The effect of plant density on seed yield and quality of carrot (Daucus carota L.)

The hypothesis that by increasing carrot (Daucus carota) plant density the contribution to seed yield by the primary umbels would increase, and that therefore both seed yield and seed quality would increase, was examined in two experiments in different years in Canterbury. A radial trial design provided plant densities from 2 to 84 plants/m2 and from 4 to 100 plants/m2 in experiments one and two respectively. Seed yield increased with increasing plant density in both experiments, and at the highest density the primary umbels contributed 90% (experiment one) and 60% (experiment two) of the seed yield. In both experiments seeds from the primary umbels had a greater thousand seed weight and higher germination than those from the other order umbels, and for the second experiment they also had higher seed vigour. The quality of seeds from the primary umbels was consistently higher than that of seeds from the secondary umbels across all plant densities, and for the latter, both germination and seed vigour declined as plant density increased. These results therefore support the hypothesis, and densities higher than the 20 plants/m2 currently used commercially have the potential to increase both seed yield and quality. Keywords: seed production, primary umbels, germination, vigour, plants/m2