Triticeae Genomics and Genetics, 2024, Vol.15, No.3, 121-124 http://cropscipublisher.com/index.php/tgg 122 Figure 1 Wheat yield and yield-related traits in drought season of 2018 vs favorable season of 2019 The results of the statistical significance tests (p-values) further validated the credibility of these observations. For example, the significance level for the decrease in grain weight was less than 0.01, and the reduction in the number of spikelets was less than 0.001. Decreases in thousand-grain weight, spike length, and the number of spikes also showed varying degrees of statistical significance, indicating that drought has a statistically significant impact on wheat yield parameters. Therefore, these data reveal the extensive negative impact of drought on wheat production traits, particularly yield-related traits. This finding is crucial for guiding future wheat breeding work for drought resistance because it provides direct evidence of wheat growth traits under drought conditions and emphasizes the importance of considering drought resistance and yield improvement in wheat breeding. The relationship between the genetic diversity and geographic distribution of wheat varieties is depicted through a three-dimensional principal component analysis (PCA) plot (Figure 2). In Figure 2a, two broad groups are identified: local varieties (LR) and modern varieties (MV). The data points for the LR group are more dispersed within the PCA space, indicating greater genetic variability among these varieties; conversely, the MV group is relatively concentrated, suggesting higher genetic similarity among modern varieties. Figure 2b further subdivides the LR group into three subgroups based on geographical origin, consisting of local varieties from Afghanistan, Iran, and Turkey, while the MV group is shown as a separate cluster. It is observable that LR groups from different geographic origins are distinctly separated in the PCA plot, demonstrating genetic differences based on geographic distribution. Although the MV group is separated from the LR groups in the PCA plot, it also shows a tendency to be close to the Turkish LR group in Figure 2b, which may reflect that modern varieties have potentially retained or borrowed genetic traits from local varieties during the breeding process. Additionally, the lines between points in Figure 2b represent the fixation index (Fst) between groups, with Fst values providing a quantitative measure of genetic differentiation between populations. Higher Fst values indicate greater genetic differentiation. The Fst values in the figure indicate some level of genetic differentiation between different LR groups, and the Fst values between the MV group and each LR group further confirm the genetic distinction between modern and local varieties. Therefore, the significant genetic diversity of local varieties reflects the genetic variations accumulated by wheat in different regions adapting to local environmental conditions. Although modern varieties exhibit lower genetic diversity, they may possess genetic connections across geographical boundaries, which is a valuable resource for future wheat breeding because these relationships can be utilized to introduce new, beneficial genetic traits.
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