Germination Of Sporangia Research Articles

Biocontrol Mechanisms of Three Plant Essential Oils Against Phytophthora infestans Causing Potato Late Blight.

Late blight, caused by the notorious pathogen Phytophthora infestans, poses a significant threat to potato (Solanum tuberosum) crops worldwide, impacting their quality as well as yield. Here, we aimed to investigate the potential use of cinnamaldehyde, carvacrol, and eugenol as control agents against P. infestans and to elucidate their underlying mechanisms of action. To determine the pathogen-inhibiting concentrations of these three plant essential oils (PEOs), a comprehensive evaluation of their effects using gradient dilution, mycelial growth rate, and spore germination methods was carried out. Cinnamaldehyde, carvacrol, and eugenol were capable of significantly inhibiting P. infestans by hindering its mycelial radial growth, zoospore release, and sporangium germination; the median effective inhibitory concentration of the three PEOs was 23.87, 8.66, and 89.65 μl/liter, respectively. Scanning electron microscopy revealed that PEOs caused the irreversible deformation of P. infestans, resulting in hyphal shrinkage, distortion, and breakage. Moreover, propidium iodide staining and extracellular conductivity measurements demonstrated that all three PEOs significantly impaired the integrity and permeability of the pathogen's cell membrane in a time- and dose-dependent manner. In vivo experiments confirmed the dose-dependent efficacy of PEOs in reducing the lesion diameter of potato late blight. Altogether, these findings provide valuable insight into the antifungal mechanisms of PEOs vis-à-vis late blight-causing P. infestans. By utilizing the inherent capabilities of these natural compounds, we could effectively limit the harmful impacts of late blight on potato crops, thereby enhancing agricultural practices and ensuring the resilience of global potato food production.

Effectiveness of Volatiles Emitted by Streptomyces abikoensis TJGA-19 for Managing Litchi Downy Blight Disease.

Litchi is a fruit of significant commercial value; however, its quality and yield are hindered by downy blight disease caused by Peronophythora litchii. In this study, volatile organic compounds (VOCs) from Streptomyces abikoensis TJGA-19 were investigated for their antifungal effects and studied in vitro and in planta for the suppression of litchi downy blight disease in litchi leaves and fruits. The growth of P. litchii was inhibited by VOCs produced by TJGA-19 cultivated on autoclaved wheat seeds for durations of 10, 20, or 30 days. Volatiles from 20-day-old cultures were more active in inhibition effect against P. litchii than those from 10- or 30-day-old cultures. These volatiles inhibit the growth of mycelia, sporulation, and oospore production, without any significant effect on sporangia germination. Additionally, the VOCs were effective in suppressing disease severity in detached litchi leaf and fruit infection assays. With the increase in the weight of the wheat seed culture of S.abikoensis TJGA-19, the diameters of disease spots on leaves, as well as the incidence rate and disease indices on fruits, decreased significantly. Microscopic results from SEM and TEM investigations showed abnormal morphology of sporangia, mycelia, and sporangiophores, as well as organelle damage in P. litchii caused by VOCs of TJGA-19. Spectroscopic analysis revealed the identification of 22 VOCs produced by TJGA-19, among which the most dominant compound was 2-Methyliborneol. These findings indicated the significant role of TJGA-19 compounds in the control of litchi downy blight disease and in improving fruit quality.

Evaluation of SYP-34773's resistance risk and its impact on the activity of mitochondrial respiratory electron transport chain complex I in Phytophthora litchii.

SYP-34773 is a low-toxicity pyrimidine amine compound, which was synthesized by modifying the lead compound diflumetorim. Previous literature has shown that it can strongly inhibit the mycelial growth of several important plant pathogens, including Phytophthora litchii. However, the resistance risk of SYP-34773 has not been reported for P. litchii. The mean effective concentration (EC50 ) value of SYP-34773 against the mycelial growth of 111 P. litchii isolates was 0.108 ± 0.008 μg mL-1 , which can be used as the baseline sensitivity for SYP-34773 resistance detection in the future. Six mutants were obtained from two parental strain through fungicide induction, whose resistance factors fell between 194- and 687-fold, with stability. Results regarding mycelial growth, sporangial production, sporangial germination, zoospore release, cystspore germination, and pathogenicity showed that the mutants' compound fitness index values were significantly lower than those of their parental isolate. Furthermore, there was no cross-resistance between SYP-34773 and diflumetorim in P. litchii. Significant inhibition of the mitochondrial complex I enzyme activity in two wild-type P. litchii isolates, but not in mutants, was observed upon treatment with SYP-34773. The resistance risk of SYP-34773 in P. litchii is moderate, and resistance management strategies should be adopted in field use. SYP-34773 is a mitochondrial complex I inhibitor, and SYP-34773-resistant P. litchii isolates did not show cross-resistance against diflumetorim. © 2023 Society of Chemical Industry.

Anti-Oomycete Effect and Mechanism of Salicylic Acid on Phytophthora infestans.

Pathogenic oomycetes infect a wide variety of organisms, including plants, animals, and humans, and cause massive economic losses in global agriculture, aquaculture, and human health. Salicylic acid (SA), an endogenous phytohormone, is regarded as an inducer of plant immunity. Here, the potato late blight pathogen Phytophthora infestans was used as a model system to uncover the inhibitory mechanisms of SA on pathogenic oomycetes. In this research, SA significantly inhibited the mycelial growth, sporulation, sporangium germination, and virulence of P. infestans. Inhibition was closely related to enhanced autophagy, suppression of translation initiation, and ribosomal biogenesis in P. infestans, as shown by multiomics analysis (transcriptomics, proteomics, and phosphorylated proteomics). Monodansylcadaverine (MDC) staining and Western blotting analysis showed that SA promoted autophagy in P. infestans by probably targeting the TOR signaling pathway. These observations suggest that SA has the potential to control late blight caused by P. infestans.

Plant glycerol suppresses brown rot of peach fruit by enhancing disease resistance

Peach fruit is susceptible to fungal contamination during postharvest storage and logistics. Brown rot resulting from Monilinia fructicola infection is one serious disease. Plant glycerol, a natural biodegradable sugar alcohol, can restrain several plant diseases. The inhibitory effect and its mechanism of plant glycerol treatment on brown rot of peach fruit were studied in current study. The findings revealed that 50 mg/g plant glycerol combined with 0.02 % Silwet L-77 surfactant could effectively delay the onset of brown rot caused by M. fructicola. But no concentrations of plant glycerol had significant inhibitory effect on sporangium germination and mycelium growth of M. fructicola. The activities of β-1,3-glucanase (GNS) and chitinase (CHI), the gene relative expression of β-1,3-glucanase (PpGNS), chitinase (PpCHI), pathogenesis-related gene 1 (PpPR1) and nonexpresser of pathogenesis-related gene 1 (PpNPR1) and salicylic acid (SA) content were markedly promoted by plant glycerol treatment. The contents of O2−, H2O2 and oleic acid were significantly repressed, but the activities of superoxide dismutase (SOD) and peroxidase (POD) and the expressions of glycerol kinase 1 (PpGLI1) and glycerol triphosphate dehydrogenase (PpGPDH) were significantly improved. Plant glycerol treatment could induce disease resistance through systemic acquired resistance (SAR) in peach fruit, which might be related to improving the synthesis of polyunsaturated fatty acids. Therefore, plant glycerol treatment is effective on inhibiting brown rot development and possesses potential application in postharvest peach fruit.

Biocontrol of Litchi Downy Blight Dependent on Streptomyces abikoensis TJGA-19 Fermentation Filtrate Antagonism Competition with Peronophythora litchii

The cultivation and overall quality of Litchi, a fruit of significant commercial value in China, are hindered by the presence of the oomycetes pathogen Peronophythora litchii. This pathogen is responsible for the occurrence of litchi downy blight, resulting in substantial economic losses during the storage and transportation of the fruit, and affects nutritional growth. Effective and environmentally safe methods to control litchi downy blight are urgently needed. The application of biocontrol agents such as Streptomyces bacteria has proven effective for controlling plant diseases. Our present study isolated the Streptomyces strain TJGA-19, identified as S. abikoensis, with potent inhibitory activity against P. litchii. The antifungal active substances are mainly in the aqueous phase of TJGA-19 fermentation filtrate extraction. The fermentation filtrate of TJGA-19 not only suppressed the pathogen growth, sporulation, and sporangia germination, but also delayed the disease development of litchi downy blight. In addition, the stability of the TJGA-19 fermentation filtrate was not sensitive to the proteinase K, temperature, white-flourescence light, or ultraviolet treatment. Furthermore, the morphology and ultrastructure of P. litchii treated with fermentation filtrate was characterized by marked shrinking and deformation, with serious disruption of plasma membrane permeabilization and the organelles. Hence, S. abikoensis TJGA-19 and its metabolites demonstrated marked efficiency against the phytopathogenic pathogen P. litchii and provide a potential candidate for controlling litchi downy blight.

Endophytic Bacillus subtilis H17-16 effectively inhibits Phytophthora infestans, the pathogen of potato late blight, and its potential application.

As a highly prevalent epidemic disease of potato, late blight caused by Phytophthora infestans poses a serious threat to potato yield and quality. At present, Chemical fungicides are mainly used to control potato late blight, but long-term overuse of chemical fungicides may lead to environmental pollution and human health threats. Endophytes, natural resources for plant diseases control, can promote plant growth, enhance plant resistance, and secrete antifungal substances. Therefore, there is an urgent need to find some beneficial endophytes to control potato late blight. We isolated a strain of Bacillus subtilis H17-16 from potato healthy roots. It can significantly inhibit mycelial growth, sporangia germination and the pathogenicity of Phytophthora infestans, induce the resistance of potato to late blight, and promote potato growth. In addition, H17-16 has the ability to produce protease, volatile compounds (VOCs) and form biofilms. After H17-16 treatment, most of the genes involved in metabolism, virulence and drug resistance of Phytophthora infestans were down-regulated significantly, and the genes related to ribosome biogenesis were mainly up-regulated. Moreover, field and postharvest application of H17-16 can effectively reduce the occurrence of potato late blight, and the combination of H17-16 with chitosan or chemical fungicides had a better effect than single H17-16. Our results reveal that Bacillus subtilis H17-16 has great potential as a natural fungicide for controlling potato late blight, laying a theoretical basis for its development as a biological agent. This article is protected by copyright. All rights reserved.

Biological control of potato late blight with a combination of Streptomyces strains and biochar

Potato late blight (PLB) caused by Phytophthora infestans is the most damaging disease in potatoes. In this study, Streptomyces and biochar (a new eco-material with the potential to improve soil and plant health) were used for the biological control of PLB. In vitro experiments showed that the six Streptomyces strains can significantly inhibit the growth of P. infestans and sporangia germination. In vivo tests showed that the six Streptomyces strains significantly inhibited the infection of P. infestans on potato tubers. After combined with biochar, the inhibition rate of Streptomyces strains against P. infestans was increased by 1.9 % to 46.1 %. In two years of field trials, the combination of six Streptomyces strains and biochar decreased the disease index by 10 % to 26 %, exhibiting better disease control than the use of either agent alone. In addition, a single application of biochar did not significantly decrease the incidence of the disease but enriched the rhizosphere in the beneficial bacterium Rhizobium. Our results highlight the potential for biological control of PLB with a combination of Streptomyces strains and biochar.

Antifungal Activity of β-Carboline Alkaloids Compound and Its Resistance Mechanism on Peronophythora Litchii

ABSTRACT Peronophythora litchii (P. litchii) is the pathogenic factor of litchi downy blight. Derivatives extracted from harmine officinalis and modified, N-(2-pyridyl)-1-phenyl-9 H-pyrido [3, 4-b] indole-3-formamide (PPPIF), could inhibited P. litchii growth and development. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses indicated that PPPIF severely damaged the mitochondria, cell wall and endomembrane system of P. litchii cells, thus abnormal morphology, as well as deformed mycelia. PPPIF could suppress mycelial growth, sporulation, sporangia germination and germ tube elongation as well. PPPIF also caused a series of physiological and biochemical changes of P. litchii, including the serious deviation of extracellular pH, the obvious increase of the content of extracellular reducing sugar and malondialdehyde, the notable decrease of soluble protein and the activity of NADH oxidase. Furthermore, PPPIF seriously raised openness of membrane permeability transporter (MPTP) and markedly decreased the transmembrane potential (Δψm) and the activity of enzyme complex I–complex V in respiratory chain of mitochondria. The current research suggests that PPPIF may act upon the mitochondrion of P. litchii, then respiratory chain complex activity was blocked and energy metabolism disrupted or inhibited, resulting in the growth inhibition of P. litchii. Above results have strengthened our understanding of P. litchii resistance mechanisms and may help in the development of more potent inhibitors against plant diseases in the fields.

The Molecular Mechanisms of Phytophthora infestans in Response to Reactive Oxygen Species Stress.

Reactive oxygen species (ROSs) are critical for the growth, development, proliferation, and pathogenicity of microbial pathogens; however, excessive levels of ROSs are toxic. Little is known about the signaling cascades in response to ROS stress in oomycetes such as Phytophthora infestans, the causal agent of potato late blight. Here, P. infestans was used as a model system to investigate the mechanism underlying the response to ROS stress in oomycete pathogens. Results showed severe defects in sporangium germination, mycelium growth, appressorium formation, and virulence of P. infestans in response to H2O2 stress. Importantly, these phenotypes mimic those of P. infestans treated with rapamycin, the inhibitor of target of rapamycin (TOR, 1-phosphatidylinositol-3-kinase). Strong synergism occurred when P. infestans was treated with a combination of H2O2 and rapamycin, suggesting that a crosstalk exists between ROS stress and the TOR signaling pathway. Comprehensive analysis of transcriptome, proteome, and phosphorylation omics showed that H2O2 stress significantly induced the operation of the TOR-mediated autophagy pathway. Monodansylcadaverine staining showed that in the presence of H2O2 and rapamycin, the autophagosome level increased in a dosage-dependent manner. Furthermore, transgenic potatoes containing double-stranded RNA of TOR in P. infestans (PiTOR) displayed high resistance to P. infestans. Therefore, TOR is involved in the ROS response and is a potential target for control of oomycete diseases, because host-mediated silencing of PiTOR increases potato resistance to late blight.

Biocidal activity of plant-derived compounds against Phytophthora infestans: An alternative approach to late blight management

The current study aimed to evaluate the potential biocontrol capabilities of different essential oils (EOs) including juniper, tea tree, clove, thyme, cinnamon, turmeric, pepper and rosemary at application rates of 0.41, 0.83, 1.66, 3.33 and 6.66 μL mL−1 for control of Phytophthora infestans; the causal agent of potato late blight in vivo and under greenhouse conditions. In particular we tested the highly pathogenic genotype, EU-13-A2. Plant extract Timbor® (Thymus vulgaris-derived compound) was similarly applied as an alternative reference to the essential oils. The effectiveness of plant compounds was initially determined by measuring the effective dose (ED50) reducing P. infestans sporangial germination by 50%. Among the nine tested compounds, thyme and tea tree EOs showed the strongest inhibitory effect on sporangial germination, with ED50 values between 0.12 and 0.37 μL mL−1, compared to the fungicide control Ranman-top® (160 g L−1 Cyazofamide). Clove EO, thyme EO and Timbor® significantly inhibited P. infestans mycelial growth even at the lowest concentration tested (0.41 μL mL−1). Inhibitory effects of compounds were also assessed in response to late blight in vivo, and the results were then compared with greenhouse screening. In the detached-leaflet assay, pepper, rosemary EOs and Timbor® showed reduction of disease development at all concentrations except for 0.41 μL mL−1. In dose–responses, rosemary, thyme EO and Timbor® were the most effective compounds in reducing late blight (more than 80% disease reduction) over time. Within a 35-day period, these compounds also resulted in the lowest level of disease severity in susceptible potato plants (cv. Bintje) when treated 12 h before inoculation, demonstrating their protective effect against late blight under greenhouse conditions. This study presents evidence for the potential use of commercial plant derived compounds as botanical fungicides against P. infestans to control infection on potato plants.

Preliminary Investigation of Effect of Neem-Derived Pesticides on Plasmopara halstedii Pathotype 704 in Sunflower under In Vitro and In Vivo Conditions.

Two neem-derived pesticides were examined under in vitro and in vivo conditions to test their efficacy in controlling Plasmopara halstedii pathotype 704, a causal agent of downy mildew in sunflower. All the tested concentrations of neem leaf extract and the highest concentration of commercial neem product significantly reduced the sporangial germination under in vitro conditions. In in vivo experiment, 3-days old pre-treated seedlings with both concentrations of neem leaf extract and the highest concentration of commercial product showed a significant reduction in the infection indicating possible systemic effect of neem. When the seedlings were treated following the infection with P. halstedii (i.e., post-treatment), only the highest concentrations of neem leaf extract and the commercial product showed a significant reduction in the infection indicating curative effect of neem. Possibilities for the control of P. halstedii with neem-derived pesticides are discussed.

Phytophthora capsici PcFtsZ2 Is Required for Asexual Development and Plant Infection.

In bacteria, FtsZ proteins form a Z ring that is the initial step preceding septal fission. FtsZ proteins enable the division of mitochondria in early eukaryotes and are present in some kingdoms but have been lost in animals, fungi, and plants. Here, we have identified two Phytophthora capsici ortholog genes of Escherichia coli FtsZs, designated PcFtsZ1 and PcFtsZ2. Overexpression of PcFtsZ2 in E. coli fully complemented the overexpression phenotype of EcFtsZ. In contrast, overexpression of PcFtsZ1 in E. coli had minimal impact on cell division and separation. Thus, we focused on evaluating the impact of altered expression of PcFtsZ2 in P. capsici, as it exhibited the strongest phenotype. PcFtsZ2 was expressed at the highest levels in mycelia, sporangia, and germinating cysts, as well as in late infection. PcFtsZ2 mis-expression lines showed aberrant asexual growth and development of P. capsici. Alterations in the expression of PcFtsZ2 changed the distribution of mitochondria in hyphae and sporangia and, also, affected the number, size, and shape of actin plaques. Silencing of PcFtsZ2 restrained growth and development of invasive structures, especially cysts and sporangia, substantially inhibiting the ability of transformants to cause blight lesions. In overexpressed transformant lines, cyst and sporangial germination rates were only half that of controls, but hyphal growth from direct germination of sporangia was more rapid than controls. These transformant lines were only slightly impaired in virulence relative to controls. This study emphasizes the essential role of the evolutionarily conserved FtsZ2 proteins in affecting cytoskeleton dynamics.

A spectrophotometric approach for determining sporangium and zoospore viability of Plasmopara viticola

AbstractA spectrophotometric method for determining the viability of sporangia and zoospores of the oomycete Plasmopara viticola (causal agent of grapevine downy mildew) is described and evaluated to overcome the limitations of currently available methods for assessing propagule viability. Sporangia produced on leaf discs in the laboratory were harvested at different days after the initiation of sporulation (DAS) to yield differences in sporangium viability. Sporangia were suspended in sterile water, the suspensions were placed in a cuvette, and sporangium germination was monitored in a spectrophotometer (λ = 600 nm) at 2‐ to 3‐min intervals for 5 hr. Absorbance started to increase after sporangia were suspended in water for ~30–60 min followed by major peak(s) for younger sporangia (1–3 DAS), whereas low to no increase in absorbance was observed for senescent sporangia (>7 DAS). Microscopic observation confirmed that the increase in absorbance corresponded to the release and active swimming of zoospores, whereas absorbance decreased when zoospores encysted and settled. A positive correlation (r = .839, p = .0365) was observed when the time to the initial increase in absorbance was plotted against the age of sporangia. The time to the absorbance peak (marking the time of maximum zoospore movement) was shortest for immature sporangia (0 DAS), longest for young sporangia (2 DAS) and decreased for mature and senescent sporangia. A similar pattern was observed for the standardized area under the absorbance curve (indicating the overall quantity of zoospores released), for which values were lowest for immature and senescent sporangia, highest for young sporangia and intermediate for mature sporangia. Consistent patterns obtained across two independent experiments suggest that the method is reproducible and may be further developed for other zoospore‐releasing pathogens.

<em>In-vitro</em> studies on effect of fungicides against mycelial growth and sporangial germination of <em>Phytophthora infestans </em>(Mont) de Bary) causing late blight of potato

Late blight of potato is most destructive disease. In the present study, a total of eleven fungicides, out of which eight systemic/translaminar funcides cymoxanil 50 WP, cymoxanil 8 + mancozeb 72 WP, cymoxanil 8 + mancozeb 64 WP, metalaxyl 8 + mancozeb 64 WP, metalaxyl 32 WP, fenamidone 10 + mancozeb 50 WP, difenoconazole 25 EC, dimethomorp 50 WP at concentrations of 10, 50, 100, 200 and 500 mg ml-1and three protectants viz. propineb 70 WP, mancozeb 70 WP and chlorothalonil 70 WP at concentrations of 100, 200, 500, 1000 and 2000 mg ml-1 were tested against the mycelia growth and sporangial germination ability on V8 agar medium by using poison food technique invitro. It was found that all the tested fungicides significantly inhibited the growth of mycelium compared to the control (untreated). Among the systemic fungicides dimethomorph exhibited the minimum overall mycelial growth of 38.86 mm followed by cymoxanil 8 + mancozeb 72 WP sustaining a radial growth of 43.00 mm compared to a radial mycelial growth 85.73 mm obtained in unamended check plates. An increasing trend in inhibition of mycelial growth was observed as the concentration of each fungicide was increased, such that each fungicide at 200-500 µg/ml exhibited more than 90 per cent inhibition of mycelia growth, compared to 10 µg/ml which yielded less than 10 per cent inhibition. Among protectant fungicides mancozeb exhibited highest inhibition percent with minimum mycelial growth of 46.77 mm followed by propineb yielding the mycelial growth of 50.13 mm as compared to 85.73 mm growth obtained in un amended check. The results also revealed that all the fungicides significantly reduced the sporulation and germination ability of the sporangia at all the test concentrations. Among systemic fungicides, dimethomorph proved most effective allowing sporangia germination to the extent of only 31.80 percent followed by metalaxyl + mancozeb 64 WP and cymoxanil+ mancozeb 72 WP with sporangia germination of 36.53-37.00 per cent as compared to 80.66 per cent germination observed in un-amended check (control) plates.Among the protectants.

Endophytes and Epiphytes From the Grapevine Leaf Microbiome as Potential Biocontrol Agents Against Phytopathogens.

Plants harbor diverse microbial communities that colonize both below-ground and above-ground organs. Some bacterial members of these rhizosphere and phyllosphere microbial communities have been shown to contribute to plant defenses against pathogens. In this study, we characterize the pathogen-inhibiting potential of 78 bacterial isolates retrieved from endophytic and epiphytic communities living in the leaves of three grapevine cultivars. We selected two economically relevant pathogens, the fungus Botrytis cinerea causing gray mold and the oomycete Phytophthora infestans, which we used as a surrogate for Plasmopara viticola causing downy mildew. Our results showed that epiphytic isolates were phylogenetically more diverse than endophytic isolates, the latter mostly consisting of Bacillus and Staphylococcus strains, but that mycelial inhibition of both pathogens through bacterial diffusible metabolites was more widespread among endophytes than among epiphytes. Six closely related Bacillus strains induced strong inhibition (>60%) of Botrytis cinerea mycelial growth. Among these, five led to significant perturbation in spore germination, ranging from full inhibition to reduction in germination rate and germ tube length. Different types of spore developmental anomalies were observed for different strains, suggesting multiple active compounds with different modes of action on this pathogen. Compared with B. cinerea, the oomycete P. infestans was inhibited in its mycelial growth by a higher number and more diverse group of isolates, including many Bacillus but also Variovorax, Pantoea, Staphylococcus, Herbaspirillum, or Sphingomonas strains. Beyond mycelial growth, both zoospore and sporangia germination were strongly perturbed upon exposure to cells or cell-free filtrates of selected isolates. Moreover, three strains (all epiphytes) inhibited the pathogen’s growth via the emission of volatile compounds. The comparison of the volatile profiles of two of these active strains with those of two phylogenetically closely related, inactive strains led to the identification of molecules possibly involved in the observed volatile-mediated pathogen growth inhibition, including trimethylpyrazine, dihydrochalcone, and L-dihydroxanthurenic acid. This work demonstrates that grapevine leaves are a rich source of bacterial antagonists with strong inhibition potential against two pathogens of high economical relevance. It further suggests that combining diffusible metabolite-secreting endophytes with volatile-emitting epiphytes might be a promising multi-layer strategy for biological control of above-ground pathogens.

Fungichromin Production by Streptomyces padanus PMS-702 for Controlling Cucumber Downy Mildew.

Streptomyces padanus PMS-702 strain produces a polyene macrolide antibiotic fungichromin and displays antagonistic activities against many phytopathogenic fungi. In the present study, experimental formulations were assessed to improve the production of fungichromin, the efficacy of PMS-702 on the suppression of sporangial germination, and the reduction of cucumber downy mildew caused by Pseudoperonospora cubensis. PMS-702 strain cultured in a soybean meal-glucose (SMG) medium led to low levels of fungichromin accumulation and sporangial germination suppression. Increasing medium compositions and adding plant oils (noticeably coconut oil) in SMG significantly increased fungichromin production from 68 to 1,999.6 μg/ml. Microscopic examination reveals that the resultant suspensions significantly reduced sporangial germination and caused cytoplasmic aggregation. Greenhouse trials reveal that the application of PMS-702 cultural suspensions reduced downy mildew severity considerably. The addition of Tween 80 into the synthetic medium while culturing PMS-702 further increased the suppressive efficacy of downy mildew severity, particularly when applied at 24 h before inoculation or co-applied with inoculum. Fungichromin at 50 μg/ml induced phytotoxicity showing minor necrosis surrounded with light yellowish halos on cucumber leaves. The concentration that leads to 90% inhibition (IC90) of sporangial germination was estimated to be around 10 μg/ml. The results provide a strong possibility of using the S. padanus PMS-702 strain as a biocontrol agent to control other plant pathogens.

Control of late blight in organic farming with low copper dosages or natural products as alternatives to copper

The aim of this paper is to explore appropriate alternative products to copper for the control of late blight disease in organic farming. In fact, due to its persistence and toxicity, copper appears incompatible with organic farming’s objectives of environmentally friendly farming. The effect of plant extracts, inorganic products, microorganisms and chitosan were investigated in vitro and in a greenhouse pot trial. The in vitro tests consisted of evaluating both the development of oomycete colonies on an agar medium supplemented with the tested products at various concentrations and the inhibiting effect of products on sporangial germination. The greenhouse trial was carried out on 5-week-old tomato seedlings cv. Cuore di Bue di Albenga. Tomato seedlings were transplanted into pots containing pasteurized soil and were then treated with the investigated products. After 24 h, they were inoculated with a sporangial suspension of Phytophthora infestans. The disease severity for each pot was estimated. The results showed a remarkable inhibitory effect on hyphae growth and sporangia germination of the tested products. Under greenhouse experiments, all treatments significantly reduced late blight in comparison with water control plants. The best results were obtained with the formulation containing copper at low doses and leaf licorice extract. In conclusion, the results of this study show that it is possible to reduce the dependency on copper in crop protection by using low copper dosages or natural products.

Evaluation of copper alternative products to control grape downy mildew in organic farming

The aim of this work was to investigate the efficacy of copper alternative products of natural origin against Plasmopara viticola to reduce or replace the use of copper in organic farming. The identification of new active and sustainable substances is in fact of priority importance because of the environmental impact of copper. The activity of the products was investigated in laboratory and greenhouse conditions. The laboratory tests included the evaluation of the effect of products on mycelial growth, using artificially inoculated leaf disks, and on sporangial germination. The greenhouse experiments were carried out on grape seedlings cv. Malvasia di Candia treated with products and inoculated, after 24 h, with sporangial suspension of P. viticola. The results both of laboratory and greenhouse tests showed inhibitory activity performed by several botanicals (licorice leaf extract, Yucca schidigera extract), by ALD1901 product, a derivative from Saccharomyces cerevisiae yeast, by Vacciplant formulation containing laminarin and by inorganic products as potassium hydrogen carbonate and MenoRame formulation based on micro-doses of copper and zeolites. The identification of sustainable approaches to manage grape downy mildew is very important to enhance the quality of organic production.

INDUCTION OF SYSTEMIC DISEASE RESISTANCE IN CUCUMBER PLANTS TREATED BY THE SPRAY OF SOME BIOTIC AND ABIOTIC AGENTS TO CONTROL DOWNY MILDEW DISEASE

Certain amounts of inducers, i.e Salicylic acid, Oxalic acid, and yeast extract as biocontrol agent as well as the fungicide Aquacid, used as foliar spray treatments proved to be effective in reducing downy mildew severity (DS) caused by ( P s e u d o p e r o n o s p o r a c u b e n sis ) on cucumber plants under greenhouse and field condition. In vitro , the tested fungicide, resistance inducing chemicals (RIC) and biocontrol agent highly inhibited sporangial germination of P . cubensis fungus compared with the control, Aquacid fungicide and the biocontrol agent were more effective on sporangial germination than chemicals RIC. Under greenhouse condition, severity of downy mildew disease decreased, significantly. Some Plant growth parameters i.e Plant length and fresh weight were significantly increased when the fungicide and RIC were applied as compared with the control. In field experiments, foliar application with fungicide Aquacid (2.5g/L) as a comparison treatment, Salicylic acid, Oxalic acid, and the yeast extract in concern, significantly reduced the disease severity of downy mildew with the averages of 7.25, 25.43, 30.0 and 16.40 %, respectively compared with untreated plants in the first season 2016 and the same trend was cleared in the second season 2017 with the averages of 6.50, 24.15, 25.45and 13.33%, respectively. Moreover, all exercised treatments significantly increased all of the studied growth parameters, i.e. plant length, leaves number, number of flowers, fresh and dry weight/plant. The treatments showed remarkable increase physiological aspects (Peroxidase activity and total phenol content) and similar reduction in disease severity of downy mildew revealing the most superior positively correlation with both peroxidase activity and total phenol content.