Gametophytic competition as influencing gene flow between wild and cultivated forms of pearl millet (Pennisetum typhoides)

Intergametophytic competitions with prepotency of autopollen have been previously described in some cultivated lines of pearl millet (Pennisetum typhoides (Burm.) Stapf &Hubb.). This paper reports the analysis of intergametophytic competitions between pollen from wild and cultivated plants on stigmas of both wild and cultivated plants. Three inbred lines (two cultivated and one wild) and two land races (one cultivated and one wild) were used, each of them as pollen donors as well as plant receptors. These populations represent in some instances allopatric and sympatric evolutionary situations between wild and cultivated forms. Deviations from the equiprobability of gamete encounters for almost all progeny are clearly demonstrated and reveal a large amount of male gametophytic fitness variability in land-race populations. There is no marked hierarchy between pollen sources for their competitive ability, but taking into account the pollen-pistil interactions, preferential wild-wild and cultivated-cultivated gamete associations are noticeable. Thus, pollen competitions establish a fine reproductive limit between allopatric populations as well as between wild and cultivated sympatric populations. This soft reproductive "barrier" controls the gene flow between adjacent populations and could explain the success of pearl millet domestication, allowing the wild and cultivated types to keep their phenotypic integrity despite the gene flow.Key words: pearl millet, intergametophytic competitions, gene flow, domestication.