Evaluating morpho-phenological and yield traits of bread wheat cultivars and near-isogenic lines in response to terminal heat stress in Ahvaz, Iran

Heat stress is a growing threat to food security and agricultural production. Terminal heat stress is a major abiotic stress especially in tropical and sub-tropical regions dramatically affecting crop growth and yield. The use of early-heading bread wheat cultivars is an appropriate method for many grain-producing regions experiencing terminal heat stress. In this experiment, the effect of terminal heat stress was assessed on morpho-phenological and yield traits of bread wheat cultivars and near-isogenic lines. The objective of this study was to use cultivars and near isogenic lines with early flowering to investigate the effect of earliness on grain yield and some phenological and agronomic traits of bread wheat in order to obtain superior cultivars and isogenic lines in terms of tolerance to heat stress caused by late sowing date.

The experiment was carried out in split-plots based on randomized complete block design with three replications in Shahid Chamran University of Ahvaz, Iran, in 2022-2023. The main plots included two sowing dates, November 23 and January 23 (normal and late sowing dates, respectively), and the sub-plots consisted seven bread wheat cultivars and near-isogenic lines (Roshan, Kalheydari, Mahdavi, Roshan’s near-isogenic line, Kalheydari’s near-isogenic line, Mahdavi’s near-isogenic line, and Mehrgan as control). Sowing date with desired temperature was considered as control, and late sowing date was considered as heat stress to ensure heat stress coincided with flowering and grain-filling phases. The data regarding grain yield, spike weight, grain number per spike, grain weight per spike, 1000-grain weigh, biological yield, harvest index, plant height, days to heading, and days to maturity was recorded.

The results of this experiment showed that there was a significant difference between bread wheat cultivars and isogenic lines in terms of most studied traits. Heat stress induced by late sowing caused a significant decrease in grain yield of cultivars and near-isogenic lines through a significant reduction in spike weight, grain number per spike, grain weight per spike, and 1000-grain weight. Reduction values ​​of the traits in cultivars were more than their near-isogenic lines. Heat stress led to a significant decrease in the grain yield of Roshan cultivar, Roshan’s near-isogenic line, Kalheydari cultivar, Kalheydari’s near-isogenic line, Mahdavi cultivar, Mahdavi’s near-isogenic line, and Mehrgan cultivar by 36, 35, 31, 31, 35, 32, and 30%, respectively, compared to normal sowing date as control. Decrease values in cultivars were almost similar to their near-isogenic lines, but Mahdavi’s cultivar and near-isogenic line as well as Mehrgan cultivar showed the highest grain yield in both sowing dates compared to other cultivars and isogenic lines. The isogenic lines were approximately 7 to 14 days earlier in maturity than their cultivars. In near-isogenic lines of Roshan, Kalheydari and Mahdavi, reducing the number of days from sowing to heading (5, 6, 11 days, respectively), and the number of days from sowing to full maturity (8, 7, 14 days, respectively) as two main components of earliness, caused to minimize exposure to terminal heat stress during the flowering and grain filling phases, and higher grain yield and stability.

Overall, the results of this experiment showed that the studied near-isogenic lines were superior to cultivars in term of grain yield, and agronomic and morphological traits. Mahdavi’s near-isogenic line using the earliness strategy and shortening the number of days to flowering and maturity had the highest grain yield and stability, it is recommended along with Mehrgan cultivar for both normal and late sowing date conditions in Khuzestan region.