The aim of the current work is the screening of 123 Iranian wheat (Triticum aestivum L.) landraces (spring and winter genotype) for drought tolerance using morphological and physiological characteristics. An initial screening of wheat landraces was performed based on shoot and root traits, relative water content (RWC) and parameters extracted from polyphasic chlorophyll fluorescence. Significant variability was observed for all physiological and morphological traits among wheat genotypes in the assessed germplasm. Although a decrease in morphological characteristics was obvious in drought-treated plants, there were genotypes with increased root length even after drought stress, suggesting that selection inside the landraces for long roots is possible even under drought pressure. The genotype-by-trait biplot of spring wheat vs the six morphological and physiological traits permitted us to select genotypes that are near the outstanding traits as an indicator of drought stress tolerance. In genotype ‘L-82', minimum decrease of root weight (35.41%), RWC (20.71%), seed number (14.96%), seed weight (31.19%), and thousand-kernel weight (TKW) (19.09%) was observed in drought-treated plants relative to its control. On the other hand, this ratio increased by 67.7% and 1.5% for root/shoot ratio and root length, respectively. It was also recorded that the performance index for the photochemical activity (PIabs, chlorophyll parameter derived from Kautsky curve), as a very sensitive parameter to environmental stress, can be used effectively for screening wheat landraces under drought stress. RT-qPCR assay revealed relative maintenance of photosynthesis rate in tolerant genotype even after drought stress treatment. These characteristics effectively enabled us to identify a set of contrasting cultivars differing in their tolerance to drought stress.
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