Evaluation of bread wheat genotypes tolerance to seed aging at germination stage using quantitative stress tolerance indices

Background and Objectives: Wheat, as one of the main food sources in the world, plays an important role in ensuring food security. In this context, the quality of wheat seeds is a key factor in the success of cultivation and achieving optimal yield in the field. One of the most important factors that can reduce seed quality is seed aging. This phenomenon occurs over time and as a result of seeds being exposed to unfavorable environmental conditions such as high temperature and humidity, especially during storage, and causes a decrease in germination capacity and weakness in the initial growth of seedlings. The aim of this study was to evaluate the viability of bread wheat genotypes using tolerance indices under accelerated aging conditions.

Materials and Methods: In this study, 228 bread wheat genotypes, including landraces and cultivars, were investigated as a factorial experiment in a completely randomized design under accelerated aging treatment at four levels of zero, 48, 72 and 96 hours in 2022-2023 year. Germination percentage was measured as an index of seed yield, and the response of genotypes to aging stress was evaluated using quantitative tolerance indices such as STI, GMP, YSI, MP, HAR, SSI, TOL, and the new WGMI index. Data analysis was performed using statistical methods of correlation coefficient, principal component analysis (PCA), and cluster analysis. Data correlation analysis was performed using SPSS version 26 software. Cluster analysis dendrograms (heatmaps) were prepared using the gplots, d3heatmap, and dendextend packages, and principal component analysis biplots were prepared using the factoextra and FactoMineR packages in R software version 4.3.2

Results: Boxplot results showed that there was a significant statistical difference between different levels of accelerated aging in most of the indices (P < 0.0001). Based on all the studied indices except TOL and SSI, a significant decrease in germination percentage was observed with increasing aging time. The results of correlation analysis showed that indices such as STI, GMP, HAR, MP and YSI had a positive and significant correlation with performance under stress and effectively identified resistant genotypes. In contrast, TOL and SSI indices showed a negative correlation with germination percentage under stress and helped identify sensitive genotypes. Based on the results of cluster analysis at accelerated aging levels of 48 and 72 hours, bread wheat genotypes were classified into three main groups in terms of the studied indices and based on germination percentage. At the accelerated aging level of 96 hours, the genotypes were placed in two main groups. The genotypes of the first group were identified as the best and most resistant genotypes to seed aging in all three stress levels. Based on the WGMI index, genotypes with stable and balanced performance in all aging stress levels were well distinguished. Based on the results obtained, the cultivars ALVAND, FONG and KARAJ1, along with the landraces 626215, 627410, 626978, 627849, 624944, 627414, 623090 and 624846, are introduced as the most resistant genotypes to seed aging.

Conclusion: The findings of this study showed that the simultaneous use of different stress tolerance indices and multivariate statistical methods as an effective and accurate tool could help identify and select genotypes tolerant to seed aging. The genotypes identified in this study can be used as suitable parents in breeding programs to improve traits related to seed viability. These genotypes can also be used in genomic evaluation programs to identify genes and QTLs affecting seed vigor.