Embryo development and time of cutting in cool temperate carrot seed crops

A survey of carrot (Daucus carota L.) seed production in south-eastern Australia between 2002 and 2004 identified the occurrence of seeds with rudimentary embryos as a major cause of poor germination. Relationships among embryo size, cutting time, seed quality and yield were studied in Nantes, Amsterdam and Kuroda cultivars grown in Tasmania during the 2004 season. Under field conditions, maximum seed size was attained 40-60 days after full bloom, but embryo development continued up to 90 days after full bloom. In five commercial seed lines, >85% germination was recorded for seeds harvested between 55 and 87 days from full bloom, after the onset of yield losses through shattering in some lines. Seed chlorophyll content was a more reliable indicator of seed maturity than seed moisture content or thermal time from peak bloom. The data obtained in this study are consistent with the theory that the occurrence of rudimentary embryos in carrot seed lots is linked to the time of cutting and indicate that the current commercial practice of harvesting at the onset of seed shatter may be inappropriate for optimum seed quality in cool temperate climates. Hence, there appears to be potential to develop a reliable indicator of carrot seed maturity based on seed chlorophyll content.