Comparison of horizontal spread of white clover (Trifolium repens L.) grown under two artificial light sources differing in their content of blue light

The effects of blue light on the growth and development of different branches were studied to determine if variations in the blue light supply modified the horizontal spread of white clover. Cuttings of white clover ('Huia') were grown for 56 d in two controlled chambers under conditions similar except for level of blue light (BL). The horizontal spread of white clover was characterised by the phyllochron, internode length and branching or flowering of different axes. The responses to a reduction in BL were different according to axis degree: (1) on the main axis, lowering HL slightly decreased the phyllochron and had no effect on internode length or stolen length; (2) on older primary blanches, it decreased their phyllochron, but reduced stolen length due to a reduction in internode length; (3) on secondary branches, it increased the phyllochron and decreased internode length, triggering a strong reduction in stolen length (up to 54%). Moreover, an increase in BL reversed these effects. The switch to lower BL or higher BL hall no effect on internode length of primary branches, but triggered changes in internode length of the main axis. These differential effects of variations in BL on the morphogenesis of different branches are discussed in relation to 1:he clonal integration of variations in light composition. Changes in the horizontal spread of white clover induced by BL could play a role, combined with responses to low red:far-red ratio and low photosynthetic photon flux (PPF) in the strategy of horizontal colonisation and shade-avoidance of white clover. (C) 1998 Annals of Botany Company.