Low-copy nuclear gene and McGISH resolves polyploid history of Eleusine coracana and morphological character evolution in Eleusine

Eleusine coracana (L.) Gaertn. (finger millet) is the third most important cereal crop in semiarid regions of the world, but the degree of relatedness of finger millet with other species in the genus is unverified. The study of morphological character evolution in Eleusine Gaertn. has lagged behind due to lack of relevant research. Polyploidy history of finger millet was analyzed using waxy sequences together with multicolor genomic in situ hybridization (McGISH). In the waxy phylogenetic tree, sequences of 2 homoeologous loci were isolated from 3 tetraploids: Eleusine coracana, E. africana Kenn.-O'Byrne, and E. kigeziensis S. M. Phillips. The 3 species grouped with E. indica (L.) Gaertn. and E. tristachya (Lam.) Lam. in the W-A1 clade (A-type sequences). The W-B1 and W-B2 clades (B-type sequences) were composed of the E. africana-E. coracana and the E. jaegeri Pilg.-E. kigeziensis subclades, respectively. Eleusine indica probes produced stronger signals of relative intensities across A-genome chromosomes of finger millet than did the E. tristachya probes. The waxy phylogenetic tree and McGISH evidence support E. indica and E. tristachya (or its extinct sister or ancestor) as the primary and secondary A-genome parents for finger millet, respectively. The most likely scenario is that the B-genome donor is extinct. Five morphological characters were found to be homoplasious by optimization on waxy gene tree.