Differentiating M. sativa ssp. sativa and ssp. falcata accessions
using molecular markers
Patricia M. Cazcarro and E. Charles Brummer
Iowa State University, Ames, IA 50011
Cultivated alfalfa, Medicago sativa ssp. sativa, grown in most regions of the
world owes few of its agronomic qualities to ssp. falcata. However, ssp.
falcata possesses desirable cold, drought, and grazing tolerances (Oakley and
Garver, 1917). Further, significant heterosis has been expressed in some
sativa x falcata crosses (Wilsie, 1958; Sriwatanapongse and Wilsie, 1968).
Several studies have shown falcata germplasm to be genetically distinct from
sativa (Kidwell et al., 1994; Crochemore et al., 1996; Ghérardi et al.,
1998). The objective of this experiment is to identify falcata accessions
most distinct from sativa germplasm to guide development of improved falcata
populations with complementary allelic structures to Midwestern U.S. breeding
populations. We are examining putatively native accessions to study the
geographical distribution of alfalfa diversity to guide germplasm enhancement
efforts. The native ranges of falcata and sativa overlap to a considerable
extent, but allopatric regions also occur: solely falcata grows in northern
regions of Russia, Scandinavia, Mongolia, and China while sativa is the only
subspecies in southern Europe, the Middle East, and Northern Africa (Ivanov,
1980; Lesins and Lesins, 1979). Ten accessions of each subspecies were
selected from regions of coexistence and ten sativa and nine falcata
accessions were selected from allopatric habitats, forming four
"superpopulations" of sympatric sativa, sympatric falcata, allopatric sativa,
and allopatric falcata. In addition to these 39, two M. prostrata accessions
are included as an outgroup. Several types of molecular markers (RAPD, SSR,
and RFLP) are being screened against two individuals of each accession.
Genetic distances, calculated from the marker data, are used to cluster the
various accessions. We are less interested in within population variation
for this experiment, but rather in how the variation is structured over large
geographical zones. Several questions will be discussed: Do sympatric and
allopatric accessions form distinct clusters within each subspecies? Do
sympatric accessions of each subspecies resemble each other more than they
resemble their respective allopatric accessions? Though alfalfa populations
contain considerable genetic diversity, significant differentiation among
populations has also been reported (e.g Brummer et at., 1991). To get a
clear picture of allelic differentiation among these accessions, a large
number of polymorphic bands need to be screened. Results will be discussed
relative to the usefulness of this method for detecting potentially useful
germplasm.
References
Brummer, E.C., et al. 1991. Theor. Appl. Gen. 83:89-96.
Crochemore, M-L. et al. 1996. Agronomie 16:421-432.
Ghérardi, M. et al. 1998. Theor. Appl. Genet. 96:406-412.
Kidwell, K.K., et al. 1994. Crop Sci. 34:230-236.
Ivanov, A.I. 1988. Alfalfa. Translated by A.K. Dhote. Amerind Pub. Co.
Pvt. Ltd., New Delhi.
Lesins, K. and I. Lesins. 1979. Genus Medicago (Leguminosae): A taxogenetic
study. Kluwer, Dordrecht, The Netherlands.
Oakley, R.A. and S. Garver. 1917. USDA Bull. 428. U.S. Gov. Print. Office,
Washington, D.C. 70 pp.
Sriwatanapongse, S. and C. P. Wilsie. 1968. Crop Sci. 8:465-466.
Wilsie, C.P. 1958. 16th Alfalfa Imp. Conf., Ithaca, NY. p. 21-33.
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