Enzyme diversity in pearl millet (Pennisetum glaucum L.)

Abstract

One hundred and eighty-eight accessions of wild millet, Pennisetum glaucum L. subsp. monodii [syn. P. violaceum (Lam.). L. Rich], representative of the species' geographic distribution, were studied by electrophoresis for polymorphism in eight enzymes: alcohol dehydrogenase (ADH), catalase (CAT), β-esterase (EST), glutamate oxalo acetate transaminase (GOT), malate dehydrogenase (MDH), 6-phosphogluconate dehydrogenase (PGD), phosphoglucoisomerase (PGI), and phosphoglucomutase (PGM). The frequencies of 46 alleles at 12 loci controlling the eight enzyme systems were analyzed by principal component analysis and confirmed by discriminant analysis. A pattern of enzymic variation corresponding to geographical zonation in five groups was discerned: Western Group (Senegal, Mauritania, western Mali), Central Group (eastern Mali and Niger), Aïr Group (Aïr Mountains of Niger), West Chad Group, and Darfur Group (encompassing eastern Chad and western Sudan). Nei's diversities varied from 0.161±0.010 in the Aïr Group to 0.243±0.004 in the Central Group. Comparison with Sahelian cultivated millet showed clear-cut divergence between populations of wild and cultivated millet in each region, even where they grow sympatrically. Cultivated and wild millet equal total Nei's diversity, but their locus by locus diversities are different. Wild millet, particularly populations growing far from the crop (allopatric wild accessions), is the most diverse for Got A, Pgd A, and Cat A, whereas cultivated millets are the most diverse for Pgm A and Pgi A. Allopatric wild millet populations are more divergent from cultivated populations than sympatric wild millets. The cultivated millets closest to wild millet were from western Mali, with the most remote in the Darfur Group. Based on these results, the process of pearl millet domestication is discussed.