Evaluation of drought tolerance among wheat landraces based on yield and integral selection indices

Wheat plays a key role in providing human food, providing 54% of the energy of every human being. Drought is a global problem that has placed major constraints on increasing wheat production in arid and semi-arid regions such as Iran. Among the various stresses, the most difficult to measure in terms of measurement is drought stress; Because different mechanisms lead to resistance. Drought stress is one of the most important factors that may be caused by low rainfall, high temperatures and high winds. The plant's reaction to it depends on the stage of growth in which the stress occurs. Different methods have been proposed for the identification and screening of drought tolerant, tolerant and drought sensitive cultivars. The most important of them include: drought Susceptibility Index, Yield Index (YI), Stress Tolerance Index (STI), Geometric Mean Productivity (GMP), Harmonic Mean (HMP), Modified Stress Tolerance Index (MSTI), Drought Resistance Index, Drought susceptible index, drought response index, non-biotic stress tolerance index, relative efficiency index (REI), Schneider stress intensity index (SSSI) and mean relative productivity (MRP).  Also, the total rank has been used for better conclusions about all indicators. The aim of this study was to evaluate the drought tolerance of native bread wheats based on yield indices and integrated selection index under stress and non-stress conditions, as well as selection of water-tolerant stress-tolerant genotypes and to investigate the relationship between yield and drought resistance indices.

To evaluate the drought tolerance of 25 wheat genotypes, this experiment was carried out based on a randomized complete block design with three replications under stress and non-stress conditions at Razi University of Kermanshah, Iran, from 2016 to 2017. Studied indices including: drought Susceptibility Index, Yield Index (YI), Stress Tolerance Index (STI), Geometric Mean Productivity (GMP), Harmonic Mean (HMP), Modified Stress Tolerance Index (MSTI), Drought Resistance Index, Drought susceptible index, drought response index, non-biotic stress tolerance index, relative efficiency index (REI), Schneider stress intensity index (SSSI) and mean relative productivity (MRP). All required statistical calculations including correlation coefficients, calculation of statistical indicators and parameters and drawing of biplot diagram were performed by EXCEL, SPSS and STATISTICA software.

Significant difference between genotypes for all indices and yield in both conditions were obtained. There is a significant and positive correlation between GMP, STI, HMP, MSTI, MRP, MP YI and REI indices with yield performance in non-stress and stress environments. STS and ISI indices showed that genotypes 10(WC.4987) and 15(WC.47638) were superior. Based on the bioplat obtained from the first and second main components, genotypes 24(WC.4583), 11(WC.47615), 4(WC.47341), 22(WC,47467), 21(WC, 47640), 12(WC.4612) and 16(WC.47638) are suitable for both conditions due to their proximity to the superior indices. Priciple components analysis in stress and non-stress conditions showed that the first two components (57.21%) and the second component (41%) together explained 98.21% of the variance. Drought tolerant cultivars show different results based on one index. For example, according to STI index, genotypes 10, 18, 15 and 20 were identified as drought tolerant, but according to GMP index, genotypes 10, 18, 15 and 13 were identified as drought tolerant genotypes. Due to differences in the results, the ranking was used for more accuracy. Based on total rankings, mean rankings and standard deviation of rankings, genotypes 8, 10 and 15 had the best rankings and were known as drought tolerant genotypes and genotypes 4, 11 and 22 as susceptible genotypes. As a result, these genotypes can be used for crossbreeding and genetic analysis for resistance, through various methods such as diallel analysis, mapping, marker selection, and so on.

The rate of yield reduction due to stress varies in different genotypes. Tolerant genotypes have the lowest yield loss and susceptible genotypes have the highest yield loss. The correlation between drought resistance and yield indices under stress and non-stress conditions showed that MP, STI, GMP, HMP, MSTI, YI, MRP and REI indices are suitable for selecting high yield genotypes under two conditions. According to the three-dimensional biplot, genotypes 10, 15 and 18 were superior in stress and non-stress conditions. According to STS and ISI indices, genotypes 8, 10 and 15 were more tolerant. Using one or a small number of indices to select drought tolerant cultivars will have different results, so ranking was used; In ranking based on total rankings, mean rankings and standard deviation of rankings, genotypes 8, 10 and 15 had the best rankings and were known as drought tolerant genotypes and genotypes 4, 11 and 22 as susceptible genotypes. . For more accurate results, these experiments should be repeated for more years so that these genotypes can be used as promising lines to increase production yield.