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Field and Growth Chamber Evaluations for Root-Lesion Nematode Resistance in Alfalfa¹

Large populations of root-lesion nematodes (Pratylenchus penetrans) have caused difficulties in establishing and maintaining alfalfa (Medicago sativa L.) at the North Central Experiment Station in Grand Rapids, MN. Nematicide application at the time of seeding is necessary to obtain acceptable stand establishment. Our objective was to develop methodology necessary to breed alfalfa with resistance to the root-lesion nematode. Vigorous and nonvigorous plants were selected from a severely damaged 2-year-old cultivar trial having a high population of root-lesion nematodes (about 13 cm^-3 of soil). These selections, their S₁ and half-sib progeny were evaluated for resistance in the same field. Significant variability existed among alfalfa entries for stand establishment, root weight, and shoot weight under high levels of root-lesion nematodes. The same entries were inoculated with root-lesion nematodes and observed in a growth chamber test at 25°C for a 48-day growth period. Significant variability was observed among alfalfa entries for shoot weight, root weight, fibrous root score, and numbers of nematodes in the root. Screening and evaluation methods in the growth chamber and in the field rated alfalfa entries similarly (r=0.72, 18 degrees of freedom). Both methods would be effective when breeding for resistance. Root weight appeared to be the best selection criterion for growth chamber evaluations and shoot weight was the most important characteristic for field evaluations.

Key Words: Medicago sativa L. • Alfalfa breeding • Pratylenchus penetrans

² Graduate research assistant, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota; researcfi geneticist, USDA-ARS in the Dep. of Agronomy and Plant Genetics, Univ. of Minnesota; and professor,Dep, of Plant Pathology, Univ. of Minnesota, St. Paul, MN 55108, respectively.

Received for publication August 17, 1983.