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

Abstract

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 BL slightly decreased the phyllochron and had no effect on internode length or stolon length; (2) on older primary branches, it decreased their phyllochron, but reduced stolon 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 stolon length (up to 54%). Moreover, an increase in BL reversed these effects. The switch to lower BL or higher BL had 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 the 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.