Effects of post-flowering drought and supplemental irrigation on grain yield and agro-phenological traits in durum wheat

Water deficit and unbalanced distribution rainfall in the Mediterranean rainfed regions are major problems threatening agricultural sustainability, especially durum wheat (Triticum turgidum L. var. durum) production. This study aimed to investigate the effects of drought and supplemental irrigation in post-flowering stage on traits performance of durum wheat trials and to identify traits that significantly contribute to increase the grain yield of durum wheat under different water regimes and recommend new genotypes adapted to climate change. An eight-year field study was conducted from 2014 to 2022, consisting of 36 field experiments, 18 under rainfed and 18 under supplemental irrigation (two times irrigation in flowering and grain-filling stages) conditions through six experimental series of elite durum wheat yield trials each with same genotypes. In each experiment, grain yield, 1000-kernel weight (TKW), plant height (PLH), days to heading (DHE) and maturity (DMA) were recorded. Drought stress tolerance index (STI) and mean productivity (MP) were applied to differentiate high-performing and drought tolerant durum wheat genotypes in each experimental series. The combined analysis of variance for traits studied of each experimental series indicated that the year, water stress treatment, genotype and their interaction effects were significant. For grain yield, year was the main source of variation and had the highest impact on genotypes performance. The results indicated that the supplemental irrigation, depending on genetic materials, significantly increased grain yield (18.7%-45.8%), TKW (8.2%-12.9%), and PLH (1.1%-8.2%) compared with the rainfed condition across years. Supplemental irrigation exhibited for no significant effect on the increase of the maturity time (0.2%-2.2%) of genotypes tested compared with the rainfed condition. The results confirmed the systematic effects of post-flowering drought on yield, grain weight and plant stature of durum wheat. A positive and significant trend (R2=0.62; P<0.01) was observed between yield production in rainfed condition and cumulative rainfall, showing that in 62% of the cases higher rainfall resulted in higher performance. TKW and PLH significantly and positively correlated with mean yield in the both rainfed and irrigated conditions, suggesting the importance of these two traits in breeding programs to assist in developing high yielding genotypes under different water regime conditions. Evaluation of genotypes in terms of mean yield and stability performance using GGE biplot, resulted in identification of superior lines that outperformed the check cultivars. The STI and MP were desirable selection criteria for high yielding and drought tolerant genotypes, thus high yielding genotypes that are tolerant to drought would be expected to have good yield stability in stressful environments. The results highlight the significant effects of drought stress after flowering upon grain yield, and the significant contribution of 1000-kernel weight and plant height to increase grain yield under different water regimes, that could be utilized to aid breeding of high-performing and drought tolerant durum wheat genotypes under the future climate conditions.