Comparison of Horizontal Spread of White Clover (Trifolium repensL.) Grown Under Two Artificial Light Sources Differing in their Content of Blue Light

The effects of blue light on the growth and development of differentbranches were studied to determine if variations in the bluelight supply modified the horizontal spread of white clover.Cuttings of white clover (‘Huia’) were grown for56 d in two controlled chambers under conditions similar exceptfor level of blue light (BL). The horizontal spread of whiteclover was characterised by the phyllochron, internode lengthand branching or flowering of different axes. The responsesto a reduction in BL were different according to axis degree:(1) on the main axis, lowering BL slightly decreased the phyllochronand had no effect on internode length or stolon length; (2)on older primary branches, it decreased their phyllochron, butreduced stolon length due to a reduction in internode length;(3) on secondary branches, it increased the phyllochron anddecreased internode length, triggering a strong reduction instolon length (up to 54%). Moreover, an increase in BL reversedthese effects. The switch to lower BL or higher BL had no effecton internode length of primary branches, but triggered changesin internode length of the main axis. These differential effectsof variations in BL on the morphogenesis of different branchesare discussed in relation to the clonal integration of variationsin light composition. Changes in the horizontal spread of whiteclover induced by BL could play a role, combined with responsesto low red:far-red ratio and low photosynthetic photon flux(PPF) in the strategy of horizontal colonisation and shade-avoidanceof white clover.Copyright 1998 Annals of Botany Company Blue light, branching, horizontal spread, morphogenesis, phyllochron, plant development, plant morphology, stolon growth,Trifolium repensL., white clover.