contamination of cultures, as P. medicaginis is a poor competitor. PLANT GROWTH OPTIONS AND RANGE OF CONDITIONS Vigorous plants are desirable. Use of lightweight potting mix best if plants are to be pulled during scoring. INOCULATION CONDITIONS AND RANGE OF CONDITIONS Temperatures from 15 to 25ƒC are acceptable. Light during infection not required. HELPFUL INFORMATION Plants may be cut back at scoring and regrowth used for different disease evaluation. Isolation of fungus can be made by suspending diseased leaves over water agar plates and transferring trapped spores to oatmeal agar. Fungus usually does not kill stems or plants. ALTERNATIVE METHODS The greenhouse method is most dependable and can be done year round. A field method has been used and described by Frosheiser(1). REFERENCES      1. Frosheiser, F.I. 1984. In Standard tests to characterize pest resistance in alfalfa. USDA Misc. Pub. No. 1434.          p. 22.      2. Leath, K.T., and R.R. Hill, Jr. 1984. In Standard tests to characterize pest resistance in alfalfa. USDA          Misc.Pub. No. 1434. p. 21.

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