Identification of drought tolerant barley (Hordeum vulgare L.) genotypes using drought tolerance indices

Introduction Barley is the fourth most important cereal worldwide and it is well adapted to some of abiotic stresses.Late season drought stress is the most important limiting factor in production of barley. The existence of variations in response to drought stress, promotes breeders to look for the new genetic variations among barley genotypes in order to improve yield under water stress conditions (Jallel et al., 2004). Drought tolerance indices based on grain yield in both normal and water stress conditions enable breeders to identify drought tolerant genotypes (Zare et al., 2012).   Materials and methods In order to identify barley drought tolerant genotypes and correlation between yield components and drought tolerance indices, 79 foreign genotypes and an Iranian control variety were evaluated under normal irrigation and water stress conditions in an experimental field at college of agriculture, Shiraz University, during growing season 2012-13. The experiment was conducted as split plot based on randomized complete block design in three replicates. Each barley genotype was grown on 4 rows of 2 meters length. In normal irrigation treatment, plants were irrigated every week to field capacity level, while irrigation was completely stopped after 3-leaf stage in water stress treatment. Yield and yield components including number of spikes, number of seeds per spike, thousand grain weight and biological yield were measured in both normal irrigation and water stress conditions. The following drought tolerance indices were calculated using grain yield under normal irrigation and water stress conditions: Stress susceptibility index (SSI) (Fisher et al., 1978), Mean Productivity (MP) and Tolerance index (TOL) (Rosielle et al., 1981), yield index (YI) (Lin et al., 1986), Harmonic Mean Productivity (HMP), Stress Tolerant Index (STI) and Geometric Mean Productivity (GMP) (Fernandez, 1992).   Results and discussion Biological yield, spikes number and thousand grain weight exhibited a significantly positive correlation with the stress tolerance indices. The high correlation between drought tolerance indices and thousand grain weight (Shahmoradi et al., 2011), number of spikes and biological yield (Dolatpanah et al., 2011) have been also reported in previous researches. Among various drought tolerance indices, MP, GMP, HMP and STI demonstrated highest positive and significant correlation with yield under both normal irrigation and water stress conditions and they were introduced as the best indices for identification of drought tolerant genotypes. These results are in consistence with the reports in a similar research carried out by Khokhar et al. (2012). In addition, according to results of principal component analysis, the first two components named as tolerant and yield stability component and susceptibility component, respectively, were able to explain 97% of the total variation. Based on different statistical analyses, the genotypes number 88 and 145 were identified as the most drought tolerant genotypes. Cluster analysis based on tolerance indices and yield under both normal and water stress conditions classified 80 varieties into four separate groups related to their response to water stress conditions.   Conclusion The yield components of thousand grain weight and number of spikes as well as biological yield can effectively contribute to selection of barley drought tolerant genotypes as it was demonstrated by their high correlation with drought tolerance indices. The results of this research on identification and clustering of tolerant and susceptible barley genotypes can be used in barley breeding programs and to increase the diversity of Iranian barley germplasm towards production of new drought tolerant cultivars.