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PM disease symptoms on leaves of S (Kompo) and IR (Otto) courgette genotypes. (a) Indicated pattern of whitish powdery colonies of P. xanthii spread over a leaf of the S genotype 8 d pai (Kompo −/+), while the RS treated leaves (Kompo, +/+; Otto +/+) and the IR leaf (Otto −/+) show none or reduced colony formation, respectively. (b) The same pattern of infection is maintained at 12 d pai. All leaves in a, b are at the same developmental stage. (c) PM severity (mean % leaf area damaged ± 1 SD) on leaves of the IR and S genotypes treated with water (−) or RS (+) at the indicated time points. For each sample six plants were used and from each plant the average of % infected area of all leaves was calculated. Error bar represents standard deviation of mean. Statistical significance was based on Student's t test. *P ≤ 0.05.
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Powdery mildew (PM) caused by Podosphaera xanthii is one of the most important courgette diseases with high yield losses and is currently controlled by fungicides and sulphur applications in conventional and organic production. Plant derived elicitors/inducers of resistance are natural compounds that induce resistance to pathogen attack and promote...
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Context 1
... (b) RS-treated and untreated plants. 7 d after P. xanthii inoculation, fungal colonies were visible as small white powdery spots on the leaf surfaces of controls (water treated) plants of the S genotype Kompo, while colonies on the leaf surfaces of control plants of the IR genotype Otto were less distinct, bearing less conidiophores and mycelium (Fig. 3a). In contrast, no P. xanthii colonies could be detected on both S and IR genotype plants treated with RS 14 d pai (Fig. 3b). PM severity on RS-treated plants of both genotypes grown at the same time and under the same conditions to those sampled for analysis, was significantly reduced for up to 14 d pai when compared to water treated ...
Context 2
... spots on the leaf surfaces of controls (water treated) plants of the S genotype Kompo, while colonies on the leaf surfaces of control plants of the IR genotype Otto were less distinct, bearing less conidiophores and mycelium (Fig. 3a). In contrast, no P. xanthii colonies could be detected on both S and IR genotype plants treated with RS 14 d pai (Fig. 3b). PM severity on RS-treated plants of both genotypes grown at the same time and under the same conditions to those sampled for analysis, was significantly reduced for up to 14 d pai when compared to water treated plants (Fig. ...
Context 3
... 3a). In contrast, no P. xanthii colonies could be detected on both S and IR genotype plants treated with RS 14 d pai (Fig. 3b). PM severity on RS-treated plants of both genotypes grown at the same time and under the same conditions to those sampled for analysis, was significantly reduced for up to 14 d pai when compared to water treated plants (Fig. ...
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Crop plants have coevolved phytohormone-mediated defenses to combat and/or repel their colonizers. The present study determined the effects of jasmonic acid (JA) accumulation during aphid infestation on the preference and performance of Sitobion miscanthi Takahashi (Hemiptera: Aphididae), and its potential role in fine-tuning hormone-dependent resp...
Citations
... Likewise, there was no difference in the application method, although the severity was slightly lower in the treatments applied preventively; that is, the time of application did not influence the severity of the disease in the chili pepper plants (Table 4). The effect of the application of Regalia ® Maxx may be because the components of this extract can stimulate the synthesis of phytoalexins and C-glycosdsil (cucumarin) which accumulate in the penetration site of the fungus, in addition to promoting the lignification of the cell wall and an increase in the activity of the enzymes chitinases, peroxydases and -1,3 glucanasas, which affect the colonization and survival of the pathogen (Fofana et al., 2005) Similarly, Margaritopoulou et al. (2020) reported that the extract of Reynoutria sachalinensis causes defenses in the plants, especially as consequence of the induction of the salicylic acid path. Su et al. (2012) mention that the extract of R. sachalinensis can induce resistance in the plants through induction of phytoalexins and production of phenolic compounds, an increase in the production of proteins related to the defense, and accumulation of species that are reactive to oxygen, lignification, and formation of papillas on the cell walls. ...
Objective: The objective of the research was to evaluate in in vitro, greenhouse and field conditions, the effectiveness of biological, botanical and chemical pesticides for the control of Macrophomina pseudophaseolina.
Design/methodology/approach: In vitro, greenhouse and field experiments were carried out to evaluate the control effect of different pesticides for the control of M. pseudophaseolina.
Results: It was determined that all the evaluated strains of Trichoderma spp. they had a fungistatic effect against M. pseudophaseolina, and T. reesei showed the greatest antagonism and antibiosis against M. pseudophaseolina.
High, medium and low doses of NeemAcar® and high and medium doses of Regalia® Maxx inhibited 100% the growth of M. pseudophaseolina mycelium. In the greenhouse, the lowest percentage of severity was obtained
in the treatment with Regalia® Maxx, T. reesei. In the field, the lowest severity was determined with the application of NeemAcar® CE, Headline®.
Limitations on study/implications: Our results are essential for the management
of this disease by producers.
Findings/conclusions: The implementation of the use of Trichoderma spp.,
botanical pesticides and chemical insecticides is recommended for the control
of M. pseudophaseolina.
... The active ingredients in Milstop ® (potassium bicarbonate), Cyclone ® (citric and lactic acid) and Suffoil-X ® (mineral oil) are all considered to be 'physical' in their mode of action, altering leaf surface pH and osmotic pressure or desiccating/coating mycelium and spores [6]. The active ingredient in Regalia Maxx ® is an extract from the giant knotweed Reynoutria sachalinensis and was shown to be effective against pathogens such as B. cinerea and powdery mildew on cannabis as well as on various other crops [63][64][65][66]. This product enhances plant defense responses through the salicylic acid (SA)-dependent pathway by inducing the accumulation of plant defence chemicals such as hydrogen peroxide and formation of mechanical plant defences such as callose papillae [66,67]. ...
... The active ingredient in Regalia Maxx ® is an extract from the giant knotweed Reynoutria sachalinensis and was shown to be effective against pathogens such as B. cinerea and powdery mildew on cannabis as well as on various other crops [63][64][65][66]. This product enhances plant defense responses through the salicylic acid (SA)-dependent pathway by inducing the accumulation of plant defence chemicals such as hydrogen peroxide and formation of mechanical plant defences such as callose papillae [66,67]. Additional research is needed to explore the breadth to which Regalia Maxx ® can control other pathogens and the duration of the protection offered following application. ...
... The potential for inducing plant defense responses before pathogen infection has not yet been developed to a practical level for cannabis. However, as discussed earlier, Regalia Maxx (Reynoutria sachalinensis) when applied to cannabis plants can reduce pathogens such as Botrytis cinerea and powdery mildew, confirming reports in the literature of the efficacy through presumed induction of defence responses and pathogen reduction [63][64][65][66][67]. Weekly applications are recommended to ensure on-going protection on cannabis plants. ...
The increased cultivation of high THC-containing Cannabis sativa L. (cannabis), particularly in greenhouses, has resulted in a greater incidence of diseases and molds that can negatively affect the growth and quality of the crop. Among them, the most important diseases are root rots (Fusarium and Pythium spp.), Botrytis bud rot (Botrytis cinerea), powdery mildew (Golovinomyces ambrosiae), cannabis stunt disease (caused by Hop latent viroid), and a range of microbes that reduce post-harvest quality. An integrated management approach to reduce the impact of these diseases/microbes requires combining different approaches that target the reproduction, spread and survival of the associated pathogens, many of which can occur on the same plant simultaneously. These approaches will be discussed in the context of developing an integrated plan to manage the important pathogens of greenhouse-grown cannabis at different stages of plant development. These stages include maintenance of stock plants, propagation through cuttings, vegetative growth of plants, and flowering. The cultivation of cannabis genotypes with tolerance or resistance to various pathogens is a very important approach, followed by the maintenance of pathogen-free stock plants. When combined with cultural approaches (sanitation, management of irrigation, and monitoring for diseases) and environmental approaches (greenhouse climate modification), a significant reduction in pathogen development and spread can be achieved. The use of preventive applications of microbial biological control agents and reduced risk biorational products can also reduce disease development at all stages of production in jurisdictions where they are registered for use. The combined use of promising strategies for integrated disease management on cannabis plants during greenhouse production will be reviewed. Future areas for research are identified.
... Cell wall extract from the mushroom Pleurotus 7 ostreatus enhanced defence against Septoria and mildew in wheat and grapevine, respectively [75,76]. Similarly, extracts of giant knotweed (Reynoutria sachalinensis) improved the resistance of courgette to Podosphaera xanthii in an SA-dependent manner [77]. Extracts from the seaweeds Ascophyllum nodosum, Cystoseira myriophylloides, Laminaria digitata, and Fucus spiralis represent a significant portion of plant-based elicitors [78,79]. ...
Fungal pathogens pose a major threat to food production worldwide. Traditionally, chemical fungicides have been the primary means of controlling these pathogens, but many of these fungicides have recently come under increased scrutiny due to their negative effects on the health of humans, animals, and the environment. However, the use of fungicides with less of an environmental impact tends to result in the development of resistance in populations of phytopathogenic fungi. Therefore, new environmentally friendly alternatives that provide adequate levels of disease control are needed to replace chemical fungicides—if not completely, at least partially. A number of alternatives to conventional chemical fungicides have been developed, including plant defence elicitors (PDEs), biological control agents (fungi, bacteria and mycoviruses), biofungicides, RNA interference (RNAi) methods, and resistance breeding. This article reviews the conventional and alternative methods available to manage fungal pathogens, discusses their strengths and weaknesses, and identifies potential areas for future research.
... This is consistent with what was mentioned by Salam et al. [24], who showed that plant extracts have several mechanisms in inhibiting fungi, including physical inhibition through the occurrence of an adsorption process for the plant extract molecules on the surface of spores and mycelium and thus impede the reproduction process or by mechanical inhibition, where it was found that after drying the plant extract on the surface of the leaves, it forms a solid membrane around the spores and sclerotia, which leads to the prevention of their germination, and that all these activities of the plant extract positively affected the resistance of the plant against the fungus, and this is consistent with a number of researchers who used plant extracts to control fungal diseases. Margaritopoulou et al. [25] reported that the extract of Reynoutria sachalinensis proved to be effective in controlling powdery mildew on zucchin, and it significantly reduced conidia germination. Billet et al. [26] also found that stilbenoid-rich grape cane extract (GCE) was effective against downy mildew on Grape P. viticola reduced infection by 35%, and the alcoholic extract of aloe vera leaves was effective in inhibiting M. phaseolina by 96.36% [27]. ...
A field experiment was carried out to test the efficiency of potassium silicate and wild eggplant Solanum eleaegnifolium normal and nano for the management of downy mildew disease on cucumber caused by Pseudoperonospora cubensis under greenhouse conditions by reducing the incidence and severity of the disease and its reflection on the efficiency of the control and the area under the disease progress curve AUDPC compared to the fungicide Energy Previcur (Hcl - Propamocarb and Fosetyl-aluminum). The results of phenotypic and molecular diagnosis using polymerase chain reaction (PCR) technology for the two tested isolates showed that they are Pseudoperonospora cubensis . The nucleotide sequences were deposited in the gene bank under accession numbers ON509850 and ON509851. The results of the field trial indicated that the normal potassium silica at a concentration of 2.5 ml L ⁻¹ prevented the disease completely, with a severity rate and infection rate of 0.00%, it gave the highest reduction recorded with significant differences from the control treatment infected with artificial infestation 45.90% and 24.27%, respectively. They are followed by the normal and nano fungicide treatments. With regard to the effect of different treatments on the percentage of control, the results showed that the highest control percentage was recorded in the treatment of normal potassium silicates (100%), followed by the treatment of nano silicates (65.88%). Whereas, treatments of alcoholic and nano eggplant wild extract gave 51.64% and 50.50%, respectively, and 63.04 % and 63.09 % for the normal and nano fungicides, respectively.
... The finding of higher levels of CRF infestation in cabbage and Sclerotinia disease incidence in lettuce in mineral NPK compared with FYM-fertilized crops is consistent with previous studies which reported that high mineral N fertilizer inputs result in higher disease severity and/or an inhibition of plant resistance responses to biotrophic diseases/pests [8][9][10]27,60]. ...
... However, the finding that the use of NPK as fertilizer resulted in (i) higher N concentrations in potato tubers and cabbage and lettuce heads, but (ii) lower phenolic concentrations in potato, cabbage and lettuce, (iii) lower glucosinolate concentrations in cabbage, (iv) lower vitamin C concentrations in potato and cabbage, and (v) lower vitamin B 9 concentrations in potato and lettuce, was not surprising, since there has been mounting evidence that high mineral N-fertilizer inputs result in a down-regulation of the synthesis of certain secondary metabolites in plants and especially phytochemicals (e.g., phenolics) that are part of constitutive and inducible resistance responses to biotic or abiotic stress factors [8][9][10]60,66]. The finding that glucosinolate concentrations were significantly lower in cabbages grown after spring beans compared with winter barley also supports the conclusion that high N-availability was the main driver for lower phytochemical phenolic concentrations. ...
Background: There is increasing evidence that the reliance on synthetic chemical pesticides and mineral fertilizers in agriculture has significant negative environmental and/or health impacts and poses a risk for future food security. Systematic reviews/meta-analyses showed that organic production systems, which omit the use of agrochemicals, produce crops with lower yields, but superior nutritional composition. However, the agronomic parameters responsible for differences in crop yields and nutritional quality are poorly understood. Methods: Here we report results for four field vegetable crops from the Nafferton Factorial Systems Comparison (NFSC) trial. This long-term factorial field experiment was designed to (i) identify effects of growing season/climatic variation, and contrasting rotational designs, crop protection protocols and fertilization regimes used in organic and conventional systems on crop health, yield and nutritional parameters and (ii) estimate the relative importance of climatic and agronomic drivers for crop health, yield and nutritionally relevant quality parameters. Quality parameters monitored in harvested products, included phenolic, glucosinolate, vitamin C, vitamin B9, carotenoid, cadmium (Cd), nickel (Ni), lead (Pb) and glycoalkaloid concentrations. Results: Climatic conditions during the growing season were found to have a larger impact on crop yield and quality than the agronomic factors (pre-crop, crop protection, fertilization) studied. However, the (i) interactions between growing season with contrasting climatic conditions and agronomic factors identified by ANOVA for crop health, yield and quality parameters and (ii) the associations between the three climatic drivers (precipitation, temperature, radiation) and crop yield and quality parameters differed substantially between the four crop plant species. Among the agronomic factors, fertilization had a substantially larger impact compared with both pre-crop and crop protection. Specifically, crop yields were found to be significantly increased by the use of (i) conventional fertilization and crop protection methods in potato, (ii) conventional fertilization, but organic crop protection methods in cabbage, and (iii) conventional fertilization regimes in lettuce, while none of the agronomic factors had a significant effect on onion yields. When important crop pest and diseases were assessed, (i) conventional crop protection resulted in significantly lower late blight severity in potato, while (ii) organic crop protection resulted in lower bird damage and cabbage root fly (CRF) incidence in cabbages, and Sclerotinia incidence in lettuce and (iii) organic fertilization resulted in lower CRF and Sclerotinia incidence in cabbage and lettuce respectively. When concentrations of nutritionally relevant phytochemicals were compared, organic fertilization resulted in significantly higher phenolic concentrations in potato, cabbage and lettuce, higher glucosinolate and carotenoid concentrations in cabbage, higher vitamin C concentrations in potato and cabbage and higher vitamin B9 concentrations in potato and lettuce—but lower concentrations of toxic glycoalkaloids in potato. Significant effects of crop protection protocols on phytochemical concentrations were only detected in cabbage with conventional crop protection resulting in higher glucosinolate and vitamin B9 concentrations. When toxic metal concentrations were compared, organic fertilization resulted in significantly lower Cd concentrations in all four crops and lower Ni concentrations in potato, cabbage and onion. Significant effects of crop protection were only detected in cabbage, where organic crop protection resulted in lower Ni concentrations. Pb concentrations were not affected by any of the agronomic factors. The potential implications of results for improving (i) strategies to reduce the use of non-renewable resources and environmental impacts of vegetable production and (ii) the productivity of organic and other low-input vegetable production systems without compromising food quality are discussed. Conclusions: The study confirms that organic vegetable production protocols result in higher concentrations of phenolics and other nutritionally desirable phytochemicals, but lower concentrations of the toxic metals Cd and Ni in harvested products. It also demonstrates, for the first time, that this is primarily due to differences in fertilization regimes. The finding that in three of the four crops (cabbage, lettuce and onion) the application of synthetic chemical crop protection products had no measurable positive impact on crop health and yield should be considered in the context of the growing concern about health impacts of pesticide use in field vegetable crops.
... In this context, tea tree oil has been reported to exhibit antifungal and antibacterial properties, inhibiting powdery mildew of barley (Terzi et al., 2007). Also, a salicylic acid (SA) analog or ethanolic extracts of Giant Knotweed can induce resistance in a wide range of hosts (Ramasamy et al., 2015;Margaritopoulou et al., 2020). However, there is a lack of EOproducts against plant pathogenic bacteria and bacterial diseases. ...
... However, our findings agree with the fact that many EOs are involved in host defense mechanisms against plant pathogens, resulting in reduction of disease development (Batish et al., 2008). For example, the foliar application of ethanolic extracts from Giant knotweed induced SA-dependent defense responses in cucumber plants, and reduce powdery mildew severity (Margaritopoulou et al., 2020). Likewise, lavender EO induced overexpression of genes related to SA and ethylene/jasmonic acid pathways in sorghum plants (Rashad et al., 2022). ...
The activity of Eucalyptus essential oil against eleven strains pertaining to six species of plant pathogenic bacteria was studied using growth inhibition and contact assays. All strains were susceptible to the formulation EGL2, and Xylella fastidiosa subspecies and Xanthomonas fragariae were the most sensitive. The bactericidal effect was strong causing 4.5 to 6.0 log reductions in survival in 30 min at concentrations in the range of 0.75 to 15.0 μl/ml depending on the bacteria tested. Transmission electron microscopy of the formulation EGL2 against the three X. fastidiosa subspecies studied allowed the observation of a strong lytic effect on bacterial cells. In addition, the preventive spray application of EGL2 to potted pear plants subsequently inoculated with Erwinia amylovora significantly decreased the severity of infections. Almond plants treated by endotherapy or soil drenching, and then inoculated with X. fastidiosa showed a significant decrease in disease severity as well as in the levels of the pathogen, depending on the strategy used (endotherapy/soil drenching, preventive/curative). The treatment by endotherapy in almond plants induced the expression of several genes involved in plant defense. It was concluded that the reduction of infections by the Eucalyptus oil treatments was due to the combination of its bactericidal and plant defense induction activities.
... There is mounting evidence that N availability not only affects plant growth and crop yield, but also the expression of resistance mechanisms and nutritional quality parameters in crops [1]. Specifically, phenolic compounds, which have anti-microbial activity, are a component of both constitutive and salicylic acid (SA)-inducible systemic resistance mechanisms in plants and it has been shown that increasing N availability to plants significantly reduces the concentrations of phenolic compounds and resistance against a range of biotrophic diseases in a dose-dependent manner [13][14][15][16][17]. Phenolics are also the main phytochemical group with antioxidant activity in crops whereby increased dietary intake of phenolics/antioxidants has been linked to human health benefits, including a reduced risk of cancer, type-2 diabetes and cardiovascular disease [1,18,19]. ...
Agronomic protocols (rotation, tillage, fertilization and crop protection) commonly used in organic and conventional crop production differ significantly and there is evidence that modern varieties developed for conventional high-input farming systems do not have the combination of traits required for optimum performance in organic farming systems. Specifically, there is evidence that prohibition on the use of water-soluble, mineral N, P and K fertilizers and synthetic pesticide inputs in organic farming results in a need to revise both breeding and selection protocols. For organic production systems, the focus needs to be on the following: (i) traits prioritized by organic farmers such as high nutrient use efficiency from organic fertilizer inputs, competitiveness against weeds, and pest and disease resistance, (ii) processing quality parameters defined by millers and bakers and (iii) nutritional quality parameters demanded by organic consumers. In this article, we review evidence from variety trials and factorial field experiments that (i) studied to what extent there is a need for organic farming focused breeding programs, (ii) investigated which traits/trait combinations should be targeted in these breeding programs and/or (iii) compared the performance of modern varieties developed for the conventional sector with traditional/older varieties favored by organic farmers and/or new varieties developed in organic farming focused breeding programs. Our review focuses on wheat because there have been organic and/or low-input farming focused wheat breeding programs for more than 20 years in Europe, which has allowed the performance of varieties/genotypes from organic/low-input and conventional farming focused breeding programs to be compared.
... The extract of Reynoutria sachalinensis (a Polygonaceae) was observed to be efficient against such diseases as powdery mildew. It was found that the effect of this extract was linked with the SA signaling pathway [99]. Crushed fenugreek seeds (Trigonella foenum-graecum) were found to be effective against powdery mildew in grapevine and melon, but it was demonstrated that they induce the release of p20 caspase-1 fragment, suggesting the involvement of the NLRP3 inflammasome [100]. ...
Systemic acquired resistance is a powerful mechanism, based on the salicylic acid (SA) signaling pathway, which allows plants to resist to a wide range of pathogens. High SA, moreover, plays a key role in plant tolerance to abiotic stress. It seems, therefore, desirable to supply analogs of SA or stimulate the production of endogenous SA. Unfortunately, the chemical substances or physical means used for this effect often display a variable efficacy. After providing a review of them, we defend three major ideas: (i) plant resistance inducers (PRIs) must be combined for higher efficacy, notably for exploiting synergic effects between the SA and other signaling pathways, (ii) disease pressure can be reduced by exploiting the fungicidal properties displayed by some PRIs, (iii) biostimulants and crop management techniques should be used to ensure that plants have the resources they need to synthesize the compounds and structures required for efficient and lasting resistance. Some PRIs could also be used for their biostimulant effects in stress conditions. It could be concluded that holistic approaches which jointly address the issues of defense and tolerance stimulation, disease pressure and resource availability in plants are the ones that will allow for substantial reduction in fungicide use without sacrificing crop performance.
... Besides, Pasini et al. (1997) reported that potassium salts of fatty acid fungicides may exhibit a phytotoxicity on some crops, but no phytotoxicity was observed for the fungicide on hemp in this study. R. sachalinensis and potassium silicate fungicides have exhibited efficacy against different types of powdery mildew on various crops in multiple studies (Dallagnol et al. 2012;Ghanmi et al. 2004;Kanto et al. 2007;Kim et al. 2002;Margaritopoulou et al. 2020;Menzies et al. 1991;Scott and Punja 2021;Shetty et al. 2012). Our findings further support these initial reports. ...
Powdery mildew is a common disease of hemp in greenhouses in Tennessee. Fungicide efficacy data can support the use or approval of new fungicides. Therefore, two greenhouse experiments were conducted to assess the efficacy of nine commercial fungicides against powdery mildew. 'BaOx2' or 'Sweetened' hemp cultivars, which are susceptible to powdery mildew, were inoculated with a conidial suspension one day before or one or seven days after the first fungicide application. Two additional fungicide applications were made at 7-day intervals by thoroughly spraying the plants using a hand-held sprayer. Control plants were sprayed with water only. Weekly disease incidence and severity ratings were done three times. Disease index (DI) and the Area Under the Disease Progress Curve were calculated. All the fungicides significantly reduced powdery mildew symptoms. Compared to the control plants, disease reductions ranged from 76% to 100%. Bonide sulfur, Luna Experience, and MilStop exhibited "excellent" efficacy, reducing disease by 96% to 100%. Cinnerate, Exile, Regalia, and Sil-Matrix exhibited "very good" efficacy, reducing disease by 86% to 95%. Defguard and Stargus exhibited "good" efficacy, reducing disease by 76% to 85%. Koch's postulates were performed with the PM isolate used in this study. The isolate recovered following inoculation was found to be identical to the original isolate used in the experiments. The isolate was identified as Golovinomyces ambrosiae based on ITS, IGS, and β-tubulin sequencing and phylogenetic analysis with nucleotide sequences from closely related species. These findings provide useful information for the control of hemp powdery mildew and further research.
... The initial foliar spraying with the bioagent was performed 30 d after planting, and spraying was performed every 15 d in the early morning. All groups of plants were artificially inoculated with an aqueous conidial suspension of P. xanthii 24 h after the first treatment (freshly collected P. xanthii conidia were suspended in deionized water to a concentration of 10 5 conidia mL −1 water),), as described in [23]. All other horticultural practices were performed as recommended for summer squash. ...
... We further studied the responses of squash plants to the treatments by determining the level of plant hormones in the leaves. SA is a plant hormone that plays a pivotal role in plant defense against biotrophic and semi-biotrophic pathogens [23]. When comparing treated and non-treated plants under natural infection with powdery mildew, lower amounts of JA and SA were observed in the water-treated control. ...
Squash (Cucurbita pepo L.) is a globally important vegetable, the production of which is severely constrained by powdery mildew caused by Podosphaera xanthii. In this study, we examined the effects of Trichoderma asperellum (MW965676), Streptomyces rochei (MN700192), and a mixture of the two foliar sprays with or without shikimic acid seed priming treatment on powdery mildew severity, plant growth, and total yield during the 2020–2021 and 2021–2022 growing seasons. We also studied their immune eliciting properties by examining their enzymatic, phenolic, and hormonal functions. The combination of Trichoderma asperellum, Streptomyces rochei, and shikimic acid triggered plant defense responses, which elicited enzyme activities such as peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), phenolic compound accumulation, and increased salicylic acid (SA) and jasmonic acid (JA) content. This approach yielded high-quality results in the control of powdery mildew during the two growing seasons under greenhouse conditions. Additionally, relatively large statistical differences in plant growth, total yield, mineral components, and physiological traits were observed. A GC–MS analysis of Trichoderma asperellum (MW965676) showed hemin cation as a major component, while Streptomyces rochei (MN700192) contained 2,4-di-tert-butyl phenol and the hexadecenoic acid methyl ester. With respect to the morphological changes induced by powdery mildew and the treatments, plants treated with a mixture of Trichoderma asperellum, Streptomyces rochei and shikimic acid showed an improvement in the thickness of the midvein, increased dimensions of the main midvein bundle, a larger number of xylem rows in the main midvein bundle, greater mean diameters of vessels and of parenchyma cells in the ground tissues, as well as increased thickness of the upper and lower epidermis, lamina, palisade tissue and spongy tissue. This extensive, new study is the first step toward a more profound understanding of the use of Trichoderma asperellum and Streptomyces rochei with shikimic acid-primed seeds as a potential alternative technique for attenuating powdery mildew infection in squash.
