Heritability of Crown Traits in Alfalfa

The crown is the transitional structure connecting the shoots and roots of alfalfa ( Medicago sativa L.) and is associated with the persistence and productivity of the crop. Information on the inheritance of alfalfa crown morpbological traits could facilitate the genetic modification of crown morphology. Our objectives were to estimate heritability of five crown traits and to determine the effect of plant spacing and location on the expression of crown traits. Progenies from design II matings and diallels were evaluated at two Minnesota locations. In October 1991, plants were dug and evaluated for crown depth, crown width, number of crown stems, crown stem width, and number of crown buds. Plant‐spacing effects were determined by evaluating single plants at the ends of the plot separately from plants in the middle. Progenies responded similarly to the extra growing space at the ends of the plots. General combining ability (GCA) effects were important for determining heritability for crown stem width, while both GCA and specific combining ability (SAC) were important for crown width and number of crown stems. Heritability estimates for these crown traits ranged from 22 to 80%. No or few genetic effects were found for number of crown buds and crown depth. Results suggest that selection programs for crown stem width and number of crown stems with uniform plant spacing in one location would be successful. Selection programs for crown width may have limited success, and selection for number of crown buds and crown depth would not be effective.