Reticulate evolution in Panicum (Poaceae): the origin of tetraploid broomcorn millet, P. miliaceum.
Panicum miliaceum (broomcorn millet) is a tetraploid cereal, which was among the first domesticated crops, but is now a minor crop despite its high water use efficiency. The ancestors of this species have not been determined; we aimed to identify likely candidates within the genus, where phylogenies are poorly resolved. Nuclear and chloroplast DNA sequences from P. miliaceum and a range of diploid and tetraploid relatives were used to develop phylogenies of the diploid and tetraploid species. Chromosomal in situ hybridization with genomic DNA as a probe was used to characterize the genomes in the tetraploid P. miliaceum and a tetraploid accession of P. repens. In situ hybridization showed that half the chromosomes of P. miliaceum hybridized more strongly with labelled genomic DNA from P. capillare, and half with labelled DNA from P. repens. Genomic DNA probes differentiated two sets of 18 chromosomes in the tetraploid P. repens. Our phylogenetic data support the allotetraploid origin of P. miliaceum, with the maternal ancestor being P. capillare (or a close relative) and the other genome being shared with P. repens. Our P. repens accession was also an allotetraploid with two dissimilar but closely related genomes, the maternal genome being similar to P. sumatrense. Further collection of Panicum species, particularly from the Old World, is required. It is important to identify why the water-efficient P. miliaceum is now of minimal importance in agriculture, and it may be valuable to exploit the diversity in this species and its ancestors.
McDonald Institute for Archaeological Research, University of Cambridge, Downing Street, Cambridge CB2 3ER, UK hvh22@cam.ac.uk.
Harriet V
HV
Hunt
University of Leicester, Department of Biology, Leicester LE1 7RH, UK.
Farah
F
Badakshi
N.I. Vavilov Research Institute of Plant Industry, 42-44, Bolshaya Morskaya Street, 190000, St Petersburg, Russia.
Olga
O
Romanova
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK.
Christopher J
CJ
Howe
Department of Archaeology and Anthropology, University of Cambridge, Downing Street, Cambridge CB2 3DZ, UK.
Martin K
MK
Jones
University of Leicester, Department of Biology, Leicester LE1 7RH, UK.
J S Pat
JS
Heslop-Harrison
D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D060365:Chloroplast Proteins / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D017404:In Situ Hybridization, Fluorescence; D008969:Molecular Sequence Data; D008897:Panicum / Q000145:classification* / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D057891:Tetraploidy
D060365:Chloroplast Proteins; D010940:Plant Proteins
Crop ancestors; Panicum; domestication; genomic in situ hybridization; hybridization; polyploidy