Medicago sativa L. is a tetraploid perennial forage legume of great agronomical interest. The increasing need for its use under water-deficit conditions as well as low-input systems demands further improvement of its drought tolerance. On the other hand, Medicagoarborea L. is a perennial leguminous shrub, which is knownas a drought-tolerant species. In the present study, drought stress responses of the aforementioned medicago species, along with their hybrid, named Alborea, were comparatively assayed at the morphological, physiological, biochemical, and transcriptional levels. In particular, transcript abundance of representative genes that: (a) control ion transport, intracellular Na + /H + antiporters(NHX1) and rare cold inducible2A (RCI2A); (b) have an osmotic function ∆1-pyrroline-5-carboxylate synthetase 1 (P5CS1); and (c) participate in signaling pathways and control cell growth and leaf function stress-induced mitogen-activated protein kinases kinases (SIMKK), Zinc Finger (ZFN), apetala2/ethylene-responsive element binding (AP2/EREB), basic leucine zipper (bzip) and Medicago sativa Helicase 1(MH1) were evaluated. Under well-watered conditions, the studied population of Alborea showed the highest stem elongation rate and photosynthetic rate that were dramatically reduced under drought conditions compared to M. sativa and M. arborea. Under drought conditions, the studied population of M. arborea showed less reduction of relative water content, all gas-exchange parameters, less lipid peroxidation, and more antioxidant capacity. Moreover, transcriptional analysis demonstrated that the population of M. arborea exhibited significantly higher transcript levels of drought-responsive genes in both leaves and roots under drought stress conditions. M. sativa has better antioxidant capacity than Alborea and had a higher induction of stress-related genes, thus it performs better than Alborea under drought conditions. Among the studied genes, it seems that AP2/EREB play a critical role in the response of the studied population to drought stress.

Salinity is a major limiting factor in crop productivity worldwide. Medicago sativa L. is an important fodder crop, broadly cultivated in different environments, and it is moderately tolerant of salinity. Medicago arborea L. is considered a stress-tolerant species and could be an important genetic resource for the improvement of M. sativa’s salt tolerance. The aim of the study was to evaluate the seedling response of M. sativa, M. arborea, and their hybrid (Alborea) to salt shock and salt stress treatments. Salt treatments were applied as follows: salt stress treatment at low dose (50 mM NaCl), gradual acclimatization at 50–100 and 50–100–150 mM NaCl, and two salt shock treatments at 100 and 150 mM NaCl. Growth rates were evaluated in addition to transcriptional profiles of representative genes that control salt uptake and transport (NHX1 and RCI2A), have an osmotic function (P5CS1), and participate in signaling pathways and control cell growth and leaf function (SIMKK, ZFN, and AP2/EREB). Results showed that the studied population of M. sativa and M. arborea performed equally well under salt stress, whereas that of M. sativa performed better under salt shock. The productivity of the studied population of Alborea exceeded that of its parents under normal conditions. Nevertheless, Alborea was extremely sensitive to all initial salt treatments except the low dose (50 mM NaCl). In addition, significantly higher expression levels of all the studied genes were observed in the population of M. arborea under both salt shock and salt stress. On the other hand, in the population of M. sativa, NHX1, P5CS1, and AP2/EREB were highly upregulated under salt shock but to a lesser extent under salt stress. Thus, the populations of M. sativa and M. arborea appear to regulate different components of salt tolerance mechanisms. Knowledge of the different parental mechanisms of salt tolerance could be important when incorporating both mechanisms in Alborea populations.

Soil salinity is a major constrain of crop productivity. Upland cotton (Gossypium hirsutum L.) is an important fiber crop worldwide and a major agricultural product in Greece. Two commercial cotton cultivars (‘Hersi’ and ‘ST 318’) were studied to compare their response under non-saline and saline conditions in a greenhouse experiment. Salt stress on plants was imposed by two different approaches: a gradual and an initial acclimatization to a non-lethal NaCl concentration (150 mM). To explore salt stress responses, growth (height of plants, roots, shoots and leaves dry weight, reproductive shoots, Salinity Sensitivity Index), gas exchange (Photosynthetic rate, Stomatal conductance, Transpiration rate and Water Use Efficiency) and biochemical parameters (proline, H2O2 and MDA content), were examined as well as ion homeostasis. ‘Hersi’ had significantly higher dry weight of roots, shoots and leaves, lower salinity sensitivity index of roots compared to ‘ST 318’.  In this regard, it appears that ‘Hersi’ cultivar performed better than ‘ST 318’ to increased salinity conditions, due to better control of gas exchange parameters and K+/Na+ homeostasis as well as better membrane integrity. Furthermore, the gradual acclimatization to the 150 mM NaCl concentration had a milder effect on both cultivars compared to the initial acclimatization.   ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 3, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********

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