EXPERIMENTAL-STUDY OF GENE FLOW BETWEEN WILD AND CULTIVATED PENNISETUM-GLAUCUM

Under natural conditions, wild and cultivated pearl millet, Pennisetum glaucum (L.) R.Br., exchanged genes for millenia and, nevertheless, m aintain high morphological differentiation. Under experimental conditi ons in the Sahel, hybridization between wild and cultivated pearl mill et was measured using isozymic markers and interpreted in relation to the phenology of the plants. Gene flows were asymmetric, engendering 8 % of hybrids in the progeny of the wild phenotype, 45% in that of the cultivated phenotype, and 39% in that of the intermediate ''shibra'' p henotype; these last two phenotypes constitute the sample of cultivate d pearl miller. The proportion of hybrids in the progeny of the wild s ample was time dependent during the flowering phase of cultivated pear l millet. The proportion of hybrids produced by the cultivated pearl m illet was not time dependent. In the seeds produced by the cultivated phenotype along its reproductive phase, the proportion of viable seeds was negatively correlated with the frequency of hybrids. Likewise, th e speed of germination of seeds produced by the cultivated or the shib ra phenotypes was negatively correlated with the frequency of the hybr ids that they contained. The effects of balancing among genetic interm ixing, isolation and reproduction barriers, and differential anthropic and natural selection pressures are discussed to better understand th e evolution and the maintenance of the polymorphism of Pennisetum glau cum.