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, oxyg en tension), size of seeds, position of the umbels on the mother plant s, and pollination conditions of male-sterile plants in hybrid seed pr oduction. All seeds tested germinated over a large range of temperatur es (5-35 degrees C). However, low temperatures (5-10 degrees C) and te mperatures above 30 degrees C reduced germination. Seeds were also sen sitive to oxygen deprivation, but their sensitivity to hypoxia depende d on the cultivar. The germination responses of seeds to temperature a nd oxygen depended on their size, particularly at sub- and supra-optim al temperatures. The largest seeds (1.8-2.1 mm) of commercial lots usu ally germinated better at 5 degrees C and were more sensitive to oxyge n deprivation than the smallest ones (1.2-1.8 mm). Experiments perform ed with open pollinated plants showed that seeds produced by umbels of first and second orders germinated faster and at higher percentages t han those collected on third-order umbels. Evidence for the involvemen t of pollination conditions in the germination quality of carrot seeds was given by pollination by honey bees of male-sterile plants cultiva ted at various distances from the pollen donors. The longer the distan ce of the mother plants from the pollinating plants, the lower the see d yield, the heavier the mean seed weight, the more difficult the germ ination of seeds, and the higher their sensitivity to oxygen deprivati on.