Organisation de la variabilité enzymatique des populations marocaines de luzerne (Medicago sativa L.): structures géniques et génotypiques

Abstract

Five enzymatic loci have been analyzed electrophoretically to study the genic and genotypic structures of 20 populations of alfalfa (Medicago sativa L.) from Morocco. Five different geographical origins were considered: Ziz, Drâa and Dadès (three oases in the Sahara), Demnate, and oases from mountainous regions. For comparison, three cultivars (African, Moapa, Europe) and four populations (one from Sudan, two from Spain, and one from Provence) of foreign origin were included in the study. The genic structures of the above 27 populations or cultivars allowed a good discrimination among populations and origins. The alleles with low frequency played a significant role in the discrimination and the discrimination was better when established on the basis of allelic diversity than on genotypic structures. The Flemish cultivar Europe differed from all other mediterranean material (African, Moapa, Provence, Morocco populations) but closely resembled two Spanish ecotypes from Mielga. The cultivars African and Moapa proved to be different from the Morocco populations. The latter could be divided into two different genic pools: one consisted of the Demnate populations, the other grouped populations of the Sahara and mountainous oases with no clear distinction between geographical origins. Genotypic structures based on the analyses of 30 plants from each population or cultivar did not allow to discriminate among populations. To study fixation indices and verify the panmictic equilibrium hypothesis, the number of specimen per population or cultivar had to be increased for a few populations. All the populations or cultivars analyzed showed a lack of heterozygous plants and the hypothesis of a Hardy–Weinberg equilibrium could not be accepted. Frequencies of monogenic individuals and digenic duplexes were high, but tetragenic individuals were infrequent.Key words: alfalfa, isozymes, genic structures, genotypic structures, infrequent alleles.[Journal translation]