Investigating the response mechanisms of bread wheat mutants to salt stress

Mutation breeding is among the most critical approaches to promoting genetic diversity when genetic diversity is narrowed for a long time using traditional breeding methods. In the current study, 15 wheat mutants created by gamma radiation and three salt-tolerant wheat cultivars were studied under no salinity stress (Karaj) and salinity stress (Yazd) during three consecutive growing seasons from 2017 to 2020 (M05 to M07 generations mutants). Results showed that salinity induced lipid peroxidation and enhanced ion leakage in all genotypes however, M6 and M15 showed the least ion leakage increment. It was also observed that the activity of antioxidant enzymes including SOD, CAT, POX, APX and GR increased with salinity; the maximum increase in antioxidant activity was belonged to M15, M09, M06 and M05. All genotypes had higher protein content in salinity stress conditions; M07 and M12 showed the lowest (1.8%) and the highest (17.3%) protein increase, respectively. Zeleny sedimentation volume increased under salinity stress conditions in all genotypes except M06, C2, C3, and M07. The result indicated that salinity stress increased wet gluten in all genotypes. M10 and M08 showed the highest (47.8%) and the lowest (4%) wet gluten increment, respectively. M06 and M11 mutants showed the lowest (6.1%) and the highest (60.7%) decrement of grain yield due to salinity stress, respectively. Finally, M04, M05, M07, M13, and M14 were known as genotypes with high grain yield in both no salinity and salinity stress conditions. In other word, these genotypes have higher yield stability. The results of the current study revealed that gamma irradiation could effectively be used to induce salinity tolerance in wheat.

Relationship between nitrapyrin and varying nitrogen application rates with nitrous oxide emissions and nitrogen use efficiency in a maize filed

Reducing nitrogen losses can be accomplished by mixing fertilizers with nitrification inhibitors (NI). In some agricultural systems, increasing soil N supply capacity by the use of NI could lead to improved N use efficiency (NUE) and increased crop yields. This study examined the effect of different N rates and NI in maize in the north of Iran. The maize was fertilized with urea at three levels (69, 115 and 161 kg N.ha^-1) alone or with nitrapyrin as NI. Increasing the N application rate resulted in a considerable rise in growing-season N₂O emissions. When nitrapyrin was used, N₂O emissions were dramatically reduced. NI treatment reduced N₂O emissions in the growth season by 88%, 88%, and 69% in 69, 115, and 161 kg of N.ha^-1, respectively. NI treatment reduced yield-scaled N₂O emissions; the lowest quantity of yield-scaled N₂O was found in 69 N + NI (0.09 g N₂O-N kg^-1 N uptake). Additionally, grain yield increased by 19%, 31% and 18.4% after applying NI to 69 N, 115 N, and N69, N115 and N161. Results showed that 115 N + NI and N69 treatments showed the highest (65%) and lowest (29%) NUEs, respectively. Finally, our findings show that NI can reduce N₂O emissions while increasing NUE and yield, but that the application method and rate of nitrapyrin application need to be improved in order to maximize its mitigation potential.

Evaluating the role of gamma irradiation to ameliorate salt stress in corn

PURPOSE

Salt stress is a significant issue in corn cultivation leading to corn yield reduction, especially in the arid and semi-arid regions. Nuclear technologies, along with other standard methods, can be used as an efficient method for mitigating salt stress effects on plants.

MATERIALS AND METHODS

In this research, gamma irradiation (GI) was studied on seeds in the salt stress amelioration of corn in laboratory and field conditions. A total of five doses of gamma rays (25, 50, 100, 150 and 200 Gy) were applied to corn seeds (SC.703) at the laboratory under saline and control conditions. The best gamma-ray treatment (25 Gy) was selected for studying corn under salt stress in the field condition.

RESULTS

The length of the radicle, seminal roots and shoot, dry weight of radicle, and seminal roots were affected by salt stress (p <.001). However, GI affected only the radicle and seminal root length (p < .001). The radicle length was decreased as much as 3, 11, 17, 25, and 27% in 25, 50, 100, 150 and 200 Gy of GI, respectively. In addition, the seminal root length was decreased in all GI treatments except 25 Gy (p < .05). Plants derived from seeds exposed to GI (25 Gy) had a higher chlorophyll content of 1, 17, and 29% at V3 (third leaf stage), R1 (silk stage, p < .001), and R4 (dough stage, p < .001), respectively. In GI treatment, the soluble carbohydrate content was significantly higher (p < .001) at all three measurement stages and the soluble protein was significantly higher (p < .001) only at the R4 stage. Moreover, proline content was higher in GI (25 Gy) at V3 (58%, p < .05) and R1 (98%, p < .001) treatment stages.

CONCLUSION

Since plants from gamma-irradiated seeds had a greater plant weight and their economic traits (cob and grain weight) were higher compared to control plants under salt stress conditions, it can be concluded that a low dose of GI may ameliorate the effect of salt stress on the corn plants.

Reducing nitrous oxide emissions from irrigated maize by using urea fertilizer in combination with nitrapyrin under different tillage methods

The aim of this study was to evaluate the effectiveness of nitrification inhibitor (nitrapyrin; NI) as a mitigation option for yield-scaled emissions of nitrous oxide (N₂O) under tillage management and urea fertilization in the irrigated maize fields in northern Iran. A split-plot experiment was performed based on a randomized completed blocks design with three replicates. The main plots were the levels of tillage practices (conventional tillage (CT) and minimum tillage (MT), and the subplots were the fertilizer treatments (control, urea, and urea + NI). The gas samples for measuring N₂O emissions were collected during the maize growing season from June to September, using opaque manual circular static chambers. Soil samples were taken at 0-10 cm to determine water-filled pore space, ammonium (NH₄⁺), and nitrate (NO₃^-) concentrations in the soil. When the crop reached physiological maturity, maize was harvested to measure grain yield, biomass production, N uptake of aboveground, and nitrogen use efficiency (NUE). The results showed that the applying NI in combination with urea reduced the total N₂O emissions by up to 58% and 64% in MT and CT, respectively. In the urea + NI treatment, mean soil concentrations of NH₄⁺ and NO₃^- were significantly higher (20%) and lower (23.5%), respectively, compared with other treatments. The NI reduced the yield-scaled N₂O-N emission up to 79% and 55% for CT and MT, respectively. Furthermore, compared to treatment with urea alone, the application of NI increased the NUE of the MT and CT systems by an average of 55% and 46%, respectively. This study emphasized that the application of nitrapyrin should be encouraged in irrigated maize fields, in order to minimize N₂O emissions and improve NUE and biomass production.

Application of gamma rays on salinity tolerance of wheat (Triticum aestivum L.) and expression of genes related to biosynthesis of proline, glycine betaine and antioxidant enzymes

We investigated the effects of salinity stress and gamma radiation on salinity tolerance in wheat crops. To this end, mutant lines were generated by exposing Arg and Bam wheat varieties at the primordial state to 150 and 200 gamma radiation doses in the field. The top 15 mutant lines were specified for cultivation in the fifth-generation under two conditions, including non-stress and salinity stress. According to Fernandez's model, the three mutant lines had high yields under both conditions. The three mutant lines were selected with their two parents, and then, cultivated in a completely randomized factorial design in a greenhouse under non-stress and salinity conditions. The mutant lines showed significantly higher osmotic adjustment, leaf relative water content (RWC), potassium ion concentration, soluble sugar content and lower proline (Pro), and glycine betaine (GB) content than the parents at both the vegetative (VEG) and reproductive (REP) stages under salinity conditions. The expression of genes involved in the Pro biosynthesis pathway, P5CS and P5CR genes, in mutant lines were less than their parents, and conversely, P5CDH in mutant lines was more than their parents. The changes in the expression of CMO and BADH genes involved in the GB synthesis pathway indicated that the mutant lines had less gene expression compared to their parent genotypes of Arg and Bam. The results indicated an increase in antioxidant activity in the mutant lines compared to their parents. Consequently, irradiated plants have probably adapted to the salinity stress by increasing the osmotic adjustment, RWC, potassium ion concentration, and soluble sugar content, as well as activating antioxidant enzymes.

Changes in photosynthetic pigments and chlorophyll-a fluorescence attributes of sweet-forage and grain sorghum cultivars under salt stress

Water shortage leads to a low quality of water, especially saline water in most parts of agricultural regions. This experiment was designed to determine the effects of saline irrigation on sorghum as a moderately salt-tolerant crop. To study salinity effects on photosynthetic pigment attributes including the chlorophyll content and chlorophyll fluorescence, an experiment was performed in a climate-controlled greenhouse at two vegetative and reproductive stages. The experimental design was factorial based on a completely randomized design with five NaCl concentrations (control, 50, 100, 150, and 200 mM), two grain and sweet-forage sorghum cultivars (Kimia and Pegah, respectively) and four replications. According to the experimental data, there were no significant differences between two grain and sweet-forage cultivars. Except for 100 and 150 mM NaCl, salinity significantly decreased the chlorophyll index and pigment contents of the leaf, while it increased the chlorophyll-a fluorescence characteristics. Although salinity reduced photosynthetic pigments and the crop yield, either grain or sweet-forage cultivars could significantly control the effect of salinity between 100 and 150 mM NaCl at both developmental stages, showing the possibility of using saline water in sorghum cultivation up to 150 mM NaCl.