The survey of enzyme polymorphism in West African pearl millet cultivars reported by Tostain et al. 1987 has been extended to include populations from other regions of Africa and from India. The eight enzyme systems studied included: alcohol dehydrogenase, β-esterase, catalase, phosphoglucoisomerase, phosphoglucomutase, 6-phosphogluconate dehydrogenase, glutamate oxaloacetate transaminase, and malate dehydrogenase. One-hundred-ninety-nine populations of millet were analyzed, including 74 populations studied earlier. No new enzyme diversity was observed. Intrapopulation diversity ranged from 70%-90% of the total diversity, depending on their regions of origin. Four principal groups were distinguished in the following decreasing order of diversity: early-maturing cultivars from West and East Africa, late - maturing cultivars from West and East Africa, cultivars from India, and cultivars from southern Africa. The early-maturing cultivars were distributed between two principal focal points from East Africa in the East to Mali in the West. In the center were found millets from Niger which were most diverse. Indian and southern African cultivars were distinct, with the former appearing relatively similar to those of Niger, and the latter somewhat similar to late-maturing cultivars from West Africa, a diverse group that included late-maturing cultivars from East Africa. Based on the results obtained, an evolutionary hypothesis proposed here includes: multiple domestications in the Sahel, creation of early-maturing cultivars and their migration eastwards to India plus a southwards migration to Sudanian zone, and creation of late-maturing cultivars and their migration simultaneously westwards, eastwards, and southwards to southern 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.

No abstract

The compatibility between gynoecia of different penicillarian millets (Pennisetum glaucum and P purpureum) and pollens from some other Poaceae was evaluated in order to determine whether different penicillarian pistils showed the same pistil-pollen interactions with a same non-penicillarian pollen and to determine whether compatibility was dependent on the genetic divergence or the degree of sympatric evolution of the mating partners . Ten pearl millet lines (P glaucum subsp . glaucum), six wild pearl millet accessions (P glaucum subsp . monodii ) and one P purpureum accession were pollinated with five other Pennisetum species : P pedicellatum, P polystachyon, P schweinfurthii, P squamulatum, P ramosum, and with three species from other genera : Cenchrus ciliaris, Panicum maximum and Zea mays . Each male species was represented by a unique accession . Pollen grain germination on the stigmata and pollen tube growth in the gynoecia were monitored by means of fluorescence microscopy after aniline blue staining . Significant compatibility differences were observed between a given pollen and gynoecia from different P glaucum accessions . But there was no evidence of compatibility differences between the three female taxonomic groups . The eight pollen parents can be classified into three groups according to their mean degree of compatibility with the different penicillarian gynoecia . P ramosum, P schweinfurthii and P squamulatum showed a high compatibility : more than 50% of penicillarian gynoecia had pollen tubes at the micropyle, six hours after pollination . Zea mays, Cenchrus ciliaris and Panicum maximum showed a low compatibility : pollen tubes were arrested in the style . P pedicellatum and P polystachyon showed nil compatibility : few pollen grains germinated on the stigmata and very rare tubes reached the entry of the style, where they stopped . It must be noted that such a strong gametic barrier has been observed only with pollinator species sympatric to pearl millet .

The occurrence of seed malformation in association with reduced thousand grain weight and germination ability has been observed in crosses between cultivated female plants and wild male plants. A survey of 16 cultivated accessions (P. glaucum subsp, glaucum) and 11 wild accessions (P. glaucum subsp, monodii) ranging over the whole species diversity showed this postzygotic incompatibility was general, but its intensity varied greatly with the cultivated female accession used and very little with the wild male parent origin. About 15 % of the 123 cultivated x wild crosses observed gave normal seeds. Seed malformation has never been observed in crosses between cultivated accessions and appeared independent of genetic distances between the parents. The reciprocal crosses between wild female plants and cultivated male plants gave normal-looking seeds with good germination but consistently reduced thousand grain weight. Both seed malformation and seed small size are an expression of a genetic imbalance. These slight reproductive barriers seem to have been built during the domestication process.