Showing papers in "Journal of Agronomy and Crop Science in 2013"

Hydrochar and Biochar Effects on Germination of Spring Barley

Abstract: Within the framework of climate change mitigation by sequestrating recalcitrant carbon in soil, biochar is considered as a promising soil amendment. Testing any such soil additives is vitally important, as they should not cause abiotic stress for plants due to chemical constituents they may contain. Thus, germination tests with spring barley (Hordeum vulgare) were conducted to assess phytotoxic effects of biochar, hydrochar and process-water from hydrothermal carbonization (HTC) as soil amendments. Additionally, single-component tests with substances found in process-waters were carried out with cress (Lepidium sativum). While biochars generally had no effect on germination, hydrochars and process-waters significantly inhibited germination. The dissolved organic carbon content predicted the germination-inhibiting effects observed. Three compounds resulted in partial (guaiacol) or total (levulinic acid and glycolic acid) inhibition of cress seed germination, and three others (acetic acid, glycolaldehyde dimer and catechol) had a negative impact on growth. Phytotoxic substances in chars appeared to be mostly water soluble and volatile. Pre-treatments of hydrochars and process-waters (i.e. storage and washing) were able to reduce germination inhibition. While phytotoxic substances that are generated during HTC stay in the products, biochars from kiln carbonization of the same feedstocks had no negative effects on germination, likely because volatiles evaporate during the conversion. Our study highlights the importance of comprehensively testing carbonized products for their compatibility with agricultural and horticultural systems.

Seed Priming with Ascorbic Acid Improves Drought Resistance of Wheat

Abstract: The study, consisting of two independent experiments, was conducted to evaluate the role of seed priming with ascorbic acid (AsA) in drought resistance of wheat. In the first experiment, seeds of wheat cultivars Mairaj-2008 and Lasani-2008 were either soaked in aerated water (hydropriming) for 10 h or not soaked (control). In the second experiment, seeds of same wheat cultivars were soaked in aerated (2 mm) AsA solution (osmopriming) or water (hydropriming) for 10 h. In both experiments, seeds were sown in plastic pots (10 kg) maintained at 70 % and 35 % of water-holding capacity designated as well watered and drought stressed, respectively. Both experiments were laid out in a completely randomized design with six replications. Drought caused delayed and erratic emergence and disturbed the plant water relations, chlorophyll contents and membranes because of oxidative damage; however, root length in cultivar Lasani-2008 was increased under drought. Hydropriming significantly improved the seedling emergence and early growth under drought and well-watered conditions; however, improvement was substantially higher from osmopriming with AsA. Similarly, osmopriming with AsA significantly improved the leaf emergence and elongation, leaf area, specific leaf area, chlorophyll contents, root length and seedling dry weight. Owing to increase in proline accumulation, phenolics and AsA, by seed priming with AsA, plant water status was improved with simultaneous decrease in oxidative damages. These improved the leaf emergence and elongation, and shoot and root growth under drought. However, there was no difference between the cultivars in this regard. In conclusion, osmopriming with AsA improved the drought resistance of wheat owing to proline accumulation and antioxidant action of AsA and phenolics, leading to tissue water maintenance, membrane stability, and better and uniform seedling stand and growth.

Response of Sorghum to Abiotic Stresses: A Review

Abstract: Sorghum [(Sorghum bicolor L.) Moench] is a highly productive crop plant, which can be used for alternative energy resource, human food, livestock feed or industrial purposes. The biomass of sorghum can be utilized as solid fuel via thermochemical routes or as a carbohydrate substrate via fermentation processes. The plant has a great adaptation potential to drought, high salinity and high temperature, which are important characteristics of genotypes growing in extreme environments. However, the climate change in the 21st century may bring about new challenges in the cultivated areas. In this review, we summarize the most recent literature about the responses of sorghum to the most important abiotic stresses: nutrient deficiency, aluminium stress, drought, high salinity, waterlogging or temperature stress the plants have to cope with during cultivation. The advanced molecular and system biological tools provide new opportunities for breeders to select stress-tolerant and high-yielding cultivars.

Soybean Pollen Anatomy, Viability and Pod Set under High Temperature Stress

Abstract: High temperature (HT) stress is one of the major environmental factors influencing yield of soybean (Glycine max L. Merr.) in the semi-arid regions. Experiments were conducted in controlled environments to study the effects of HT stress on anatomical changes of pollen and their relationship to pollen function in soybean genotype K 03-2897. Objectives of this study were to (a) quantify the effect of HT stress during flowering on pollen function and pod set and (b) observe the anatomical changes in pollen grains of soybean plants grown under HT stress. Plants were exposed to HT (38/28 °C) or optimum temperature (OT, 28/18 °C) for 14 days at flowering stage. HT stress significantly decreased in vitro pollen germination by 22.7 % compared to OT. Pollen from HT stress was deformed; it had a thicker exine wall and a disintegrated tapetum layer. HT stress decreased pod set percentage (35.2 %) compared to OT. This study showed that decreases in pollen in vitro germination by HT stress were caused by anatomical changes in pollen, leading to decreased pod set percentage under HT stress.

Infrared Thermal Imaging as a Rapid Tool for Identifying Water-Stress Tolerant Maize Genotypes of Different Phenology

Abstract: The main task of this research was to evaluate canopy temperature and Crop Water Stress Index (CWSI) by assessing genotype variability of maize performance for different water regimes. To that end, three hundred tropical and subtropical maize hybrids with different phenology in terms of date of anthesis were evaluated. The influence of phenology on the change in canopy temperatures and CWSI was not equal during the three dates of measurement. At the end of vegetative growth (82 days after sowing, DAS) and at the blister stage (DAS 97), a high significant difference in temperatures and CWSI (P < 0.001) were obtained between the early- and late-maturity genotypes. During anthesis (DAS 89), phenology had a significant effect (P < 0.01) only for the well-watered genotypes, while under water-stress conditions, no differences were found between early and late genotypes in terms of canopy temperature and CWSI. High significant differences (P < 0.001) in stomatal conductance (gs) between early and late genotypes for different treatments were observed. A relationship (R2 = 0.62) between gs and canopy temperature was obtained. Under a water-stress canopy, temperature was measured at anthesis, which was negatively correlated with grain yield of the early (r = −0.55)- and late (r = −0.46)-maturity genotypes in the water-stressed condition.

Assessing Light Competition for Cereal Production in Temperate Agroforestry Systems using Experimentation and Crop Modelling

Abstract: In every agroforestry system, the tree canopy reduces the incident radiation forthe crop. However, cereal varieties were selected, and most crop growth modelswere designed for unshaded conditions, so both may be unsuited to agroforestryconditions and performance. In southern France, durum wheat productivity wasmonitored over 2 years in an agroforestry system including walnut trees andunder artificial shade conditions. Yield components were measured in both fulland reduced light conditions. The cereal yield was always decreased by shade; byalmost 50% for the heaviest shade conditions (31% of light reduction). The maineffect of the shade was the reduction in the number of grains per spike (35% atthe most) and in the weight of grains (16% at the most). The mean grain weightwas moderately affected, while the protein content was increased in shaded con-ditions (by up to 38% for artificial shade). Consequently, the protein yield perhectare was less reduced by the shade than the dry matter grain yield. A cropmodel (STICS) was also used to simulate the crop productivity in full light andshaded conditions, but the crop LAI and the yield components were not correctlysimulated in the shade. The simulations emphasized the sensitivity of the wheatgrain filling to shade during the critical period, 30 days before flowering, for yieldelaboration. Further experimental and modelling studies should take intoaccount the heterogeneity of shade intensity due to the shape of the tree crown,the width of the crop alley and the orientation of the tree rows and the modifica-tion of carbon allocation inside the plant.IntroductionConcerns over the long-term sustainability of intensivemonoculture systems have resulted in a heightened interestin agroforestry systems that integrate trees into short-termproduction systems, in temperate areas. Recent studiesshow that tree-based intercropping systems, which inte-grate hardwood species, offer many benefits for the envi-ronment, such as reducing soil erosion and N leaching, andincreasing carbon sequestration (Albrecht and Kandji2003) and landscape biodiversity (Quinkenstein et al.2009). Agroforestry systems create a wide range of biophys-ical interactions between the crop and the trees. Some ofthe competitive interactions for resources (water, light andmineral elements) have been documented for a variety ofpractices in the tropics (Cannell et al. 1998, Albrecht andKandji 2003, Bellow and Nair 2003). Moreover, the differ-ent species may improve each other’s environment. This isknown as ‘facilitation’ (Vandermeer 1989).The water and N availability have often been studied intemperate and Mediterranean agroforestry systems (Joseet al. 2000a,b, Miller and Pallardy 2001, Livesley et al.2004). In Mediterranean areas, water stress is one of themain production constraints for cereals, particularlydurum wheat. This is a consequence of the variability ofthe frequency and amount of rainfall during the growingseason (Garcia del Moral et al. 2005, Katerji et al. 2008).Light availability is greatly modified in agroforestry sys-tems compared to cropping systems based on annual cropssuch as soybean (Rivest et al. 2009), corn (Reynolds et al.

Response of Antioxidant Enzymes, Phytochelatins and Glutathione Production Towards Cd and Zn Stresses in Cajanus cajan (L.) Millsp. Genotypes Colonized by Arbuscular Mycorrhizal Fungi

Abstract: Most metal polluted natural environments are contaminated with multiple metals, and arbuscular mycorrhizal (AM) fungi are among the extracellular strategies to avoid metal toxicity. To understand the interaction between Cd, Zn and AM fungi Glomus mosseae, two genotypes (Sel 85N and P792) of pigeonpea (Cajanus cajan L. Millsp.), differing in their metal tolerance, were chosen for study. Results revealed that root dry weights were more severely affected than shoot dry weights as both the metals were accumulated in roots than in the aerial parts. Mycorrhization promoted biomass yields by decreasing metal content in plant tissues. Exposure to the metals resulted in oxidative burst (high H2O2, malondialdehyde contents and electrolyte leakage), which was accompanied by decreased membrane stability. However, increase in the level of total non-protein thiols (TNP-SH) and the activity of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione reductase (GR) suggested that all these parameters were synergistic in combating heavy-metal-induced oxidative stress. Zn supplementation proved to be inhibitory for Cd-induced oxidative stress. AM fungi alleviated oxidative stress through enhanced production of TNP-SH as well as through upregulation of antioxidant enzymes. Sel 85N exhibited lesser oxidative damage and more efficient defence mechanism than P792.

Transpiration Response of Maize Hybrids to Atmospheric Vapour Pressure Deficit

Abstract: Maize (Zea mays L.) yield is often restricted by low soil water availability, particularly late in the growing season. To increase yields, genetic options for more effective use of available soil water are being explored. One option is to select genotypes that have restricted transpiration rate under high vapour pressure deficit (VPD) conditions so that soil water is conserved for use later in the growing season. While genetic variation for this trait has been identified within several crop species, such variation has never been explored in maize. The objective of this study was to examine transpiration rate of 35 single-cross hybrids to determine whether hybrids can be identified that express limited transpiration under high VPD. Two sets of experiments were undertaken in which plants were exposed to a range of VPD in chambers. A two-phase transpiration response was observed in 11 hybrids in which there was a threshold VPD above which transpiration rate was restricted. The VPD threshold varied from 1.7 to 2.5 kPa among these hybrids. Eight hybrids were included in both sets of experiments, and the same results were obtained in both experiments, indicating that expression of the trait was consistent.

Assessment of Groundnut under Combined Heat and Drought Stress

Abstract: In semi-arid regions, particularly in the Sahel, water and high-temperature stress are serious constraints for groundnut production. Understanding of combined effects of heat and drought on physiological traits, yield and its attributes is of special significance for improving groundnut productivity. Two hundred and sixty-eight groundnut genotypes were evaluated in four trials under both intermittent drought and fully irrigated conditions, two of the trial being exposed to moderate temperature, while the two other trials were exposed to high temperature. The objectives were to analyse the component of the genetic variance and their interactions with water treatment, year and environment (temperature) for agronomic characteristics, to select genotypes with high pod yield under hot- and moderate-temperature conditions, or both, and to identify traits conferring heat and/or drought tolerance. Strong effects of water treatment (Trt), genotype (G) and genotype-by-treatment (GxTrt) interaction were observed for pod yield (Py), haulm yield (Hy) and harvest index (HI). The pod yield decrease caused by drought stress was 72 % at high temperature and 55 % at moderate temperature. Pod yield under well-watered (WW) conditions did not decrease under high-temperature conditions. Haulm yield decrease caused by water stress (WS) was 34 % at high temperature and 42 % under moderate temperature. Haulm yield tended to increase under high temperature, especially in one season. A significant year effect and genotype-by-environment interaction (GxE) effect were also observed for the three traits under WW and WS treatments. The GGE biplots confirmed these large interactions and indicated that high yielding genotypes under moderate temperature were different to those at high temperature. However, several genotypes with relatively high yield across years and temperature environments could be identified under both WW and WS conditions. Correlation analysis between pod weight and traits measured during plant growth showed that the partition rate, that is, the proportion of dry matter partitioned into pods, was contributing in heat and drought tolerance and could be a reliable selection criterion for groundnut breeding programme. Groundnut sensitivity to high-temperature stress was in part related to the sensitivity of reproduction.

The Effect of Constraining the Intensity of Solar Radiation on the Photosynthesis, Growth, Yield and Product Quality of Tomato

Abstract: Recent studies propose the combination of electrical energy and plant production, in which often only radiation peaks were used for energy production. Then, the effect on plant growth is assumed to be negligible. However, photosynthesis is known to be a monotonically increasing function of radiation. We studied the response of tomato to constraining the intensity of solar radiation. Tomato crops in greenhouse compartments were shaded when the outside photosynthetic photon flux density (PPFD) exceeded 640 and 1280 μmol m−2 s−1, resulting in a 57 % and 34 % reduction in the PPFD integral over the growing period compared to the non-shaded control. Constraining the intensity of solar radiation significantly reduced photosynthesis, growth and yield of tomato plants. Model-derived estimates of reduction in crop dry matter increment were 50 % and 28 % for the strongly and moderately PPFD constrained crops. However, measured plant dry matter increment decreased only by 31 % and 19 %, respectively, that is, light use efficiency increased markedly. This indicates a strong adaptation of the plant's metabolism to cope with the limitation in light availability such as increasing the specific leaf area and reducing respiration. Surprisingly, this was only of little concern to the fruit quality, because no effect of constraining PPFD on the concentration of total dry matter, sugars and lycopene in the fruits could be observed. The concentration of titratable acids was significantly increased, however, when constraining PPFD, while s-carotene was slightly decreased. When combining plant and energy production, yield reductions in systems that reduce the supply of solar radiation to crops only at high irradiances will be less considerable than in systems that permanently shade the crop. However, yield losses in tomato production remain significant in both system types.

Comparative Effects of Salt and Water Stress on Seed Germination and Early Embryo Growth in Two Cultivars of Sweet Sorghum

Abstract: In semiarid regions of the Mediterranean basin, water and salinity stresses restrict crop establishment. The effects of salt and water stress on seed germination and early embryo growth (radicle and shoot growth) were investigated in laboratory in two cultivars of sweet sorghum [Sorghum bicolor (L.) Moench] – cv. ‘90-5-2′ and cv. ‘Keller’ – to verify how these stresses may limit crop growth during the very early stages of growing season. Six water potentials (w) of the imbibition solution (from 0 to � 1.0 MPa) in NaCl or polyethylene glycol (PEG) for salt and water stress tests, respectively, were studied. Daily germination was recorded, and radicle and shoot lengths and dry weights (DWs) were measured 2 days after initial germination. Seed germination was reduced (8–30% lower than control) by water stress at w <� 0.6 MPa and was delayed (approx. +10 h) already at � 0.4 MPa. Salt stress only prolonged germination time. Shoot and root growth was adversely affected by water stress (PEG), whereas the effect of salt stress was less relevant. Cv. ‘90-5-2’ was less sensitive than cv. ‘Keller’ to both stresses. These cultivars exhibited a greater sensitivity to abiotic stresses in terms of root and shoot growth; therefore, other parameters beside germination, such as early embryo growth rate, may help in evaluating sorghum lines for adaptation to semi-arid areas.

Effects of Increasing Salinity Stress and Decreasing Water Availability on Ecophysiological Traits of Quinoa (Chenopodium quinoa Willd.) Grown in a Mediterranean‐Type Agroecosystem

Abstract: Quinoa is a native Andean crop for domestic consumption and market sale, widely investigated due to its nutritional composition and gluten-free seeds. Leaf water potential (Ψleaf) and its components and stomatal conductance (gs) of quinoa, cultivar Titicaca, were investigated in Southern Italy, in field trials (2009 and 2010). This alternative crop was subjected to irrigation treatments, with the restitution of 100 %, 50 % and 25 % of the water necessary to replenish field capacity, with well water (100 W, 50 W, 25 W) and saline water (100 WS, 50 WS, 25 WS) with an electrical conductivity (ECw) of 22 dS m−1. As water and salt stress developed and Ψleaf decreased, the leaf osmotic potential (Ψπ) declined (below −2.05 MPa) to maintain turgor. Stomatal conductance decreased with the reduction in Ψleaf (with a steep drop at Ψleaf between −0.8 and 1.2 MPa) and Ψπ (with a steep drop at Ψπ between −1.2 and −1.4 MPa). Salt and drought stress, in both years, did not affect markedly the relationship between water potential components, RWC and gs. Leaf water potentials and gs were inversely related to water limitation and soil salinity experimentally imposed, showing exponential (Ψleaf and turgor pressure, Ψp, vs. gs) or linear (Ψleaf and Ψp vs. SWC) functions. At the end of the experiment, salt-irrigated plants showed a severe drop in Ψleaf (below −2 MPa), resulting in stomatal closure through interactive effects of soil water availability and salt excess to control the loss of turgor in leaves. The effects of salinity and drought resulted in strict dependencies between RWC and water potential components, showing that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under stress, resulting in osmotic adjustment at turgor loss. The extent of osmotic adjustment associated with drought was not reflected in Ψπ at full turgor. As soil was drying, the association between Ψleaf and SWC reflected the ability of quinoa to explore soil volume to continue extracting available water from the soil. However, leaf ABA content did not vary under concomitant salinity and drought stress conditions in 2009, while differing between 100 W and 100 WS in 2010. Quinoa showed good resistance to water and salt stress through stomatal responses and osmotic adjustments that played a role in the maintenance of a leaf turgor favourable to plant growth and preserved crop yield in cropping systems similar to those of Southern Italy.

High Temperature‐Induced Repression of the Rice Sucrose Transporter (OsSUT1) and Starch Synthesis‐Related Genes in Sink and Source Organs at Milky Ripening Stage Causes Chalky Grains

Abstract: High temperatures during rice grain ripening reduced yield and grain quality. The proportion of milky white grains was 43.6 % at 30 °C but only 6.5 % at 25 °C. Grain filling was initially faster at 30 °C and finished earlier, and the final dry matter content was less, than at 25 °C. High temperature strongly suppressed the expression of the sucrose transporter gene OsSUT1 and starch synthesis-related genes SuSy2, AGPS2b, BEIIb and Granule-bound starch synthase in grains during early grain filling; the transcription levels of OsSUT1 at 14 days after flowering (DAF) were about 60 % lower in grains, flag leaf blade, flag leaf sheath and first leaf sheath. These facts are possibly involved in the earlier termination of grain filling at 21 DAF, following the rapid rise of grain dry weight from 0 to 7 DAF, due to possible reduction in assimilate supply via OsSUT1 under the high temperature. When panicles were partly clipped, the resultant increase in assimilate supply to the remaining grains significantly upregulated the expression of OsSUT1 and the starch synthesis-related genes at 14 DAF, which consequently accelerated starch accumulation in the grains and ultimately increased the grain weight of remaining grains at 30 °C. These results indicate that high temperature during grain filling reduces grain yield and quality by changing the expression of OsSUT1 and starch synthase-related genes, resulting in earlier ripening due to hastened or premature assimilate supply to grains.

The Alleviating Effect of Elevated CO2 on Heat Stress Susceptibility of Two Wheat (Triticum aestivum L.) Cultivars

Abstract: This study analysed the alleviating effect of elevated CO2 on stress-induced decreases in photosynthesis and changes in carbohydrate metabolism in two wheat cultivars (Triticum aestivum L.) of different origin. The plants were grown in ambient (400 l ll 1 ) and elevated (800 l ll 1 )C O2 with a day/night temperature of 15/10 °C. At the growth stages of tillering, booting and anthesis, the plants were subjected to heat stress of 40 °C for three continuous days. Photosynthetic parameters, maximum quantum efficiency of photosystem II (PSII) photochemistry (Fv/Fm) and contents of pigments and carbohydrates in leaves were analysed before and during the stress treatments as well as after 1 day of recovery. Heat stress reduced PN and Fv/Fm in both wheat cultivars, but plants grown in elevated CO2 maintained higher PN and Fv/Fm in comparison with plants grown in ambient CO2. Heat stress reduced leaf chlorophyll contents and increased leaf sucrose contents in both cultivars grown at ambient and elevated CO2. The content of hexoses in the leaves increased mainly in the tolerant cultivar in response to the combination of elevated CO2 and heat stress. The results show that heat stress tolerance in wheat is related to cultivar origin, the phenological stage of the plants and can be alleviated by elevated CO2. This confirms the complex interrelation between environmental factors and genotypic traits that influence crop performance under various climatic stresses.

Apoplastic Na+ in Vicia faba Leaves Rises After Short‐Term Salt Stress and Is Remedied by Silicon

Abstract: Salinity primarily affects plants by inhibiting shoot growth. Salt-sensitive plants have been suggested to accumulate Na+ within their leaf apoplast under salinity, leading to a reduced water status. Evidence related to apoplastic Na+ accumulation is still enigmatic. We have focused on the effect of a short-term salt treatment by using the salt-sensitive Vicia faba. Moreover, we have examined the role of silicon in alleviating sodium accumulation in the apoplast. Salt-sensitive field beans have been subjected to increasing levels of salinity, with and without the addition of silicon under hydroponic conditions. We have demonstrated that the dicot Vicia faba exhibits a rise in Na+ concentration in the leaf apoplast at higher salinity levels; this is significantly ameliorated by the addition of silicon. Further, enhanced shoot growth under high salt treatment in the presence of added silicon is correlated with a significant decrease in Na+ concentration in the leaves. The novelty of the current study is the detection of a high Na+ concentration in the leaf apoplast of the salt-sensitive dicot field bean. Our results support Oertli's hypothesis that extracellular salt accumulation can lead to wilting leaves, plant growth reduction and cell death.

Effect of Phosphorus Nutrition on Growth and Physiology of Cotton Under Ambient and Elevated Carbon Dioxide

Abstract: Phosphorous deficiency in soil limits crop growth and productivity in the majority of arable lands worldwide and may moderate the growth enhancement effect of rising atmospheric carbon dioxide (CO2) concentration. To evaluate the interactive effect of these two factors on cotton (Gossypium hirsutum) growth and physiology, plants were grown in controlled environment growth chambers with three levels of phosphate (Pi) supply (0.20, 0.05 and 0.01 mM) under ambient and elevated (400 and 800 lmol mol 1 , respectively) CO2. Phosphate stress caused stunted growth and resulted in early leaf senescence with severely decreased leaf area and photosynthesis. Phosphate stress led to over 77 % reduction in total biomass across CO2 levels. There was a below-ground (roots) shift in biomass partitioning under Pi deficiency. While tissue phosphorus (P) decreased, tissue nitrogen (N) content tended to increase under Pi deficiency. The CO2 9 Pi interactions were significant on leaf area, photosynthesis and biomass accumulation. The stimulatory effect of elevated CO2 on growth and photosynthesis was reduced or highly depressed suggesting an increased sensitivity of cotton to Pi deficiency under elevated CO2. Although, tissue P and stomatal conductance were lower at elevated CO2, these did not appear to be the main causes of cotton unresponsiveness to elevated CO2 under severe Pi-stress. The alteration in the uptake and utilization of N was suggested due to a consistent reduction (18–21 %) in the cotton plant tissue N content under elevated CO2.

Frost Hardiness Expression and Characterisation in Wheat at Ear Emergence

Abstract: Occasionally, wheat can be exposed to overnight freezing temperatures whilst it is in the early reproductive stage and considerable frost damage can occur. In the vegetative stage, full expression of frost tolerance genes can be gained when plants are exposed to acclimation temperatures (4 °C). Paradoxically, wheat during flowering has limited or no ability to effectively acclimate or re-acclimate and it demonstrates frost sensitivity during this stage. Using a combined approach involving infrared thermography and molecular analysis, the causes and effects of frost-induced damage to wheat during ear emergence were investigated. It was demonstrated that frost damage only occurs to wheat ears if the temperature falls below −5 °C but some ears, and some spikelets on frozen ears do not freeze but supercool and escape freezing. In whole plant freezing experiments, spikelets showed both complete and partial sterility upon maturation and this was linked to parallel infrared observation of detached ears showing full or partial freezing of spikelets. It was hypothesised that wherever spikelet freezing occurred the spikelet was sterile and grain production per ear was drastically reduced, and in contrary, spikelet survival was as a result of supercooling. Molecular analysis of the upregulation of Cbf14 showed that as ear emergence progressed the ability to induce Cbf14 decreased but at early stages of ear emergence Cbf14 was able to be induced by exposure to acclimating temperatures (4 °C). The hypothesis that the lack of the ear to acclimate is because of the incapability to induce the CBF transcription factor was only partially upheld in this investigation. Further work is needed to elucidate more precisely the molecular incompetency for the acclimation of wheat during ear emergence.

Effects of Increasing Temperatures on Spikelet Fertility in Different Rice Cultivars based on Temperature Gradient Chamber Experiments

Abstract: Spikelet sterility in rice (Oryza sativa L.) induced by high temperatures is a major concern given global warming predictions. We studied differences among eight rice cultivars in spikelet fertility at five different temperature levels in temperature gradient chamber (TGC) experiments. Six japonica and two indica cultivars were exposed to high-temperature gradients in TGCs during the 2005 flowering season. Spikelet sterility increased with temperature in TGCs and differed among cultivars because of both variations in temperature tolerance and timing of heading. The correlation between spikelet fertility of individual panicles and both air temperature and panicle temperature during flowering was analyzed to compare tolerances among cultivars. The temperature (T75) at which spikelet fertility was 75 % of maximum ranged from 34 to 39 °C air temperature and differed significantly among cultivars. Indica varieties had higher T75 values than japonica varieties. The T75 values based on panicle temperature also differed among cultivars, but the difference between indica and japonica varieties were less significant. We concluded that the higher temperature tolerances of indica cultivars in our experiments could be attributed to lower spikelet temperatures, and cultivars with similar spikelet temperatures still had different heat tolerances due to differences in pollination ability.

Maize Hybrid Variability for Transpiration Decrease with Progressive Soil Drying

Abstract: Drought is ubiquitous in rainfed cropping systems and often limits maize yields. The sensitivity of transpiration response early in progressive soil drying is a trait with potential to improve crop drought resistance. Simulation studies demonstrated that increased sensitivity to drying soil leading to restricted transpiration rates results in conservation of soil water during vegetative stages for possible use during grain filling. In contrast to other crops, there have been no studies characterizing genotypic variability for this trait in maize. Experiments in controlled environments were conducted to characterize the fraction of transpirable soil water (FTSW) threshold on drying soil for 36 hybrids selected for variation in the field for drought resistance, regions of adaptation and stay green. While FTSW thresholds varied among hybrids from 0.60 to 0.33, these thresholds were not uniformly associated with level of drought resistance in the field. Nevertheless, this study demonstrated a high FTSW threshold corresponded with drought resistance observed in some modern maize germplasm (hybrids #7, 17, 24, 27 and 32). This knowledge can enable breeding work seeking to exploit this adaptive trait to improved drought tolerance in low threshold FTSW germplasm.

Leaf Cell‐Wall Components as Influenced in the First Phase of Salt Stress in Three Maize (Zea mays L.) Hybrids Differing in Salt Resistance

Abstract: The leaf cell wall (CW) chemical composition of three maize (Zea mays L.) hybrids (salt-resistant SR 03 and SR 12, salt-sensitive Pioneer 3906) was investigated in the first phase of salt stress (100 mm NaCl) compared with the control (1 mm NaCl) treatment to investigate whether changes in CW composition were responsible for shoot growth reduction. Salt treatment caused a strong inhibition in shoot growth with a concomitant increase in the ratio between CW dry mass (DM) and shoot fresh mass (FM) and a decrease in CW cellulose concentrations in all hybrids. NaCl caused a large increase in the concentrations of total and non-methylated uronic acid (UA) in salt-sensitive Pioneer 3906 and salt-resistant SR 12. The onset of the accumulation of non-methylated UA was delayed in SR 12, which indicates that this may be one reason for the better growth performance of this hybrid under salt stress compared with Pioneer 3906. It is concluded that a low accumulation of non-methylated UA in leaf CW may, among other mechanisms, contribute to salt resistance in the first phase of salt stress.

Carbohydrates Accumulation and Remobilization in Wheat Plants as Influenced by Combined Waterlogging and Shading Stress During Grain Filling

Abstract: Wheat plants were subjected to combined waterlogging and shading stress (WS) at 0–7, 8–15, 16–23 and 24–31 days after anthesis (DAA), respectively. Compared to the non-stressed plants, WS significantly decreased the final grain yield. Grain number was dramatically lowered by WS imposed at 0–7 DAA but hardly affected by other WS treatments; while the thousand-kernel-weight was unaffected by WS imposed at 0–7 DAA and lowered by other WS treatments. Photosynthate accumulation in the stem was decreased by WS imposed at 0–7 and 8–15 DAA, but was unaffected by WS imposed at later stages. Grain-filling rate was decreased, although the apparent remobilization of carbohydrate reserves from stem to grain was stimulated under WS. The carbohydrate reserves stored in the lower stem internodes were activated earlier and remobilized much more than those in the upper internodes; however, the proportion of the apparent remobilized reserves among the different stem internodes was consistent for all treatments. WS decreased contents of fructans, fructose and sucrose in the stem, which coincided with increased activity of fructan exohydrolase and decreased activities of sucrose-1-fructosyltransferase and fructan-1-fructosyltransferse. The results indicate that post-anthesis WS stimulated carbohydrate reserves remobilization by modifying the activities of the fructans-catalysing enzymes in the stem.

Effects of Exogenous Abscisic Acid on Antioxidant System in Weedy and Cultivated Rice with Different Chilling Sensitivity under Chilling Stress

Abstract: Two chilling-tolerant genotypes, that is, weedy rice WR03-45 and cultivated rice Lijiangxintuanheigu and two chilling-sensitive genotypes, that is, weedy rice WR03-26 and cultivated rice Xiuzinuo were used in this study to investigate the effects of exogenous abscisic acid (ABA) on protection against chilling damage as well as on changes in physiological features. The results showed that under chilling stress the increased levels of superoxide radical (), hydrogen peroxide (H2O2) and malondialdehyde (MDA) in WR03-45 and Lijiangxintuanheigu were lower than those in WR03-26 and Xiuzinuo. Activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR)) and non-enzymatic antioxidants (ascorbate acid (AsA) and reduced glutathione (GSH)) were enhanced in WR03-45 and Lijiangxintuanheigu, whereas they were decreased significantly in WR03-26 and Xiuzinuo. Application of exogenous ABA reduced the chilling damage in the four genotypes. The pre-treatment with ABA decreased the levels of , H2O2 and MDA caused by chilling stress in the four genotypes through increasing the activities of SOD, CAT, APX, GR and the contents of AsA and GSH in the four genotypes under chilling stress. Moreover, pre-treatment with Fluridone, the ABA biosynthesis inhibitor, prohibited the effects of ABA through enhancing the oxidative damages and suppressing the antioxidant defence systems under chilling stress. The results indicate the mechanism for rice with chilling tolerance is to enhance the capacity of antioxidant defence systems under chilling stress. Furthermore, ABA plays important roles in the tolerance of rice against chilling stress for it could induce the capacity of whole antioxidant defence systems including enzymatic and non-enzymatic constitutions under chilling stress.

Genetic Variation for Heat Tolerance During the Reproductive Phase in Brassica rapa

Abstract: We investigated heat tolerance at the reproductive stage in six spring-type B. rapa accessions and one B. juncea accession as a control. Plants were subjected to two temperature treatments for seven days in controlled environmental rooms, beginning one day before the first open flower on the main stem inflorescence. The high-temperature treatment ranged from 25 ° Ct o 35°C during 16 h light and 25 °C during 8 h dark. The control temperature treatment was set at 23 °C during 16 h light and 15 °C during 8 h dark. Soil moisture was maintained at close to field capacity to avoid drought stress. Main stem buds that emerged during the treatment period were tagged, and pod and seed production was recorded at each reproductive node. Leaf temperature depression and leaf conductance increased in the high-temperature treatment which indicated that plants were not drought stressed. A leafy vegetable type of B. rapa from Indonesia was the most tolerant to high temperature, as defined by its ability to set seed equally well in the control and high-temperature treatments, followed by an oilseed type from Pakistan. Pollen viability remained above 87 % in all accessions and treatments. We conclude that bud number and length, and pod number produced under high temperatures, might provide a useful preliminary screen for high-temperature tolerance and that B. rapa may be a valuable source of heat tolerance in canola (B. napus).

Why Randomize Agricultural Experiments

Abstract: This study illustrates the importance of randomization using two hypothetical field trials, one with a marked systematic trend and the other with a more erratic spatial pattern. The insights from these two examples are reinforced by analysis of a uniformity trial and a small simulation study. Results illustrate that both model-based spatial analysis and randomization-based analysis assuming independent errors are valid with full randomization but may be invalidated when randomization is lacking. It is concluded that randomization provides protection against different forms of spatial trend. The examples given in the study serve as a general reminder that agricultural experiments should be randomized whenever possible.

Effects of Ozone on Leaf Senescence, Photochemical Efficiency and Grain Yield in Two Winter Wheat Cultivars

Abstract: The adverse effects of tropospheric ozone (O3) on crop photosynthesis, growth and yield have been documented in numerous studies over the last decades, but little information from field experimentation exists on how modern European winter wheat cultivars respond to O3. Two winter wheat cultivars (Astron and Pegassos) differing in development characteristics were exposed to non-filtered ambient air or non-filtered air plus 30 ppb and non-filtered air plus 60 ppb O3 (8 h day−1) in open-top field chambers. At several dates during growth, green leaf area was determined by destructive harvests. Leaf gas exchange, pigment content and xanthophyll cycle activity, and photochemical efficiency by chlorophyll a fluorescence were measured. O3 exposure induced accelerated senescence with no difference between cultivars. Photosynthesis declined especially in Pegassos; however, stomatal conductance was hardly affected by O3. Pigment contents were reduced by O3 exposure, and de-epoxidation index increased. Photochemical efficiency (Fv/Fm) declined, whereas actual quantum yield (ΦPSII) did not respond to O3. O3 exposure reduced grain yield in both cultivars. However, yield of Pegassos was more affected by O3 exposure than yield of Astron, suggesting a higher O3 sensitivity of Pegassos. The data presented in this manuscript indicate a need to test whether high-yield varieties such as Pegassos are particularly sensitive to O3 exposure.

Leaf Gas Exchange Characteristics of Jatropha as Affected by Nitrogen Supply, Leaf Age and Atmospheric Vapour Pressure Deficit

Abstract: Facing a steadily increasing world energy demand, jatropha, among other energy crops, has been reported to potentially contribute to biofuel production. A basic characterisation of plant responses to abiotic environmental factors is important for assessing the model-assisted potential of this plant in view of the many agro-ecological zones in which jatropha is presently cultivated. Two pot experiments and two field studies were used to record gas exchange parameters in response to light, nitrogen supply, atmospheric vapour pressure deficit (VPD), leaf age and time of measurements. Variation of N supply from 0 to 16 mm resulted in lower rates of photosynthesis (A) and stomatal conductance (gs) of treatment 0 mm N compared with other N levels, whereas the light compensation point (IC), quantum yield (QY) and dark respiration rates (Rd) were similar in all treatments. In the field, diurnal effects were evident with higher light-saturated photosynthetic rate (Amax) and QY and lower IC and Rd in the morning than in the afternoon. Considering leaf age effects, fully expanded leaves had a lower Amax compared with expanding leaves and this variation in leaf gas exchange was not related to changes in the chlorophyll index value (SPAD) which steadily increased with leaf age. QY of field and greenhouse plants varied from 0.023 to 0.037 and was substantially lower than in C3 plants. A was positively correlated with gs in a hyperbolic function. A varied from 0.64 to 21.13 μmol m−2 s−1 and gs varied from 12 to 469 mmol m−2 s−1. With increasing VPD, gs decreased, but this response differed between the field experiments and the two pot experiments which contrasted each other distinctively. Applying the inverse logistic function of Webb (Ecological Modeling, 56 (1991), 81), the maximal stomatal conductance of jatropha was in the range of 382 mmol m−2 s−1 and gs is predicted to be close to zero at 5 kPa. These data altogether indicate that light absorption characteristics of single leaves and carbohydrate status parameters should be investigated further to explain the low QY and the pronounced diurnal variation.

Growth, Development and Yield of Crambe Abyssinica Under Saline Irrigation in the Greenhouse

Abstract: Salinity is one of the major factors limiting agricultural productivity in arid and semi-arid regions. Saline areas around the world are increasing and sources of fresh water are decreasing. The increasing importance of the use of brackish water to supplement regular irrigation has demonstrated a need for finding new potential plants with tolerance to irrigation with saline water which can be used in industrial agriculture. The aim of this study was to determine whether irrigation with brackish water of Crambe Abyssinica, a plant commonly used for industrial oil production and for ornamental purposes and with high economical value, especially in Central Asia and the Aral Sea region, is feasible. One more goal was to study how it influences growth and development, seed and oil yield and some physiological parameters such as photosynthesis, transpiration, chlorophyll content, osmotic potential and accumulation of fresh and dry weight. The effects of three salinity levels, 3, 6 and 9 dS m−1, were investigated in a greenhouse experiment during two consecutive years. Results of this study showed that growth of Crambe abyssinica in arid zones and irrigation with mild saline water up to EC 6 dS m−1, mostly common in these areas is feasible, suggesting tolerance to moderate salinity levels and feasibility of its culture in areas of the Aral Sea with adequate salinity levels. Consequently, in spite of the fact that biomass and seed yield were significantly decreased in plants irrigated with brackish water, Crambe abyssinica might be cultivated as an alternate source of green biomass and for industrial vegetable oil under conditions not suitable for conventional plant production.

Drought Resistance of C4 Grasses Under Field Conditions: Genetic Variation Among a Large Number of Bermudagrass (Cynodon spp.) Ecotypes Collected from Different Climatic Zones

Abstract: Predictions of extreme weather resulting from climate change will present huge challenges for scientists trying to maintain and increase agricultural production. A greater frequency of dry periods is predicted placing emphasis on the development of plant varieties that are able to maintain performance in dry conditions. The aim of this research was to determine the genetic variation for drought resistance among a large range of potential pasture or turf bermudagrasses (Cynodon spp.). Four hundred and sixty genotypes including ecotypes collected from different climatic zones of Australia, and commercial cultivars were established in the field and assessed during natural and imposed drought periods. Using descriptors of drought resistance such as turf quality and green cover, genotypes were classified into different groups; 436 genotypes were clustered into ten groups in one experiment, and 72 genotypes were clustered into three groups in a second. There was a high correlation of response (r = 0.78) for 47 genotypes common to both experiments suggesting that the drought resistance techniques used to group genotypes were robust. Physiological analyses of the genotypes within the superior drought resistance groups indicated that these group members were probably able to extract more available soil water during the drought period. No commercial cultivars were found in the most drought resistance groups. These field studies also suggested that future collections of bermudagrass ecotypes designed to select for drought resistance might best be carried out from regions that experience Mediterranean climates. The field evaluations presented here did not correlate well with drought resistance determined in previously reported shallow lysimeter (40 cm deep) experiments.

Nitrogen Assimilation and Growth of Cotton Seedlings under NaCl Salinity and in Response to Urea Application with NBPT and DCD

Abstract: Salinity stress and inefficient nitrogen fertilization adversely affect cotton growth and yield. The effect of salinity on the growth and stress response of cotton seedlings and the effect on N-use efficiency from the use of the inhibitors of urease (NBPT) and nitrification (DCD) under salinity stress were studied in growth chambers. The study consisted of three levels of salinity – low (0.45 dS m−1), moderate (8 dS m−1) and high (16 dS m−1) – and five N treatments – unfertilized control, 100 % N rate with urea, 80 % N rate with urea, 80 % N rate with urea +NBPT and 80 % N rate with urea +NBPT + DCD. The results indicated that salinity stress reduced plant growth (low leaf area and plant dry matter), decreased N assimilation (low NR, GS and protein), increased plant stress response (high GR and SOD), and decreased leaf chlorophyll, stomatal conductance and quantum yield. Addition of NBPT to urea improved N uptake by 22 % under low salinity; however, this effect was not observed with increasing salinity. No benefit of addition of DCD was observed in any of the parameters collected. In conclusion, salinity stress hindered the performance of the additive NBPT and negatively affected the growth and physiology of cotton.

Phosphorus Fertilization and Fungal Inoculations Affected the Physiology, Phosphorus Uptake and Growth of Spring Wheat Under Rainfed Conditions on the Canadian Prairies

Abstract: Somefungal specieshave beenshown toimprove plant growthunder drought conditions and to increase plant phosphorus (P) uptake from the soil. How moisture limitation, P availability and fungal inoculation interact to affect plant physiology and growth is, however, poorly understood. Here, we studied the combined effects of fungal (arbuscular mycorrhizal fungi (AMF) or Penicillium spp.) inoculations and phosphorus (P) fertilization (0, 45 and 90 kg ha � 1 ) on the net rate of photosynthesis, water-use efficiency, P uptake and growth of spring wheat (Triticum aestivum var. Superb) under field conditions at two locations (Castor and Vegreville) in Alberta, Canada. Both fungal inoculation and P application increased the rate of photosynthesis. Under the same P level, AMF inoculation had a greater positive effect on the rate of photosynthesis than Penicillium inoculation. The AMF inoculation increased the instantaneous water-use efficiency (WUEi) of plants at Castor, but not at Vegreville. Leaf carbon isotope discrimination (CID, D 13 C) increased with the rate of P application but was not affected by fungal inoculations. Phosphorus concentrations of stem and seed increased with both fungal inoculation and P application irrespective of location, with AMF inoculation showing the largest effects. The interaction between P addition and fungal inoculation was significant for stem P concentration in Vegreville. Both fungal inoculation and P application increased the leaf area index (LAI), biomass production and grain yield at both locations. Under the same P level, AMF inoculation had a greater positive effect on LAI, biomass production and grain yields than Penicillium inoculation. Morphological characters such as spike length and kernels/spike were also improved by fungal inoculation and P application at both locations. We conclude that the studied sites were deficient in P availability, and both fungal inoculation and P application improved P uptake and crop productivity, while the effect of fungal inoculation on water-use efficiency was site specific.