Evaluation of different bread wheat cultivars in some physiological characteristics, thermal requirement and crop yield in Kermanshah region

The rapid increase in the world population and the need to increase agricultural production, and on the other hand, the rapid change of climate conditions, are the significant challenges facing the world in the coming years. Wheat, the most important plant in the cereal family, plays a vital role in the world's food security now and in the future. Therefore, producing new cultivars with high yields and carefully selecting cultivars suitable for cultivation in different climatic zones are important future research priorities.

This study investigated the reaction of different bread wheat cultivars regarding yield and its components. It also aimed to study the growing degree days (GDD) and some physiological traits related to cold tolerance in different bread wheat cultivars. This study was conducted as two independent experiments during the 2013-14 cropping year at the research field, Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran. The first experiment was a randomized complete block design with three replications. Treatments included 12 bread wheat cultivars (Norstar, Zarin, Kavir, Baz, Sivand, Alvand, Pishgam, Pishtaz, Orum, Shahryar, Bahar, and Parsi). The second experiment was a factorial experiment in a randomized complete block design with three replications. In this experiment, 12 bread wheat cultivars were evaluated as the first factor and sampling times as the second factor in three levels: early January, early February, early March.

The results of this study showed that Sivand and Parsi spring cultivars with the highest plant growth rate in different stages of development, with 5170 and 5100 kg/ha, respectively, and Norstar winter cultivar with the lowest plant growth rate in various stages of development, with 2230 kg/ha, had the lowest value of grain yield. The correlation between grain yield, growing degree days requirement to flowering, and physiological maturity were negatively significant. Cultivars with lower grain yield had higher growing degree day’s requirements. Examination of the growing degree days requirement of cultivars up to the flowering stage showed that, on average, spring cultivars had lower growing degree day requirements than winter cultivars. The accumulation of soluble sugars in the crown of winter and intermediate cultivars during winter was higher than spring cultivars. The accumulation of soluble sugars in the wheat crown was downward during the winter, so at the beginning of winter, the crown had a higher sugar content than in the middle and late winter. Winter and intermediate cultivars, on average, had higher leaf greenness and maximum photochemical efficiency of photosystem II than spring cultivars.

According to the results obtained in the study area, on average, winter and intermediate cultivars were superior to spring cultivars in terms of physiological traits related to cold tolerance. But, due to the obtained seed yield. However, according to the grain yield obtained in this study, spring cultivars are more recommended among cultivated cultivars than the other two growth types in Kermanshah and similar climate zones.