Introduction and Objective: Temperature is the most crucial factor determining the growth duration of agricultural plants. However, with rising temperatures, growth and development accelerate, leading to a reduction in the plant's lifespan. This phenomenon is a major factor contributing to decreased yields in hot regions. Identifying suitable genotypes for cultivation in the southern region of Fars Province is of particular importance. Evaluating a collection of new lines in this area makes it possible to achieve this goal. Given the special program of the Seed and Plant Improvement Research Institute aimed at increasing wheat self-sufficiency, this study was conducted to identify high-yielding and promising bread wheat genotypes in southern Fars Province.
Materials and Methods: To evaluate several pure lines of bread wheat, two experiments were conducted during the agricultural years 2021-2022 and 2022-2023 at the Darab Agricultural and Natural Resources Research Station. The lines examined in this study were sourced from research centers and stations in Karaj, Darab, and Zabol, as well as double haploid lines developed through a joint program between the Seed and Plant Improvement Research Institute and Florimand Deprée Company. During the growth and development stages of the plant, observations were made on certain agronomic traits, including planting dates, days to heading, days to maturity and plant height . After harvesting each of the lines, additional traits were examined, such as thousand grain weight, seed filling period, seed filling rate  and grain yield. The first year's experiment included 156 pure bread wheat lines along with four local control varieties (Chamran 2, Mehrgan, Sarang, and Barat), executed in an augmented design. From these lines, 77 were selected for the Darab region in the second year, which were then tested alongside three local control varieties (Mehrgan, Barat, and Sarang) in an alpha lattice design (10×8) with two replications. In both years, the selection of superior lines was performed using the Multi-Genotype Ideotype Distance Index (MGIDI) based on morpho-phenological traits.
Results: The analysis of variance for agronomic traits in the first year's experiment indicated no significant differences among blocks (except for the trait "days to heading"). The calculated coefficients of phenotypic variation showed that traits such as grain yield (18.92%), thousand grain weight (19.68%), and grain filling rate (20.91%) exhibited greater variability compared to other studied traits. This result suggests a suitable diversity among the evaluated lines, which can lead to improved grain yield through proper selection. Heat maps of various traits in the examined lines corroborated this finding. The results indicated that the mean grain yield in selected lines increased compared to controls and all lines combined; specifically, the mean grain yield increased from 5.04 tons per hectare to 5.86 tons per hectare in selected lines. The highest and lowest yields among selected lines were associated with line number 155 (7.2 tons per hectare) and line number 92 (5.12 tons per hectare), respectively. The mean grain yield for control genotypes Barat, Chamran 2, Mehrgan, and Sarang were 5.13, 4.72, 4.95, and 5.90 tons per hectare, respectively. The significant effects of lines in the second year across various traits indicate appropriate diversity and improved genetic gain. The MGIDI index for six studied traits showed differential selection for desirable traits, with the grain filling rate exhibiting an undesirable selection differential of -0.01%. The highest and lowest percentages of selection differential corresponded to "days to heading" (5.30%) and "grain filling rate" (0.01%), respectively. Additionally, the total desirable positive and negative differentials were 6.73% and -11.39%, respectively, indicating the efficiency of selection using the MGIDI index. Factor analysis revealed that the first two factors accounted for 72.4% of the variation. The MGIDI index categorized lines based on "days to heading," "grain filling duration," and "grain filling rate" for the first factor, while for the second factor, it was based on "days to maturity," "thousand grain weight," "grain yield," and "plant height." Results from strength and weakness charts indicated that both factors successfully categorized most superior lines based on their ideal values across all internal traits. Among the selected lines using the MGIDI index, lines G49, G28, G38, G21, G44, G59, G50, G53, G77, G35, G16, G41, and G79 were identified as superior in this research. Pearson correlation results showed a significant correlation between grain yield and thousand grain weight at a 5% probability level, indicating indirect selection for high-yielding lines through traits such as thousand grain weight.
General Conclusion: The MGIDI index efficiently identified the top lines based on all traits. In the pedigree of the 10 selected lines, there is a common parent named OASIS, which likely contributed to the superiority of these lines compared to other tested lines. Based on these results, it is recommended to use these lines to enhance wheat breeding programs in the hot and dry southern regions.