Enzyme diversity in pearl millet (Pennisetum glaucum) : 1. West Africa.

Polymorphism in twelve genes coding for eight enzymes in pearl millet (Pennisetum glaucum (L.) R. Br.): alcohol dehydrogenases (ADH), catalases (CAT), β-esterases (EST), glutamate oxaloacetate transaminases (GOT), malate dehydrogenases (MDH), 6-Phosphogluconate dehydrogenases (PGD), phosphoglucoisomerases (PGI) and phosphoglucomutases (PGM), was observed by electrophoresis on 74 cultivated samples and 8 wild samples from West Africa. Six genes: Est A, Adh A, Pgm A, Cat A, Pgi A, Pgd A contain 95% of the total variation. Principal component analyses and discriminant analyses of the 82 samples described by 46 allelic frequencies showed an almost complete separation into 3 groups: wilds, early maturing cultivars and late maturing cultivars. The early group has the highest enzyme diversity, with cultivated millets from Niger showing the most diversity. The high diversity of the early group and its extensive divergence from West-African wild millets suggest, firstly, the existence, elsewhere in Africa of other enzymatically different sources of wild millet, and secondly, the occurrence, prehistorically, of several different domestications. The late group of cultivars has the lowest variability and a relatively low coefficient of differentiation. This relatively homogeneous enzyme structure does not seem to be associated to ecology. A hypothesis is advanced suggesting that West African late-cultivars were derived from a common cultivated early complex. This complex must have been distributed across the Sudanian zone and must have been later sumitted to modifications by limited gene flow with local early maturing cultivars.