Evaluation of drought tolerance indices in promising barley lines (Hordeum vulgare L.)

Drought is one of the most important factors limiting the environment for plant growth and productivity, especially in the flowering and filling stages of barley. A study was conducted to compare some statistical methods and different indicators of stress tolerance with the aim of introducing an ideal method for selecting drought tolerant lines. After wheat, barley is one of the most important crops. Barley is the fourth cereal crop in the world after wheat, corn and rice. One of the factors affecting the production of plants is water defecit, and barley has more efficient mechanisms against water shortage than other grains. Because it has higher relative drought tolerance compared to other grains. In these arid and semi-arid regions like Iran, the presence of drought stress during plant growth is a natural problem.

In this study, 18 diverse barley lines at two water levels (normal conditions and water deficit stress) were examined. This experiment was performed as a randomized complete block design with three replications at the Seed and Plant Improvement Research Institute of Karaj, Iran in 2020. Drought tolerance and susceptibility indices were assessed. These indices included stress sensitivity index, mean productivity, tolerance, stress tolerance index, geometric mean productivity, harmonic mean productivity, performance under stress conditions (Ys) and normal (Yp) conditions. Correlation coefficient between yield in drought and irrigation conditions and other stress indicators was estimated according to statistical techniques. Correlation between indices and grain yield under stress and normal conditions was calculated using Minitab software. Selection based on multiple traits in breeding programs is likely to be effective in improving grain yield under drought stress conditions. The purpose of this study is to identify the most suitable indicators and compare different stress tolerance indicators to select high-yielding and drought-tolerant lines and to identify the superior barley line.

The highest GMP and MP were related to 4 and 13 lines. Based on tolerance index (TOL), genotype 1 had the lowest and line 7 showed the highest level of tolerance, respectively. Based on MP and GMP indices, 4, 7 and 13 lines had high drought tolerance. A high positive and significant correlation was observed between MP, GMP, Ys, Yp, which indicates that these indices are suitable for identifying drought tolerant lines. Based on the results of the principal component analysis and the bi-plot diagram, it was observed that the lines tolerant to drought stress are almost consistent with the clustering pattern of tolerant lines and the lines sensitive to drought stress are also consistent with the clustering of sensitive lines. MP and GMP indices are suitable for evaluating drought tolerance because they showed a high correlation with grain yield under normal conditions and under water stress. The closeness of 4 and 13 lines to GMP, MP, HARM, Ys indicates the tolerance of these lines to drought stress and therefore they can be suggested as drought tolerant lines.

Selection of drought tolerant lines based on a combination of tolerance indices can provide useful criteria for drought tolerance. A high positive and significant correlation was observed between MP, GMP, Ys, Yp, which indicates that these indices are suitable for identifying drought tolerant lines. These results help the modifier to select lines in different environments. Principal component analysis showed that it is important to introduce genotypes with desirable traits such as genotypes with high yield and resistance to drought stress. It is possible to speed up the improvement of new barley cultivars by using stress tolerance indicators by breeders. In general, 4, 7, and 13 lines were drought tolerant and can be used for barley improvement programs. Based on principal component analysis, drought sensitive and tolerant lines were consistent with cluster analysis. Exploiting the results of the present study can help breeders to select and identify genotypes that have relative tolerance to drought stress.