THE RELATIONSHIP BETWEEN FALL DORMANCY AND GERMPLASM SOURCE IN NORTH-AMERICAN ALFALFA CULTIVARS

Most of the genetic diversity of North American alfalfa cultivars has been accounted for by nine germplasm sources listed in descending orde r of winter hardiness as follows: Medicago sativa ssp. falcata, Ladak, M, sativa ssp. xvaria, Turkistan, Flemish, Chilean, Peruvian, Indian and African. In most instances, the breeder assigns a fall dormancy sc ore and the relative proportions of each of the nine germplasm source for each cultivar at registration. The fall dormancy score (1 = dorman t to 9 = non-dormant), determined by measuring plant height in October after harvest in early September, is used to indicate cultivar adapta tion for different regions. This study examines the relationship betwe en plasm composition and plant height, the equivalence of fall dormanc y. The signs on the partial regression coefficients of a multiple regr ession analysis of plant height on the proportional content of the nin e sources of germplasm showed that the fall dormancy fell essentially into two classes, namely, a dormant category, comprising cultivars con taining a large contribution of Falcata and Ladak, and a non-dormant c ategory, in which Indian and African germplasm predominate. This does not necessarily preclude the influence of any of the other germplasm s ources on fall dormancy, since they represent a rich source of diversi ty. However, nine distinct classes were not recognisable, perhaps beca use of the lack of an exact equivalence between fall dormancy class an d plant height of the fall regrowth. Since these observations have not been derived in a common nursery, the latitude and latitude x cultiva r effects have been disregarded. These limitations should be recognize d when using the currently assigned fall dormancy ratings to predict c ultivar adaptation.