EFFECTS OF PRODUCTION FACTORS ON GERMINATION RESPONSES OF CARROT SEEDS TO TEMPERATURE AND OXYGEN

Various sources of germination heterogeneity of carrot (Daucus carota L.) seeds were investigated: germination conditions (temperature, oxygen tension), size of seeds, position of the umbels on the mother plants, and pollination conditions of male-sterile plants in hybrid seed production. All seeds tested germinated over a large range of temperatures (5-35 degrees C). However, low temperatures (5-10 degrees C) and temperatures above 30 degrees C reduced germination. Seeds were also sensitive to oxygen deprivation, but their sensitivity to hypoxia depended on the cultivar. The germination responses of seeds to temperature and oxygen depended on their size, particularly at sub- and supra-optimal temperatures. The largest seeds (1.8-2.1 mm) of commercial lots usually germinated better at 5 degrees C and were more sensitive to oxygen deprivation than the smallest ones (1.2-1.8 mm). Experiments performed with open pollinated plants showed that seeds produced by umbels of first and second orders germinated faster and at higher percentages than those collected on third-order umbels. Evidence for the involvement of pollination conditions in the germination quality of carrot seeds was given by pollination by honey bees of male-sterile plants cultivated at various distances from the pollen donors. The longer the distance of the mother plants from the pollinating plants, the lower the seed yield, the heavier the mean seed weight, the more difficult the germination of seeds, and the higher their sensitivity to oxygen deprivation.