title: Cessation of tillering in spring wheat in relation to light interception and red : far-red ratio.
abstract: OBJECTIVE
  The production of axillary shoots (tillering) in spring wheat (Triticum aestivum) depends on intraspecific competition. The mechanisms that underlie this competition are complex, but light within the wheat canopy plays a key role. The main objectives of this paper are to analyse the effects of plant population density and shade on tillering dynamics of spring wheat, to assess the canopy conditions quantitatively at the time of tillering cessation, and to analyse the relationship between the tiller bud and the leaf on the same phytomer.
  
  
  METHODS
  Spring wheat plants were grown at three plant population densities and under two light regimes (25 % and 100 % light). Tiller appearance, fraction of the light intercepted, and red : far-red ratio at soil level were recorded. On six sampling dates the growth status of axillary buds was analysed.
  
  
  RESULTS
  Tillering ceased earlier at high population densities and ceased earlier in the shade than in full sunlight. At cessation of tillering, both the fraction of light intercepted and the red : far-red ratio at soil level were similar in all treatments. Leaves on the same phytomer of buds that grew out showed more leaf mass per unit area than those on the same phytomer of buds that remained dormant.
  
  
  CONCLUSIONS
  Tillering ceases at specific light conditions within the wheat canopy, independent of population density, and to a lesser extent independent of light intensity. It is suggested that cessation of tillering is induced when the fraction of PAR intercepted by the canopy exceeds a specific threshold (0.40-0.45) and red : far-red ratio drops below 0.35-0.40.
authors.affiliation: Crop and Weed Ecology, Plant Sciences Group, Wageningen University, Haarweg 333, 6709 RZ Wageningen, The Netherlands. jochem.evers@wur.nl
authors.forename: Jochem B
authors.initials: JB
authors.lastname: Evers
authors.forename: Jan
authors.initials: J
authors.lastname: Vos
authors.forename: Bruno
authors.initials: B
authors.lastname: Andrieu
authors.forename: Paul C
authors.initials: PC
authors.lastname: Struik
mesh_terms: D010788:Photosynthesis; D018515:Plant Leaves; D018520:Plant Shoots / Q000502:physiology / Q000528:radiation effects*; D011156:Population Density; D013472:Sunlight; D014908:Triticum / Q000502:physiology / Q000528:radiation effects*