Decreased Shoot Dry Weight Research Articles

Effect of Salt Stress on the Growth, Physiology, and Mineral Nutrients of Two Penstemon Species

Penstemons are a diverse group of flowering plants valued for their ability to enhance the visual appearance of urban landscapes. Penstemon barbatus (Cav.) Roth ‘Novapenblu’ (rock candy blue® penstemon) and Penstemon strictus Benth ‘Rocky Mountain’ (rocky mountain beardtongue) are widely used in landscapes, but their tolerance to soil salinity remains poorly understood. This study aimed to investigate the effects of salinity levels at electrical conductivities (ECs) of 1.0 (nutrient solution), 2.5, 5.0, 7.5, and 10.0 dS⋅m−1 on two penstemons (P. barbatus and P. strictus). Penstemons were irrigated with nutrient or saline solution for 8 weeks and various growth and physiological data were recorded before harvest. Salinity stress degraded the visual quality of penstemon species and led to a reduction in the growth rate and biomass production. Leaf burn and necrosis were observed in penstemons because of salinity stress. The visual score of P. barbatus and P. strictus decreased with increasing EC levels in the saline solution. When irrigated with saline solution at an EC of 7.5 dS⋅m−1, Penstemon barbatus and P. strictus had severe-to-moderate foliar salt damage with average visual scores of 1.7 and 2.5, respectively (0 = dead plant; 5 = excellent plant without any foliar damage). The two penstemon species had severe foliar salt damage or were dead when irrigated with saline solution at an EC of 10.0 dS⋅m−1. There were 87% and 92% decreases in the leaf area of P. barbatus and P. strictus, respectively, when irrigated with saline solution at an EC of 10.0 dS⋅m−1 compared with those in the control. Although not statistically significant, there were 7% to 18% decreases in shoot dry weight of P. barbatus when irrigated with saline solutions at ECs of 2.5 to 10.0 dS⋅m−1 compared with control. However, P. strictus displayed declines of 13% to 31% in shoot dry weight as the salinity levels of the irrigation solution increased. As the salinity levels increased, the net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration (E) rates decreased. Furthermore, sodium (Na+) and chloride (Cl−) contents of P. barbatus and P. strictus increased with the increase in salinity levels of the treatment solution. Consequently, P. barbatus and P. strictus demonstrated sensitivity to salinity stress at ECs of 7.5 and 10.0 dS⋅m−1. This study provides important insights for their effective utilization in landscaping practices within saline-prone areas.

Plant responses to UV-A1 radiation are genotype and background irradiance dependent

A large fraction of solar UV radiation that reaches the Earth’s surface is in the UV-A1 waveband (350–400 nm). Despite its prevalence, it is unknown how strongly plant genotypes differ in their response to UV-A1, and how their responses to UV-A1 depend on the photosynthetic photon flux density (PPFD). We grew several horticultural (tomato, cucumber, and two lettuce cultivars) and a model species (Arabidopsis thaliana) under low (LL; 150 μmol m−2 s−1) and high PPFD (HL; 550 μmol m−2 s−1), each of which was paired with UV-A1 (peaking at 365 nm) at irradiances of 0, 20, and 100 µmol m−2 s−1. Arabidopsis was the most strongly affected, as under LL, addition of UV-A1 resulted in early flowering, changes in leaf shape, and strong decreases in shoot dry weight (∼40%). In all species, UV-A1 exposure induced photoinhibition (low Fv/Fm) only under LL, but not under HL. Under HL, exposure to UV-A1 also induced strong decreases in the concentrations of UV-absorbing compounds and anthocyanins in arabidopsis (Columbia-0) and lettuce cv. Klee, but not in other genotypes. Altogether, we found that UV-A1 had only mild effects on the morphology of horticultural species (e.g., petiole angle, leaf shape and curvature), did not significantly alter biomass or leaf biochemical compound concentrations, and these effects were almost entirely unaffected by background PPFD. In contrast, these traits were strongly affected by UV-A1 in arabidopsis, highlighting the importance of not relying solely on model species when exploring environmental effects on plants. We conclude that plant responses to UV-A1 radiation depend on genotype and background irradiance.

A meta-analysis reveals differential sensitivity of cold stress responses in the maize leaf.

Maize (Zea mays), a cold-sensitive crop, requires cold tolerance for extending the length of the growing season in temperate climates. However, response curves to different cold temperatures and exposure durations are lacking.We used a meta-analysis approach using data from literature to investigate the effect of cold stress in the maize leaf. We constructed response curves to temperature and exposure durations for 18 key parameters related to leaf growth, photosynthesis, oxidative stress, antioxidants, and the phytohormone ABA. To determine their relevance for cold tolerance, we compared cold tolerant Flint and cold sensitive Dent lines. Treatment temperatures ranged from -20°C to 20°C for cold and from 12°C to 30°C for control and exposure duration from 3 min to 60 days. We found interacting effects of temperature and exposure durations on different response parameters. The strongest difference between Flint and Dent was observed for electrolyte leakage (EL).Our results show that the commonly used 4°C for cold and 25°C for control with medium cold exposure (1-7 days) induces a 50% decrease in shoot dry weight and leaf area and that EL is an easy and reliable indicator for cold tolerance studies.

Maize plant (Zea mays) uptake of organophosphorus and novel brominated flame retardants from hydroponic cultures

The root uptake and root-shoot translocation of seven organophosphorus flame retardants (OPFRs) and four novel brominated flame retardants (NBFRs) were assessed in this investigation using hydroponic grown maize plants (Zea mays). Three initial liquid concentrations for each considered compound were examined (i.e., 0.3 μg L−1, 3 μg L−1, 30 μg L−1). The results indicated that the 30 μg L−1 treatments were phytotoxic, as they resulted in a significant decrease in shoot dry weight. Plant-driven removal of the tested FRs decreased with the increasing initial spiking level and were reportedly higher for the NBFRs (range 42%–10%) than OPFRs (range 19%–7%). All the considered FRs were measured in the roots (range 0.020–6.123 μg g−1 dry weight -DW-) and shoots (range 0.012–1.364 μg g−1 DW) of the tested plants, confirming that there was uptake. Linear relationships were identified between the chemical concentrations in the plant parts and the tested hydroponic concentrations. Root concentration factors were positively correlated with the specific lipophilicity (i.e., logKow) of the tested FRs and were determined to be higher for the NBFRs than the OPFRs. The NBFRs had a higher root uptake rate than the OPFRs, and this trend was more significant with the increasing treatment concentrations. Shoot/root concentration factors were found to be lower than the unity value for 10 of the 11 tested compounds. These results can be related to the specific molecular configurations and the occurrence of different functional groups in the tested compounds. The results will help to improve risk assessment procedures and fine tune our understanding of human receptor responses to the ingestion of maize crops grown on agricultural sites irrigated with water contaminated by FRs.

Diverse genotypic variations of photosynthetic capacity, transpiration and antioxidant enzymes of lily hybrids to increasing salinity stress

Salinity stress can severely affect plant growth and physiology. The objective of this study was to investigate growth, photosynthetic and antioxidant responses of lily hybrids (Lilium asiatica × Lilium asiatica, Lilium asiatica × Lilium longiflorum) under different levels of salinity stress. Ten lily hybrids were subjected to 0 (control, no salinity), 35-, 70- and 140-mM NaCl for 15 d in a greenhouse, respectively. Across hybrids, shoot fresh weight (SFW), shoot dry weight (SDW), chlorophyll (Chl), and photosynthetic rate (Ps) decreased, and intercellular CO2 (Ci) and activity of superoxide dismutase (SOD) increased starting at 35 mM NaCl, compared to the control; while reductions of transpiration rate (E), stomatal conductance (gs) and peroxidase (POD) activity were observed starting at 70 mM NaCl. All the parameters mentioned above plus chlorophyll fluorescence (Fv/Fm) decreased at 140 mM NaCl, but the SDW to SFW ratio (DW FW−1), proline and malondialdehyde (MDA) content were unaffected by salinity stress. Significant treatment by hybrid interactions were found in all traits except for Chl, DW FW−1, proline, and MDA. The principal component (PC1) had the larger loading values for Ps, E, and gs, and PC2 exhibited the larger loading values for SFW and SDW under both control and salinity treatments. Lily hybrids varied largely in growth and physiological activity in response to salinity. At 140 mM NaCl, some hybrids had a lower reduction in SDW and relatively less declines in Ps, E, gs, SOD and POD, and some hybrids had higher reductions in SFW, SDW, and SOD but lower reductions in Fv/Fm, Ps, E, and gs, while other hybrids had a lower decrease in SDW but higher reductions in E, gs, SOD and POD and a higher increase in Ci. The results indicated maintenance of photosynthetic capacity, transpiration and antioxidant enzyme activities contributed to plant growth, thus enhancing salinity tolerance in the most tolerant lily hybrids.

The yield potential and growth responses of licorice (Glycyrrhiza glabra L.) to mycorrhization under Pb and Cd stress

The effects of mycorrhization (inoculation and non-inoculation) on growth and quality of two ecotypes (Baft and Ramjerd) of Glycyrrhiza glabra L. under heavy metals stress (0, 300 Pb + 20 Cd (H1) and 600 Pb + 40 Cd (H2) (mg kg−1) was investigated. Higher concentration of heavy metals decreased shoot dry weight in Baft (7.05%) and Ramjerd (43.34%) than control. Root dry weight increased in mycorrhizal Baft (28.23%) and Ramjerd (31.84%) ecotypes under H2 than non-mycorrhizal plants. In mycorrhizal plants, root colonization percentage decreased 37.07% in H2 than control. Increasing heavy metals concentration led to increase of total antioxidant activity and total phenol content. Mycorrhizal Ramjerd showed the lowest shoot Pb concentration in both heavy metals concentrations and the highest root Pb concentration (107.25% higher than non-mycoorhizal one) in H2. For both ecotypes, the lowest shoot Cd concentration observed in mycorrhizal plants under H1 and mycorrhizal plants had more root Cd concentration (33.83 mg kg−1 dry matter) than non-mycorrhizal ones. In both concentrations of heavy metals, the lowest Pb (0.026) and Cd (0.153) translocation factor (TF) observed in mycorrhizal plants. Based on the results, licorice with TF< 1 is not a hyperaccumulator plant but stabilizes Cd and Pb in root. Novelty statement: Licorice is a well-known medicinal plant that its root and rhizome contains diverse applications in pharmaceutical and food industries. The main source of licorice supply is through harvesting from natural habitats of Iran (one of the first exporters of licorice in the world), which during the last years have been exposed to heavy metals contamination. Therefore, the growth response of the plant in polluted habitats and most importantly, the concentration of heavy metals especially in belowground parts of the plant need more consideration. Hence, this research was carried out with an objective to investigate growth and yield potential response of two ecotypes of licorice to mycorhization under heavy metal stress (Cd and Pb) and the mechanism of heavy metal management in above and belowground parts of licorice in order to achieve its potential for further sustainable phytoremediation programs and most importantly considering the heavy metal accumulation in rhizomes and roots in accordance with world standards for medicinal and edible consumption.

Regulation of Agronomic Traits, Nutrient Uptake, Osmolytes and Antioxidants of Maize as Influenced by Exogenous Potassium Silicate under Deficit Irrigation and Semiarid Conditions

Understanding the link between the protective role of potassium silicate (K2SiO3) against water shortage and the eventual grain yield of maize plants is still limited under semiarid conditions. Therefore, in this study, we provide insights into the underlying metabolic responses, mineral nutrients uptake and some nonenzymatic and enzymatic antioxidants that may differ in maize plants as influenced by the foliar application of K2SiO3 (0, 1 and 2 mM) under three drip irrigation regimes (100, 75 and 50% of water requirements). Our results indicated that, generally, plants were affected by both moderate and severe deficit irrigation levels. Deficit irrigation decreased shoot dry weight, root dry weight, leaf area index (LAI), relative water content (RWC), N, P, K, Ca, Fe, Zn, carotenoids, grain yield and its parameters, while root/shoot ratio, malondialdehyde (MDA), proline, soluble sugars, ascorbic acid, soluble phenols, peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and ascorbate peroxidase (APX) were improved. The foliar applications of K2SiO3 relatively alleviated water stress-induced damage. In this respect, the treatment of 2 mM K2SiO3 was more effective than others and could be recommended to mitigate the effect of deficit irrigation on maize plants. Moreover, correlation analysis revealed a close link between yield and the most studied traits.

Auxin and proline producing rhizobacteria mitigate salt-induced growth inhibition of barley plants by enhancing water and nutrient status

Although inoculation with plant growth-promoting rhizobacteria (PGPR) can improve crop salt tolerance, it is not always clear how these beneficial microbes affect plant ionic and water status. To investigate this phenomenon, three salt-tolerant bacteria were used to inoculate barley plants cultivated under salt stress. The bacterial strains Bacillus mojavensis S1, B. pumilus S2 and Pseudomonas fluorescens S3 showed an increase in IAA and proline production when cultivated on 100 and 200 mM NaCl supplemented medium. A salt-sensitive barley cultivar Rihane was grown at 0 and 100 mM of NaCl, with or without bacterial inoculation. Salt treatment decreased shoot dry weight of uninoculated plants by about 25%. In uninoculated plants, salinity decreased leaf water potential 0.8 MPa, increased roots and shoots Na+ concentrations by approximately 59% and 89% respectively and increased proline concentration. Bacterial inoculation with strains S1 and S3 prevented salt-induced reduction of shoot dry weights respectively by 54% and 46%, and root dry weights by almost 40%. These two bacterial strains enhanced stomatal conductance and CO2 assimilation of plants subjected or not to salt. Under saline conditions, all bacterial strains decreased root and shoot Na+ concentrations, improved leaf water potential and the strain S1 maintained it close to control values. Salinity stress was mainly alleviated in barley plants after inoculation with S1 and S3 strains, having respectively high proline and IAA productions under 200 mM of NaCl, which contribute to the alleviation of salt stress and stimulate root development, enhancing water and nutrient uptake by plants. Future prospects of the PGP potential of halotolerant bacterial species will extend their application in agriculture.

Salinity modifies heavy metals and arsenic absorption by the halophyte plant species Kosteletzkya pentacarpos and pollutant leaching from a polycontaminated substrate.

Phytomanagement of polycontaminated soils is challenging, especially in areas simultaneously affected by salinity. The wetland halophyte plant species Kosteletzkya pentacarpos was cultivated in a column device allowing leachate harvest, on a polycontaminated spiked soil containing Cd (6.5 mg kg−1 DW), As (75 mg kg−1 DW), Zn (200 mg kg−1 DW) and Pb (300 mg kg−1 DW) and irrigated with salt water (final soil electrical conductivity 5.0 ms cm−1). Salinity increased Cd bioavailability in the soil and Cd accumulation in the shoots while it had an opposite effect on As. Salinity did not modify Pb and Zn bioavailability and accumulation. Cultivating plants on the polluted soil drastically reduced the volume of leachate. In all cases, salinity reduced the total amounts of heavy metals removed by the leachate and significantly increased the proportion of Cd and Zn removed by the plants. Heavy metal contamination induced a decrease in shoot dry weight and an increase in malondialdehyde (an indicator of oxidative stress); both symptoms were alleviated by the additional presence of NaCl but this positive impact was not related to increase in protecting phytochelatins synthesis. It is concluded i) that bioavailability estimated by the 0.01M CaCl2 extraction procedure is not fully relevant from the heavy metal mobility, ii) that salinity decreased heavy metal percolation, especially in soils cultivated with K. pentacarpos and iii) that salinity improves plant tolerance to heavy metals in K. pentacarpos and that this species is a promising plant material for phytoremediation of polycontaminated soils.

A non-toxic polymer enhances sorghum-mycorrhiza symbiosis for bioremediation of Cd

In this study, the effect of a mycorrhizal symbiosis on the translocation of Cd from Cd-polluted soil to sorghum roots was investigated using rhizoboxes. A factorial experiment (two factors including fungus inoculation and Cd contamination) in a completely randomized design with three replicates was performed. In the rhizobox rhizosphere compartment, plants were cultivated in uncontaminated soil and mycorrhizal inoculation (inoculated with Claroideoglomus etunicatum or non-inoculated) was performed, and in the other compartment, the soil was contaminated with Cadmium (Cd) at one of three levels (0, 100mgkg-1 using a non-toxic organic polymer (poly (N-vinyl succinate))-Cd, or 100mgkg-1 using Cd-nitrate). Cd pollution resulted in a significant decrease in shoot dry weight (from 7.52 to 6.18 and 6.68g pot-1, from control to polymer-Cd and nitrate-Cd respectively), root mycorrhizal colonization (from 32.33% to 8.16% and 8.33%), shoot phosphorus concentration (from 3.14 to 2.80 and 2.76gkg-1), and soil carbohydrate (from 12.05 to 10.74 and 10.24mgg-1), and also resulted in significant increases in soil glomalin (from 595.55 to 660.52 and 690.39μgg-1). The use of mycorrhizal fungi increased the glomalin content of the soil and improved the studied parameters. The results revealed the key role of Claroideoglomus etunicatum in translocation of Cd in the rhizobox and also in precise control of Cd concentration of plant tissues (increase or decrease of them depending on Cd composition and Cd availability). Poly(N-vinyl succinate) increased Cd availability and Cd concentration of shoot tissue (5.19mgkg-1) compared to nitrate-Cd (3.68mgkg-1) and could be recommended for improving phytoremediation.

Phenotypic variation of cassava root traits and their responses to drought.

Premise of the StudyThe key to increased cassava production is balancing the trade‐off between marketable roots and traits that drive nutrient and water uptake. However, only a small number of protocols have been developed for cassava roots. Here, we introduce a set of new variables and methods to phenotype cassava roots and enhance breeding pipelines.MethodsDifferent cassava genotypes were planted in pot and field conditions under well‐watered and drought treatments. We developed cassava shovelomics and used digital imaging of root traits (DIRT) to evaluate geometrical root traits in addition to common traits (e.g., length, number).ResultsCassava shovelomics and DIRT were successfully implemented to extract root phenotypes, and a large phenotypic variation for root traits was observed. Significant correlations were found among root traits measured manually and by DIRT. Drought significantly decreased shoot dry weight, total root number, and root length by 84%, 30%, and 25%, respectively. High adventitious root number was associated with increased shoot dry weight (r = 0.44) under drought.DiscussionOur methods allow for high‐throughput cassava root phenotyping, which makes a breeding program targeting root traits feasible. We suggest that root number is a breeding target for improved cassava production under drought.

Effects of 1-aminocyclopropane-1-carboxylate and paclobutrazol on the endogenous hormones of two contrasting rice varieties under submergence stress

Phytohormone play important roles in regulating developmental processes and signaling networks involved in plant responses to submergence stress. We studied the growth, leaf endogenous hormonal levels and related genes of two contrasting rice genotypes (IR64 and IR64-Sub1) pretreated with 1-aminocyclopropane-1-carboxylate (ACC) and paclobutrazol (PB) under submergence conditions. Submergence promoted underwater shoot elongation, chlorophyll degradation and expression of OsCIPK15, altered the leaf endogenous hormone levels, accelerated the yellowing and senescence of leaves, and decreased shoot dry weight and the plant survival rate. IR64 was more sensitive to submergence stress, showing larger increases of leaf GAs, ABA, IAA contents and the expression of OsCPS1, OsGA20ox1 and OsIAA11, which in IR64-Sub1 were significantly decreased with prolonged stress. Furthermore, IR64 showed decreased ZR content, cZOGT1 expression, GA/ABA and ZR/IAA, while IR64-Sub1 showed opposite trends. Shoot elongation, leaf yellowing and senescence, GAs and IAA contents and the expression of OsCPS1, OsGA20ox1 and OsIAA11 in submerged rice leaves were enhanced by ACC application, whereas PB treatment showed opposite effects, and the effects on underwater elongation of PB and Sub1 were clearly superimposable. Compared with GA/ABA, ZR/IAA was not only suitable for non-Sub1 genotypes, but also more accurate in reflecting the submergence characteristics in IR64-Sub1. These findings improve our understanding of the intricate web of connections between plant hormones that regulate physiological responses to stress.

Elimination of the Effect of Some Herbicides on the Growth of Zea mays and Accumulation in the Soil Using Urea

ABSTRACT: This study evaluates the effect of urea on growth of herbicide-treated maize and its accumulation in the soil. When the seedlings were 15 days old, the plots were divided into five groups. One group served as control, two received treatments with metolachlor and isoproturon at the dose of 1.5 kg ha-1 and 2.5 L ha-1, respectively. The two remaining groups received the same dose of herbicide along with urea added at a rate of 129 kg ha-1. The application of the two herbicides appeared to cause a significant decrease in shoot dry weight, photosynthetic pigments, d-aminolevulinate dehydratase enzyme [ALA-D, EC 4.2.1.24] and total soluble carbohydrates of the maize plants. The application of urea appeared to alleviate the effects of both herbicides on maize growth. A statistical analysis demonstrated a significant association between the soil criteria and the accumulation of herbicides in it. This study clearly highlights the urgent need for use of urea to retract the effects of herbicides on maize growth.

The bean rhizosphere Pseudomonas aeruginosa strain RZ9 strongly reduces Fusarium culmorum growth and infectiveness of plant roots

A faba bean rhizospheric Pseudomonas aeruginosa isolate RZ9 was used for studying its antifungal activity and protecting effects of faba bean and common bean against the root pathogen Fusarium culmorum strain MZB47. The dual culture tests showed that RZ9 inhibits MZB47 in vitro growth by 56%. When mixing RZ9 cell suspension with MZB47 macroconidia at equal proportion, the macroconidia viability was reduced with 70%. Pathogenicity tests conducted in sterile conditions showed that MZB47 caused an intense root rotting in faba bean ‘Aquadulce’ plantlets and a slight level in common bean ‘Coco blanc’. This was associated to significant decreases in plant growth only in ‘Aquadulce’, reducing shoot dry weight (DW) by 82% and root DW by 70%. In soil samples, MZB47 caused severe root rotting and induced significant decreases in shoot DW (up to 51%) and root DW (up to 60%) for both beans. It was associated to a decrease in nodule number by 73% and 52% for faba bean and common bean, respectively. Biocontrol assays revealed that the inoculation of RZ9 to MZB47-treated plantlets enhanced shoot DWs (25% and 110%) and root DWs (29% and 67%), in faba bean and common bean, respectively. Moreover, root rotting levels decreased and nodule number increased in treated compared to untreated plantlets. Collected data highlighted the disease severity of F. culmorum and demonstrated the potential of using RZ9 in controlling Fusaria root diseases in beans. Thereby, the current study represents the first report on the biocontrol effectiveness of P. aeruginosa against F. culmorum in beans.

Genetic analysis of rootstock-mediated nitrogen (N) uptake and root-to-shoot signalling at contrasting N availabilities in tomato

Selecting rootstocks for high nitrogen acquisition ability may allow decreased N fertilizer application without reducing tomato yields, minimizing environmental nitrate pollution. A commercial hybrid tomato variety was grafted on a genotyped population of 130 recombinant inbred lines (RILs) derived from Solanum pimpinellifolium, and compared with self- and non-grafted controls under contrasting nitrate availabilities (13.8 vs 1.0mM) in the nutrient solution.Grafting itself altered xylem sap composition under N-sufficient conditions, particularly Na+ (8.75-fold increase) concentration. N deprivation decreased shoot dry weight by 72.7% across the grafted RIL population, and one RIL rootstock allowed higher total leaf N content than the best of controls, suggesting more effective N uptake.Sixty-two significant QTLs were detected by multiple QTL mapping procedure for leaf N concentration (LNC), vegetative growth, and the xylem sap concentrations of Mn and four phytohormone groups (cytokinins, gibberellins, salicylic acid and jasmonic acid). Only three LNC QTLs could be common between nitrogen treatments. Clustering of rootstock QTLs controlling LNC, leaf dry weight and xylem sap salicylic acid concentration in chromosome 9 suggests a genetic relationship between this rootstock phytohormone and N uptake efficiency. Some functional candidate genes found within 2 Mbp intervals of LNC and hormone QTLs are discussed.

Effects of Silicon Application on Wheat Growth and Some Physiological Characteristics under Different Levels and Sources of Salinity

ABSTRACTWe investigated the effects of silicon (Si) and the levels and sources of salinity on the growth and some physiological properties of wheat (Triticum aestivum cv. Chamran) in a sandy loam soil under greenhouse conditions. Treatments comprised four Si levels (8, 50, 100 and 150 mg kg−1 soil), four salinity levels (0.46, 4, 8 and 12 dS m−1) and two salinity sources (sodium chloride (NaCl) and four-salt combination). Salts combination included NaCl, sodium sulfate (Na2SO4), calcium chloride (CaCl2) and magnesium sulfate (MgSO4) at a molar ratio of 4:2:2:1. The experiment was arranged as a completely randomized design in a factorial manner, with three replications. Increasing salinity level resulted in a significant decrease in shoot dry weight, chlorophyll content and catalase (CAT) activity, and it caused a marked increase in proline and glycine betaine (GB) concentrations and superoxide dismutase (SOD) enzyme activity. The stimulating effect on GB accumulation and SOD activity was more intense in NaCl-treated plants. However, the source of salinity had no significant effect on shoot dry weight, chlorophyll and proline concentrations, and CAT activity. Si application enhanced all the above-mentioned parameters, except for proline. The suppressing effect of salinity on shoot dry weight, chlorophyll concentration and CAT activity was alleviated by Si supplementation. The stimulating effects of Si fertilization on shoot dry weight and chlorophyll concentration became more pronounced at higher salinity levels. It could be concluded that a decrease in soil osmotic potential, nutrient imbalance and increasing reactive oxygen species (ROS) in salt-treated plants caused growth suppression, while Si supply decreased the deleterious effects of excess salt on wheat growth. Consequently, it appears that when wheat plants are to be grown in salt-affected soils, it is highly recommended to supply them with adequate available silicon (Si).

English

A field experiment was conducted during the 2006 cropping season in Ofla district in southern Tigray to assess the response of bread wheat (Triticum aestivum L.) varieties to nitrogen and phosphorus fertilizer rates. Factorial combinations of two wheat varieties (HAR1685 and Shehan), four N rates (0, 23, 46 and 69 kg N/ha), and four P rates (0, 10, 20 and 30 kg P/ha) were laid out in split plot design (varieties in the main plot and N-P fertilizer rates to the sub plots) with three replications. The variety HAR1685 exhibited significantly higher values for&nbsp; grain yield, harvest index, total N uptake, grain P uptake, N apparent recovery, and agronomic efficiency but had shorter plant height and maturity period. Shehan on the other hand, exhibited higher values for tiller number per plant, plant height, shoot dry weight at 50% flowering and at physiological maturity, biomass yield, straw yield. Application of N and P fertilizers significantly (P&lt;0.01) influenced plant height, shoot dry weight at physiological maturity, and tiller number per plant. The variety-P-N interactions were highly significant for grain yield, biomass yield, harvest index, and straw yield. The increase and decrease in shoot dry weight at 50% flowering, grain yield, biomass yield harvest index, straw yield and available soil phosphorus at harvesting did not show a consistent trend. However, an increasing trend was observed when the rate of N increased from 0 to 69 kg N/ha. Non-significance difference due to the interaction of P and N with respect to plant height, number of tillers per plant, initial plant stand, 1000 kernels weight ,days to 50% flowering and total soil nitrogen at harvest was observed. The grain and straw N and P contents and uptakes, increased with N and P levels but the apparent recovery and agronomic efficiency of N and P fertilizers decreased with increasing N and P rates in both varieties. Grain and biomass yields were significantly and positively correlated with most of the agronomic parameters, grain N and P contents, grain N and P uptakes, and total N and P uptakes. Moreover, grain and straw N and P contents and their uptakes were strongly and positively correlated with applied N and P respectively.&nbsp; Even though it is one year in one location study, it can be concluded that the released variety HAR1685 had high grain yield potential, strong stems, medium plant height, heavier kernel weight, higher harvest index, and shorter maturing period and responsive&nbsp; to higher N and P rates. The shortcoming of the experiment was it was conducted in a single location. It should be repeated in more than one location. &nbsp; Key words: Bread wheat, nitrogen, phosphorous, soil, physical, chemical.

Drought stress had a predominant effect over heat stress on three tomato cultivars subjected to combined stress

BackgroundAbiotic stresses due to environmental factors could adversely affect the growth and development of crops. Among the abiotic stresses, drought and heat stress are two critical threats to crop growth and sustainable agriculture worldwide. Considering global climate change, incidence of combined drought and heat stress is likely to increase. The aim of this study was to shed light on plant growth performance and leaf physiology of three tomatoes cultivars (‘Arvento’, ‘LA1994’ and ‘LA2093’) under control, drought, heat and combined stress.ResultsShoot fresh and dry weight, leaf area and relative water content of all cultivars significantly decreased under drought and combined stress as compared to control. The net photosynthesis and starch content were significantly lower under drought and combined stress than control in the three cultivars. Stomata and pore length of the three cultivars significantly decreased under drought and combined stress as compared to control. The tomato ‘Arvento’ was more affected by heat stress than ‘LA1994’ and ‘LA2093’ due to significant decreases in shoot dry weight, chlorophyll a and carotenoid content, starch content and NPQ (non-photochemical quenching) only in ‘Arvento’ under heat treatment. By comparison, the two heat-tolerant tomatoes were more affected by drought stress compared to ‘Arvento’ as shown by small stomatal and pore area, decreased sucrose content, ΦPSII (quantum yield of photosystem II), ETR (electron transport rate) and qL (fraction of open PSII centers) in ‘LA1994’ and ‘LA2093’. The three cultivars showed similar response when subjected to the combination of drought and heat stress as shown by most physiological parameters, even though only ‘LA1994’ and ‘LA2093’ showed decreased Fv/Fm (maximum potential quantum efficiency of photosystem II), ΦPSII, ETR and qL under combined stress.ConclusionsThe cultivars differing in heat sensitivity did not show difference in the combined stress sensitivity, indicating that selection for tomatoes with combined stress tolerance might not be correlated with the single stress tolerance. In this study, drought stress had a predominant effect on tomato over heat stress, which explained why simultaneous application of heat and drought revealed similar physiological responses to the drought stress. These results will uncover the difference and linkage between the physiological response of tomatoes to drought, heat and combined stress and be important for the selection and breeding of tolerant tomato cultivars under single and combine stress.

Effect of waterlogging at different growth stages on some morphological traits of wheat varieties.

Excess rainfalls may be the cause of waterlogging in soil, which affects the growth and development of wheat. Therefore, the objectives of this study were to examine the effects of waterlogging on shoot and root growth and physiological characteristics of wheat. Three experiments were conducted: experiment 1 (E1): evaluation of seedling growth on ten Iranian winter wheat varieties with waterlogging periods (1-4, 4-8, 8-12, and 12-16 days starting from seed germination). Seminal roots and plumule were investigated at seedling. The others are E2: pretreatment of waterlogging (15days) at tillering and stem elongation stages and its effects on shoot and root growth at anthesis stage and experiment 3 (E3): pretreatment of waterlogging (15days) at tillering and jointing stages and its effects on yield and yield components and also evaluation of stress tolerance indexes. The results of the seedling growth test (E1) showed that 1-4- and 4-8-day waterlogging severity reduced seminal root length (94.5 to 93.7%) and plumule length (86.2 to 50.0%) compared to control. Results of E2 indicated that waterlogging stress decreased shoot dry weight, root dry weight, total secondary root length, and chlorophyll a + b content of flag leaf by 28-31, 44-35, 20-31, and 28-35%, respectively. Also, result of E3 showed that the grain yields of wheat varieties at two conditions of stress were different in base tolerance indexes. In general, the responses of wheat varieties to waterlogging were different at the three experiments. The varieties that had the most of dry weight and length of the root were tolerant. Thus, it is possible to use these characteristics as an index for selecting the varieties with tolerance to waterlogging.

Salicylic Acid and UV-B/C Radiation Effects on Growth and Physiological Traits of &lt;i&gt;Satureja hortensis&lt;/i&gt; L.

Higher UV irradiation may affect the structure of ecosystems directly or indirectly. In the present work, Satureja hortensis L. defence mechanisms against UV stress was studied with or without salicylic acid (SA). For this aim, a factorial based experimental was conducted on completely randomized design with three UV treatments (control, UV-B and UV-C) as first factor and two SA levels (0 and 1 mM) as second factor. The results showed UV-B and C decreased shoot dry weight, plant height (PH), node number (NN), inter-node distance (IND), root length (RL), leaf area index (LAI) and chlorophyll content, but increased stem diameter (SD), leaf thickness (LTh), total flavonoid content (TFC), total phenolic content (TFC) and antioxidant activity. Plants treated with SA (1 mM) showed higher growth factors than non-treated one. It seems that SA can be used as an alternative substance against UV stress.