Effect of variations of phenological traits and photosynthetic materials allocation on grain yield of bread wheat under different moisture conditions

Introduction Grain growth in wheat depends on current photosynthesis and stem water-soluble carbohydrates (WSC). In semiarid regions with terminal drought, grain filling in wheat crops may depend more on stem WSC content than on current assimilates. Reduction in grain yield under drought is attributed to shorter duration of linear grain growth despite increased contribution of stem reserves to grain yield. The amount of stem reserves is measured either by changes in stem dry weight (indirect method) or by stem WSC content (direct method). Genotypic variation in the rate and duration of linear grain growth and in percent contribution of stem reserves to grain yield has a little evaluated in wheat. Materials and Methods The objectives of this study were estimated heritability and the relationship among phenological characteristics and allocation of photosynthetic materials yield in recombinant inbred lines of spring wheat under normal and terminal water defect. Plant materials used in this experiment, include 148 bread wheat recombinant inbred lines derived from the cross between Yecora Rojo and genotype No. 49. Lines were produced at Riverside University and through of Center of Excellence Molecular Breeding, University of Tabriz was placed at the disposal of this research. Studied lines with parents were planted on research farms of Mahabad University and Miyandoab Agricultural Research Center in 2014-2015. In both experiments used alpha lattice design with two replications under normal and water defect conditions. Irrigation in stress and non-stress treatments was done after 90 mm evaporation from class A pan, depending on the temperature and evapotranspiration until heading stage. In water deficit stress treatment, irrigation was stopped at heading stage. Measuring of these traits were done sampling before and anthesis stage. Results and Discussion Under both conditions positive and negative transgressive segregation were observed for grain yield, day to flowering, day to physiologic mature and grain filling period, allocation of photosynthetic material to stems, remobilization and remobilization portion in grain yield. Under normal moisture conditions, remobilization and in water difict conditions, grain yield had the highest phenotypic and genotypic variation. In normal condition the highest and the least broad and narrow sense heritability was estimated for the allocation of photosynthetic material to stems by 84.81 and 42.30% and allocation of photosynthetic material to leaf by 30.86 and 15.73% respectively. in water defect condition, days to headage showed the highest broad and narrow sense heritability by 90.86 and 45.43% and allocation of photosynthetic material to leaf by 52.38 and 26.19% showed the lowest amount The highest genetic gain in both conditions was related to grain yield, day to flowering, day to physiological mature, grain filling period, of allocation photosynthetic material to stem and photosynthesis remobilization. Furthermore In both conditions, grain yield showed a positive and significant correlation with days to heading, allocation of photosynthetic material to stems and spike and remobilization rate, and showed a negative and significant correlation with ratio of allocation photosynthetic material to spike and stem. Based on regression and path analysis treats in normal condition allocation of photosynthetic material to stems, remobilization portion in grain yield, remobilization rate and allocation of photosynthetic material to stems and spike and remobilization rate(R2= 0.87) and in water defict condition, remobilization portion in grain yield, remobilization rate (R2= 0.86) had a significant effect on the grain yield variations. Conclusions In this study, the remobilization rate had a direct and positive effect and remobilization portion in grain yield on grain yield had a direct and negative effect on the grain yield and identified as most effective traits. Therefore, it can be concluded that genotypes that have the ability to remobilization higher photosynthetic materials can have higher grain yield under both normal and water stress conditions and selecting such genotypes will help us achieve high-yielding genotypes