Salah El-Hendawy

Growth, ion content, gas exchange, and water relations of wheat genotypes differing in salt tolerances

Although the mechanisms of salt tolerance in plants have received much attention for many years, genotypic differences influencing salt tolerance still remain uncertain. To investigate the key physiological factors associated with genotypic differences in salt tolerance of wheat and their relationship to salt stress, 13 wheat genotypes from Egypt, Australia, India, and Germany, that differ in their salt tolerances, were grown in a greenhouse in soils of 4 different salinity levels (control, 50, 100, and 150 mM NaCl). Relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), photosynthesis, chlorophyll content (SPAD value), and leaf water relations were measured at Days 45 and 60 after sowing. Mineral nutrient content in leaves and stems was determined at Day 45 and final harvest. Salinity reduced RGR, NAR, photosynthetic rate, stomatal conductance, water and osmotic potentials, and K + and Ca 2+ content in stems and leaves at all times, whereas it increased leaf respiration, and Na + and Cl − content in leaves and stems. LAR was not affected by salinity and the effect of salinity on SPAD value was genotype-dependent. Growth of salt-tolerant genotypes (Sakha 8, Sakha 93, and Kharchia) was affected by salinity primarily due to a decline in photosynthetic capacity rather than a reduction in leaf area, whereas NAR was the more important factor in determining RGR of moderately tolerant and salt-sensitive genotypes. We conclude that Na + and Cl − exclusion did not always reflect the salt tolerance, whereas K + in the leaves and Ca 2+ in the leaves and stems were closely associated with genotypic differences in salt tolerance among the 13 genotypes even at Day 45. Calcium content showed a greater difference in salt tolerance among the genotypes than did K + content. The genotypic variation in salt tolerance was also observed for the parameters involved in photosynthesis, and water and osmotic potentials, but not for turgor pressure.

Differential effect of moderate salinity on growth and ion contents in the mainstem and subtillers of two wheat genotypes

Abstract To understand the differential effect of moderate salinity on the growth and ion contents in mainstem and subtillers of wheat plants, two spring wheat (Triticum aestivum L.) genotypes (Sakha 8 and Thasos) were grown in a greenhouse in soil with or without salinity. Both the above-ground dry weight and the leaf area at day 55 after sowing, as well as the grain yield, grain number, spikelet number, straw dry weight and above-ground dry weight at plant maturity, were determined. Inorganic ion content in young leaves at day 55 after sowing was also analyzed. The results showed that the above-ground dry weight and leaf area in the subtillers (T1 and T2) at day 55 after sowing were greatly reduced by salinity. Compared with the effect of salinity on subtiller growth, the mainstem was much less affected during the vegetative growth stages, whereas there was a similar effect of salinity on the grain yield between the mainstem and subtillers. The reduction in the grain yield of Sakha 8 by moderate salinity mainly resulted from a decrease in the number of tillers, whereas in addition to a reduction in the number of tillers in the salt-sensitive genotype Thasos, the grain yield in mainstem and subtillers was further reduced during the grain filling. Both wheat genotypes are more sensitive to salt stress during the vegetative growth stages than in the reproductive stages. The salt-tolerant genotype Sakha 8 is characterized by the exclusion of Na+ in the leaves. Thus, under moderate saline conditions the greater reduction in subtillers may result from an ion imbalance in the salt-tolerant genotype Sakha 8 and from Na+ toxicity in the salt-sensitive genotype Thasos.

Hyperspectral reflectance sensing to assess the growth and photosynthetic properties of wheat cultivars exposed to different irrigation rates in an irrigated arid region

Simultaneous indirect assessment of multiple and diverse plant parameters in an exact and expeditious manner is becoming imperative in irrigated arid regions, with a view toward creating drought-tolerant genotypes or for the management of precision irrigation. This study aimed to evaluate whether spectral reflectance indices (SRIs) in three parts of the electromagnetic spectrum ((visible-infrared (VIS), near-infrared (NIR)), and shortwave-infrared (SWIR)) could be used to track changes in morphophysiological parameters of wheat cultivars exposed to 1.00, 0.75, and 0.50 of the estimated evapotranspiration (ETc). Significant differences were found in the parameters of growth and photosynthetic efficiency, and canopy spectral reflectance among the three cultivars subjected to different irrigation rates. All parameters were highly and significantly correlated with each other particularly under the 0.50 ETc treatment. The VIS/VIS- and NIR/VIS-based indices were sufficient and suitable for assessing the growth and photosynthetic properties of wheat cultivars similar to those indices based on NIR/NIR, SWIR/NIR, or SWIR/SWIR. Almost all tested SRIs proved to assess growth and photosynthetic parameters, including transpiration rate, more efficiently when regressions were analyzed for each water irrigation rate individually. This study, the type of which has rarely been conducted in irrigated arid regions, indicates that spectral reflectance data can be used as a rapid and non-destructive alternative method for assessment of the growth and photosynthetic efficiency of wheat under a range of water irrigation rates.

Comparative Performance of Multivariable Agro-Physiological Parameters for Detecting Salt Tolerance of Wheat Cultivars under Simulated Saline Field Growing Conditions

Field-based trials are crucial for successfully achieving the goals of plant breeding programs aiming to screen and improve the salt tolerance of crop genotypes. In this study, simulated saline field growing conditions were designed using the subsurface water retention technique (SWRT) and three saline irrigation levels (control, 60, and 120 mM NaCl) to accurately appraise the suitability of a set of agro-physiological parameters including shoot biomass, grain yield, leaf water relations, gas exchange, chlorophyll fluorescence, and ion accumulation as screening criteria to establish the salt tolerance of the salt-tolerant (Sakha 93) and salt-sensitive (Sakha 61) wheat cultivars. Shoot dry weight and grain yield per hectare were substantially reduced by salinity, but the reduction was more pronounced in Sakha 61 than in Sakha 93. Increasing salinity stress caused a significant decrease in the net photosynthesis rate and stomatal conductance of both cultivars, although their leaf turgor pressure increased. The accumulation of toxic ions (Na+ and Cl-) was higher in Sakha 61, but the accumulation of essential cations (K+ and Ca2+) was higher in Sakha 93, which could be the reason for the observed maintenance of the higher leaf turgor of both cultivars in the salt treatments. The maximum quantum PSII photochemical efficiency (Fv/Fm) and the PSII quantum yield (ΦPSII) decreased with increasing salinity levels in Sakha 61, but they only started to decline at the moderate salinity condition in Sakha 93. The principle component analysis successfully identified the interrelationships between all parameters. The parameters of leaf water relations and toxic ion concentrations were significantly related to each other and could identify Sakha 61 at mild and moderate salinity levels, and, to a lesser extent, Sakha 93 at the moderate salinity level. Both cultivars under the control treatment and Sakha 93 at the mild salinity level were identified by most of the other parameters. The variability in the angle between the vectors of parameters explained which parameters could be used as individual, interchangeable, or supplementary screening criteria for evaluating wheat salt tolerance under simulated field conditions.

The genetic basis of spectral reflectance indices in drought-stressed wheat

Drought imposes a major constraint over the productivity of wheat, particularly in arid and semi-arid production zones. Here, the genetic basis of spectral reflectance indices was investigated in drought-stressed wheat by comparing, under two contrasting moisture regimes, the performance of an F6 recombinant inbred line (RIL) population bred from a cross between the drought tolerant cultivar Pavon76 and the sensitive cultivar Yecora Rojo. The parents and RILs were genotyped with respect to both a set of microsatellite (SSR) loci and a number of known drought-responsive genes. In all, 28 quantitative trait loci (QTL) controlling dry weight per plant, water content of the above-ground biomass, leaf water potential, canopy temperature, and spectral reflectance indices traits were identified. The loci were distributed over 11 chromosomes, belonging to each of the three wheat sub-genomes. There were important location-flanking markers Barc109 and Barac4 on chromosome 5B relating to dry weight per plant accumulation under the limited irrigation regime. The same region-harbored QTL associated with leaf water potential, canopy temperature, and ratio index under the limited irrigation regime. Linkage between the known drought-responsive genes and aspects of the drought response was established. Some of QTL were of substantial enough effect for their linked markers to be likely usable for the marker-assisted breeding of drought tolerance in wheat.

Effects of arbuscular mycorrhizal fungi on the growth of two turfgrasses grown under greenhouse conditions

ABSTRACT The need for salinity resistance in turfgrass is increasing because of the enhanced use of effluent and other low-quality water for turfgrass irrigation. Although most turfgrasses form an arbuscular mycorrhizal fungus (AMF) symbiosis, there is little information on the mycorrhization of turfgrass species. Therefore, the aim of this study was to determine the effects of three AMF species, Glomus intraradices Schenck & Smith, Glomus etunicatum Becker & Gerdemann, and Glomus deserticola Trappe & John, and a mixture thereof on the growth, productivity, and nutrient uptake of two species of cool-season turfgrasses, Challenger Kentucky bluegrass (Poa pratensis L.) and Arid tall fescue (Festuca arundinacea Schreb.), and to relate the effects to colonization of the roots by mycorrhiza to assess the dependency of the plants (mycorrhizal dependency [MD]). Following the experimental period (4 months) and measurements, the mycorrhizal inoculated plants had significantly greater biomass production compared to that of non-inoculated plants. MD and shoot mineral contents (particularly P) differed among turfgrass hosting AMF, and the highest value (13%) occurred for P. pratensis and F. arundinacea seedlings colonized with G. intraradices and G. deserticola, respectively. The P content was highest for the F. arundinacea/mixed AMF combination compared to other treatments. We confirmed that mycorrhizal inoculation (P. pratensis/G. intraradices and F. arundinacea/mixed AMF combinations) enhanced plant productivity and nutrient uptake (especially P) even under non-optimum conditions.

Arbuscular mycorrhizal fungi mitigates heavy metal toxicity adverse effects in sewage water contaminated soil on Tagetes erecta L

ABSTRACT The aim of this experiment was to evaluate the impact of colonization with arbuscular mycorrhizal (AM) fungus Glomus constrictum on the biomass production, flower quality, chlorophyll content, macronutrients and heavy metals content of marigold (Tagetes erecta L.) planted under uncontaminated soil and watered with various rates of sewage water. Sewage water utilization significantly decreased biomass production, characters of flower, nutrient concentration and rates of mycorrhizal colonization of mycorrhizal (M) and non-mycorrhizal (NM) marigold as compared to control untreated plants especially at the higher rates, but the reduction rate was proportionally higher in non-AM treatments. Mycorrhizal plants had significantly greater yield, relative chlorophyll content, leaf area, flower quality and element (P, N, K and Mg) content compared to non-inoculated marigold plants irrigated with or without sewage water. Furthermore, AM inoculation had highly decreased heavy metal (Zn, Co, Mn, Cu) content in tissues as compared to equivalent non-inoculated plants grown under sewage water application. Growing marigold with AM inoculum can reduce toxicity of heavy metals and enhance biomass production and P uptake. The results support the view that AM have a protective function for the host plant, hence playing a potential function in soil polluted immobilization processes, and thus are of assessing the potential of phytoremediation of heavy metals in sewage water contaminated soil.

Non-invasive spectral detection of the beneficial effects of Bradyrhizobium spp. and plant growth-promoting rhizobacteria under different levels of nitrogen application on the biomass, nitrogen status, and yield of peanut cultivars

High-throughput phenotyping using spectral reflectance measurements offers the potential to provide more information for making better-informed management decisions at the crop canopy level in real time. The aim of this study was to investigate the suitability of hyperspectral reflectance measurements of the crop canopy for the assessment of biomass, nitrogen concentration, nitrogen uptake, relative chlorophyll contents, and yield in 2 peanut cultivars, Giza 5 and Giza 6. Peanuts were grown under field conditions and subjected to 3 doses of nitrogen fertilizer with or without the application of 2 bio-fertilizers, Bradyrhizobium spp. or plant growth-promoting rhizobacteria. Simple linear regression of normalized difference spectral indices and partial least square regression (PLSR) were employed to develop predictive models to estimate the measured parameters. The tested spectral reflectance indices were significantly related to all measured parameters with R2 of up to 0.89. The spectral reflectance index values differed at the same level of nitrogen fertilizer, as well as among the 3 levels of nitrogen fertilizer application for inoculation with Bradyrhizobium and co-inoculation with Bradyrhizobium and plant growth-promoting rhizobacteria. The calibration models of PLSR data analysis further improved the results, with R2 values reaching 0.95. The overall results of this study indicate that hyperspectral reflectance measurements monitoring peanut plants enable rapid and non-destructive assessment of biomass, nitrogen status, and yield parameters of peanut cultivars subjected to various agronomic treatments.

Impacts of fertigation via surface and subsurface drip irrigation on growth rate, yield and flower quality of Zinnia elegans

Drip irrigation combined with split application of fertilizer nitrogen (N) dissolved in the irrigation water (i.e. drip fertigation) is commonly considered best management practice for water and nutrient efficiency. This research was conducted to study the influence of drip fertigation in combination with or without N fertilizers on vegetative growth, flowering quality, nutrients concentration in plants and soil fertility after the harvest of zinnia ( Zinnia elegans). A field experiment was conducted using a randomized complete block split plot design with two systems of drip irrigation (surface and subsurface drip irrigation) and 4 nitrogen rates (0, 30, 60, and 120 kg∙ha–1) as the main and split plots, respectively. The results revealed that vegetative growth rate, flowering characteristics , plant chemical contents, plant uptake and available soil from N, P, K, Fe, Mn, and Zn of zinnia increased significantly with increasing N level up to 120 kg∙ha–1. A similar trend was also found in the post-harvest soil fertility and nutrient uptake that approved the importance of drip fertigation with N fertilizers. Subsurface drip irrigation system was found to be more efficient than surface drip irrigation system to obtain maximum yield accompanied by the highest nutrients concentration in zinnia plants and soil fertility after harvest.

Saving Water in Arid and Semi-Arid Countries as a Result of Optimising Crop Evapotranspiration

Although water covers about 71 percent of our planet surface, 98 percent of it has too high salt content to be used for drinking water, for irrigation, or even for most industrial purposes. Fresh water represents one percent of all the water on the earth and is distributed unevenly on the earth surface. As a result of the dramatic increase in population, in economic activities, and a subsequent increase in water usage, the world fresh water resources became scarce during the past decades (Postel et al., 1996; Hoekstra & Chapagain, 2007). Shortage of water currently plagues almost every country in North Africa and the Middle East (MENA) to the extent that hampers economic growth and threats social stability. Most importantly, the scenarios for global environmental change suggest a future increase in aridity and in the frequency of extreme events in many areas of the earth. Economists believe that water problem cannot be solved until water is considered as economic good. There is an urgent need to develop appropriate concepts and tools to do so. Evapotranspiration (ET) is defined simply as the sum of the amount of water returned to the atmosphere through the processes of evaporation (moisture loss from the soil) and transpiration (biological use and release of water by vegetation). Crops are different in their response to water stress at a given growth stage. Therefore, estimating ET is an important tool to calculate the actual crop water requirements in given conditions. As a result, optimizing ET may contribute in solving water shortage problems at two levels, the farm level and the national/global level. Firstly, at the farm level, the process of water irrigation losses has two main components: one due to evapotranspiration losses, and the other including the losses resulting from the percolation of water beneath the root zone in excess of any required leaching for salinity management. Therefore, saving water on the farm level can be achieved by using deficit