بررسي روند تغييرات عملكرو، رقابت درون گونه اي و رقابت بين گونه اي در برخي ارقام گندم ايراني در طي 50 سال اخير

Variation in yield and intra-specific competition ability of Iranian wheat cultivars during the last 50 years

In four separate experiments, ecophysiological characteristics of a wide rank o1 Iranian wheat cultivars were studied during 1377 and 1378 growing seasons. In the tirsl trial, 12 bread wheat cultivars released during the last 44 years were studied under the same agronomic pranks. In the second trial, 6 cultivars selected from the first trial were planted under the recommended agronomic practices for maximum attainable yield of each cultivar. In the third trial, the same 6 cultivars were grown with wild oat at the density of 80 plant/m2 and managed as mentioned for the second trial. The fourth trial was similar to the second one, but the planting density was set at optimum (recommended), 33% and 66%, higher than optimum. Result of the first two trials showed that there has been an increasing trend in yield of wheat cultivars associated with the year of their release. There was a positive and significant correlation between grain yield and harvest index (r=0.65 and 0.93 for the years 1377 and 1378, respectively). Competition ability of wheat cultivars has also been enhanced in the course of their release as it was evident by a higher yield, a lower weed biomass, and a greater competitiveness index (Cl) of the new compared to the old cultivars when infested by wild oat. Increasing plant density above the recommended level optimum led to a yield reduction in all cultivars, hut this yield reduction was not significant. Ir was concluded that during the last 51) years, wheat cultivars have been improved for higher grain yield and better interspecific competition ability. However, interaspecific competition ability of cultivars was not changed significantly.