March, 1991                                                                                                           PDF Version

Anthracnose Resistance
Colletotrichum trifolii Bain & Essary
Nichole O'Neill

PLANT CULTURE

Growth Chamber
Container.................. 10-cm plastic pots or flats
Medium....................Potting soil mix
Temp/Light................23C; 16+ hour daylength
No. of Plants.............50 per replication
No. of Reps...............14 minimum
Other........................Control insects and fertilize as necessary
  
INOCULUM CULTURE
  
Source ....................Infected stem tissue
Storage.....................Soil or silica gel (7)
Temperature..............4C
Storage Life ..............Up to several years
  
INOCULATION PROCEDURE
  
Age of Plant..............7-14 days (take stand counts at 7 days)
Type of Inoc..............Spore suspension with 2 drops Tween per L distilled water, taken from 7 day old cultures incubated at 23C on half strength oatmeal agar
Concentration ...........2X106 spores per mL
Method ....................Spray to runoff, approx. 3 mL per pot or 5 to 10 mL per flat; place in mist chamber to maintain 100% R.H. for 48 hours 23C
  
INCUBATION
  
Location....................Growth room or greenhouse at 23C
Age at Rating ...........10 to 14 days after inoculation
  
RATING

Resistance is assessed as a percent of the stand surviving 10 to 14 days after inoculation.
CHECK CULTIVARS (Race 1)
  Approximate Expected Resistance (%) Acceptable Range of Reaction (%)
Resistant    
Arc** 65-70 45-80
Saranac AR** 45 40-60
Susceptible    
Saranac** 1 0-5

Values for resistant standards are percent survivors.

DISTRIBUTION AND SEVERITY OF
      ANTHRACNOSE (Race 1)

Anthracnose, Collelotrichum trifolii Bain & Essary (Click on the map for a larger version; see the key here).

SOURCE OF INOCULUM

Name .......... Nichole O'Neill
Address ...... USDA, ARS
Soybean and Alfalfa Research
B-001
Beltsville, MD 20705
Phone.......... 301 -344-3331
  
SCIENTISTS WITH EXPERTISE
  
Name .......... Nichole O'Neill
Address ...... USDA, ARS
Soybean and Alfalfa Research
B-001
Beltsville, MD 20705
Phone ......... 301-344-3331
  
Name .......... Craig Grau
Address ...... University of Wisconsin
1630 Linden Drive
Madison, WI 53706
Phone ......... 608-262-6289
CORRELATION TO FIELD REACTION


Cultivars occasionally appear more resistant in the field than indicated by seedling tests, but generally, good 
correla tions are observed between greenhouse and field tests.

RACES

Race 2 of Colletotrichum trifolii was discovered in a limited area in 1978 but is not considered serious. Saranac AR is resistant to both races, Arc is resistant to race 1 and susceptible to race 2, and Saranac is susceptible to both. Saranac AR is approximately 45% resistant to race 2.
 
CULTURE OPTIONS AND RANGE OF CONDITIONS

Stock cultures should be maintained because cultures can lose virulence after several transfers.
 
HELPFUL INFORMATION

Using mixtures of isolates will minimize error due to differences in virulence among isolates.

ALTERNATIVE METHODS

Succulent stems of mature plants can be tested for suscepti bility by needle inoculation (5). Individual seedlings can be evaluated by cotyledon assay (1). A very young seedling test also gives good results very quickly if only percent resistance is required (3).

REFERENCES

1. Cucuzza, J.D., and J. Kao. 1986. In vitro assay of excised cotyledons of alfalfa (Medicago sativa) to screen for resistance to Colletotrichum trifolii. Plant Disease 70:111- 115.

2. Elgin, J.H., Jr., and S.A. Ostazeski. 1982. Evaluation of selected alfalfa cultivars and related Medicago species for resistance to race 1 and race 2 anthracnose. Crop Sci. 22:39-42.

3. Morrison, R.H. 1977. A seedling test for evaluating alfalfa for resistance to anthracnose. Pl. Dis. Reporter. 61:35-37.

4. O'Neill, N.R., Elgin, J.H., Jr. and C.J. Baker. 1989. Characterization of induced resistance to anthracnose in alfalfa by races, isolates, and species of Colletotrichum. Phytopathology 79:750-756.

5. Ostazeski, S.A., and Elgin, J.H., Jr. 1982. Use of hypodermic inoculations of alfalfa for identifying host reactions and races of Colletotrichum trifolii. Crop Sci. 22:545-546

6. Ostazeski, S.A., and Elgin, J.H., Jr. 1984. Standard tests to characterize pest resistance in alfalfa cultivars. U.S. Agric. Res. Serv. Misc. Publ. 1434. 38 pp.

7. Smith, D. 1984. Maintenance of fungi. Pp.87-88. In Maintenance of microorganisms, a manual of laboratory methods. Ed. by Kirsop, B.E. and J.J.S. Snell. Academic Press.

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