Environmental Stresses in Crop Sciences
Year:2011 | Volume:4 | Issue:1|Papers Count:8

The application of micronutrients can improve the growth and yield of crops under stress conditions. In order to investigate the effect of micronutrient foliar application and irrigation regimes on black cumin, a field experiment carried out in Agricultural Research Center of Bojnord, Iran, in 2009. The experiment was conducted as split plots in a randomized complete block design with three replications. Irrigation intervals of7, 14 and 21 days were considered as main factors and five micronutrient foliar application steps including: control, B, Zn and Fe in 2, 3 and 4 PPT, respectively as well as a mixture of three above mentioned elements were considered as sub plots. Results showed that the irrigation regimes significantly affected plant height, subsidiary branches, capsule number per plant, number of seeds per plant and capsule, 1000 grain weight, grain and biological yield and harvest index, so that increasing the irrigation period decreased all of the above mentioned traits. The maximum grain yield obtained by seven-day irrigation regime. Moreover, foliar application of micronutrients significantly affected plant height, capsule number per plant, number of seeds per plant and capsule, grain and biological yield and harvest index. The differences amongst micronutrients spraying treatments and the control were significant for all above mentioned traits. Foliar application with the mixture of three micronutrients resulted in the greatest grain yield.

Drought stress is one of the most important problems of crop production in arid and semiarid regions of the world. The application of materials like superabsorbent polymers in soil could increase water retention in soil which results in reducing water use and fertilizer leaching. Such materials might decrease the impact of water deficiency on plants and improve the yield in the arid and semiarid regions. In order to study the effect of superabsorbent under drought stress conditions on yield, yield components and some physiological characteristic of corn (Zea mays L.), a split plot experiment based on RCBD was conducted with three replications at Research Farm of Birjand Islamic Azad University. Irrigation treatments with three levels (I1=100, I2=70 and I3=40 percents of plant water requirement) were considered as the main plot and the superabsorbent with four levels (S1=0, S2=35, S3=70 and S4=105 kg per hectare) were chosen as subplot. Results showed that the drought stress and superabsorbent had a significant effect on the yield and water use efficiency. The highest seed yield was recorded at optimum irrigation treatment (100 percent plant water requirement) and 105 kg superabsorbent per hectare and the lowest seed yield was observed at the most severe stress treatment (40 percent plant water requirement) and the control treatment (lack of superabsorbent). It seems that superabsorbent causes yield increase through decreasing the negative effects of drought stress on plant. So any factor that increases the seed yield, might directly affect the water use efficiency.

Soil and water salinity are amongst the severe and progressive problems worldwide which affects most cropland areas of Iran. Using endophytic microorganisms (which are amongst the most important soil microorganisms) to alleviate the detrimental effect of environmental stresses such as salinity is recently globally considered. In order to test the effects of Azospirillum strains and fungus Piriformospora indica on wheat growth and physiological characteristics under salinity stress, a factorial experiment based on RCBD was conducted with three replications in the greenhouse of the College of Agriculture of Ilam University in 2011. Treatments included five bioinoculants (P. indica, salt adapted and non-adapted Azospirillum strains, dual inoculation of the both microorganisms and non-inoculated control) as well as four salinity levels (0.2, 4, 8 and 12 dSm-1). Results showed that P. indica had a significant positive effect on wheat growth, aboveground fresh and dry biomass, chlorophyll content and osmolite solutes of inoculated wheat plants under saline and non-saline conditions, so that fungus inoculation reduced the detrimental effects of salinity stress and caused an improved plant growth. Infested plants by Azospirillum strains resulted in higher biomass, higher osmolite solute as well as higher chlorophyll content. Biomass and chlorophyll content in plant infested by salt-adapted Azospirillum strains were higher than that of those inoculated with non-salt-adapted Azospirillum strains. Results obtained from the present study indicated that endophytic microorganisms might be used to increase the growth and yield of wheat plants under saline conditions.

Water deficit is amongst the crop growth limiting factors and oxidative stress as a secondary stress occurs as a result of drought and water deficit. In order to study the effect of different salicylic acid levels in reducing water deficit impact on some growth characteristics of pot marigold plant, a factorial experiment was conducted based on CRD with three replications in Research Greenhouse of Faculty of Agriculture, Ferdowsi University of Mashhad during 2010-11. Experimental factors were salicylic acid concentration (0, 100 and 200 mM) and water deficit (100, 50 and 25 percent of soil field capacity). Results showed that different salicylic acid levels had a significant effect on leaf area and number, fresh and dry weight of plant, the number of lateral branches and flower number per plant, chlorophyll index, quantum yield, seed dry weight and seed number per plant. Leaf area and leaf number, the number and length of lateral branches, fresh and dry weight of plant, dry weight of flowers per plant, chlorophyll index, stomatal conductance, quantum yield were significantly reduced by a reduction in irrigation water. The interaction effects showed that 100 Mm of SA significantly reduced the impact of deficit irrigation at 50% FC, so that leaf area, the number of flowers per plant, seed dry weight and seed number per plant were significantly increased. It seems that SA increases plant stress tolerance through antioxidant production under stress condition and to some extent improves plant growth and dry weight of pot marigold under the conditions of this experiment.

Studying the relationships between yield components gives an outstanding aid to understand the physiological basis of crop yield. A Field experiment was conducted to evaluate the yield and yield components of drought-tolerant and susceptible cultivars of wheat under drought stress, at the Ferdowsi University of Mashhad Research Field. Experiment was set up as a split plot design with 5 irrigation treatments (as main plots), 2 cultivars (as sub plots) with 3 replications. Irrigation treatments included irrigation at the rate of full crop water requirement (FI, first control), without irrigation during spring (NI, second control), irrigation at the rate of 75% crop water requirement (75%FI), irrigation at the rate of 50% crop water requirement (50%FI) and irrigation at the rate of 25% crop water requirement (25%FI), and cultivars also included Pishgam (drought-tolerant) and Gascogne (drought-susceptible). Results showed that the differences among irrigation treatments and varieties were significant for yield components, economical and biological yields. The number of ear.m-2 and number of grain.ear-1 were decreased by reducing water supply, while 1000-grain weight was increased. Raise of 1000-grain weight could not compensate for the reduction of ear and grain number, therefore, economical and biological yield was decreased by reducing water supply. Harvest index was also decreased by reducing water supply. Overall, the tolerant cultivar showed a better performance in terms of economical yield, biological yield and water use efficiency comparing with the susceptible one, but it had lower harvest index than susceptible cultivar. Results showed that retention of greater ear number per unit area and greater grain production per ear were the most important prominence factors of tolerant cultivar comparing with the susceptible one. The efficacy of FAO Penman-Monteith method in evaluation of wheat water requirement was also assessed reliable.

Biosaline agriculture is one of the approaches to increase crop production under the existing situation of resources. Amongst halophytes, Kochia scoparia has been taken into consideration by researchers. Kochia is a mesohalophytes, C4 plant which has a good adaptability to different soil types. In order to evaluate the salinity effect on ion accumulation of kochia plant and its mechanism for salinity tolerance, a RCBD experiment was conducted with seven levels of saline water (1.5, 7, 14, 21, 28, 35 and 42 dSm-1) using drainage water with three replications in the northern region of Golestan province during 2009. Results showed that salinity significantly decreased biomass production. Salt tolerance of kochia at reproductive (salt tolerance index of 34) and flowering stage (salt tolerance index of 32) was greater than the vegetative growth stage (salt tolerance index of 24). Salinity had a significant effect on the accumulation of Na+, K+ and Cl- and the highest amount of ions were accumulated in leaves. Kochia’s root system played a selective role for absorption and transportation of Na+. Moreover, selective absorption of K+ was increased by accumulating Na+ in root media and maintained the Na/K ratio in plants. Kochia showed high tolerance to accumulation of Cl- in leaves. Results of this study showed that Kochia is a salt excluder halophyte.

Success of seed germination and seedling establishment of perennial grasses, which are sensitive to environmental stresses, is of great importance in the renovation and amendment of pastures. To achieve this, seed priming technique was evaluated in improving germination rate and seedling vigor of five perennial cool season grasses including Bromus confinis, Elymus elongatum, Agropyron pectiniforme ،Festuca ovina ،Festuca arundinaceae using Polyethylene Glycol 8000 for 0, 0.5, 1, 1.5, 2, and 2.5 MPa concentrations and 0, 2, 4, 6, and 8 days duration (D). The study was conducted as a factorial experiment based on CRD with four replications. ANOVA results showed that there were significant differences between all studied traits and their interactions for germination rate and seedling components (P<0.01). Seed priming significantly increased germination rate comparing with the control (non-primed), so that there were 127.9, 77.8, and 66.5% increase in germination rate comparing with the control (2 days in 2 MPa) for B. confinis, A. pectiniforme and E. elongatum, respectively, and 96.5% increase for F. arundinaceae (6 days in 1.5 MPa) whereas the lowest increase in germination rate (15%) was observed for F. ovina (4 days in 2.5 MPa). The regression analysis revealed that increasing PEG concentration decreased shoot and root dry weight for all species except F. arundinaceae and F. ovina. The greatest seedling growth reduction was detected for large seeded species B. confinis, and E. elongatum when treated for long duration (more than 2 days) and low concentrations of PEG. Overall, The results of this study suggested that seed priming with higher concentrations of PEG about 2 and 2.5 MPa and 2 days seed storage duration plays an important role in the success of grasses seed priming technique and also it revealed that small seeded species might show a better response to priming in improving seed germination and seedling establishment than that of large seeded ones.

Development of new cultivars which produce an acceptable grain yield with minimum irrigation in spring and provide high sustainable yield in different environments is of great importance in expansion of breeding programs. Field experiments were conducted with 171 International barley genotypes that had been received from ICARDA (SPII07 Nursery) including CVs Reyhan03 as a check using systematic design under both normal irrigation and late season limited water conditions at Karadj and Mashhad agricultural research stations in 2005-06cropping season. Tolerance and susceptibility of the genotypes to drought stress were calculated using STI, SSI, TOL, MP and GMP indices. Based on results in Mashhad and Karadj stations and considering the grain yield under both normal and stressed conditions as well as drought tolerance and susceptibility indices, genotypes no 159, 160, 162, 116, 104 and 106 were determined as the most tolerant genotypes and genotypes no 131, 64, 24, 26, 130, 63, 30 and 118 as the most susceptible genotypes. Pearson correlation coefficients were used to determine the relationships between the grain yield and studied indices. These coefficients showed that MP, GMP and STI indices had a positive significant correlation with grain yield under both normal and stressed conditions which indicates these indices can be considered as the most appropriate indices for the selection of tolerant genotypes.