Wheat Seedling Growth and Developmental Response to Incident Photosynthetically Active Radiation1

Abstract

AbstractShade from residues of previous crops in high residue seedbeds may limit development of winter cereal seedlings. A growth chamber experiment with photosynthetic photon flux densities of 140, 275, or 500 µmol−2s−1 for 12 h each day was designed to reveal the growth and development patterns of winter wheat (Triticum aestivum L. em Thell.) under light limiting conditions. Daily totals of light received during winter months at 46°N Lat are within this range. Leaf and tiller growth and development were observed daily on 6 to 12 separately potted plants in each of seven treatments for 1 month after emergence. At 140 µmol m−2s−1, a higher fraction of specific tiller buds failed to elongate than at either higher irradiance. Failure to elongate one tiller bud did not influence the point of development of subsequent tillers. Plants developed at 0.0097,0.0117, and 0.0138 leaves per degree day (0°C base) under 140, 275, and 500 µmol m−2s−1 treatments, respectively. An average of only four tillers per plant were present after 27 days under 140 µmol m−2s−1 while 12 tillers per plant were produced under 500 µmol m−2s−1. The basic relationship between main stem leaf and individual tiller development was not changed by different amounts of light. Specific tillers appeared at essentially the same point in plant development regardless of irradiance. At 140 µmol m−2s−1, the slower leaf development and reduced tillering both contributed to reduce plant weights to only one‐fifth those from the 500 µmol m−2s−1 treatment. The irradiance required for maximum development rate of winter wheat seedlings exceeds that expected in shaded areas of a seedbed from November through February at 46° N Lat. Based on this experiment, irradiance will not change the point of development of specific tillers relative to main stem leaf development. Irradiance will influence the fraction of plants with specific tillers and the rate (leaves per degree day) of leaf appearance. Leaf development rate (leaves per degree day) appears to be buffered by short term (a few days) energy reserves. Winter wheat seedlings that are shaded over winter will skip a higher fraction of the early tillers (T0, T1) than unshaded seedlings, reducing the population of potentially large heads.