Trend of Changes in Grain Yield and Some Physiological Traits in Spring Bread Wheat Cultivars Released Between 1951-2008 in Iran

To study the trend of changes in grain yield، growth indices، stem soluble carbohydrates and canopy temperature in 15 spring bread wheat cultivars released between 1951-2008 in Iran، a field experiment was carried out using randomized complete block design with three replications in Research Field Station of Seed and Plant Improvement Institute in Karaj، Iran، in 2011-2012 cropping cycle. Results showed that grain yield has increased by 35 kg ha-1 year-1 from 1951 to 2008. The highest grain yield (5. 38 kg ha-1) belonged to Parsi a recently released cultivar and the lowest grain yield (2. 81 kg ha-1) obtained from Sholeh an old cultivar. Analysis of variance showed that the growth indices; crop growth rate (CGR)، relative growth rate (RGR) and leaf area index (LAI) were significantly different (P ≤ 0. 01) among spring bread wheat cultivars. The modern cultivars research to maximum LAI earlier than older cultivars. The leaf area duration (LAD) was also longer in modern cultivars. Most of cultivars reserved carbohydrates in pedunde and penultimate internode in 14 days after anthesis and then remobilized it to developing grains. The quantity of reserved stem soluble carbohydrates was greater in penultimate internode. Canopy temperature at anthesis stage was cooler in modern cultivars.