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

Tillering is important in establishing the yield potential of spring barley (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) modulate barley tillering patterns. Experiments were designed to determine (i) the extent to which shifts in light quality associated with the presence of neighboring plants modulate barley tillering patterns in the absence of shading and competition for soil resources, (ii) barley responses to sudden changes in light quality during the tillering phase, (iii) the influence of plant spacing on response to shifts in light quality, and (iv) the impact of the response to shifts in light quality on productivity. Plants within treatment rows were grown 18 cm from densely sown border rows of barley. Barriers set into the soil assured negligible competition between border and treatment rows for soil resources during the early growing season. The borders functioned to reflect light, especially far-red (FR), which reduced R/FR within the treatment rows without shading them. Tiller production was reduced in bordered plants relative to unbordered controls. The removal of borders at 20 d after emergence (DAE) caused an increase in treatment row tiller production, whereas the imposition of borders at 20 DAE halted tillering. 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 early season shifts in light quality associated with FR reflection from neighboring plants contribute to modulating barley tillering under field conditions.