INRA SGAP Montpellier Domaine de Melgueil. 34130 Mauguio. France

In Spain, wild and cultivated populations of alfalfa grow in parapatry in many locations. A previous study has shown that wild and cultivated populations are weakly differentiated for nuclear molecular and biochemical markers (2,3), but strongly for morphological characteristics (1,4). Here, we report on a study of mitochondrial variability and examine the relationship between mitotypes and agro-morphological traits.

MtDNA variation was characterized through Southern blot hybridization of total DNA to mtDNA sequences, the patterns detected with the different enzyme*probe combinations were associated to define mitotypes. Six mitotypes could be defined among the 173 plants surveyed: two were detected only in Wild populations, one was specific to Medicago falcata. The three remaining were found in both wild and cultivated populations. Four to 5 mitotypes were observed in a single wild population which was extremely important compared to the overall variability detected (5).

For both vegetative and reproductive characters, analysis of variance detected significant differences between wild and cultivated populations. The cultivated one was characterized by a higher ability to grow in Spring, a larger volume, an erect growth habit, and the absence of rhizome, flowered earlier, and displayed larger inflorescences with more flowers and a better seed production. Wild type differed from one another for approximately the same characters: growth habit, number of rhizomes, earliness and seed production. Among the 4 wild populations studied, associations between phenotype and mitotype were only found in one population. This association is more likely to result from a linkage disequilibrium between cytoplasmic and nuclear genes and not from a direct involvement of cytoplasmic genes.

The occurrence of ‘cultivated’ mitotypes in wild populations and the lack of mitotype/phenotype relationship suggests that no reproductive isolation between sympatric wild and cultivated plants exists and assume that recurrent seed flow from cultivated populations is quite frequent.

References.

(2) Jenczewski E, Prosperi JM, and Ronfort J 1999a. Evidence for gene flow between wild and cultivated Medicago sativa (Leguminosae) based on allozyme markers and quantitative traits. American Journal of Botany. 86(5), 677-687.

(3) Jenczewski E, Prosperi JM, and Ronfort J 1999b. Differentiation between natural and cultivated populations of Medicago sativa (Leguminosae) from Spain: analysis with random amplified polymorphic DNA (RAPD) markers and comparison to allozymes. Molecular Ecology. 8, 1317-1330.

(4) Prosperi JM, Jenczewski E. and Ronfort J. 2000. Genetic diversity of landraces and wild populations of Medicago sativa collected in Spain (in press).

(5) Muller MH, Balsera C, Génier G, Prosperi JM, Roussel S, Santoni S, Soudière O, Tauzin D, Vabre M et Ronfort J.2000. Mitochondrial DNA diversity and phenotypic variation in wild and cultivated populations of Medicago sativa: insights into the dynamics of contact between the two related forms. Genetic Selection and Evolution (in press)