Effects of root restriction and growth regulator treatments on the growth of carrot (Daucus carota L.) seedlings

Abstract

The growth of carrot (Daucus carota L.) seedlings in clear polystyrene vials (7.5 × 2.5 cm diameter) which were either perforated or unperforated and suspended in a large container containing nutrient solution was compared with that of similar seedlings grown directly in the main container. After 28 days plants grown in the perforated, aerated vials had smaller shoots, tap roots (c 20 percent reduction) and fibrous roots (c 60 percent reduction) than unrestricted plants. In the absence of adequate aeration, the effects of root restriction were greater. Foliar applications of ethephon to the leaves of unrestricted plants reduced shoot weights but had little effect on either tap root or fibrous root weights, or even increased tap root weight at lower concentrations. Silver thiosulphate, aminovinylglycine and a highly mobile cytokinin (SD8339) all slightly enhanced shoot growth of restricted plants but had no effect on either tap roots or fibrous root development. It is suggested that although root restriction effects may be partly mediated by endogenous hormones, it seems unlikely that such effects are due solely to stimulation of ethylene production or a reduction in endogenous cytokinin levels.