Journal of Crop Breeding

Extended Abstract
Background: Wheat (Triticum aestivum L.) is one of the most important cereals to ensure the food security of the growing human population. This crop provides approximately 19% of total calories, 21% of protein, and a large amount of nutrients in the daily human diet. Most of the rain-fed areas in Iran are facing the problem of rainfall deficiency and the lack of proper rainfall distribution during the growing season. Iranian bread wheat cultivars have different pedigrees and sources, as the main factor separating the cultivars. The exchange of breeding materials with different origins helps improve agricultural production and strengthens world food security. It is necessary to evaluate such germplasms in field conditions, and the agronomic and physiological traits of wheat are of special importance in this context. The production of dry winter wheat is very important for some geographical regions of Iran, including the northwest of the country, and reduces the vulnerability to global climate change. Therefore, the present research was carried out to evaluate agronomic and physiological traits and group dryland winter wheat genotypes with different origins under supplemental irrigation and rain-fed conditions. This study also seeks to identify drought stress-tolerant genotypes using tolerance indices.
Methods: In total, 110 bread wheat genotypes from commercial cultivars, international stocks, advanced lines, and landraces of dryland winter bread wheat were investigated in this experiment. These genotypes were cultivated in the form of an Alpha-Lattice experimental design with two replications in the Dryland Agricultural Research Institute (DARI) located in Maragheh during the 2020-2021 crop year. Supplementary irrigation was 50 mm after planting, and the second irrigation was performed in the spring of the following year. Phenological stages included days to flowering, days to maturity, and grain-filling period. The greenness rate was measured using an NDVI device in two stages of spike emergence and three weeks after anthesis. Plant height, thousand-kernel weight, grain yield, biological yield, and harvest index were the other traits. Relationships between traits were analyzed based on Pearson's correlation coefficients. The Principal Component Analysis (PCA) biplot and the cluster analysis dendrogram based on Euclidean distance and Ward's grouping method were drawn in the R program. Canonical discriminant analysis (CDA) was performed based on the origin of wheat genotypes in SPSS 26 software. Various stress tolerance indices (TOL, MP, GMP, HM, SSI, STI, YI, YSI, and RSI) were used to select tolerant genotypes.
Results: The greenness rate in the spike emergence stage had a positive and high correlation with its value in three weeks after anthesis. In supplementary irrigation and rain-fed conditions, grain yield had a positive and significant relationship with plant height and biological yield. In both environments, the genotypes were widely distributed in the biplot space, which indicated high diversity among them in terms of agronomic and physiological traits. Based on cluster analysis in rain-fed and supplementary irrigation conditions, 110 studied wheat genotypes were classified into four groups, and the genotypes in the third group contained more grains and biological yields in both dendrograms. Examining the distribution of the origin of genotypes in the dendrogram of cluster analysis indicated that cultivars tolerant to drought stress and native stands were present in the other groups under the conditions of supplementary irrigation, except for the fourth group, but Sardari morphotypes were mainly in the fourth group. In rain-fed conditions, on the other hand, most of the genotypes with the origin of cultivars tolerant to drought stress, landraces, and CIMMYT Institute lines were placed in the fourth group. The results of CDA analysis based on the origin of wheat genotypes indicated that the lines created by the CIMMYT center had the greatest distance from the cultivars from Turkey under both environmental conditions. In supplementary irrigation conditions, landraces and Sardari morphotypes, as well as in rain-fed conditions, cultivars tolerant to drought stress and landraces were highly similar. Genotypes with codes 46, 81, and 8 under supplementary irrigation and genotypes with codes 8, 110, and 94 under rain-fed produced the highest grain yields, respectively. Genotypes 106, 34, and 55 presented the lowest TOL value and were the most desirable genotypes in terms of this index. The Sardari cultivar (G8) and a rainfed line (G9) were recognized as the most suitable genotypes in terms of MP, GMP, HM, and STI. Genotypes 106, 34, and 44 were the most tolerant genotypes simultaneously by SSI, YSI, and RSI indices. Finally, genotypes 110, 67, and 8 had high sum rank (SR) and average rank (AR).
Conclusion: Among the 110 wheat genotypes studied, there was an acceptable diversity for agronomic and physiological traits under rain-fed and supplementary irrigation conditions. In supplementary irrigation, landraces and Sardari morphotypes, and under rain-fed conditions, landraces and drought stress-tolerant cultivars were highly similar to each other. A dryland line of the Iranian origin (G8), along with two foreign lines selected from CIMMYT trials (genotypes 67 and 110), were the most desirable and tolerant genotypes based on the average ranks obtained from stress tolerance indices, which can be used in future crossing programs.