The effect of strobilurins on leaf gas exchange, water use efficiency and ABA content in grapevine under field conditions

Metabolic Study of Cucumber Seeds and Seedlings in the Light of the New, Controversial Trend of Preventive Use of Systemic Fungicides

Cucumber is one of the most commonly produced vegetable crops. The greatest economic losses in the yields of these crops have resulted from fungal infections—powdery mildew and downy mildew. The action of fungicides not only affects the fungi, but can also lead to metabolic disorders in plants. However, some fungicides have been reported to have positive physiological effects. Our research focused on the action of two commercially available fungicides, Scorpion 325 SC and Magnicur Finito 687,5 SC, on plant metabolism. Two approaches were used to check the effect of the fungicides at the early stage of plant development when metabolic changes occur most dynamically: spraying on the leaves of cucumber seedlings and presowing seed treatment. The application of the fungicide formulation as a presowing seed treatment caused perturbations in the phytase activity, leading to disorders in the energetic status of the germinating seeds. In addition, the tested preparations changed the morphology of the germinating seeds, limiting the growth of the stem. Furthermore, the application of the tested fungicides on seedlings also showed a disruption in the energetic status and in the antioxidative system. Therefore, the use of pesticides as agents causes a “green effect” and requires a much deeper understanding of plant metabolism.

The role of microbial communities on primary producers in aquatic ecosystems: Implications in turbidity stress resistance

Expanding the stress tolerance and adaptation potential of primary producers is of importance for the restoration and management of aquatic ecosystems. Microorganisms have been reported to mediate improved resistance toward different abiotic stresses of primary producers in terrestrial and marine ecosystems. However, it is not clear about the role of microbial communities in the turbidity resistance of primary producers, when aquatic ecosystems are under turbidity pressure. In this study, key microbes and the action path which enhance turbidity tolerance of primary producers were recognized by mesocosm and various multivariate statistical methods. Remarkable decrease of the biomass of primary producers was found with the increase of turbidity. Significant differences in microbial community under different turbidity pressure were recognized and key microbes which may expand the turbidity tolerance of primary producers were further identified. Rhodobacter and Rhodoferax were selected as key microbes by the investigation of keystone species in the microbial ecological network and significant discriminant taxa under different turbidity stress. The action path for microbial communities to help primary producers cope with turbidity pressure was found through structural equation model, and in which the increase of key microbes may expand the turbidity tolerance of primary producers through enhancing the microbial loop. The results may provide a new insight for aquatic ecosystems to resist turbidity stress, and provide a theoretical basis for the management and restoration of aquatic ecosystems.

Management of Phytophthora cinnamomi Using Fungicides and Host Plant Defense Inducers Under Drought Conditions: A Case Study of Flowering Dogwood

Phytophthora cinnamomi is considered one of the most destructive pathogens of ornamental crops. Different fungicides and host plant defense inducers were tested for their efficacy in managing Phytophthora root rot in drought conditions. In this study, the drought conditions were maintained by evaluating the moisture-holding capacity of the pine bark in a 10.2-cm nursery container. Four controls and nine different treatments were used in two trials for this greenhouse study. All treatments were drench-applied as a preventative or curative treatment. Seedlings were artificially inoculated with P. cinnamomi. Regular irrigation was carried out using overhead irrigation for 1 month after inoculation. Irrigation was regulated by drip irrigation after the first month. A moisture level of 15% to 18% of total moisture-holding capacity was maintained using the gravimetric method throughout the drought period. Physiological parameters of the seedlings were recorded a week after seedlings were drought stressed. In both trials of preventative and curative treatments, all treatments were able to suppress the disease significantly except Orkestra Intrinsic. Orkestra Intrinsic had a disease severity statistically similar to the inoculated and stressed control in trial 1 of the curative treatment. Net photosynthesis, stomatal conductance, and leaf moisture potential were significantly greater in seedlings treated with Subdue MAXX, Signature Xtra, and Empress Intrinsic in both trials of preventative and curative treatments. Effective quantum yield of Photosystem II was significantly lower in the inoculated stressed control in both trials of preventative and curative treatments. Net chlorophyll content through the SPAD meter showed higher values for Subdue MAXX treated seedlings compared with the noninoculated nonstressed controls in trial 1 as both a curative and preventative application. In trial 2, Subdue MAXX and Signature Xtra were the best curative treatments, whereas Empress Intrinsic, Interface, and Subdue MAXX were the best preventative treatments for higher chlorophyll content. This case study will help growers perform successful management of Phytophthora root rot in woody ornamental crops during drought or water deficit conditions.

Protective role of tebuconazole and trifloxystrobin in wheat (Triticum aestivum L.) under cadmium stress via enhancement of antioxidant defense and glyoxalase systems

Cadmium (Cd) is a toxic metal and an environmental pollutant that significantly reduces plant growth and productivity. Proper management can ameliorate dysfunction and improve the plant growth and productivity exposed to Cd. Therefore, the present study was conducted to explore the protective role of the fungicides tebuconazole (TEB) and trifloxystrobin (TRI) in helping wheat (Triticum aestivum L. cv. Norin 61) seedlings to tolerate Cd. Five-day-old hydroponically grown seedlings were allowed to mild (0.25 mM CdCl₂) and severe (0.5 mM CdCl₂) Cd stress separately and with the fungicides (2.75 µM TEB + 1.0 µM TRI) for the next four days. Compared to control, the level of H₂O₂ in the seedlings exposed to mild and severe Cd stress alone increased by 81 and 112%, respectively. The accumulation of Cd also increased in the wheat seedlings along with declining mineral nutrients under Cd stress. The protective effect of TEB and TRI was observed with the enhancement of the antioxidant defense and methylglyoxalase systems and reduction in oxidative damage. Applying TEB and TRI reduced MDA (by 9 and 18%), EL (by 21 and 17%), MG (by 12 and 17%), and LOX activity (by 37 and 27%), respectively, relative to Cd stress alone. Cadmium uptake also decreased in the shoots (by 48 and 50%, respectively) and roots (by 23 and 25%, respectively) of the fungicide-treated wheat seedlings under mild and severe Cd stress, relative to stress alone. These results indicate the exogenous application of TEB and TRI is a promising approach to improve Cd tolerance in wheat plants. Further investigation is needed under field conditions and for other crop species to determine the Cd-tolerance induced by TEB and TRI application.

Exogenous Tebuconazole and Trifloxystrobin Regulates Reactive Oxygen Species Metabolism Toward Mitigating Salt-Induced Damages in Cucumber Seedling

The present study investigated the role of tebuconazole (TEB) and trifloxystrobin (TRI) on cucumber plants (Cucumis sativus L. cv. Tokiwa) under salt stress (60 mM NaCl). The cucumber plants were grown semi-hydroponically in a glasshouse. Plants were exposed to two different doses of fungicides (1.375 µM TEB + 0.5 µM TRI and 2.75 µM TEB + 1.0 µM TRI) solely and in combination with NaCl (60 mM) for six days. The application of salt phenotypically deteriorated the cucumber plant growth that caused yellowing of the whole plant and significantly destructed the contents of chlorophyll and carotenoids. The oxidative damage was created under salinity by increasing the contents of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and electrolytic leakage (EL) resulting in the disruption of the antioxidant defense system. Furthermore, in the leaves, stems, and roots of cucumber plants increased Na⁺ content was observed under salt stress, whereas the K⁺/Na⁺ ratio and contents of K⁺, Ca²⁺, and Mg²⁺ decreased. In contrast, the exogenous application of TEB and TRI reduced the contents of MDA, H₂O₂, and EL by improving the activities of enzymatic and non-enzymatic antioxidants. In addition, ion homeostasis was regulated by reducing Na⁺ uptake and enhanced K⁺ accumulation and the K⁺/Na⁺ ratio after application of TEB and TRI. Therefore, this study indicates that the exogenous application of TEB and TRI enhanced salt tolerance in cucumber plants by regulating reactive oxygen species production and antioxidant defense systems.

Enhancing the abiotic stress tolerance of plants: from chemical treatment to biotechnological approaches

Abiotic stresses affect crop plants and cause decreases in plant quality and productivity. Plants can overcome environmental stresses by activating molecular networks, including signal transduction, stress perception, metabolite production and expressions of specific stress-related genes. Recent research suggests that chemical priming is a promising field in crop stress management because plants can be primed by chemical agents to increase their tolerance to various environmental stresses. We present a concept to meet this objective and protect plants through priming of existing defense mechanisms avoiding manipulation of the genome. In addition, recent developments in plant molecular biology include the discovery of genes related to stress tolerance, including functional genes for protecting cells and regulatory genes for regulating stress responses. Therefore, enhancing abiotic stress tolerance using a transgenic approach to transfer these genes into plant genomes has attracted more investigations. Both chemical priming agents and genetic engineering can enhance regulatory and functional genes in plants and increase stress tolerance of plants. This review summarizes the latest findings of chemical priming agents and major achievements in molecular approaches that can potentially enhance the abiotic stress tolerance of plants.

Strobilurins as growth-promoting compounds: how Stroby regulates Arabidopsis leaf growth

Strobilurins are an important class of agrochemical fungicides used throughout the world on a wide variety of crops as protection against fungal pathogens. In addition to this protective role, they are reported to also positively influence plant physiology. In this study, we analysed the effect of Stroby® WG, a commercially available fungicide consisting of 50% (w/w) kresoxim-methyl (KM) as active strobilurin compound, on Arabidopsis leaf growth. Treatment of seedlings with Stroby resulted in larger leaves due to an increase in cell number. Transcriptome analysis of Stroby-treated rosettes demonstrated an increased expression of genes involved in redox homeostasis, iron metabolism and sugar transport. Stroby treatment strongly induced the expression of the subgroup Ib basic helix-loop-helix (bHLH) transcription factors, which have a role in iron homeostasis under iron-limiting conditions. Single loss-of-function mutants of three bHLHs and their triple bhlh039, bhlh100 and bhlh101 mutant did not respond to Stroby treatment. Although iron and sucrose content was not affected, nitric oxide (NO) levels and nitrate reductase (NR) activity were significantly increased in Stroby-treated rosettes as compared with control plants. In conclusion, we suggest that the Stroby-mediated effects on growth depend on the increased expression of the subgroup Ib bHLHs and higher NO levels.

Host Resistance and Chemical Control for Management of Sclerotinia Stem Rot of Soybean in Ohio

Recent outbreaks of Sclerotinia stem rot (SSR) of soybean in Ohio, along with new fungicides and cultivars with resistance to this disease, have led to a renewed interest in studies to update disease management guidelines. The effect of host resistance (in moderately resistant [MR] and moderately susceptible [MS] cultivars) and chemical control on SSR and yield was evaluated in 12 environments from 2014 to 2016. The chemical treatments evaluated were an untreated check, four fungicides (boscalid, picoxystrobin, pyraclostrobin, and thiophanate-methyl), and one herbicide (lactofen) applied at soybean growth stage R1 (early flowering) alone or at R1 followed by a second application at R2 (full flowering). SSR developed in 6 of 12 environments, with mean disease incidence in the untreated check of 2.5 to 41%. The three environments with high levels of SSR (disease incidence in the untreated check >20%) were used for further statistical analysis. There were significant effects (P < 0.05) of soybean cultivar and chemical treatment on SSR levels. Significantly lower levels of SSR were observed in MR cultivars. Both boscalid and lactofen reduced SSR but did not increase yield. Pyraclostrobin increased SSR compared with the untreated check in the three environments with high levels of disease. In the six fields where SSR did not develop, chemical treatment did not increase yield, nor was the yield from the MR cultivar significantly different from the MS cultivar. For Ohio, MR cultivars alone were effective for management of SSR in soybean fields where this disease has historically occurred.

Effect of Pyraclostrobin Application on Viral and Bacterial Diseases of Tomato

Quinone outside inhibitors (QoI) are powerful fungicides, which have been reported, additionally to their fungicide activity, to increase plant capacity to activate cellular defense responses and to promote plant growth. In this work, the effect of the QoI class fungicide pyraclostrobin was examined against Cucumber mosaic virus (CMV), Potato virus Y (PVY) and Pseudomonas syringae pv. tomato in tomato plants following artificial inoculation of the plants with the pathogens. Under controlled environmental conditions, pyraclostrobin delayed viral and bacterial disease development, even if P. syringae pv. tomato internal population levels were not affected significantly. In contrast, under field conditions in commercial greenhouses, a reduced CMV disease incidence throughout the tomato cultivation period was recorded. Gene expression analysis indicated an effect of pyraclostrobin application on tomato MAPKs transcript levels and a possible interference with plant stress responses.

Physiological changes promoted by a strobilurin fungicide in the rice-Bipolaris oryzae interaction

Strobilurins are among the most important fungicides that are used for plant disease control worldwide. In addition to their fungicide effect, strobilurins can also improve crop physiology. Nonetheless, the impact of azoxystrobin (Az), the main marketed strobilurin, on rice physiology is still unknown. Detailed gas exchange measurements and chlorophyll a fluorescence analysis were used to examine the Az effects on the photosynthetic performance of rice plants (cultivar Metica-1) either challenged or not with Bipolaris oryzae, the causal agent of brown spot. Az impaired carbon (C) fixation in the non-inoculated plants in a manner that was not related to photochemical or biochemical limitations, but rather to decreased stomatal conductance that limited the CO2 influx into the mesophyll cells. The photosynthesis of rice plants that were not sprayed with Az dramatically decreased upon B. oryzae infection, which was chiefly governed by photochemical and biochemical limitations. The energy surplus that was caused by limited C fixation in the rice plants that were treated with Az and inoculated with B. oryzae was thermally and effectively dissipated until 72h after inoculation. In Az absence, however, this mechanism was not sufficient to prevent chronic photoinhibition to photosynthesis. The inoculated plants were not able to fully capture and exploit the collected light energy, but these constraints were greatly limited in the presence of Az. In conclusion, Az impaired the photosynthetic performance of non-infected plants by diffusive constraints, but prevented, to a greater extent, the damage to the photosynthetic apparatus during the infection process of B. oryzae.

Chemical Priming of Plants Against Multiple Abiotic Stresses: Mission Possible?

Crop plants are subjected to multiple abiotic stresses during their lifespan that greatly reduce productivity and threaten global food security. Recent research suggests that plants can be primed by chemical compounds to better tolerate different abiotic stresses. Chemical priming is a promising field in plant stress physiology and crop stress management. We review here promising chemical agents such as sodium nitroprusside, hydrogen peroxide, sodium hydrosulfide, melatonin, and polyamines that can potentially confer enhanced tolerance when plants are exposed to multiple abiotic stresses. The challenges and opportunities of chemical priming are addressed, with the aim to boost future research towards effective application in crop stress management.

Kresoxim-methyl primes Medicago truncatula plants against abiotic stress factors via altered reactive oxygen and nitrogen species signalling leading to downstream transcriptional and metabolic readjustment

Biotic and abiotic stresses, such as fungal infection and drought, cause major yield losses in modern agriculture. Kresoxim-methyl (KM) belongs to the strobilurins, one of the most important classes of agricultural fungicides displaying a direct effect on several plant physiological and developmental processes. However, the impact of KM treatment on salt and drought stress tolerance is unknown. In this study we demonstrate that KM pre-treatment of Medicago truncatula plants results in increased protection to drought and salt stress. Foliar application with KM prior to stress imposition resulted in improvement of physiological parameters compared with stressed-only plants. This protective effect was further supported by increased proline biosynthesis, modified reactive oxygen and nitrogen species signalling, and attenuation of cellular damage. In addition, comprehensive transcriptome analysis identified a number of transcripts that are differentially accumulating in drought- and salinity-stressed plants (646 and 57, respectively) after KM pre-treatment compared with stressed plants with no KM pre-treatment. Metabolomic analysis suggests that the priming role of KM in drought- and to a lesser extent in salinity-stressed plants can be attributed to the regulation of key metabolites (including sugars and amino acids) resulting in protection against abiotic stress factors. Overall, the present study highlights the potential use of this commonly used fungicide as a priming agent against key abiotic stress conditions.

Redox Strategies for Crop Improvement

SIGNIFICANCE

Recently, the agro-biotech industry has been driven by overcoming the limitations imposed by fluctuating environmental stress conditions on crop productivity. A common theme among (a)biotic stresses is the perturbation of the redox homeostasis.

RECENT ADVANCES

As a strategy to engineer stress-tolerant crops, many approaches have been centered on restricting the negative impact of reactive oxygen species (ROS) accumulation.

CRITICAL ISSUES

In this study, we discuss the scientific background of the existing redox-based strategies to improve crop performance and quality. In this respect, a special focus goes to summarizing the current patent landscape because this aspect is very often ignored, despite constituting the forefront of applied research.

FUTURE DIRECTIONS

The current increased understanding of ROS acting as signaling molecules has opened new avenues to exploit redox biology for crop improvement required for sustainable food security.

Photosynthetic and antioxidative alterations in coffee leaves caused by epoxiconazole and pyraclostrobin sprays and Hemileia vastatrix infection

Coffee leaf rust (CLR), caused by Hemileia vastatrix, is a major disease affecting coffee production worldwide. In this study, an in-depth analysis of the photosynthetic performance of coffee leaves challenged or not with H. vastatrix and sprayed with either epoxiconazole (EPO) or pyraclostrobin (PYR) was performed by combining chlorophyll a fluorescence images, photosynthetic pigment pools and the activities of chitinase (CHI), β-1,3-glucanase (GLU), peroxidase (POX) and catalase (CAT). The CLR severity was higher in the control plants, but reduced in plants sprayed with both PYR and EPO. Also, the CLR severity was reduced in plants sprayed with PYR compared with plants sprayed with EPO. Plants sprayed with either EPO or PYR showed maximal photosystem II quantum efficiency (Fv/Fm) values ranging from 0.78 to 0.80, which were quite similar to those obtained with inoculated plants (values ranging from 0.74 to 0.77). The decreases in the Fv/Fm ratio values and parallel increases in the F0 values in the inoculated plants, which were not observed in the control plants (sprayed with water) and were confirmed by images of the initial fluorescence (F0) and Fv/Fm parameters in the regions of the leaf tissue containing pustules and in the asymptomatic leaf tissue, indicated that photosynthesis was negatively impacted. When effective photosystem II quantum yield (Y(II)) values approached zero with a high photosynthetic photon flux density, high values of quantum yield of regulated energy dissipation (Y(NPQ)) in association with a high carotenoid concentration were noted in the inoculated plants sprayed either with PYR or EPO. The increased CLR severity in inoculated plants in contrast to inoculated plants sprayed with either PYR or EPO was associated with greater POX activity and a reduced photosynthetic pigment concentration. POX and CAT activities were increased in inoculated plants sprayed with either EPO or PYR when compared with control plants. CHI and GLU activities were maintained at high levels in the leaves of inoculated plants, regardless of the fungicide sprayed, indicating that CHI and GLU are less important for coffee resistance against CLR. The results of the present study clearly demonstrated that plants sprayed with either EPO or PYR showed milder CLR symptoms with adequate photosynthetic performance and optimal conditioning of their antioxidant systems.

Influence of Open Alleys in Field Trials Assessing Yield Effects from Fungicides in Corn

Including open alleys at ends of plots is a common practice when field-testing foliar fungicides used in corn production. Open alleys facilitate movement of workers and equipment between plots during spray application. Open alleys affect crop yield estimates in small plots typically used in replicated, randomized experimental designs, because of reduced interplant competition. However, no published research has tested whether the alley effect interacts with fungicide to bias the assessment of the agronomic effects of the latter. We tested this hypothesis over 2 years by evaluating yield with and without application of Headline AMP (containing pyraclostrobin and metconazole) plus nonionic surfactant applied once at VT/R1 in 7.6-m plots separated on their ends by 1.5-m alleys free of aboveground vegetation. In each plot, data were collected from seven subplots, each measuring 1.09 m of row-length and running parallel to the long axis of the plot. Consistent with previous reports, yields of subplots were substantially higher toward plot ends than in the central areas of plots. Surprisingly, a significant (P < 0.10) fungicide × subplot interaction was observed in both experiments, indicating that the yield response from fungicide depended on subplot position within the plot. However, yield differences due to fungicide were trivial when comparing regression-based yield estimates from all seven subplot positions to those obtained from only the centermost three subplot positions. Our study does not lend support to the hypothesis that the open-alley design creates a meaningful bias in assessment of treatment effects due to foliar fungicides in corn. However, additional research on this question is warranted, given the complexities of comparing results in large-scale plots vs. small plots, the limitations of our study, and the widespread use of fungicides on field corn in the United States.