Understanding the physiological mechanisms that control drought tolerance in crop plants is vital for effective breeding. In this study, we characterized drought stress responses in four sorghum cultivars exhibiting differential levels of drought tolerance at pre-and post-anthesis. Greenhouse-grown plants were subjected to two types of drought treatment, water stress (WS) and desiccant-induced water stress (DA), timed to occur at pre-and post-anthesis. Multiple physiological measurements were then made revealing varying responses among the experimental cultivars. The pre-and postflowering drought-tolerant cultivar P898012 showed a significantly higher net photosynthetic rate, higher transpiration rate, and greater stomatal conductance compared to the drought-susceptible cultivars at both pre-and post-anthesis. A significantly greater stomatal size was also detected in P898012, while the highest stomatal density was found in the drought-susceptible cultivar P721Q. Meanwhile, the two post-flowering drought-tolerant cultivars P898082 and B35 had a higher starch content and exhibited greater osmotic potential under post-anthesis water stress. Compared to WS and wellwatered control plants, a greater increase in root biomass was observed in P898012 under DA at pre-anthesis. This finding suggests that plants invested more assimilates into the roots under severe DA at pre-anthesis. Overall, our results show good conformity between drought tolerance in sorghum and key physiological mechanisms of stomatal conductance, root growth patterns, and starch accumulation, all of which act as coping mechanisms during critical drought-sensitive growth stages. | INTRODUCTIONDrought is one of the key abiotic stresses limiting crop productivity worldwide (Cha-um et al., 2012), affecting plant productivity by inducing stomatal closure, and thereby reducing photosynthesis (Németh et al., 2002) and growth (Bibi et al., 2012). With growing effects of climate change, the development of drought-tolerant and climateresilient crops is essential for survival under unfavorable environmental conditions and maintenance of high yield. Plants respond to water stress via a series of cellular events involving physiological, morphological and biochemical processes. Under water stress, photosynthesis decreases, osmotic potential is reduced, and consequently, the availability of photosynthetic assimilates and energy becomes limited. During pre-anthesis assimilation, the necessary resources for grain filling temporarily accumulate within the stem as non-structural carbohydrates such as starch, sucrose, monosaccharides, isoprenoids, and fructans (Schnyder, 1993;Jensen and Wilkerson, 2017). It has been suggested that genotypes that can synthesize and store large amounts of starch could potentially exhibit improved grain yield by mobilizing these reserves to the grains when photosynthesis is inhibited

Background: Definitive comparison on root traits of wheat landraces, ancient wheat species and wild wheat relatives are scarce. Those adaptive genetic resources with superior root and shoot traits can be utilized in breeding programs. Questions: Do modern wheats have more superior root and shoot traits than ancient wheat species and wild wheat relatives? Studied species: We performed large-scale screening for significant root and shoot traits of 47 different genotypes including cultivars, lines, landraces, ancient wheat species and wild wheat relatives belonging to 14 different species. Study site and years: was carried out in Central Anatolian Conditions of Turkey from October, 2013 to July, 2014. Methods: This study was conducted at 200 cm long tube under field weather conditions where plants can translate superior performance. Results: A wide range of variations in terms of root and shoot traits were observed among the screened wheat cultivars, lines, landraces, ancient wheat species and wild wheat relatives. The grain yield per plant and root length per plant varied from 2.11 to 12.30 g and 134.7 to 250.7 cm in the cultivars, lines and landraces, respectively, while they ranged from 0.23 to 6.49 g and 170.0 to 240 cm in the ancient wheat species and wild wheat relatives. Conclusions: The superior genotypes that had longer root system and high grain yield can be considered in breeding programs to improve high yielding genotypes and deep-rooted system. Key words: Modern and ancient wheats, wild wheat relatives, root and shoot traits, screening Botanical Sciences (1):

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This study was conducted to investigate root and shoot traits of wild, ancient and modern wheat genotypes belonging to 8 different species at long tubes under field weather conditions. It was found significant differences between genotypes with regard to root and shoot traits. The research results indicated that root biomass distribution of genotypes at GS 31 ad GS 69, respectively was found 59.2% and 56.3% in 0-30 cm, 76.7% and 71.9% in 0-60 cm. Modern wheats (Çeşit 1252(Çeşit , Konya 2002 and Triticum vavilovii (ancient wheat) had high root biomass distribution in top soil. In the study, species with AABBDD genomes had higher root length than those with AABB, AABBGG and AA genomes. Triticum dicoccoides, Triticum timopheevii and Triticum monococcum had lower values than other genotypes in terms of root length, crown root number, root biomass, shoot biomass and plant height at both growth stages (GS 31 and GS 69), while Triticum vavilovii and Triticum spelta (hexaploid) took part in the front. Accordingly, Triticum vavilovii and Triticum spelta may be used in breeding programs to improve new modern cultivars with high root and shoot traits.