Get to Know Our Early Alumni: Harold H. Flor

April 29, 2020

The Graduating Class of 1924

The Graduating Class of 1924:  Left to Right: Helen Hart, M.A., L.W. Melancher, M.S., R. U. Colter, M.S., H. H. Flor, M.S. R. M. Nelson, M.S., D. L. Bailey, Ph.D.


Spring semester is a time to celebrate our graduates!  And since 1907, the Department of Plant Pathology has trained nearly 1,000 graduate students!  Many of our alumni have gone on to contribute significantly to the field of plant pathology, establishing highly productive and impactful careers.  Among them was Harold H. Flor (M.S., 1924; Ph.D., 1929).  Flor is best remembered for his groundbreaking “Gene-for-Gene Hypothesis”, a core tenet of plant pathology that is taught to this day.  As a USDA scientist in North Dakota, Flor studied the impact of the flax rust pathogen (Melampsora lini) on flax (Linum usitatissimum), documenting race specificity.  Flor was among the first to recognize that pathogen races correspond to variants of genetic resistance in the host.  His model predicts that for every resistance gene in a host plant, there exists a corresponding virulence gene in the pathogen, with the outcome (disease or no disease) dictated by the distribution of host and pathogen genes in the landscape.  Today, we understand this model at a molecular level, with numerous cloned host resistance genes and numerous cloned pathogen effector genes.  While many exceptions and variations in host-microbe interactions exist, the core concepts of the Gene-for-Gene Hypothesis underpin much of our functional understanding today and the model has contributed to the management of many pathogens of agricultural importance.  In honor of his contributions to the field of plant pathology, Harold Flor was named a recipient of the E.C. Stakman Award in 1967.  Flor was also named a Fellow of the American Phytopathological Society in 1965, served as President in 1967, and received the APS Award of Distinction in 1980.  A frequent visitor to his alma mater throughout his professional life, Flor was a famed player of “kitten ball”, as our annual softball game was once called.