FAR-RED LIGHT REFLECTED FROM NEIGHBORING VEGETATION PROMOTES SHOOT ELONGATION AND ACCELERATES FLOWERING IN SPRING BARLEY PLANTS

Field experiments were conducted in St Paul, MN, USA, to test the hypo thesis that early season declines in the red:farred ratio (R:FR) assoc iated with FR reflection from neighbouring leaves have a role in regul ating barley development. Treatment plants were grown adjacent to dens ely sown border rows of barley. The borders functioned to reflect far- red (FR), which reduced R:FR within the treatment plant light environm ent without shading treatment plants. Barriers were set in the soil to minimize root interactions between treatment plants and borders. Trea tment plants were spaced either 2 or 16 cm apart. The presence of bord ers significantly increased shoot leaf and internode lengths at both p lant spacings. Leaf sheath length data suggest that interactions betwe en 2 cm spaced treatment plants enhanced plant responsiveness to the p resence of borders. Border treatments shortened the period of vegetati ve growth prior to initiation of main shoot floral primordia. Bordered plants formed fewer main shoot leaves, initiated internode elongation at a lower node, and had slightly earlier heading dates than unborder ed controls. Leaf appearance rate was not influenced by border treatme nts. We conclude that barley shoot development is photomorphogenically modulated by R:FR. Early season shifts in R:FR could have a significa nt influence on shoot development given that barley has the capacity t o detect and developmentally respond to declines in R:FR associated wi th FR reflection from neighbours.