Document Type

Thesis - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School



In the North Central Region, Phoma herbarum var. medicaginis Rab. And Cercospora zebrine Pass. Cause more damage to alfalfa than other components of the blackstem complex. The objectives of this investigation were: (1) to determine the ecological relationship between the two pathogens, and (2) to obtain some information regarding the genetic systems in alfalfa which condition the reaction to the two fungi. A diallel set was established from eight diploid, heterozygous clones of alfalfa. One P. herbarum and two C. zebrine isolates were used. Three leaves from each plant were excised, placed in a Syracuse watch0glass, sprayed with the inoculum, floated on a 2 percent sugar solution and incubated at 68-72 F in the dark for six days. Since it was difficult to distinguish between the types of lesions produced by each pathogen parasitizing the same tissue, the gross infection was used as a basis to determine the relationship between the two fungi. The magnitude in level of infection produced by the various treatments suggested that the relationship was not neutral, and a certain type of interaction between the two pathogens did exist. Analysis of diallel crosses indicated that dominant and recessive genes in the host plants were involved in controlling resistance to both pathogens. IN addition to dominance, epistatic gene action seemed to play a major role in controlling the reaction of the host plants to both pathogens. Is was concluded that concurrent selection for resistance to both fungi is feasible.

Library of Congress Subject Headings

Alfalfa -- Diseases and pests


Includes bibliographical references




South Dakota State University