Temporal variation in phenological characteristics, grain yield, and yield components of spring bread wheat (Triticum aestivum L.) cultivars released in Iran between 1952 and 2009

To estimate genetic progress and the variation in agronomic characteristics and phenology in 15 bread wheat (Triticum aestivum L.) cultivars released in Iran between 1952 and 2009, a field experiment was conducted at the Seed and Plant Improvement Institute’s Research Field Station in Karaj, Iran, in the 2009-2010 and 2010-2011 growing seasons. Temporal variation trends of the measured traits revealed that grain yield and related traits have increased in more recently released cultivars, though thousand-grain weight has changed only slightly compared with older cultivars released during 1952-2009. Number of days to heading and to anthesis did not change in modern cultivars, but grain-filling period and days to physiological maturity did increase. Grain number spike-1 and rate of grain growth increased but plant height decreased in more recently released cultivars.