VARIETAL RESISTANCE OF PLUMS TO BROWN-ROT 



By W. D. Valleau,' 



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 plurns {Primus spp.) appears to rot much more readily than that of 

 others. The rot is due to attacks of the brown-rot fungus, Sclerotinia 

 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 

 1 91 3. 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)- 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 

 sUght 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. JI. 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. 392-393- 



Journal of Agricultural Research, Vol. V, No. 9 



Dept. of Agriculture, Washington, D. C. Nov. 29, 1915 



ba (365) Minn.-7 



