VARIETAL RESISTANCE OF PLUMS TO BROWN-ROT 
By W. D. Valleau, 1 
Research Assistant in Fruit-Breeding Investigations, Agricultural Experiment Station 
of the University of Minnesota 
INTRODUCTION 
In the control of plant parasites a great deal of attention has recently 
been paid to the possibilities of producing resistant plants by breeding. 
In the plum-breeding plots of the Minnesota Fruit-Breeding Station at 
Excelsior it is very noticeable that the fruit of certain seedling varieties 
of plums (Prunus spp.) appears to rot much more readily than that of 
others. The rot is due to attacks of the brown-rot fungus, Sderotinia 
cinerea (Bon.) Wor. As a knowledge of the factors controlling resist¬ 
ance is necessary for intelligent effort in breeding work, a study of the 
resistance of plums to the brown-rot fungus was begun in the spring of 
1913. The following is a report of the results obtained on the nature 
of parasitism of the fungus and on varietal resistance of plums to the 
fungus. 
HISTORICAL SUMMARY 
TAXONOMIC REVIEW 
The life history of the brown-rot fungus has been rather completely 
worked out, both in this country and in Europe. Woronin (1900) 2 made 
a very complete comparative study of Monilia fructigena and M. cinerea . 
Two years later Norton (1902) discovered and described the apothecial 
stage of the American form and referred M. fructigena Persoon to 5 . fructi¬ 
gena (Pers.) Schroter. Shortly after this, Aderhold and Ruhland (1905) 
found and described a perfect stage of Sclerotinia spp. on apples, which 
they concluded to be that of M. fructigena . They also found a perfect 
stage of the apricot brown-rot fungus, M. laxa, the Monilia stage of which 
can not be distinguished morphologically from that of M. cinerea. A 
comparison of the perfect stage of the apricot fungus with the perfect 
stage of the peach fungus of this country, sent to them by Norton, 
showed differences in ascus and ascospore sizes, and these, with the 
slight differences which they found in the ability of the two species, 5. 
cinerea and 5 . laxa, to infect plum flowers, led them to the conclusion 
1 The work was carried on under direction of the Division of Plant Pathology and Botany, Department 
of Agriculture, University of Minnesota. The writer wishes to acknowledge indebtedness for suggestions, 
assistance, and criticism to the following: Dr. E. M. Freeman and Dr. E. C. Stakman, Prof. R. W. Thatcher, 
of the Division of Chemistry, and Dr. M. J. Dorsey, of the Division of Horticulture, in whose laboratory 
the work was carried on. The writer also wishes to express his appreciation of the assistance rendered by 
Mr. Ernest Dorsey in the photomicrographic work and to Dr. C. O. Rosendahl for suggestions and the use 
of apparatus. 
2 Bibliographic citations in parentheses refer to 'Literature cited,” p. 392-395. 
Vol. V, No. 9 
Nov. 29,1915 
(365) Minn.—7 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
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