Depositing capacity of winter wheat stem segments under natural drought during grain filling in Ukrainian forest steppe conditions

Drought is a major abiotic factor adversely affecting wheat productivity. Water deficit reduces significantly photosynthesis and hence the remobilization of stored assimilate reserves from the stem becomes important sources for grain filling. We assessed the ability of different stem internodes and leaf sheaths to deposit and remobilize reserve assimilates as well as their role in grain yield formation in 6 winter wheat varieties under drought conditions during the period of grain filling. The dry weight and content of water-soluble carbohydrates in the dry matter of stem internodes and leaf sheaths of the main shoot was determined at anthesis, the beginning of milk ripeness and full grain ripeness. The total amount of water-soluble carbohydrates in stem segments was calculated as the product of their specific content in the dry matter of the stem segment and its mass. The amount of remobilized dry matter and water-soluble carbohydrates for each segment was estimated as the difference between the appropriate values at anthesis or milk ripeness and full ripeness. The maximum accumulation of water-soluble carbohydrates in the stem was reached at early milk ripeness. The most productive varieties Kyivska 17 and Horodnytsia had the largest amount of remobilized water-soluble carbohydrates in all internodes. Depositing capacity of the second and third (counting from the top) internodes was higher compared to others and has a significant effect on the grain productivity of wheat varieties studied. Despite significant variability and strong genotype x year interaction of the relationships between depositing capacity traits of different stem segments and grain productivity, mainly tight correlations were found for dry matter and total water-soluble carbohydrates accumulation and remobilization in second and third internodes with yield and grain weight per spike. The obtained data suggests that the remobilization of deposited water-soluble carbohydrates is an important factor contributing to the filling of winter wheat grain in arid conditions and more detailed studies of relationships of depositing capacity of individual stem segments with yield can be useful for development of breeding tools for further genetic yield improvement.