study of changes wheat yield and related traits in temperate semi-humid conditions

to study the yield and change the attributes associated with it, the field experiments were conducted at the gorgan university of agricultural sciences research farm, gorgan, iran in the growing seasons of 2007-2008 and 2008-2009 under well-watered conditions. the 16 cultivars were sown in a randomized complete block design with three replications. the results showed that during breeding activities in order to improve wheat yield there has been no change traits such as number of nodes, number of tillers per plant, number of grains per spikelet and seed weight, but other attributes have changed. number of grains per spike and grain number per unit area increased in 38 years of the release 28.87% and 24.74% respectively, ie per year was observed 0.78% and 0.80% improvement respectively. the most important reason for increasing the number of seeds per square meter was increasing grain number per spike. in grain yield, biological yield and harvest index increase has been equal to 24.83%, 16.16% and 8.18% respectively. also plant height was decreased by 0.25% and spike length was increased by 0.27% per year of release. generally more than 89% overall yield was justified by changing variables such as harvest index, biological yield and grain number per spike.