Foxtail (Setaria spp.) Seed Germination Process

 

Vivipary and foxtail seed germination-dormancy phenotype heterogeneity
Schematic diagram of germination states of giant foxtail caryopses 
Caryopsis germination states
Coleoptile emergence
The seed hull germination lid


Vivipary and foxtail seed germination-dormancy phenotype heterogeneity.  The first good evidence we had that foxtail parent plants, individual panicles, shed seed with different germination requirements came when we observed new seed germinating (vivipary, pre-harvest sprouting) in the pollen excluding bags we placed over seedheads to harvest all the seed (below).  The dogma was that parent foxtail plants shed seed that was all uniformly dormant.  This has proved to be quite wrong.

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Schematic diagram of germination states of giant foxtail caryopses


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Caryopsis germination states.

A giant foxtail (Setaria faberii) caryopsis with a slightly swollen embryo forcing cracks longitudinally in the caryopsis coat overlying the middle of the embryo.  Notice the cute residual stigma still remaining from fertilization (left).  In our research on seed germination we refer to this as the S1R1 germination state (first shoot, first root).

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Another, more advanced, S1R1 caryopsis germination state.

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S1R2 caryopsis germination state (first shoot; second root).  Note the appearance of the trichomes along the edges of the coleorhiza, diagnostic of R2.

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A S2R3 (second shoot; third root) germination state of the giant foxtail (Setaria faberii) caryopsis.  The coleoptile is enlarged, elongated and curving slightly upward (top right), while the coleorhiza has completely emerged (center left), as has the trichome hairs (center left) and the radicle (lower left).

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A S2R3 (second shoot; third root) germination state of the giant foxtail (Setaria faberii) caryopsis.  The coleoptile is enlarged, elongated and curving slightly upward (left center), while the coleorhiza has completely emerged (center right), as has the trichome hairs (center right) and the radicle (upper right).

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Coleoptile emergence.

The emergence of the coleoptile (center; the shoot) from the distal end of the seed, between the lemma (top) and the palea (bottom), the two parts of the seed hull.  The coleoptile is in the S2 germination state.

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First true leaf (cotyledon) (left) emerging from the end of the coleoptile (right).

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The seed hull germination lid.

View of the basal end of the giant foxtail (Setaria faberii) seed. The germination lid (top center) has allowed the coleorhiza (root) within to slightly protrude from the lemma (top) portion of the hull.  The palea is the hull bottom. Notice the pedicel-vascular connection juncture scar at the basal end of the seed (center; the placental pore entrance).

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Side view of the germination lid opening slightly to allow the slightly protruded coleorhiza to emerge from within the lemma portion of the seed hull.

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©jdekker-2003