Variation in the Essential Oil Composition,Antioxidant Capacity,and Physiological Characteristics of Pelargonium graveolens L. Inoculated with Two Species of Mycorrhizal Fungi Under Water Deficit Conditions

In recent years, the application of arbuscular mycorrhizal fungi (AMF) has been considered to be an important strategy for improving crop yield and quality. In the present study, a factorial experiment based on a complete randomized design with two factors was performed to investigate the effect of AMF and water stress on the essential oil (EO) composition, antioxidant activity, and physiological and morphological characteristics of rose-scented geranium (Pelargonium graveolens L.). The factors included AMF inoculation (Rhizophagus intraradices, Funneliformis mosseae, and a mixture of both species) and irrigation levels [well-watered (WW), moderate drought stress (MDS), and severe drought stress (SDS)]. The main EO constituents were citronellol (31–37%) and geraniol (9–14%) in all treatments. Under water-stress conditions, some constituents increased, such as geraniol and geranyl formate, whereas others decreased, such as linalool, menthone and rose oxide. Overall, the highest amount of citronellol (37.3%) and geraniol (14.8%) was obtained in the plants inoculated with F. mosseae and R. intraradices under WW and MDS conditions, respectively. Antioxidant activity, total flavonoids, and phenolics were increased because of AMF inoculation, whereas a different trend was observed for the phenolic and flavonoid contents under water-stress conditions. Furthermore, water deficit elevated the amount of soluble carbohydrates as well as the proline content, whereas the amount of proline was lower in inoculated plants than in non-inoculated ones. All the growth parameters were improved in the AMF-inoculated plants compared to non-inoculated ones under different irrigation regimes. Drought conditions decreased the photosynthetic pigments and efficiency, whereas AMF plants ameliorated the adverse effect of drought conditions. In general, mycorrhizal inoculation resulted in an improvement in the growth parameters as well as the phytochemical and physiological characteristics of rose-scented geranium.

     

Consequences of inoculation with native arbuscular mycorrhizal fungi for root colonization and survival of <Emphasis Type="Italic">Artemisia tridentata</Emphasis> ssp. <Emphasis Type="Italic">wyomingensis</Emphasis> seedlings after transplanting

In arid environments, the propagule density of arbuscular mycorrhizal fungi (AMF) may limit the extent of the plant–AMF symbiosis. Inoculation of seedlings with AMF could alleviate this problem, but the success of this practice largely depends on the ability of the inoculum to multiply and colonize the growing root system after transplanting. These phenomena were investigated in Artemisia tridentata ssp. wyomingensis (Wyoming big sagebrush) seedlings inoculated with native AMF. Seedlings were first grown in a greenhouse in soil without AMF (non-inoculated seedlings) or with AMF (inoculated seedlings). In spring and fall, 3-month-old seedlings were transplanted outdoors to 24-L pots containing soil from a sagebrush habitat (spring and fall mesocosm experiments) or to a recently burned sagebrush habitat (spring and fall field experiments). Five or 8 months after transplanting, colonization was about twofold higher in inoculated than non-inoculated seedlings, except for the spring field experiment. In the mesocosm experiments, inoculation increased survival during the summer by 24 % (p?=?0.011). In the field experiments, increased AMF colonization was associated with increases in survival during cold and dry periods; 1 year after transplanting, survival of inoculated seedlings was 27 % higher than that of non-inoculated ones (p?<?0.001). To investigate possible mechanisms by which AMF increased survival, we analyzed water use efficiency (WUE) based on foliar ¹³C/¹²C isotope ratios (δ ¹³C). A positive correlation between AMF colonization and δ ¹³C values was observed in the spring mesocosm experiment. In contrast, inoculation did not affect the δ ¹³C values of fall transplanted seedlings that were collected the subsequent spring. The effectiveness of AMF inoculation on enhancing colonization and reducing seedling mortality varied among the different experiments, but average effects were estimated by meta-analyses. Several months after transplanting, average AMF colonization was in proportion 84 % higher in inoculated than non-inoculated seedlings (p?=?0.0042), while the average risk of seedling mortality was 42 % lower in inoculated than non-inoculated seedlings (p?=?0.047). These results indicate that inoculation can increase AMF colonization over the background levels occurring in the soil, leading to higher rates of survival.     

Effect of AMF inoculum from field isolates on the yield of green pepper,parsley, carrot,and tomato

Inoculum of an indigenous mixture of arbuscular mycorrhizal fungi (AMF) containingGlomus mosseae, Glomus fasciculatum, Glomus etunicatum, Glomus intraradices andScutellospora sp. was applied to four of the most frequently used crop species in Slovenia: green pepper (Capsicum annuum), parsley (Petroselinum crispum), carrot (Daucus carrota) and tomato (Lycopersicon esculentum). A simple, feasible, and effective protocol for application of AMF biotechnology in horticulture was adopted.Mycorrhizal inoculation significantly increased the plant biomass parameters of pepper, and parsley and the root biomass of carrots. Statistically significant correlations between biomass parameters of pepper, parsley, and the root biomass of carrots with mycorrhizal colonization parameters (mycorrhizal frequency (F%), global mycorrhizal intensity (M%) and arbuscular richness (A%) were calculated. A significant increase in chlorophyll content was observed in mycorrhizal parsley and a significant increase in carotenoids was observed in mycorrhizal parsley, carrots, and tomato fruits. A significant increase in titratable acidity of fruits from inoculated tomato plants indicates prolonged fruiting period of mycorrhizal tomatoes. In addition, inoculation with an indigenous AMF mixture significantly increased the mycorrhizal potential of soil and thus the growth of non-inoculated plants in the second season. Thus, the results confirmed the potential of applying mycorrhizal biotechnology in sustainable horticulture.     

Arbuscular mycorrhiza differentially affects synthesis of essential oils in coriander and dill

Research on the role of arbuscular mycorrhizal fungi (AMF) in the synthesis of essential oils (EOs) by aromatic plants has seldom been conducted in field-relevant conditions, and then, only limited spectra of EO constituents have been analyzed. The effect was investigated of inoculation with AMF on the synthesis of a wide range of EO in two aromatic species, coriander (Coriandrum sativum) and dill (Anethum graveolens), in a garden experiment under outdoor conditions. Plants were grown in 4-l pots filled with soil, which was either γ-irradiated (eliminating native AMF) or left non-sterile (containing native AMF), and inoculated or not with an isolate of Rhizophagus irregularis. AMF inoculation significantly stimulated EO synthesis in both plant species. EO synthesis (total EO and several individual constituents) was increased in dill in all mycorrhizal treatments (containing native and/or inoculated AMF) compared to non-mycorrhizal plants. In contrast, EO concentrations in coriander (total EO and most constituents) were increased only in the treatment combining both inoculated and native AMF. A clear positive effect of AMF on EO synthesis was found for both aromatic plants, which was, however, specific for each plant species and modified by the pool of AMF present in the soil.     

Arbuscular mycorrhizal fungi and water availability affect biomass and C:N:P ecological stoichiometry in alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) during regrowth

Ecological stoichiometry has been widely studied in terrestrial ecosystems, but these studies have been limited in terms of symbiotic association between alfalfa and arbuscular mycorrhizal fungi (AMF), especially during regrowth. To evaluate the effect of AMF on the regrowth and C:N:P stoichiometry of alfalfa (Medicago sativa L.) under well-watered and drought conditions, alfalfa plants inoculated with AMF (Rhizophagus irregularis, M), nitrogen-fixing bacteria (Sinorhizobium, R), both nitrogen-fixing bacteria and AMF or no inoculations (CK) were evaluated in a pot experiment under controlled conditions. The biomass and organic carbon (C), nitrogen (N) and phosphorus (P) nutritional status of plant leaves and roots were measured under two water treatments during regrowth. Water deficit reduced the accumulation of dry matter and the concentrations of C and N in leaves and P in roots but increased the concentrations of P in leaves and C and N in roots of alfalfa during regrowth. Compared to CK plants, inoculation significantly improved the regrowth biomass and the concentrations of C, N and P in the leaves and roots and especially increased P levels when the plant were inoculated with AMF. However, this effect of microbes on alfalfa regrowth was dependent on the soil water status. Drought reduced the C:N and C:P in the leaves and the C:N in roots, while N:P and C:P increased in the roots. Inoculation of AMF decreased the C:P and N:P in the leaves and the C:N and C:P in the roots, whereas it increased the C:N under water stress. These results indicate that AMF play a significant role in regrowth and C:N:P ecological stoichiometry after defoliation by influencing C assimilation, N and P uptake and that the responses in the leaves and the roots are opposite.     

Ecophysiological and phytochemical responses of <Emphasis Type="Italic">Salvia sinaloensis</Emphasis> Fern. to drought stress

Salvia sinaloensis Fern. (sage) is a medicinal plant containing plant secondary metabolites (PSMs) with antioxidant properties. The current study investigated the effects of drought stress on S. sinaloensis morphological and ecophysiological traits, and active constituent production. Sage plants were cultivated in controlled conditions for 34 days and exposed to full irrigation as control, half irrigation, or no irrigation. Changes in growth index (G.I.), dry biomass, leaf water potential (LWP), physiological parameters, active compounds, volatilome (BVOCs) and essential oils (EOs) were determined. Not irrigated plants showed a decrease in total chlorophyll content (~???14.7%) and growth (G.I., ~???59.4%) from day 18, and dry biomass at day 21 (??56%), when the complete leaf withering occurred (LWP, ??1.10 MPa). Moderate drought stressed plants showed similar trends for chlorophyll content and growth but kept a constant LWP (??0.35 MPa) and dry biomass throughout the experiment, as control plants. Carotenoids were not affected by water regimes. The photosynthetic apparatus tolerated mild to severe water deficits, without a complete stomatal closure. Plants under both stress conditions increased the percentage of phenols and flavonoids and showed altered BVOC and EO chemical profiles. Interestingly Camphor, the main EO oxygenated monoterpene, increased in moderate stressed plants while the sesquiterpene hydrocarbon Germacrene D decreased. The same trend was seen in the headspace under stress severity. The data evidenced a possible role of the active molecules in the response of S. sinaloensis plants to drought stress. Taking together, these findings point at S. sinaloensis as a potential drought adaptive species, which could be used in breeding strategies to obtain sages with high quality PSMs, saving irrigation water.     

Characterization of salt-tolerance mechanisms in mycorrhizal (Claroideoglomus etunicatum) halophytic grass,Puccinellia distans

Responses of Puccinellia distans, a halophytic grass to low (50 mM) and high (200 mM) NaCl salinity, were studied in a sand culture experiment without or with inoculation by arbuscular mycorrhizal fungus (AMF), Claroideoglomus etunicatum isolated from its saline habitat. Plant biomass was not influenced by salinity levels, while a tendency to a higher biomass was observed in AMF plants under both control and saline conditions. Leaf photosynthesis increased by both salinity and AMF inoculation. Despite higher transpiration rate, AMF plants had higher water-use efficiency under sever saline conditions. AMF inoculation decreased proline concentration, but increased significantly leaf osmotic potential. Antioxidative enzymes responded differently to the salt and AMF treatments depending on the salt concentration and plant organ. Nonetheless, salt-induced malondialdehyde accumulation in the leaves diminished by AMF colonization. K and Ca contents were not affected by salt, while fungal colonization increased K in the roots and Ca in both leaves and roots. Our results indicated that enhancement of photosynthesis and ion homeostasis is involved in the tolerance of P. distans to both low and high salinity. AMF inoculation increased plants’ tolerance by augmentation of the above mechanisms accompanied by improvement of water relations and protection against oxidative damage in the leaves.     

Analysis of a large dataset of mycorrhiza inoculation field trials on potato shows highly significant increases in yield

An increasing human population requires more food production in nutrient-efficient systems in order to simultaneously meet global food needs while reducing the environmental footprint of agriculture. Arbuscular mycorrhizal fungi (AMF) have the potential to enhance crop yield, but their efficiency has yet to be demonstrated in large-scale crop production systems. This study reports an analysis of a dataset consisting of 231 field trials in which the same AMF inoculant (Rhizophagus irregularis DAOM 197198) was applied to potato over a 4-year period in North America and Europe under authentic field conditions. The inoculation was performed using a liquid suspension of AMF spores that was sprayed onto potato seed pieces, yielding a calculated 71 spores per seed piece. Statistical analysis showed a highly significant increase in marketable potato yield (ANOVA, P?<?0.0001) for inoculated fields (42.2 tons/ha) compared with non-inoculated controls (38.3 tons/ha), irrespective of trial year. The average yield increase was 3.9 tons/ha, representing 9.5 % of total crop yield. Inoculation was profitable with a 0.67-tons/ha increase in yield, a threshold reached in almost 79 % of all trials. This finding clearly demonstrates the benefits of mycorrhizal-based inoculation on crop yield, using potato as a case study. Further improvements of these beneficial inoculants will help compensate for crop production deficits, both now and in the future.     

Response of snapdragon (<Emphasis Type="Italic">Antirrhinum majus</Emphasis> L.) to blended water irrigation and arbuscular mycorrhizal fungi inoculation: uptake of minerals and leaf water relations

A greenhouse study was performed in order to investigate the effects of three arbuscular mycorrhizal fungi (AMF) species on vegetative growth, water relations, and mineral composition parameters of snapdragon (Antirrhinum majus cv. Bells white) under irrigation from different water sources. Five irrigation treatments included using purely desalinized (fresh) water (DW), as a control, three different blends of DW with saline ground water from a well with increasing salinity, and one with 100% of saline well water. Inoculation with AMF enhanced growth rates and a relative water content of snapdragon plants grown under well-water irrigation. AMF also improved the leaf water potential and increased water-use efficiency of the plants. Shoot and root dry masses were higher in the AMF-treated plants than those in AMF-free plants. In both shoots and roots, concentrations of total P, Ca²⁺, N, Mg²⁺, and K⁺ were higher in the AMF-treated plants compared with AMF-free plants under salt-stress conditions. Shoot Cl^- and Na⁺ concentrations were lower in the AMF-treated plants than those in the AMF-free plants grown under well-water irrigation. Snapdragon plants exhibited a high degree of dependency on AMF; it improved plant growth rates and leaf water relations, particularly, with increasing salinity of irrigation water.     

Effect of AMF application on growth, productivity and susceptibility to Verticillium wilt of olives grown under desert conditions

The effect of arbuscular mycorrhizal fungi (AMF) on olive (Olea europaea) growth and development was followed for 4 years after transplanting in irrigated commercial orchards under arid conditions. Sites I and II were irrigated with saline water (EC?=?4.5 dS/m). In site I, the soil was infested with Verticillium dahliae and olive varieties ‘Picual’ (Verticillium susceptible) and ‘Barnea’ (relatively Verticillium tolerant) were tested. In site II, the soil was virgin soil (previously non-cultivated soil) and olive varieties ‘Souri’ and ‘Barnea’ were tested. Plants for all sites were inoculated in the nursery with Glomus intraradices alone or in a mixture with G. mosseae. Relative to non-inoculated trees, AMF colonization enhanced vegetative growth, expressed as tree height and trunk circumference, at all sites. At first commercial harvest, AMF-treated trees had higher fruit and oil yields than non-mycorrhitic controls. Under saline water irrigation, differences between inoculated and non-inoculated treatments were reduced in the slow-growing ‘Souri’ but remained apparent in the modern fast-growing ‘Barnea’. AMF colonization did not appear to improve tolerance of either ‘Picual’ or ‘Barnea’ to V. dahliae, and both were more susceptible than the non-inoculated controls. Thus inoculation of olive plants with AMF improves transplant growth and adaptation in arid areas during the first 3 years of growth and until the first commercial harvesting season.     

Mycorrhizal-Mediated Lower Proline Accumulation in Poncirus trifoliata under Water Deficit Derives from the Integration of Inhibition of Proline Synthesis with Increase of Proline Degradation

Proline accumulation was often correlated with drought tolerance of plants infected by arbuscular mycorrhizal fungi (AMF), whereas lower proline in some AM plants including citrus was also found under drought stress and the relevant mechanisms have not been fully elaborated. In this study proline accumulation and activity of key enzymes relative to proline biosynthesis (▵¹-pyrroline-5-carboxylate synthetase, P5CS; ornithine-δ-aminotransferase, OAT) and degradation (proline dehydrogenase, ProDH) were determined in trifoliate orange (Poncirus trifoliata, a widely used citrus rootstock) inoculated with or without Funneliformis mosseae and under well-watered (WW) or water deficit (WD). AMF colonization significantly increased plant height, stem diameter, leaf number, root volume, biomass production of both leaves and roots and leaf relative water content, irrespectively of water status. Water deficit induced more tissue proline accumulation, in company with an increase of P5CS activity, but a decrease of OAT and ProDH activity, no matter whether under AM or no-AM. Compared with no-AM treatment, AM treatment resulted in lower proline concentration and content in leaf, root, and total plant under both WW and WD. The AMF colonization significantly decreased the activity of both P5CS and OAT in leaf, root, and total plant under WW and WD, except for an insignificant difference of root OAT under WD. The AMF inoculation also generally increased tissue ProDH activity under WW and WD. Plant proline content significantly positively correlated with plant P5CS activity, negatively with plant ProDH activity, but not with plant OAT activity. These results suggest that AM plants may suffer less from WD, thereby inducing lower proline accumulation, which derives from the integration of an inhibition of proline synthesis with an enhancement of proline degradation.     

Morpho-physiological and phytochemical traits of (<Emphasis Type="Italic">Thymus daenensis</Emphasis> Celak.) in response to deficit irrigation and chitosan application

Thymus daenensis Celak. is an aromatic herb used as a popular medicine and its natural products in the form of extracts and essential oil have significant economic values in Iran. We hypothesized that spraying plants grown under deficit irrigation system with chitosan can be considered as an applicable method to enhance essential oil and antioxidant activity in thyme. Response of thyme to three irrigation regimes including well-watered, moderate stress, and severe stress along with three levels of chitosan application rates 0, 200, and 400 μL L^?1 was evaluated in a 2-year study in 2014 and 2015. Drought stress condition significantly shortened phenologic stages, more specifically in the first (establishment) year. All growth parameters were reduced dramatically as drought stress intensified. Imposing even moderate stress reduced leaf area as much as 59 and 44% in the first year and the second year, respectively. Biomass yield of plants grown under severe drought stress decreased substantially, whereas essential oil content and the share of thymol in thyme oil which possesses the greatest degree of biological activity improved. Maximum oil yield (1.50 g plant^?1) was obtained from plants under mild drought stress when sprayed with 400 μL L^?1 chitosan in the second year when plants were well-established. Foliar applications of chitosan reduced the adverse effect of water deficit on oil yield and improved thymol content of the essential oil. Chitosan also increased secondary metabolites including α-terpinene, p-cymene, γ-terpinene, thymol, carvacrol and β-caryophyllene. Leaf flavonoid reduced under deficit irrigation while more phenol was found in plants grown under deficit irrigation. The essential oil of thyme exhibited antioxidant property when the plants were sprayed with 400 μL L^?1 chitosan. The results of this study indicated that thyme can be grown successfully under moderate stress and that application of chitosan elicitor can to some degree compensate the negative impact of deficit irrigation on its biomass and essential oil yield.     

Nutrient allocation and photochemical responses of <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">canadensis</Emphasis> ‘Neva’ to nitrogen fertilization and exogenous <Emphasis Type="Italic">Rhizophagus irregularis</Emphasis> inoculation

Arbuscular mycorrhizal fungi (AMF) can promote plant growth performance, but their effectiveness varies depending on soil nitrogen (N) availability. To clarify the effectiveness of exogenous AMF along an N-fertilization gradient (0, 2, 10, 20, and 30 mM), the impacts of exogenous Rhizophagus irregularis and N on the growth, photochemical activity, and nutritional status of Populus?×?canadensis ‘Neva’ in natural soil were evaluated in a pot experiment. The results showed that the 10 mM N level was the optimal fertilization regime with the highest promotion effect on plant growth and the maximum quantum yield of photosystem II (PSII) (F_v/F_m). Excess N (20 and 30 mM) fertilization reduced the actual quantum yield of PSII (ФPSII) and the F_v/F_m of the plants. Regardless of the N availability, inoculated plants exhibited greater F_v/F_m values than did non-inoculated plants. The biomass of inoculated plants was significantly higher compared with the control under low N levels (0 and 2 mM). Under high N levels, inoculated plants showed significant increases in ФPSII. Moreover, the nutrient imbalance of plants inoculated with exogenous R. irregularis was eased by increasing P, Fe, Mn and Cu uptake in roots and higher P, Ca, Mg, Fe, Mn and Zn concentrations in leaves. Moreover, the F_v/F_m and ФPSII exhibited positive correlations with P, Ca, Mg and Zn concentrations in leaves. In conclusion, inoculation with exogenous R. irregularis can benefit plant fitness by improving the photochemical capacity and nutrient composition of poplar under different N levels.     

Physiological and biochemical changes in tomato cultivar PT-3 with dual inoculation of mycorrhiza and PGPR against root-knot nematode

Arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR) have potential to control soil-borne diseases including plant-parasitic nematodes. First, the effects of dual inoculation of mycorrhiza (Rhizophagus irregularis) and two stains of pseudomonads (Pseudomonas jessenii strain R62 and Pseudomonas synxantha strain R81) on tomato (Solanum lycopersicum cv. PT-3) growth were tested. Further, the physiological and biochemical changes caused by these beneficial organisms during infection by the root-knot nematode Meloidogyne incognita were studied. The experiment was conducted under glass house conditions and carried out up to one month after nematode inoculation. Plants treated with dual or individual inoculation of AMF and PGPR showed significantly enhanced plant growth and reduced nematode infection. In addition, they exhibited potent activity of phenolics (28 %) and defensive enzymes i.e. peroxidase (PO; 1.26 fold), polyphenyloxidase (PPO; 1.35 fold) and superoxide dismutase (SOD; 1.09 fold) while a significant reduction in malondialdehyde (MDA; 1.63 fold) and hydrogen peroxide (H₂O₂; 1.30 fold) content was recorded when compared to the nematode-infected plants. These findings indicate the feasibility of AMF and PGPR individually or in combinations as potential biocontrol agents for the management of root-knot nematodes.     

Acclimations to light quality on plant and leaf level affect the vulnerability of pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.) to water deficit

We investigated the influence of light quality on the vulnerability of pepper plants to water deficit. For this purpose plants were cultivated either under compact fluorescence lamps (CFL) or light-emitting diodes (LED) providing similar photon fluence rates (95 µmol m^?2 s^?1) but distinct light quality. CFL emit a wide-band spectrum with dominant peaks in the green and red spectral region, whereas LEDs offer narrow band spectra with dominant peaks at blue (445 nm) and red (665 nm) regions. After one-week acclimation to light conditions plants were exposed to water deficit by withholding irrigation; this period was followed by a one-week regeneration period and a second water deficit cycle. In general, plants grown under CFL suffered more from water deficit than plants grown under LED modules, as indicated by the impairment of the photosynthetic efficiency of PSII, resulting in less biomass accumulation compared to respective control plants. As affected by water shortage, plants grown under CFL had a stronger decrease in the electron transport rate (ETR) and more pronounced increase in heat dissipation (NPQ). The higher amount of blue light suppressed plant growth and biomass formation, and consequently reduced the water demand of plants grown under LEDs. Moreover, pepper plants exposed to high blue light underwent adjustments at chloroplast level (e.g., higher Chl a/Chl b ratio), increasing the photosynthetic performance under the LED spectrum. Differently than expected, stomatal conductance was comparable for water-deficit and control plants in both light conditions during the stress and recovery phases, indicating only minor adjustments at the stomatal level. Our results highlight the potential of the target-use of light quality to induce structural and functional acclimations improving plant performance under stress situations.     

Arbuscular mycorrhizal symbiosis alleviates detrimental effects of saline reclaimed water in lettuce plants

The present study evaluated the effects of inoculation with arbuscular mycorrhizal fungi (AMF; Glomus iranicum var. tenuihypharum sp. nova) on the physiological performance and production of lettuce plants grown under greenhouse conditions and supplied with reclaimed water (RW; urban-treated wastewater with high electrical conductivity; 4.19 dS m^?1). Four treatments, fresh water, fresh water plus AMF inoculation, RW and RW plus AMF inoculation, were applied and their effects, over time, analyzed. Root mycorrhizal colonization, plant biomass, leaf-ion content, stomatal conductance and net photosynthesis were assessed. Overall, our results highlight the significance of the AMF in alleviation of salt stress and their beneficial effects on plant growth and productivity. Inoculated plants increased the ability to acquire N, Ca, and K from both non-saline and saline media. Moreover, mycorrhization significantly reduced Na plant uptake. Under RW conditions, inoculated plants also showed a better performance of physiological parameters such as net photosynthesis, stomatal conductance and water-use efficiency than non-mycorrhizal plants. Additionally, the high concentration of nutrients already dissolved in reclaimed water suggested that adjustments in the calculation of the fertigation should be conducted by farmers. Finally, this experiment has proved that mycorrhization could be a suitable way to induce salt stress resistance in iceberg lettuce crops as plants supplied with reclaimed water satisfied minimum legal commercial size thresholds. Moreover, the maximum values of Escherichia coli in the reclaimed water were close to but never exceeded the international thresholds established (Spanish Royal Decree 1620/2007; Italian Decree, 2003) and hence lettuces were apt for sale.     

Regulated deficit irrigation in different phenological stages of potted geranium plants: water consumption, water relations and ornamental quality

The irrigation water requirements and sensitivity to water deficits of ornamental plants is of great interest to horticultural producers for planning irrigation strategies. The effect of different deficit irrigation strategies on physiological and morphological parameters in geranium plants was studied in different growth phases to evaluate how such strategies can be safely used and to ascertain whether the flowering phase is sensitive to deficit irrigation. Pelargonium × hortorum L.H. Bailey plants, grown in a controlled growth chamber, were subjected to four irrigation treatments: control (100 % water field capacity throughout the experiment), sustainable deficit irrigation (75 % water field capacity throughout the experiment), and two regulated deficit irrigation treatments that included water stress during the vegetative growth phase or during the flowering development phase. Although the total amount of irrigation water was similar in the three deficit irrigation treatments (around 80 % of the control value), the lowest values for both height and flowering were found when deficit irrigation was applied during flowering. This indicates that plant quality does not only depend on the amount of water applied but also on the time when the reduction is applied, and that flowering is the most sensitive phase to water stress. Evapotranspiration was related to the formation of inflorescences and to increased plant height. When the irrigation strategy was changed, plants increased or decreased their water consumption and stomatal conductance to adjust to the new conditions by regulating stomatal opening, although, in general, the values of both parameters remained below those observed in the control plants.     

Application of bio-fertilizers for enhancing growth and yield of common bean plants grown under water stress conditions

This study was planned to enhance the growth and productivity of common bean plants (Phaseolus vulgaris L.) grown under different water stress level by using different microorganisms as bio-fertilizer agents. Water stress is a international problem that effects on morphological, functional and chemical processes of plants occasioning in altering growth, yield and water relations of economic plants like common bean plants. The interaction effect between water stress (WW as recommended irrigation after 6 days, WS1 after 12 days and WS2 after 18 days) and inoculation with different microorganisms [AMF (Glomus mosseae) and endophytic bacteria, (Bacillus amyloliquefaciens)] used alone or in mixed was examined on the development and productivity of common bean plants. Mutual application of AMF and endophytic bacteria significantly increased the average values of most of growth, water relations (photosynthetic rate, transpiration rate and stomatal conductance) and yield parameters of common bean plants grown at WS1 and WS2 comparing with non-colonized plants. In this connection, colonization with AMF and endophytic bacteria with WS1 are the greater pods number, pod length, pods weight, 100 seeds weight, Yield by ton /Fed and water-use efficiency (WUE) by ton/ m³ than other treatments. Common bean yielded seeds had significantly increased nutrients content (nitrogen, potassium, phosphorus, magnesium and calcium), vitamin B₁, Folic acid, crude protein and crude fibers at AMF + endophytic bacteria under second water stress (WS1) when compared to other treatments.     

Phosphorus supply,arbuscular mycorrhizal fungal species,and plant genotype impact on the protective efficacy of mycorrhizal inoculation against wheat powdery mildew

A potential alternative strategy to chemical control of plant diseases could be the stimulation of plant defense by arbuscular mycorrhizal fungi (AMF). In the present study, the influence of three parameters (phosphorus supply, mycorrhizal inoculation, and wheat cultivar) on AMF protective efficiency against Blumeria graminis f. sp. tritici, responsible for powdery mildew, was investigated under controlled conditions. A 5-fold reduction (P/5) in the level of phosphorus supply commonly recommended for wheat in France improved Funneliformis mosseae colonization and promoted protection against B. graminis f. sp. tritici in a more susceptible wheat cultivar. However, a further decrease in P affected plant growth, even under mycorrhizal conditions. Two commercially available AMF inocula (F. mosseae, Solrize®) and one laboratory inoculum (Rhizophagus irregularis) were tested for mycorrhizal development and protection against B. graminis f. sp. tritici of two moderately susceptible and resistant wheat cultivars at P/5. Mycorrhizal levels were the highest with F. mosseae (38 %), followed by R. irregularis (19 %) and Solrize® (SZE, 8 %). On the other hand, the highest protection level against B. graminis f. sp. tritici was obtained with F. mosseae (74 %), followed by SZE (58 %) and R. irregularis (34 %), suggesting that inoculum type rather than mycorrhizal levels determines the protection level of wheat against B. graminis f. sp. tritici. The mycorrhizal protective effect was associated with a reduction in the number of conidia with haustorium and with an accumulation of polyphenolic compounds at B. graminis f. sp. tritici infection sites. Both the moderately susceptible and the most resistant wheat cultivar were protected against B. graminis f. sp. tritici infection by F. mosseae inoculation at P/5, although the underlying mechanisms appear rather different between the two cultivars. This study emphasizes the importance of taking into account the considered parameters when considering the use of AMF as biocontrol agents.     

Can <Emphasis Type="Italic">Bradyrhizobium</Emphasis> strains inoculation reduce water deficit effects on peanuts?

Drought is one of the environmental factors that most affects peanut cultivation in semi-arid regions, resulting in economic losses to growers. However, growth promoting bacteria are able to reduce water deficit damage in some plant species. In this context, this study aimed to evaluate the interaction of Bradyrhizobium strains reducing water stress effects on peanut genotypes by antioxidant enzymes activities, leaf gas exchanges and vegetative growth, as well as to determine the taxonomic positioning of strain ESA 123. The 16S rRNA gene of ESA 123 was amplified by PCR and sequenced by dideoxy Sanger sequencing method. An experiment was performed in greenhouse with three peanut genotypes (BRS Havana, CNPA 76 AM and 2012-4), two Bradyrhizobium strains (SEMIA 6144 and ESA 123), a mineral source of N and an absolute control (without N) under two water regimes (with and without irrigation). Seeds of peanut were sown and the plants were grown until 30 days after emergence. On the 20th day, the water deficit plants group had their irrigation suspended for 10 days. At in silico analyzes, ESA 123 presented 98.97% similarity with the type strain of B. kavangense. Leaf gas exchange was affected by water deficit; as well as alteration of antioxidant activities and reduction of vegetative growth variables. However, some plants inoculated with SEMIA 6144 and ESA 123 strains presented lower reductions and increment of some evaluated variables, mainly the ones inoculated with the ESA 123 strain, Bradyrhizobium sp. from the semi-arid region of Northeast Brazil. This data suggests beneficial effects of the peanut-Bradyrhizobium interaction in a water stress condition, specially with the ESA 123 strain.