Environmental Stresses in Crop Sciences
Year:2012 | Volume:4 | Issue:2|Papers Count:8

In order to investigate the phosphorus and iron absorption rate and some of the physiological parameters in bread wheat (Sardari cultivar) and it's ancestral wild species for inbreeding selections and gene transportation, a factorial experiment based on randomized complete block design was conducted. In this experiment, physiological characteristics and absorption rate of phosphorus and iron in bread wheat and it's ancestral wild species (Triticum Boiticum, Aegilops speltoides, Triticum diccocoides, Aegilops tauschii)were investigated under the influence of P fertilizer (in 2 levels) and spraying Fe chelate (in 2 levels). Results showed that there were significant differences amongst different species in terms of phosphorus and iron concentration of shoot. Triticum Boiticum and Triticum diccocoides had the greatest phosphorus absorption rate, whileTriticum Boiticum and Aegilops speltoides had the greatest iron absorption rate. Results showed that the application of P fertilizer increased the content of proline and soluble carbohydrates at flowering stage in all species especially the crop species (Sardari cultivar) as well as Aegilops tauschii, so that these species had the greatest proline and sugar content. Interaction effect of P fertilizer by species type on proline and soluble carbohydrates rate was significant.

Drought and salinity are the most important limiting factors of plant growth and development in many regions of the world. Using plants that have satisfactory production under such conditions would be an appropriate strategy. To evaluate the combined effects of salinity and drought stresses on kallar grass(Leptochloa fusca L. kunth), a factorial experiment based on completely randomized design with 4 replications was conducted under controlled conditions at Research Greenhouse of Collage of Agriculture, Ferdowsi University of Mashhad during 2009. The treatments were drought stress (100, 50 and 25 percent of field capacity) and salinity stress (0, 5, 10 and 20 dSm-1). Results showed that physiological traits as photosynthesis rate, transpiration rate, chlorophyll fluorescence yield, and SPAD were reduced significantly by increasing drought and salinity levels, so that the lowest values of these traits were observed under severe drought (25% FC) and salinity (20 dSm-1) stresses. Moderate drought stress (50% FC) significantly increased chlorophyll fluorescence yield, whereas low to moderate salinity stresses (EC=5-10 dSm-1) significantly increased chlorophyll fluorescence yield and SPAD value compared to the control. Root to shoot ratio of kallar grass was significantly increased at the highest level of drought stress (25% FC), while this occurred with the moderate to high salinity stress (EC=10-20 dSm-1). Moreover, kallar grass biomass was decreased about 69 and 42 % under severe drought and salinity stresses compared with the control, respectively. Combination of drought and salinity stresses showed a better response of this halophyte species to salinity stress than to drought stress, as the full irrigation (100% FC) with salinity of 20 dSm-1 did not cause a statistical difference in shoot dry weight of kallar grass compared with the moderate drought stress (50% FC) up to the salinity level of 5 dSm-1. Overall, kallar grass showed more tolerance to high levels of salinity with full irrigation than moderate irrigation, suggesting that planting of this species in lands with adequate saline and brackish water is appropriate.

The aim of this experiment was to study the freezing tolerance of Dianthus barbatus under controlled conditions and was arranged as a completely randomized design with three replications. After sowing and growing plants in the bed in mid of summer to early autumn, at mid autumn (after hardening under natural conditions), plants were placed in the thermo gradient freezer at the 7-8 leaf stage with 12 freezing temperatures (0, -2, -4, -6, -8, -10, -12, -14, -16, -18, -20, -22oC). Cell membrane stability after freezing was assessed through electrolyte leakage (EL), survival percentage and re-growth of the plants after 3 weeks in cold frame were measured by counting the number of plants and determining their proportion to the number of plants before freezing and measuring the dry matter, height and number of branches. The results indicated that the effect of different freezing temperatures were significant at all plant characteristics (P£0.05). With decreasing the temperature, EL increased significantly (P£0.05) and reach to the maximum at -22oC. Survival percentage of plants did not affect until -18oC, but all plants were died at -22oC. The 50% of plants lethal temperature (LT50) of samples according to the EL and survival were -21 and -20.3oC, respectively, while the 50% reduced dry matter temperature (RDMT50) was -16oC.

Drought stress is one of the most important problems of agriculture in arid and semiarid regions of the world. The application of substances such as superabsorbent polymers in soils may decrease fertilizers leaching and increase water retention in the soil which reduces crop water use in turn. This experiment was conducted with corn (Zea mays L.) in Dashtak, Zahedan during growing season 2012. The experiment was done as a split-plot with three irrigation regimes including irrigation to provide 60%, 80% and 100% corn water requirement (ETc) as main plots and four amounts of superabsorbent polymer (SAP) including 0, 30, 60 and 90 kg ha-1 as subplots in a completely randomized block design with three replications. The results showed that the effect of irrigation regimes, SAP levels and interaction between the two factors had significant effect on all studied traits. The regression models estimated for relative water content (RWC), chlorophyll index (CI), remobilization of photosynthetic matters (RPM), portion of remobilization to seed and seed yield indicted that applying SAP under 100% ETc had no effect on above traits, while all corn traits were improved under drought stress. The results also showed that applying 60 kg ha-1 SAP decreased corn water requirement as much as 20% and caused a seed yield and physiological characters equivalent to that of the 100% ETc.

Available water is the major factor limiting plant growth and production in arid environments. According to research studies, foliar application of methanol has an important role in drought tolerance of C3 plants. In order to evaluate the effects of foliar application of methanol on some morphological characteristics of chickpea under drought stress, a factorial experiment was conducted based on completely randomized design with three replications in 2011 at the Research Center for Sciences of Ferdowsi University of Mashhad. The first factor was different levels of methanol concentration including 0 (control), 20, 25, 30, 35 volumetric percentage (v/v), which were used as foliar applications at three times during growth season of chickpea, with 10 days intervals. Second factor was moisture regimes in two levels including 25 and 100 percent of field capacity. Results showed that there were significant differences (P£0.01) amongst methanol concentrations in terms of plant height, number of branches, leaf dry weight, leaf number per pod, root and shoot dry weight, tap root length and area root to leaf area ratio. Spraying with 25% volume level significantly increased plant height, leaf dry weight, leaf number per pod, root and shoot dry weight, tap root length, root to leaf area ration compared with the control. Interactions between drought and methanol had a significant effect (P£0.05) on traits such as dry leaf weight, leaf number per pod, shoot dry weight and leaf area. Results indicated that foliar application of methanol with 25 and 30% volume can be recommended for increasing chickpea yield.

Cadmium is a toxic element which due to its great cumulative potential in plant organs causes important morphological and physiological changes in plant structure. In order to study of effect of salicylic acid priming on reduction of chloride cadmium damage on maize seedlings, a factorial experimental based on completely randomized design with three replications was conducted at the research laboratory of University of Damghan during 2012. The experiment consisted of two factors including a salicylic acid application (application and no application) and different CdCl2 concentrations (0, 0.05, 0.1 and 0.2 mM). The results showed that increase of CdCl2 concentration resulted in reductions in photosynthesis pigments, anthocyanin and morphological characteristics of maize seedlings. However, MDA, proline and phenolic compounds of maize seedlings were increased as CdCl2 concentration increased. Priming with salicylic acid increased photosynthesis pigments, anthocyanin, phenolic compounds, proline and morphological characteristics and decreased MDA in maize seedlings compared with the control (no application of salicylic acid). Salicylic acid application at the highest concentration of CdCl2 (0.2 mM) increased chlorophyll b, carotenoid, phenolic compounds of shoot and root as 8.24, 19.64, 29.13 and 47.05%, respectively, compared to the control. This reduced the MDA of shoot and root as 27.04 and 16.19%, respectively.

Iran is amongst dry and semi-dry regions of the world and enjoys several diverse climates. The recognition of traits related to growth, yield and adaptation of sunflower, especially in relation to drought stress can remarkably affect the development of planting area and its yield increase. To study the effect of water deficiency stress and foliar application of Zn on sunflower (Helianthus annuus L.) yield and some of its physiological traits, a split plot experiment based on randomized complete block design was conducted with three replications at the Islamic Azad University of Birjand in 2010. The main plot was irrigation regime with four levels including I1=without stress (according to the plant's water demand), I2=interrupting irrigation 1 time during the vegetative growth stage, I3=interrupting irrigation 1 time during the reproductive stage, I4=interrupting irrigation during the vegetative and flowering stages and the sub plot was foliar application of zinc sulfate with three levels including Zn1=without foliar application, Zn2=0.5% concentration of zinc sulfate (2 kg/ha zinc sulfate or 659 gr ha-1 of zinc element), Zn3=1% concentration of zinc sulfate (4 kg/ha zinc sulfate or 1319 gr ha-1 of zinc element). Results indicated that irrigation ceasing significantly decreased the number of seed head, 1000- seed weight, seed yield and oil yield, while the oil percent was not affected. According to the results, applying drought stress during the vegetative and reproductive growth stages decreased seed yield and oil yield as much as 20% and 31% in comparison with the control, respectively. In addition, Zinc sulfate treatment with 1% concentration increased the 1000-seed weight, seed yield and oil percent in comparison with other treatments. In this study seed yield showed a significant reduction under the influence of drought stress. The treatment of complete irrigation (according to the plant's water demand) resulted in higher yields than other irrigation treatments. The greatest seed yield was obtained by foliar application of Zn with 1% concentration. Moreover, the least oil yield was observed where irrigation was interrupt during the vegetative and reproductive growth stages. Overall, application of Zn under water deficit conditions could be employed as a good strategy for reducing the detrimental effects of drought stress on growth and yield characteristics of sunflower.

In order to study the effects of terminal drought stress on morphological and physiological characteristics of 20 promising genotypes of barley, a split plot experiment based on randomized complete block design with three replications was conducted in the agricultural research center of Southern Khorasan during the 2007-2008 growing season. Treatments consisted of 2 levels of drought stress as main plots including the control (complete irrigation) and ceasing irrigation at 50% heading appearance, and 20 barley promising genotypes as sub plots. Results showed that ceasing irrigation at the 50% heading resulted in 14.64 and 8.12% reduction with the grain and biological yields compared to the control, respectively. Moreover, implementing drought stress from 50% heading onwards enhanced chlorophyll index, cell membrane permeability and declined the relative water content of the flag leaf. Although there were no significant differences amongst genotypes in terms of biological yield, the highest and lowest grain yields achieved with genotype numbers 18 (5997.2 kg.ha-1) and 16 (3420.8 kg.ha-1). The highest rate of chlorophyll index was recorded in genotype number 5 and 13, and the greatest amount of relative water content (80.7%) in the flag leaf was observed with the genotype number 8. According to the results of this study, genotypes number 18 and 20 provided the appropriate yield under both normal and drought stress conditions.