Selection for drought tolerance in selected germplasm of Hordeum spontaneum based on agronomical, physiological and biochemical indices;.

This research was performed on nine genotypes of Hordeum spontaneum, selected from previous evaluations, to study drought tolerance in a split plot experiment based on Randomized Complete Block Design with three replications under shelter in research field of Seed and Plant Improvement Institute. The main plot included three levels of water stress as normal irrigation, water withholding at flowering stage and no irrigation and sub-plots comprised the studied genotypes. The results indicated that the effect of drought stress on plant height, grain yield, biomass, relative water content, osmotic adjustment, stomatal conductivity, chlorophyll content, canopy temperature, catalase, ascorbate peroxidase and peroxidase, protein, malondialdehyde, and proline was significant. The results revealed that the level of proline and antioxidant enzymes increased in the studied genotypes after water stress; however the rate of increase was higher in the tolerant genotypes. It seems that survival and maintenance of high biomass and grain yield in Spontaneum under drought stress conditions is due to higher proline accumulation and hereby able to maintenance of higher leaf relative water and higher activity of antioxidant enzymes. The results of principal component analysis on the whole evaluated traits in drought stress condition located the studied genotypes in four groups. The first and second group comprised genotypes 555, 374 and 434. These genotypes had significantly higher grain yield, relative water content, chlorophyll content, enzymatic activity of peroxidase and ascorbate peroxidase and lower content of malondialdehyde, leaf temperature and osmotic potential (more negative) and therefore, were identified as tolerant genotypes. Key words: Hordeum spontaneum, Drought tolerance, Antioxidant enzymes, Relative water content, Stress tolerance index