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Inheritance and Anatomy of Root Bark Area in Alfalfa¹

The root bark of alfalfa (Medicago sativa L.) has several important physiological functions, including the storage of carbohydrate reserves. The objectives of this research were to determine the inheritance of alfalfa root bark area and compare the anatomical features of plants with a large and small proportion of root bark. Two sets of six clone diallel mating schemes were made to evaluate general combining ability (GCA) and specific combining ability (SCA) effects for root bark area. S₂, F₁, and F₂ families were produced from selected plants to study qualitative inheritance of root bark area. Two plants with contrasting root bark area were studied histologically to investigate their anatomical features.

General combining ability effects were highly significant and SCA effects were non-significant for root bark area in both diallel sets. Qualitative analyses indicated that two tetrasomically inherited non-dominant duplicate genes (RB₁ and RB₂) controlled bark area. Root cross-sections taken 63 cm from the root tip of the two plants used for anatomical studies revealed that 33 and 83% of the sectioned area was root bark. Plants with contrasting root bark area could be distinguished shortly after secondary growth was initiated. Alfalfa populations with contrasting root bark composition are being developed for use in physiological and plant breeding studies.

Key Words: Medicago sativa L. • Root anatomy • Taproot • Inheritance

² Assistant professor, Dep. of Agronomy, Colorado State Univ. Fort Collins, CO 80523 (formerly graduate research assistant, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota) and research geneticist, USDA-ARS, in the Dep. of Agronomy and Plant Genetics, Univ. of Minnesota) and research geneticist, USDA-ARS, in the Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108.

Received for publication March 30, 1981.