Evaluation of bread wheat genotypes under drought stress conditions in seedling stage using drought indices

Abstract

Introduction The existence of drought stress at the beginning of the growing season is one of the most important threatening factors in wheat production of Iran. The coleoptile length is the most important morphological trait in determining sowing depth, emergence power and seedling establishment. The coleoptile length has been used as an effective indicator for selecting the drought tolerant genotypes in wheat breeding programs. Various indices have been developed to evaluate crop response to various stresses, including tolerance index (TOL), productivity mean (MP), geometric mean productivity (GMP), harmonic mean (HM), stress tolerance index (STI), stress sensitivity index (SSI), yield index (YI), yield stability index (YSI) and relative stress index (RSI). The efficiency of each indices depends on the breeding objectives and the target environment. Materials and methods In order to evaluate some of the landrace wheat genotypes under drought stress conditions at the seedling stage, an experiment with 35 pure lines under three moisture conditions (control, drought stress with PEG6000 10% and 15%) was conducted in a completely randomized design (CRD) with three replications at Gorgan university of agricultural sciences and natural resources.. The coleoptile length was measured after eight days. The indices of MP, GMP, HM, STI, SSI, YI, TOL, RSI and YSI were calculated based on the coleoptile length values under control (Yp) and stress (Ys) conditions. Data analysis was performed using iPASTIC: an online toolkit to estimate plant abiotic stress indices. Results and discussion In control and 10%-drought stress conditions, genotypes 11 and 2 had the highest of coleoptile length. While, in 15%-drought stress conditions, genotypes 3 and 6 had the highest of coleoptile length, respectively. Also in control and 15%-drought conditions genotypes 30 and 35 and in 10%-drought stress conditions genotypes 15 and 21 had the lowest of coleoptile length. Based on MP, GMP, HM, STI and YI indices, genotypes 2 and 11 were identified as tolerant genotypes, while genotypes 15, 21 and 30 were susceptible genotypes, under 10% drought stress conditions. Under 15%-drought stress conditions, MP, GMP, HM, STI and YI indices identified genotypes 21 and 34 as the most susceptible genotypes, whereas genotypes 30 and 35 were the most susceptible genotypes. Under three moisture conditions, the coleoptile length had the highest coefficient of correlation (positive and significant) with MP, GMP, HM and STI indices. Using three-dimensional plots, the genotypes were divided into four groups A, B, C, and D. The most appropriate indices being the ability to distinguish group A, from other groups. Group A selects genotypes that have high yield in both control and stress conditions. The result showed genotypes 3, 6, 11, 16, 19, 20 and 24 were classified as group A in both drought stress conditions. The Iranian commercial cultivars (genotypes 30, 34 and 35) placed in Group D, which indicates insufficient attention to drought stress at the seedling stage, while tolerance to terminal drought stress is one of the most important goals in wheat breeding programs of Iran. Principal component analysis (PCA) showed that the first two PCAs explained 99.78% of the variation in 10%-drought stress and 99.80% in 15%-drought stress conditions. MP, GMP, HM and STI had the sharp angles with together that it indicates high correlation among mentioned indices. Multivariate biplos showed that drought tolerant genotypes were adjacent to vectors related to the best drought tolerance indices. Conclusions Correlation coefficients of drought tolerance indices showed that MP, GMP, HM and STI were the most suitable indices for selecting of drought tolerant genotypes. Based on stress tolerance indices and 3D plots, genotypes 3, 6, 11 and 24 (originated from Turkey, Afghanistan, Iran and Afghanistan, respectively) were identified as drought tolerant genotypes at the seedling stage, while genotypes 14, 15, 21, 30 and 35 were identified as the most susceptible genotypes. The landrace genotypes identified in this study could be used in breeding programs of bread wheat under drought stress at the seedling stage.