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Published in Crop Sci 13:714-717 (1973)
© 1973 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Inheritance of Phytophthora Root Rot Resistance in Alfalfa1

Nancy Shyh-Jane Lu2, D. K. Barnes3 and F. I. Frosheiser3

The inheritance of Phytophthora root rot resistance was determined in alfalfa (Medicago sativa L.) for five clones from the variety ‘Lahontan’ and six clones from ‘Vernal’ and Vernal-type varieties. A heterozygote-diallel crossing scheme was used as the basis for genetic analysis. Parent clones were selfed, intercrossed, and testcrossed to two susceptible clones. Degree of resistance was determined by type of root-rot lesion. Susceptibility appeared to be conditioned by one tetrasomic gene, Pm, with incomplete dominance. The nulliplex condition produced highly resistant plants. The simplex condition produced a moderate degree of resistance. Duplex, triplex, and quadruplex plants were increasingly more susceptible. Resistance in the Lanhontan and Vernal-type varieties appeared to be controlled by the same gene.

Key Words: Phytophthora megasperma Drechs. • Medicago sativa L. • Disease • Polyploid genetics • Genetic analysis method

1 Joint contribution from Minnesota Agricultural Experiment Station and the Agricultural Research Service, USDA. Paper No. 7897, Scientific Journal Series, Minnesota Agricultural Experiment Station. Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the M.S. degree.

2 Former Graduate Student, Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55101.

3 Research Geneticist and Research Plant Pathologist, ARS, USDA, in the Department of Agronomy and Plant Genetics and in the Department of Plant Pathology, respectively, University of Minnesota, St. Paul, MN 55101.

Received for publication June 15, 1973.




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