A Comparison of Leek (Allium porrum) and Onion (Allium cepa) Seed Development

Leek and onion seed dry weight increased exponentially for the first 31 days after flowering (DAF) but thereafter the increase in dry weight was slower. Before maximum seed dry weight was reached at 45 DAF in onion and 59 to 66 DAF in leek, seed moisture content, seed oxygen uptake and conductivity of the seed steep water fell from initially high levels. Although some seeds germinated 31 DAF in both species, full germination in both was not reached until 66–80 DAF. Tolerance of the seed to artificial drying immediately after harvesting occurred 45 DAF in onion and 74 DAF in leek. Free nuclear division continued in the endosperm until 17–22 DAF in onion and until 31–35 DAF in leek but it was not until 45 DAF in onion and 66 DAF in leek that the embryo and endosperm filled the cavity formed by the pericarp. After formation of cell walls in the endosperm the pattern of change in cell number in both species was similar. The shrunken appearance of the seed coat in leek, which occurred early in seed development, was associated with the period of free nuclear division in the endosperm and, in addition, the pericarp was thinner than in onion. There was no evidence that the shrunken seed coat early in development was associated with self as opposed to open-pollination.