water stress

The severe impact of drought and salinity on plant productivity presents a significant threat to worldwide food security. Plants exhibit the capacity to sense stimuli in their environment and adjust defense mechanisms through diverse regulatory networks to cope with abiotic stress. The complexities of drought and salinity tolerances can be deconstructed into contributing factors and mechanisms, classified under two categories: genetics and epigenetics. Epigenetic mechanisms play a role in partially attributing crop adaptation to the most formidable drought and salinity stresses. Plants respond to stress in part by undergoing stable alterations in gene expression, a process that involves the physical "marking" of DNA or its associated proteins, commonly called epigenetics. Plants utilize various epigenetic mechanisms to refine gene expression, vital for adaptation and phenotypic plasticity. These include DNA methylation, histone modifications, chromatin remodeling, epitranscriptomics, and gene silencing mediated by small RNAs. Notably, epigenetic modifications can be inherited or erased. Enhanced knowledge of epigenetics complements genetics and will aid in developing strategies to integrate them into crop improvement programs aimed at addressing adaptation to abiotic stress. This review highlights the latest and noteworthy findings regarding crop epigenetic responses to abiotic stress signals, particularly those pertinent to drought and salinity tolerance.

Drought stress is one of the most important environmental stresses affecting plant growth, yield and crop production around the world. It is believed that arbuscular mycorrhizal fungi are used for protecting plants against drought damage.Vesicular-arbuscular mycorrhizal fungi have been used in recent years to cope with water stress in many plants. In this study, the relationship between water deficit stress and mycorrhizal fungi were analyzed with mycorrhizal dependence index and chlorophyll stability in sesame (Sesamum indicum L.). The experiment was conducted in a split-plot design based on randomized complete blocks with three replications in the research field of Agricultural Research Center, West-Azerbaijan during years 2015 and 2016. The main factors consisted of normal irrigation, moderate and severe water stress and subplots included two different species of mycorrhizal fungi namely, Funneliformis mosseae and Rhizophagus intraradices. A non-inoculated plant served as the control. Mean comparison based on 2-years data showed that with increasing severity of water stress, biological water use efficiency (WUBE), oil harvest index (OHI) and protein harvest index (PHI) decreased. Using two kinds of mycorrhizal fungi F. mosseae, R. intraradices compared to non-inoculated, caused an increase in WUBE and PHI about 28 and 20% and 6 and 2%, respectively. Also in three different irrigation conditions, the effect of F. mosseae and R. intraradices was similar on chlorophyll b stability index (CSIb). The maximum and minimum WUBE (0.96 and 0.43 kg/m3), OHI (17.61 and 10.03%) and PHI (9.36 and 5.80%) were obtained under optimal irrigation and severe drought stress conditions, respectively. The maximum (34.69%) and minimum (20.26%) of mycorrhizal dependence index based on biological yield (MDIBY) were observed under severe drought stress and optimal irrigation conditions, respectively. Therefore, inoculation with mycorrhizal fungi (measured by MDIGY and MDIBY) under drought stress caused an increase in the chlorophyll (measured by TCSI). Increasing the chlorophyll led to an enhancement in the photosynthesis and promoted WUEE and WUBE. Improvement of the WUEE and WUBE caused an increase in oil and protein (measured by OHI and PHI). In severe and moderate water stresses mycorrhizal dependence index based on grain yield (MDIGY) and MDIBY increased compared to optimal irrigation. It can be concluded that for achieving high WUEE, WUBE, OHI and PHI, TCSI and as a result tolerance to the water stress can be increased.

The objectives of the present research were to evaluate the variability induced by gamma-irradiation among a population of M8 sunflower mutant lines and to identify molecular markers associated with different seed germination traits. Experiments were carried out under well watered and water-stressed conditions using a randomized blocks design, with three replications. The studied traits consisted of critical times (the time to starting germination, TSG), the time to 50% germination (T50%G) and the time to maximum germination (TMG) and the percentage of seed germination (PSG). In both conditions, a large genetic variation was observed among mutant lines. Some mutant lines showed higher values of germination parameters when compared with the original lines (AS613). Results revealed the a efficiency of gamma irradiation for inducing genetic variation in sunflower, for germination traits. A highly negative, significant correlation was observed between PSG and the critical times of germination. Mutant line “M6-39-2-1” was significantly superior to the original line, for the studied traits, under the water-stressed condition. Multiple regression analyses showed that some AFLP markers were associated with several traits. The most informative AFLP markers were “E37M62-5” and “E33M60-6” which did not have any interactions with water stress. Several markers were associated with seed germination parameters in both conditions. The markers which were associated with different traits could be used in marker-assisted selection for germination parameters.