TILLERING RESPONSE OF BARLEY TO SHIFTS IN LIGHT QUALITY CAUSED BY NEIGHBORING PLANTS

Tillering is important in establishing the yield potential of spring b arley (Hordeum vulgare L.). Two field experiments were conducted for 3 yr to test if early season shifts in the red/far-red ratio (R/FR) mod ulate barley tillering patterns. Experiments were designed to determin e (i) the extent to which shifts in light quality associated with the presence of neighboring plants modulate barley tillering patterns in t he absence of shading and competition for soil resources, (ii) barley responses to sudden changes in light quality during the tillering phas e, (iii) the influence of plant spacing on response to shifts in light quality, and (iv) the impact of the response to shifts in light quali ty on productivity. Plants within treatment rows were grown 18 cm from densely sown border rows of barley. Barriers set into the soil assure d negligible competition between border and treatment rows for soil re sources during the early growing season. The borders functioned to ref lect light, especially far-red (FR), which reduced R/FR within the tre atment rows without shading them. Tiller production was reduced in bor dered plants relative to unbordered controls. The removal of borders a t 20 d after emergence (DAE) caused an increase in treatment row tille r production, whereas the imposition of borders at 20 DAE halted tille ring. Shoot survival was increased by the presence of borders. Border effects on final spike number, biomass production, and grain yield per plant were inconsistent during the experiments. We conclude that earl y season shifts in light quality associated with FR reflection from ne ighboring plants contribute to modulating barley tillering under field conditions.