Wheat yield response to growing degree days of post/pre anthesis

The time and duration of developmental stages (phonological events) are important in grain yield determination of wheat. The aim of this research was to study the ratio of post- to pre-anthesis duration in wheat plant and to investigate its possible association with grain yield.Eighty-one wheat cultivars were grown at research farm of Moghan College of Agriculture and Natural Resources-University of Mohaghegh Ardabili under well-watered conditions during 2010-2011 growing season. The dates of anthesis, and physiological maturity were recorded. Grain filling period (GFP) was recorded as the period from anthesis to physiological maturity. With the objective of including temperature effects on the lengths of growth phases, all developmental stages were expressed in the form of growing degree days (GDD). The ratio of post to pre anthesis duration was calculated as the amount of GDD from anthesis to maturity (GFP) divided by the amount of GDD from sowing to anthesis. Results showed that examined cultivars had significantly differences with respect to grain yield where this trait range from 293 to 746 gram per square meter. Crossed Alborz, Akbari, and Naz were the most productive cultivars whereas Shahpasand, Omid, and Sardari performed visa versa. Close association (r=0.79, P < 0.01) was found between grain yield and biological yield. In addition, grain yield correlated significantly and positively with grain number per square meter (r=0.74, P < 0.01) and with thousand-grain weight (r=0.42, P < 0.01). Large variations were found among tested cultivars with respect to thermal time from sowing to anthesis.