Total Photosynthesis Research Articles

Light green leaf sectors of variegated Dracaena fragrans plants show similar rates of oxygenic photosynthesis tо that of normal, dark green leaf sectors

Adaptation and functional significance of chlorophyll deficit in the light green leaf sectors of variegated plants are little known. Efficiency of photosystem II for dark and light adapted states (Fv/Fm and ΔF/Fm’) and fluorescence decrease rates (Rfd) of light green leaf sectors of Dracaena fragrans L. were studied by methods of PAM-fluorometry and video registration. In addition, white light reflectance and transmittance of these leaf sectors were measured using an integrating sphere. Absorption was calculated from reflectance and transmittance. Net CO2 assimilation rates (PN) were measured using a flow chamber and photolytic O2 evolution rates (PAYO2) were studied by a novel method of Fourier photoacoustics which is insensitive to respiration, photorespiration and other processes of O2 uptake. All the photosynthetic parameters (Fv/Fm, ΔF/Fm’, PN and PAYO2) were found to be very close between light green and normal green leaf sectors, whereas chlorophyll content and light absorption were 7.5-fold and 1.47-fold different respectively. Contradiction between low chlorophyll absorption and high (as in normal green sectors) rate of oxygenic photosynthesis in light-green sectors was proposed to be a consequence of different contribution of cyclic electron transport around PSII (CET-PSII) and/or around PSI (CET-PSI) in the total photosynthesis occurring in these sectors. Particularly, it cannot be excluded, that some part of CET activity occurring in normal green leaf sectors may be lost in the light green sectors retaining the same linear (non-cyclic) electron transport (LET) activity as in normal green sectors.

Psammophytes Alyssum desertorum Stapf and Secale sylvestre Host Are Sensitive to Soil Flooding.

While morphological and functional traits enable hydrophytes to survive under waterlogging and partial or complete submergence, the data on responses of psammophytes-sand plants-to flooding are very limited. We analyzed the effect of 5- and 10-day soil flooding on the photosynthetic apparatus and the synthesis of alcohol dehydrogenase (ADH), heat shock proteins 70 (HSP70), and ethylene in seedlings of psammophytes Alyssum desertorum and Secale sylvestre using electron microscopy, chlorophyll a fluorescence induction, and biochemical methods. It was found that seedlings growing under soil flooding differed from those growing in stationary conditions with such traits as chloroplast ultrastructure, pigment content, chlorophyll fluorescence induction, and the dynamics of ADH, HSP, and ethylene synthesis. Although flooding caused no apparent damage to the photosynthetic apparatus in all the variants, a significant decrease in total photosynthesis efficiency was observed in both studied plants, as indicated by decreased values of φR0 and PIABS,total. More noticeable upregulation of ADH in S. sylvestre, as well as increasing HSP70 level and more intensive ethylene emission in A. desertorum, indicate species-specific differences in these traits in response to short-term soil flooding. Meanwhile, the absence of systemic anaerobic metabolic adaptation to prolonged hypoxia causes plant death.

Phenology characteristics and demographic structure of Aleppo pine in the Algerian mediterranean forest: The case study of El-Harhouria afforestation

The structural characteristics of tree populations and their spatial distribution is an essential indicator of forest health. A subjective sampling of the Aleppo pine (Pinus halepensis Mill) of El-Harhouria afforestation in Algeria made it possible to establish the characteristics of this plant formation. In this case, five plots of 900 m2 were subjected to the following dendrometric measurements: circumference, total elevation, slenderness coefficient, and density of trees. The diachronic measurement of the total photosynthesis (Normalized Difference Vegetation Index) was estimated with remote sensing methods based on Landsat images from 1986 to 2021. Data analysis showed that the average density of ligneous trees is 1,207 individuals per hectare including an average basal area of 41.95 m2/ha. The diameter and height structures of the wooded stands show a predominance of old individuals. In addition, NDVI values are correlated with the age of the trees, while low values were recorded in old trees.

A phyco-nanobionics biohybrid system for increased carotenoid accumulation in C. sorokiniana UUIND6.

Recent advancements in "phyco-nanobionics" have sparked considerable interest in the ability of microalgae to synthesize high-value natural bioactive compounds such as carotenoid pigments, which have been highlighted as an emergent and vital bioactive compound from both industrial and scientific perspectives. Such bioactive compounds are often synthesized by either altering the biogenetic processes existing in living microorganisms or using synthetic techniques derived from petroleum-based chemical sources. A bio-hybrid light-driven cell factory system was established herein by using harmful macroalgal bloom extract (HMBE) and efficient light-harvesting silver nanoparticles (AgNPs) to synthesize HMBE-AgNPs and integrating the synthesized HMBE-AgNPs in various concentrations (1, 2.5, 5 and 10 ppm) into the microalgae C. sorokiniana UUIND6 to improve the overall solar-to-chemical conversion efficiency in carotenoid pigment synthesis in microalgae. The current study findings found high biocompatibility of 5 ppm HMBE-AgNP concentration that can serve as a built-in photo-sensitizer and significantly improve ROS levels in microalgae (6.75 ± 0.25 μmol H2O2 g-1), thus elevating total photosynthesis resulting in a two-fold increase in carotenoids (457.5 ± 2.5 μg mL-1) over the native microalgae without compromising biomass yield. NMR spectroscopy was additionally applied to acquire a better understanding of pure carotenoids derived from microalgae, which indicated similar peaks in both spectra when compared to β-carotene. Thus, this well-planned bio-hybrid system offers a potential option for the cost-effective and long-term supply of these natural carotenoid bio-products.

Species-Specific and Altitude-Induced Variation in Karst Plants’ Use of Soil Dissolved Inorganic Carbon

Root-derived carbon sources supporting photosynthesis have been demonstrated to contribute to plant carbon gain in many laboratory experiments. However, it remains largely unknown whether and to what extent soil dissolved inorganic carbon (DIC) influences leaf photosynthesis in karst habitats characterized by alkaline soils with low water content. We explored this relationship by measuring the concentrations and carbon isotope signals (δ13C) of soil DIC, as well as the δ13C of water-soluble organic matter (δWSOM) in leaves of nine woody species across an altitudinal gradient in karst habitats. The δWSOM varied among species by 7.23‰ and deviated from the δ13C of photosynthates solely assimilated from atmospheric CO2 (δA) by 0.44–5.26‰, with a mean value of 2.20‰. This systematical discrepancy (δA − δWSOM) could only be explained by the contribution of soil DIC to leaf total photosynthesis (fDIC_soil). The average values of fDIC_soil considerably varied among the nine species, ranging from 2.48% to 9.99%, and were comparable with or slightly lower than those of previous laboratory experiments. Furthermore, the fDIC_soil of two species significantly increased with altitude, whereas another species exhibited an opposite pattern, suggesting a highly spatial heterogeneity of DIC utilization. The present study improved our understanding of how plants adapt to the alkaline–drought soil conditions of karst habitats and thus acquire additional carbon for growth.

Evaluation of Photosynthetic Roles of Different Canopy Strata and Capitulum on Seed Yield and its Components of Spring Safflower (Carthamus tinctorius L.)

The main source of seed filling results from the photosynthesis of the green tissue closest to the seed sinks in the capitula. To evaluate the role of different leaf strata and capitula in seed yield and its components of Safflower genotypes, a field study was performed as a factorial experiment based on RCBD in 3 replicates in East Azarbaijan Agricultural and Natural Resources Research and Education Center in 2008. The used factors in this experiment were: two Safflower genotypes including (Mahalli Esfahan and Goldasht) and defoliation in five levels: defoliation of plants in lower 1/3, middle 1/3, upper 1/3 of the stem, capitulum covered with aluminum paper and control (without defoliation). The results showed that defoliation did not affect plant height and number of pods. But, there was a highly significant difference between strata in terms of number of seeds per pod, number of seeds per plant, 1000 seeds weight, oil percentage and oil yield. The interaction of genotype×strata treatments in seeds yield and harvest index was significant. Among the defoliation treatment levels in both genotypes, the highest decrease in the seed yield compared to the control were observed in the upper 1/3 defoliation levels, whereas the lowest decrease was observed in the lower 1/3 defoliation level. The rate of seed yield reduction in Mahalli Esfahan was higher than Goldasht. The change in Goldasht seed yield was mostly due to changes in the number of seeds per plant and the number of seeds in the head. In addition, net photosynthesis, strata leaf area, and photosynthesis contribution of the upper strata compared to the lower ones were higher, and removal of the upper strata had the highest effect on seed yield through the reduction in the total photosynthesis of the whole plant. Also, covering the capitulum caused a significant decrease in the seed yield. So, head photosynthesis has a major contribution to Safflower seed yield.

Fertilizer Reduction Combined with Organic Liquid Fertilizer Improved Canopy Structure and Function and Increased Cotton Yield

The application of organic liquid fertilizer combined with chemical fertilizer is one of the key technologies used to simultaneously improve cotton yield and efficiently utilize resources. However, organic fertilizer is usually applied once as a base fertilizer during production, and few studies have been conducted on topdressing with water during the growth period. Therefore, in this study, Xinluzao 74 was used as the experimental material, and a single fertilizer application (CF) was used as a control in 2019–2020 under the conditions of integrated control of water and fertilizer with mulch drip irrigation. Five combinations of reduction in chemical fertilizer combined with organic fertilizer (OF1, OF2, OF3, OF4, and OF5) were used to investigate the influences of chemical fertilizer combined with organic liquid fertilizer on the leaf area index (LAI), canopy openness (DIFN), mean foliage tilt angle (MTA), photosynthetically active radiation (PAR), canopy apparent photosynthesis (CAP), and yield and quality of cotton. The results show that among the different fertilization treatments, the OF2 treatment had the best results, not only ensuring a suitable LAI (4.8) and maintaining a large DIFN (0.1) but also increasing the light transmittance of the middle and lower canopies (0.02–0.03). At the same time, CAP increased significantly compared with that in the CF treatment, with an average increase of 12.8%. The high value lasted for a long time, and the late decay stage remained at 8.9 μmol m−2 s−1. The ratio of the population respiration rate to total photosynthesis (CR/TCAP) decreased significantly, with an average decrease of 13.5%. Compared with that in CF, the lint yield increased by 27.0% in the other treatments. The correlation analysis showed that lint yield was positively correlated with the relative chlorophyll content (SPAD value), PAR transmittance (PARU) and CAP in the upper canopy (p < 0.05) and significantly negatively correlated with PAR transmittance (PARM) in the middle canopy and PAR transmittance (PARD) and CR/TCAP in the lower canopy (p < 0.05). Therefore, under mulch drip irrigation, the OF2 treatment (OF + 80% CF) improved the canopy structure of cotton at the late growth stage, increased the population photosynthetic rate, and increased lint yield significantly; thus, this approach can be used as an effective fertilization method to achieve the goal of decreasing costs and increasing efficiency in cotton production.

Salicylic acid mitigates the effects of mild drought stress on radish (Raphanus sativus) growth.

Water deficit is the most critical factor limiting plant growth and production and salicylic acid (SA) has potential for stress mitigation in plants; therefore, we evaluated the effect of SA on radish (Raphanus sativus L.) growth and ecophysiology under water deficit. Plants were sprayed with SA (100μM) or water (control), and irrigated at 80% (W80), 60% (W60), 40% (W40), and 20% (W20) of field capacity. The SA treatments and drought stress started 7days after sowing and lasted until the end of the cycle (30days after sowing). The morphophysiological analyses showed that radish plants had impaired growth at the lower water supply levels, but the treatment with SA reversed these growth restraints under moderate stress, leading to increases in shoot mass at W40 and storage root mass at W60 and W40. SA treatment also reversed the reduction of storage root volume at W60. The tendency of water deficit to increase F O and reduce F V /F M suggests possible damage to the photosystem II of drought-stressed plants. The parameters of gas exchange and photosynthetic pigments showed maintained photosynthetic efficiency, but total photosynthesis decreased due the lower shoot dry mass. Overall, exogenously applied SA reversed the growth restraints at W60 and W40, which revealed that SA was effective in mitigating the effects of moderate water deficit on biomass accumulation and partitioning in radish plants.

Physiological and biochemical aspects of 'Tommy Atkins' mango subjected to doses and methods of application of paclobutrazol

The paclobutrazol has been widely used to stimulate the flowering of mango trees, regulating vegetative growth and promoting changes in photosynthetic activity and in the production of photoassimilates. In this context, the objective of this study is to evaluate the effects of forms and doses of PBZ on the biochemical and physiological variables of mango, cultivar ‘Tommy Atkins,’ in the Brazilian semiarid region. The experimental design was randomized blocks in a 5 x 2 + 1 factorial design with the first factor was paclobutrazol doses applied by irrigation (0.5, 1.0, 1.5, 2.0 and 2.5 g a.i.-1, linear canopy); the second factor was two phases of collection (vegetative and flowering), and an additional treatment (control) with the application of a dose in the conventional form (2.0 g a.i.-1 linear canopy applied manually by haul), and four replications. The variables analyzed were levels of total soluble sugars, reducing sugars, non-reducing sugars, total amino acids, total soluble proteins, liquid photosynthesis, stomatal conductance, transpiration, and leaf temperature. The application of PBZ by fertigation proved more efficient than the conventional application, allowing a greater assimilation of the product by the plant and the reduction of the dose. Most biochemical characteristics showed the highest values by applying lower doses of paclobutrazol. The increase in paclobutrazol doses applied by irrigation system reduced the gas exchange of the ‘Tommy Atkins’ cultivar.

Toxicity and photosynthetic inhibition of metal-organic framework MOF-199 to pea seedlings

Metal-organic framework (MOF) materials are star materials with unique structures and properties. To ensure safe production and applications, the toxicity and environmental hazards of MOF materials should be thoroughly investigated. However, the environmental impact of MOF materials on plants is completely unknown. Herein, we reported the toxicity and photosynthetic inhibitory properties of MOF-199 to pea plants (Pisum sativum L.). MOF-199 was synthesized by hydrothermal method. MOF-199 was copper containing double-pyramid of high surface area (668 m2/g). MOF-199 accelerated the germination of pea seeds, but the total germination rates were unchanged. MOF-199 inhibited the seedling growth at high concentrations. The net photosynthetic rate increased, while the total photosynthesis capability decreased. Damage to the acceptor side of photosystem II was evidenced by chlorophyll fluorescence. Mechanistically, MOF-199 released Cu2+ in the nutrient solution, led to Cu2+ accumulations in seedlings, and promoted oxidative stress. In addition, the photosynthetic inhibitions of MOF-199 were stronger than equivalent concentrations of Cu(NO3)2, implying that MOF-199 particles also contributed to the environmental hazards. Our results highlighted the potential threat of MOF materials to plant growth and photosynthesis.

Cytokinin dynamics in xylem sap and leaves of fruiting and de-fruited sunflower hybrids of contrasting post-anthesis canopy senescence patterns during flowering and grain-filling

To determine whether xylem sap and leaf cytokinin levels were associated with live root length density (LRLD) and leaf senescence, these variables were measured in intact (control) plants and those from which florets were removed, in hybrids of contrasting post-anthesis senescence patterns. Field experiments were carried out during two consecutive seasons using sunflower hybrids (Paraiso75, stay-green [SG]; and Paraiso65, fast dry down [FDD]) of contrasting canopy senescence patterns. Crop carbon partitioning was altered by removing all florets (-F treatment) before anthesis. At crop level, the dynamics of LRLD, xylem sap flow rate, cytokinins in the xylem sap, and green leaf area index (GLAI) were measured, while at leaf level, dynamics of total chlorophyll content, trans-Zeatin content, and net photosynthesis were recorded for leaf positions 17, 20, 22, 24 and 27. In both hybrids, the –F treatment had higher LRLD, cytokinins in the xylem sap, and leaf trans-Zeatin concentration at anthesis and during the grain filling period than control plants. All measured variables decreased earlier in the control treatment than the -F treatment (in both hybrids), and in the FDD hybrid than the SG hybrid. The dynamics of xylem sap cytokinins were related to the dynamics of LRLD and that of leaf trans-Zeatin levels, contributing to contrasting canopy senescence patterns and underlying the responses to defruiting in both hybrids.

Leaf Gas Exchange Attributes and Quality Performance of Kacip Fatimah (Labisia Pumila Blume) Under Different Sources of Organic and Inorganic Fertilizers

An experiment was designed with Randomized Complete Block Designed to investigate the effects of organic and inorganic nitrogen fertilizer at 90 kg N/ha on growth and leaf gas exchange in two varieties of Labisia pumila at 15 weeks after transplanting (WAT). In this study total biomass and photosynthesis (A) were significantly (P≤0.05) different among all factor. The results indicated that chicken manure enhanced the net photosynthetic rate (11.10 µmol/m²/s), stomatal conductance (0.40 mmol/m/s) and transpiration rate (5.30 mmol/m²/s) of L.pumila significantly after 31 weeks of planting. Chicken manure and Gobi indicated higher accumulation on total phenolic and total flavonoid compared to NPK green and control. Organic fertilizers (chicken manure and Gobi) were positively influenced the leaf gas exchange and growth of L.pumila as compared to the NPK green and control. This study proved that organic fertilizer can produce a quality of L. pumila compared to NPK green. Based on the principle of organic fertilizer which is slowly release from organic fertilizer will limit the nutrient availability for plant growth and allocate more carbon to produce secondary metabolites.

A systematic dissection of the mechanisms underlying the natural variation of silique number in rapeseed (Brassica napus L.) germplasm.

SummarySilique number is the most important component of yield in rapeseed (Brassica napus L.). To dissect the mechanism underlying the natural variation of silique number in rapeseed germplasm, a series of studies were performed. A panel of 331 core lines was employed to genome‐wide association study (GWAS), and 27 loci (including 20 novel loci) were identified. The silique number difference between the more‐ and fewer‐silique lines can be attributed to the accumulative differences in flower number and silique setting rate. Each of them accounted for 75.2% and 24.8%, respectively. The silique number was highly associated with the total photosynthesis and biomass. Microscopic analysis showed that the difference between extremely more‐ and fewer‐silique lines normally occurred at the amount of flower bud but not morphology. Transcriptome analysis of shoot apical meristem (SAM) suggested that most of enriched groups were associated with the auxin biosynthesis/metabolism, vegetative growth and nutrition/energy accumulation. By integrating GWAS and RNA‐seq results, six promising candidate genes were identified, and some of them were related to biomass accumulation. In conclusion, the natural variation of silique number is largely affected by the biomass and nutrition accumulation, which essentially reflects the positive regulatory relationship between the source and sink. Our study provides a comprehensive and systematic explanation for natural variation of silique number in rapeseed, which provides a foundation for its improvement.

Contribution and consequences of xylem-transported CO2 assimilation for C3 plants.

Traditionally, leaves were thought to be supplied with CO2 for photosynthesis by the atmosphere and respiration. Recent studies, however, have shown that the xylem also transports a significant amount of inorganic carbon into leaves through the bulk flow of water. However, little is known about the dynamics and proportion of xylem-transported CO2 that is assimilated, vssimply lost to transpiration. Cut leaves of Populus deltoides and Brassica napus were placed in either KCl or one of three [NaH13 CO3 ] solutions dissolved in water to simultaneously measure the assimilation and the efflux of xylem-transported CO2 exiting the leaf across light and CO2 response curves in real-time using a tunable diode laser absorption spectroscope. The rates of assimilation and efflux of xylem-transported CO2 increased with increasing xylem [13 CO2 *] and transpiration. Under saturating irradiance, rates of assimilation using xylem-transported CO2 accounted for c. 2.5% of the total assimilation in both species in the highest [13 CO2 *]. The majority of xylem-transported CO2 is assimilated, and efflux is small compared to respiration. Assimilation of xylem-transported CO2 comprises a small portion of total photosynthesis, but may be more important when CO2 is limiting.

Model-data fusion to assess year-round CO2 fluxes for an arctic heath ecosystem in West Greenland (69°N)

Quantifying net CO2 exchange (NEE) of arctic terrestrial ecosystems in response to changes in climatic and environmental conditions is central to understanding ecosystem functioning and assessing potential feedbacks of the carbon cycle to future climate changes. However, annual CO2 budgets for arctic tundra are rare due to the difficulties of performing measurements during non-growing seasons. It is still unclear to what extent arctic tundra ecosystems currently act as a CO2 source, sink or are in balance. This study presents year-round eddy-covariance (EC) measurements of CO2 fluxes for an arctic heath ecosystem on Disko Island, West Greenland (69 °N) over five years. Based on a fusion of year-round EC-derived CO2 fluxes, soil temperature and moisture, the process-oriented model (CoupModel) has been constrained to quantify an annual budget and characterize seasonal patterns of CO2 fluxes. The results show that total photosynthesis corresponds to -202 ± 20 g C m−2 yr-1 with ecosystem respiration of 167 ± 28 g C m-2 yr-1, resulting in NEE of -35 ± 15 g C m-2 yr-1. The respiration loss is mainly described as decomposition of near-surface litter. A year with an anomalously deep snowpack shows a threefold increase in the rate of ecosystem respiration compared to other years. Due to the high CO2 emissions during that winter, the annual budget results in a marked reduction in the CO2 sink. The seasonal patterns of photosynthesis and soil respiration were described using response functions of the forcing atmosphere and soil conditions. Snow depth, topography-related soil moisture, and growing season warmth are identified as important environmental characteristics which most influence seasonal rates of gas exchange.

Effect of humic acids on the metabolism of Chlorella vulgaris in a model experiment

The effect of humic acids (HAs) on physiological processes (photosynthesis, respiration, and abundance) of green microalga Chlorella vulgaris has been studied, and the relationships between the physiological activity of HAs and their structural parameters have been investigated. It has been found that the optimum range of HA concentrations for the growth of C. vulgaris is 0.01–0.03%. In this range, the highest positive effect on total photosynthesis increment is due to hydrophilic HA preparations from fallow soddypodzolic soil (Albic Retisol) and virgin gray soil (Luvic Greyzemic Phaeozem). The minimum stimulation of respiration is noted for all HA preparations in the region of the maximum photosynthesis stimulation. At concentrations above 0.003%, all HA preparations have a negative effect: the rate of photosynthesis in C. vulgaris cells decreases, and their respiration is strongly enhanced. The abundance of C. vulgaris under the effect of all of the studied preparations under illumination increases more rapidly than in the dark. A high positive coefficient of correlation is found between the hydrophilicity of HAs calculated from 13C NMR data and the photosynthesis rate in C. vulgaris.

Carbon cycling of biological soil crusts mirrors ecological maturity along a Central European inland dune catena

Photosynthesis and respiration of biological soil crusts (BSCs) sampled along a mobile inland dune catena were determined to evaluate the applicability of Odum's P/R ratio, determined under controlled conditions, for estimation of ecosystem maturity. The theory is that in the early stages of ecological succession, the total photosynthesis (P) exceeds the rate of community respiration (R), so that the P/R ratio is >1, and that P/R approaches 1 as succession occurs. In the special case of organic pollution, the P/R ratio is typically <1. Samples were collected in the deflation zone of the dune near the crest (BSC1, thickness 2–3mm), at the lee side of grass tussocks at the slope (BSC2, thickness 2–4mm) and near the base (BSC3, thickness 4–6mm). Non-crusted sand was used as control (BSC0). Photosynthesis, respiration, crust biomass, as well as fossil and allochthonous pedogenic carbon entering the system with mineral substrate were determined. The respiration of the BSC1 was dominated by the degradation of allochthonous organic matter, leading to a diminished P/R ratio. The better developed BSC2 and BSC3 were less influenced by allochthonous organic matter, where BSC maturity increased downslope with biomass increase. No significant relation between the P/R ratio and soil water tension was found. Crust carbon pools increased and flows intensified, but mineralization constants decreased with system maturation. It was concluded that Odum's P/R ratio and accumulation of recalcitrant to biodegradation organic matter are indicative for biocrust maturity.

A new calculation method for total photosynthesis of a plant community under illumination consisting of direst and diffused light. Functioning of terrestrial ecosystems at the primary production level. Proceedings of the Copenhagen Symposium

A new calculation method for total photosynthesis of a plant community under illumination consisting of direst and diffused light. Functioning of terrestrial ecosystems at the primary production level. Proceedings of the Copenhagen Symposium

Comparative analysis of NPP changes in global tropical forests from 2001 to 2013

Net primary production (NPP) is the difference between total photosynthesis (gross primary production, GPP) and total plant respiration in an ecosystem. NPP is a key component of the terrestrial carbon cycle and is important in global climate research. Tropical forests, distributed mainly in Central Africa, Central and South America, and Southeast Asia, are among the most important ecosystems on earth. They are very important to analyses of the global carbon budget and to the projection of future climatic changes. In this study, we analyzed and compared the temporal and spatial changes of NPP within the three dominant areas of tropical forest from 2001 to 2013 by using data from the Moderate Resolution Imaging Spectroradiometer (MODIS). We found that Central and South America has the highest annual mean NPP, statistically, while the average NPP shows an increasing trend both in Central and South America and Central Africa but a decreasing trend in Southeast Asia.

Inhibitor activity of different medicinal plants extracts from Thuja orientalis, Nigella sativa L., Azadirachta indica and Bougainvillea spectabilis against Zucchini yellow mosaic virus (ZYMV) infecting Citrullus lanatus

ABSTRACTZucchini yellow mosaic virus (ZYMV) has a wide distribution in Mecca regions and is considered to be a serious threat on watermelon production. The aim of this study was to evaluate the antiviral activity of five medicinal plant extracts, against ZYMV-infecting watermelon plants. The experiment consisted of four application of soaking seeds, in vitro and in vivo experiments. The results of greenhouse experiments with individually treatments by decoction and infusion of Nigella sativa (NS) seeds in soaking and in-vitro experiment, bougainvillea and neem in pre-inoculation and thuja extract following nigella decoction in post inoculation were efficient to reduce and\\or inhibit symptoms expression infecting watermelon seedling, whereas, decoction exhibited higher antiviral activity against ZYMV than infusion. The decoction and infusion of NS seed increased the total photosynthesis pigments, total soluble intracellular protein and total phenol contents. In conclusion, the results of the present investigation propose that the bougainvillea and neem extracts may perhaps play a central function in the mechanism of acquired systemic resistance and may produce pathogenesis-related proteins that play a significant role in watermelon seedling resistance against ZYMV.