INHERITANCE AND ANATOMY OF ROOT BARK AREA IN ALFALFA

The root bark of alfalfa (M. 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 6 clone diallel mating schemes were made to evaluate general combining ability (GCA) and specific combining ability (SCA) effects for root brak 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 2 tetrasomically inherited non-dominant duplicate genes RB1 and RB2) controlled bark area. Root cross-sections taken 63 cm from the root tip of the 2 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.