Light‐mediated bioregulation of tillering and photosynthate partitioning in wheat

Abstract

The influence of plant population density on spectral distribution of light received by wheat (Triticum aestivum L. cv. Coker 797) seedlings was measured under field conditions, and effects of red and far‐red light on tillering and photosynthate partitioning were studied in controlled environments. Spectral distribution of light was measured in sunflecks at soil level in close‐, intermediate‐, and wide‐spaced field populations during the tillering stage. Close‐spaced seedlings received higher far‐red/red light ratios than wide‐spaced plants because of the larger amount of far‐red reflected from green leaves of the more numerous nearby plants. The far‐red/red light ratios in all population densities were higher in late afternoon than at noon. Close‐spaced plants developed fewer tillers, less roots and longer leaves than wide‐spaced seedlings under field conditions. In controlled environments, a higher far‐red/red ratio during photosynthetic periods resulted in fewer tillers and longer leaves; whereas, brief red or far‐red exposures at the end of each day had a more pronounced effect. Wheat seedlings that received 5‐min exposures to far‐red light at the end of the photosynthetic period each day for 20 consecutive days developed fewer tillers, longer leaves, less roots, and a higher shoot/root biomass ratio. The effects of far‐red light were reversed by red light. The light spectral shifts associated with field plant population densities and the responses to red and far‐red treatments under controlled environments suggest that phytochrome serves as a sensing mechanism that detects the amount of competition from other plants, and regulates the development of tillers and the partitioning of photosynthate between shoots and roots.