Bimodal phenotypic structure of two wild pearl millet samples collected in an agricultural area

On the basis of botanical and ecological characters, pearl millet species have been separated into three subspecies:Pennisetum americanum subsp. americanum, cultivated form,P. americanum subsp. monodii, wild form andP. americanum subsp. stenostachyum, weedy form. It has been shown, by enzyme electrophoresis, that these three forms could be discriminated between by their respective enzyme composition even in agricultural areas where they co-exist. Morphological and enzyme analyses of two seed samples collected from monodii plants growing in an agricultural area has shown that the monodii form is not isolated from cultivated plants in its reproduction. The proportion of seeds descending from a cultivated pollen is estimated respectively at 31% and 19%. However, Brunken's typology is corroborated: both samples comprise the two distinct groups of monodii and stenostachyum. This dichotomy is due to the pollen population structure having generated the analysed seeds. Detailedin situ observations on sympatric wild and cultivated populations are essential to explain the absence of recombinant monodii × cultivated pollens and the preservation of monodii millets in spite of their invasion by cultivated pollens.