Abstract
The silicon (Si) percentage in the dry matter of plants is between 0.1% and 10%, and even though its role in the metabolism of plants is not absolutely clear, Si’s positive effects on plant nutrition and plant protection against both biotic and abiotic stress are well documented. However, Si is not considered to be an essential element, so it is not always present in nutrient solutions. In this paper, an experiment was carried out in the University of Almeria’s greenhouse with hydroponic lettuce, tomato, pepper, melon, and cucumber plants. A standard nutrient solution was used as a control sample and was fertigated with Si. During the four-true-leaf seedling stage, various plant growth parameters were measured, including the dry weight and the wet weight as well as the foliar surface and the cuticle thickness of both the leaf and the stem. Additionally, in the lettuce, tomato, and pepper plants, the effect of the use of Si in the nutrient solution on the protection against the pathogen Botrytis cinerea was determined by measuring the penetration of the pathogen through the cuticle and the extension of the fungal infection by using leaf discs. The results suggest that all of the studied parameters, and both the cuticle thickness and the epidermis thickness, were increased by more than 10% on average for all of the plants. In the lettuce, tomato, and pepper plants, a beneficial effect against B. cinerea was observed when the nutrient solution containing Si was used.
Silicon is the second-most abundant element in the earth’s crust, and the percentage of Si in the dry matter of plants is between 0.1% and 10%. This quantity is equivalent to those of other macronutrients such as calcium (Ca), magnesium, and phosphorus, and in some herbaceous plants, Si is present in levels as high as other inorganic constituents (Epstein, 1999; Rafi and Epstein, 1999). After studying the Si content in 500 plant species, Ma and Takahashi (2002) suggested a classification based on their Si contents and Si:Ca ratios (Table 1). However, this classification is complex. On the one hand, the groups are somewhat arbitrary, and the Si concentration may be better considered as a continuous spectrum (Cooke and Leishman, 2011). On the other hand, there are considerable differences among genotypes within the same species (Deren, 2001; Hodson et al., 2005; Ma and Takahashi, 2002). In addition, a given genotype of a plant growing under different Si concentrations can absorb different amounts of Si (Henriet et al., 2006; Ma and Takahashi, 2002). Thus, even though Si accumulation is a phylogenetic feature according to Guntzer et al. (2012), the availability of Si determines the amount of Si absorbed by plants.
Criteria to distinguish silicon (Si) accumulators from non-accumulators (Ma and Takahashi, 2002).
Generally, dicotyledons present low Si concentrations in tissues, on the order of 0.1% by dry weight (Jones and Handreck, 1967). However, plants belonging to the orders Cucurbitales and Urticales have intermediate contents (2% to 4%), and the species belonging to the Commelinaceae, Poaceae, Equisetaceae, and Cyperaceae families generally have high Si contents (>4%) (Hodson et al., 2005) with notable differences in concentration between them; dryland grasses (such as oats and rye) have ≈1% to 3% Si, and the “wetland” Gramineae (paddy-grown rice) and Cyperaceae have 10% to 15% or even higher levels of Si (Jones and Handreck, 1967).
Most Si present in the soil is in an insoluble form, so it is not available for plants (Takahashi and Hino, 1978). In soils, the prevailing form of Si is monosilicic acid, Si(OH)4, an unionized form, in solutions with pH values below 9 (Fig. 1). On average, the Si concentration in soils is 14 to 20 mg Si/L (ranging between 3.5 and 40 mg) with a tendency to decrease at high pH values (7) when large amounts of sesquioxides are present in soils and anion adsorption is prevalent (Jones and Handreck, 1965).
Silicon (Si) forms for different concentrations and pH values (Marschner, 2012).
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Silicon (Si) forms for different concentrations and pH values (Marschner, 2012).
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Silicon (Si) forms for different concentrations and pH values (Marschner, 2012).
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Plants absorb Si by their roots in the form of monosilicic acid [nSi(OH)4], which is transported through the plant via the xylem (Epstein, 1999), condenses into solid silica (Prychid et al., 2003), and is deposited as amorphous silica, SiO2·nH2O, [referred to as opal, silica gel, or phytoliths in higher plants (Richmond and Sussman, 2003)] mainly in the epidermis and in the sheath cells of vascular bundles. Solid silica is deposited in cell walls, cell lumens, the intercellular matrix (Prychid et al., 2003), and a layer under the wax cuticle (Kim et al., 2002; Yoshida, 1981). The silica in silica cells is deposited after the protoplast is degraded, and silica is deposited to a higher degree in wounded cells and in older cells (Blackman and Parry, 1968). Silicon also can be found in the forms of monosilicic acid, colloidal silicic acid, or organosilicon compounds in plant tissues (Datnoff and Rodrigues, 2005).
Recent studies have yielded a better understanding of the transport, structure, and function of Si in higher plants (Bauer et al., 2011; Ma et al., 2011); the role it plays against a wide range of biotic and abiotic stress (Balakhnina and Borkowska, 2013; Van-Bockhaven et al., 2013); and the ecological importance of the biomineralization of Si by plants (He et al., 2014) and its possible applications in modern agriculture (Haynes, 2014). Although the beneficial effects of Si absorption are different between species and, in general, can only be observed under conditions of biotic or abiotic stress, it is difficult to develop an integral understanding of the biological function of Si and its role in the plants’ health.
Researching the possible nutritional role of Si has proven to be challenging due to its various beneficial effects on monocotyledons and dicotyledons as well as the subsequent problems that arise in studies focused solely on one genetic model (Richmond and Sussman, 2003). Although there are apparent differences between the beneficial effects caused by Si in high-accumulator and nonaccumulator plants, published enzymatic assays and elemental analysis results show that both groups responded to supplemental Si (Frantz et al., 2011). In addition, these beneficial effects manifest at multiple levels, ranging from physiological changes to altered gene expression (Khandekar and Leisner, 2011; Li et al., 2008), at least in the response of plants to copper toxicity.
Consequently, the beneficial effects of Si fertilization have the potential to mitigate the depletion of soil nutrients (Guntzer et al., 2012), so Si fertilization is an alternative to the extensive use of N–P–K fertilizers that could potentially increase plants’ resistance to diseases, pathogens, (Gurr and Kvedaras, 2010; Van-Bockhaven et al., 2013), viruses (Zellner et al., 2011), salinity, and hydric stress (Stamatakis et al., 2003; Zhu and Gong, 2014); increase their tolerance to heavy metals (Li et al., 2008; Neumann and Zur Nieden, 2001); and improve the quality and efficiency of plants (Korndorfer and Lepsch, 2001; Toresano-Sánchez et al., 2010 and 2012). Additionally, excess Si does not damage plants (Ma et al., 2001) and is an essential nutrient of great importance for human biology. Furthermore, it has been observed that Si is necessary for bones, cartilages, and connective tissues (Bissé et al., 2005).
Guntzer (2010) concluded that Si fertilization is a sustainable alternative to the intensive use of fertilizers and pesticides.
Recent studies have discussed the possibility of including Si as one of the macronutrients necessary for the nutrition of higher plants (Frantz et al., 2011; Kernan and Marx, 2000). Currently, Si is considered to be a beneficial rather than an essential nutrient for plants, and the effects of Si fertigation have frequently been demonstrated in Si-accumulator crops such as rice and sugarcane (Haynes, 2014). Silicon is not considered to be an essential element according to the classic criteria of Arnon and Stout (1939) because many plants can complete their cycles without it (Marschner, 2012), but some authors disagree with this assertion because it is very difficult to eliminate Si from the environment (Epstein, 1999). Silicon has been called “quasi-essential” or “semi-essential” by certain authors (Epstein, 1999; Ma et al., 2007; Rafi et al., 1997; Savvas et al., 2009) as well as a “nonessential beneficial plant nutrient” (Richmond and Sussman, 2003). It is not normally included in the basic composition of standard nutrient solutions (Arnon and Hoagland, 1940; Cooper, 1996; Hewit, 1966), although some authors, including Sonneveld and Straver (1994), consider it a part of the basic nutrient solutions used for cucumber, melon, and lettuce plants, especially in soilless culture.
The aim of this study is to assess the effect of adding Si to the nutrient solution used for fertigating the seedlings of five vegetable species, in three different families (Solanaceae, Cucurbitaceae, and Asteraceae) with different capacities to accumulate Si, and to investigate their vegetative growth, cuticle development, and resistance to the illness caused by B. cinerea.
Materials and Methods
Plant growth conditions and treatments.
Seeds of five horticultural species were sown on 21 Mar. 2014. The plants were grown in a greenhouse at Universidad de Almería (Spain). The temperature in the greenhouse ranged from 15–22 °C (nighttime low) to 20–32 °C (daytime high), and there was no supplemental light. The seeds were sown in polystyrene trays, and the planting density was 900 plants per m2. Subsequently, when the plants developed three true leaves, they were transplanted to 500-mL pots containing coconut fibers as a substrate as reported by Morales and Urrestarazu (2013) and Pozo et al. (2014). The plants used in the assays to determine the resistance to the illness caused by B. cinerea were lettuce, tomato, and pepper. Additionally, two Cucurbitaceae (melon and cucumber) were included in these assays to study the effect of Si on the growth of the seedlings. More details about the experiment and the plants are presented in Table 2. The plants were fertigated once every day with a standard nutrient solution (−Si) similar to that used by Sonneveld and Straver (1994), as shown in Table 3. Half of the plants of each species were additionally fertigated with a 0.65 mm Si solution (+Si). This solution was prepared with Tecnosilix® mg SL, a product supplied by Enlasa Ltd. The solution was added when the plants developed two true leaves. For the experiment, the plants were divided into four groups according to a randomized complete block design (Little and Hill, 1978; Petersen, 1994). A total of 34 replicates were used for each solution and crop: 10 plants were used for the agronomic assessment, 4 were used for measuring the cuticle thickness in stems and leaves, and 20 plants corresponding to the three vegetable species were classified as low-accumulating plants.
Dates when the experiments were conducted.
Nutrient solution used in the experiment.
Growth parameters.
Vegetative growth was measured 40 d after sowing. The plant height, number of leaves, stem diameter, and root length, as well as the wet weight of the roots, stems, and leaves, were determined. The samples were kept for 72 h in a forced air laboratory oven at 85 °C to obtain the dry weight of the roots, stems, and leaves.
Cuticle thickness.
Plants with four true leaves were used to measure the cuticle in the leaves and the stems. To measure the cuticle in the stem, cuts were performed below the cotyledons and in the middle part of the third fully developed leaf. The staining was carried out with safranin, and the cuts were performed with a microtome. A microscope was used to measure the cuticle (Fig. 2). Each leaf and stem was measured in every replicate and plant in three different spots, and the measurements were averaged.
Methodology used for measuring the cuticle in detail: (A and B) cucumber plant leaves, (C and D) tomato plant stems.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Methodology used for measuring the cuticle in detail: (A and B) cucumber plant leaves, (C and D) tomato plant stems.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Methodology used for measuring the cuticle in detail: (A and B) cucumber plant leaves, (C and D) tomato plant stems.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Procedure for inoculating B. cinerea.
The isolate of B. cinerea used in all of the experiments was obtained from an infected sweet pepper (Capsicum annuum L.) plant in a commercial greenhouse in Almeria. The isolate was grown on potato dextrose agar (PDA) and stored on 9-cm-diameter petri plates at 7 °C. Mycelial plugs from storage were used to start the cultures needed to conduct the experiments. To prepare the inoculum, spores were harvested from 3- to 4-week-old B. cinerea cultures grown on PDA in 9-cm-diameter petri plates and incubated at 22 °C with 12 h of light and 12 h of darkness. Sterile distilled water was added to each culture plate, and the spores were dislodged with a rubber policeman. The spore concentration was determined with a hemacytometer and adjusted to 106 spores/mL.
Leaves were harvested randomly from the top one-third of the plants at the first flowering growth stage. Immediately after the harvest, the leaves were transported to the laboratory in a clear plastic bag, and experiments were performed on the same day. The surfaces of the leaves were sterilized by immersion in a 10% solution of commercial bleach (35 g·L−1 sodium hypochlorite) for 5 min in the laboratory. The leaves were then rinsed in sterile distilled water and blotted dry in a laminar flow hood. A 10-mm-diameter tissue disc was cut from the internerve space of each leaf with a cork borer. The leaf discs were enclosed in 9-cm-diameter petri plates with three layers of sterilized filter paper and 3 mL of distilled water to maintain 100% relative humidity. Four leaf discs were put into each petri plate. The distance between leaf tissue discs was ≈1 cm. Half of the petri plates from each treatment were inoculated by dropping 20 μL of B. cinerea spore suspension (1.56 × 106 spores/mL) over the leaf disc center with a micropipette. As a result, we had four different treatments for each species: plants fertigated with Si and inoculated with B. cinerea (+Si +Bot.), a control sample without fertigation and inoculated with B. cinerea (−Si +Bot.), a control sample fertigated with Si and not inoculated (+Si −Bot.), and a control sample without Si or inoculation (−Si −Bot.). The inoculation was carried out according to the “leaf-disc assay–spore drop inoculation method” described by Wegulo and Vilchez (2007) with some modifications (no damage on the surfaces of the leaf discs).
The petri plates were kept in darkness for 12 h at 16–22 °C before incubation. The petri plates containing the leaf discs were arranged in a randomized complete block design, and five replicates were used. Each petri plate contained four leaf discs. The plates were kept at 16–22 °C in 12-h alternating periods of light and darkness. The necrotic area percentage was estimated 3, 7, and 14 d after the inoculation.
The WinDIAS 3 image analysis system (2009) was used to determine two different parameters: the area of fungal penetration and the severity. The area of fungal penetration (Fig. 3A-1) was directly measured by the program, and the severity was calculated from the percentage of necrotic area on leaf discs, including in this necrotic tissue the area of fungal penetration, shown by 1 in Fig. 3A and 3 in Fig. 3D and E.
Details of the methodology used for determining the extent of the damage caused by the penetration of the pathogen. (A) Leaf discs from pepper plants subjected to the four different treatments 3 d after inoculation (DAI); 1) with silicon (Si) and Botrytis cinerea inoculum (+Si +Bot.); 2) without Si and with B. cinerea inoculum (−Si +Bot.); 3) without Si and with distilled water without B. cinerea inoculum (−Si −Bot.); and 4) with Si and with distilled water without B. cinerea inoculum (+Si −Bot.). (B) Details of discs 1) and 2) that show (d) the surface on which the drop of water containing the corresponding solution was located. (C) Images from discs 1) and 2) after being processed by the image analysis software for plant diseases, WinDIAS 3; the blue area corresponds to the healthy parts of the leaf, and the red area corresponds to the part affected by the pathogen. (D) Disc leaf from a lettuce plant corresponding to the nutrient solution −Si +Bot. for 3, 7, and 14 DAI. (E) Image d after being processed by the WinDIAS 3 software: 1) area of pathogen penetration, 2) tissue unaffected, and 3) necrotic tissue; (d) approximate area and initial location of the drop containing the inoculum.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Details of the methodology used for determining the extent of the damage caused by the penetration of the pathogen. (A) Leaf discs from pepper plants subjected to the four different treatments 3 d after inoculation (DAI); 1) with silicon (Si) and Botrytis cinerea inoculum (+Si +Bot.); 2) without Si and with B. cinerea inoculum (−Si +Bot.); 3) without Si and with distilled water without B. cinerea inoculum (−Si −Bot.); and 4) with Si and with distilled water without B. cinerea inoculum (+Si −Bot.). (B) Details of discs 1) and 2) that show (d) the surface on which the drop of water containing the corresponding solution was located. (C) Images from discs 1) and 2) after being processed by the image analysis software for plant diseases, WinDIAS 3; the blue area corresponds to the healthy parts of the leaf, and the red area corresponds to the part affected by the pathogen. (D) Disc leaf from a lettuce plant corresponding to the nutrient solution −Si +Bot. for 3, 7, and 14 DAI. (E) Image d after being processed by the WinDIAS 3 software: 1) area of pathogen penetration, 2) tissue unaffected, and 3) necrotic tissue; (d) approximate area and initial location of the drop containing the inoculum.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Details of the methodology used for determining the extent of the damage caused by the penetration of the pathogen. (A) Leaf discs from pepper plants subjected to the four different treatments 3 d after inoculation (DAI); 1) with silicon (Si) and Botrytis cinerea inoculum (+Si +Bot.); 2) without Si and with B. cinerea inoculum (−Si +Bot.); 3) without Si and with distilled water without B. cinerea inoculum (−Si −Bot.); and 4) with Si and with distilled water without B. cinerea inoculum (+Si −Bot.). (B) Details of discs 1) and 2) that show (d) the surface on which the drop of water containing the corresponding solution was located. (C) Images from discs 1) and 2) after being processed by the image analysis software for plant diseases, WinDIAS 3; the blue area corresponds to the healthy parts of the leaf, and the red area corresponds to the part affected by the pathogen. (D) Disc leaf from a lettuce plant corresponding to the nutrient solution −Si +Bot. for 3, 7, and 14 DAI. (E) Image d after being processed by the WinDIAS 3 software: 1) area of pathogen penetration, 2) tissue unaffected, and 3) necrotic tissue; (d) approximate area and initial location of the drop containing the inoculum.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
The percentage of necrotic tissue on the leaf discs was obtained by dividing the area of necrotic tissue by the total area of the leaf disc and multiplying the result by 100.
Statistical analysis.
The obtained data were subjected to analysis of variance, and the means were compared by the Tukey’s test. The confidence intervals considered were 95% and 99%, and the software packages used were Statgraphics Centurion® 16.1.15 and Microsoft Office 2010.
Results and Discussion
Vegetative development.
Table 4 shows some of the main plant growth parameters observed in the experiment. The inclusion of Si in the nutrient solution used for the tomato and pepper seedlings caused a positive effect on all of the vegetative growth parameters. In the case of lettuce, all of the parameters except the number of leaves increased with the addition of Si. The cucumber plants showed an increase in the height, root length, and foliar area. The melon plant was least affected by the addition of the nutrient solution containing Si, as only an increase in the stem diameter was observed.
Vegetative growth parameters for the plants with (+Si) and without (−Si) silicon (Si) in the nutrient solution.
The wet weights (Table 5) showed similar trends to the growth parameters, although the dry weights of the stems and roots were unaffected by the addition of Si in the lettuce and cucumber (Table 6). These results suggest that even though the standard nutrient solutions used for fertigating these vegetables generally do not include Si as a nutrient element to be assimilated (Arnon and Hoagland 1940; Cooper, 1996; Hewitt, 1966), Si is beneficial for the growth of lettuce and Cucurbitaceae such as melons and cucumber, in agreement with the results of Sonneveld and Straver (1994). Additionally, Si is not used in nutrient solutions for Solanaceae, such as tomatoes and peppers, but the results of this study point to the convenience of including Si in the nutrient solution.
Wet weight (g/plant) for the plants with (+Si) and without (−Si) silicon (Si) in the nutrient solution.
Dry weights (g/plant) for the plants with (+Si) and without (−Si) silicon (Si) in the nutrient solution.
In addition, Toresano-Sánchez et al. (2010) found that the use of Si in the nutrient solution has beneficial effects on tomato production. However, Toresano-Sánchez et al. (2012) did not find a clear correlation between melon production and the use of Si in the nutrient solution.
Cuticle thickness.
The cuticle thickness normally ranges between 0.25 and 2 µm (Esau, 1977; Holloway, 1982), and even higher values, between 0.5 and 15 µm, have also been observed (Tafolla-Arellano et al., 2013). In this study, the values obtained were 2.40 and 11.56 µm for the leaf and stem cuticle, respectively, in tomato plants (Table 7). In all of the plants studied, the values obtained for the stem cuticles were higher than those obtained for the leaf cuticles. All of the values fell within the expected intervals according to Tafolla-Arellano et al. (2013). A significant or highly significant increase in the cuticle thickness was observed in all of the plants as a result of using Si. The increases in cuticle thickness were 14%, 41%, and 58% in cucumber, melon, and lettuce leaves, respectively, whereas the cuticle thickness increased by 10%, 34%, and 55% in the stems of pepper, melon, and tomato plants, respectively.
Cuticle thickness (µm) in stem and leaves for the plants with (+Si) and without (−Si) silicon (Si) in the nutrient solution.
Resistance to fungal infection.
The area affected by the pathogen is shown in Fig. 4. This area was significantly smaller in the three plants 3 d after the inoculation and remained constant in the case of the lettuce plants.
Evolution of the area affected by the pathogen over time for each one of the four different treatments used (%). +Si +Bot., −Si +Bot., +Si −Bot., and −Si −Bot. refer to the nutrient solutions with silicon (Si) and with Botrytis cinerea inoculum, without Si and with B. cinerea inoculum, with Si and without B. cinerea inoculum, and without Si and without inoculum, respectively. The different letters indicate significant differences for P ≤ 0.05 at same time after inoculation.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Evolution of the area affected by the pathogen over time for each one of the four different treatments used (%). +Si +Bot., −Si +Bot., +Si −Bot., and −Si −Bot. refer to the nutrient solutions with silicon (Si) and with Botrytis cinerea inoculum, without Si and with B. cinerea inoculum, with Si and without B. cinerea inoculum, and without Si and without inoculum, respectively. The different letters indicate significant differences for P ≤ 0.05 at same time after inoculation.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Evolution of the area affected by the pathogen over time for each one of the four different treatments used (%). +Si +Bot., −Si +Bot., +Si −Bot., and −Si −Bot. refer to the nutrient solutions with silicon (Si) and with Botrytis cinerea inoculum, without Si and with B. cinerea inoculum, with Si and without B. cinerea inoculum, and without Si and without inoculum, respectively. The different letters indicate significant differences for P ≤ 0.05 at same time after inoculation.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
The beneficial effects of Si were clearly observed 3 d after the inoculation of the affected areas for the three assessed species.
The presence of a thicker cuticle in lettuce leaves (58%) is probably related to the better protection against B. cinerea due to the presence of Si, compared with cucumber plants (14%), in which the effects were less significant, or to tomato plants, in which no significant differences were observed in the leaf cuticle.
Similar results were obtained by Lee et al. (2004) for Phytophthora capsici infection in pepper plants. They concluded that the processes by which Si provides protection against P. capsici infections and disease development are not fully understood, but their results indicate the involvement of other mechanisms that form a physical barrier against fungal penetration.
The severity of the illness caused by B. cinerea is shown in Fig. 5. Seven days after the inoculation, the severity of the disease was reduced significantly in lettuce and pepper plants that had received a Si solution. However, 14 d after the inoculation, the tissue was fully infected, and no differences were observed.
Evolution of the severity of the disease over time on leaf discs expressed as the percentage of infected area. +Si +Bot., −Si +Bot., +Si −Bot., and −Si −Bot. refer to the nutrient solutions with silicon (Si) and with Botrytis cinerea inoculum, without Si and with B. cinerea inoculum, with Si and without B. cinerea inoculum, and without Si and without inoculum, respectively. The different letters indicate significant differences for P ≤ 0.05 at same time after inoculation.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Evolution of the severity of the disease over time on leaf discs expressed as the percentage of infected area. +Si +Bot., −Si +Bot., +Si −Bot., and −Si −Bot. refer to the nutrient solutions with silicon (Si) and with Botrytis cinerea inoculum, without Si and with B. cinerea inoculum, with Si and without B. cinerea inoculum, and without Si and without inoculum, respectively. The different letters indicate significant differences for P ≤ 0.05 at same time after inoculation.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
Evolution of the severity of the disease over time on leaf discs expressed as the percentage of infected area. +Si +Bot., −Si +Bot., +Si −Bot., and −Si −Bot. refer to the nutrient solutions with silicon (Si) and with Botrytis cinerea inoculum, without Si and with B. cinerea inoculum, with Si and without B. cinerea inoculum, and without Si and without inoculum, respectively. The different letters indicate significant differences for P ≤ 0.05 at same time after inoculation.
Citation: HortScience horts 50, 10; 10.21273/HORTSCI.50.10.1447
In the case of the lettuce and pepper plants, the progression of the disease caused by B. cinerea is slowed when a nutrient solution containing Si was used. However, no clear effects were observed in the tomato plants.
The results show that fertigating with Si can be beneficial due to its contribution to plant growth and the protection it provides against pathogens such as B. cinerea; this effect has also been suggested by other authors, such as Guntzer et al. (2012). In addition, the results obtained by French-Monar et al. (2010) show that administering Si to bell pepper roots can potentially reduce the severity of the disease caused by Phytophthora while enhancing plant growth.
Authors including Chitarra et al. (2013) reported that the use of Si in hydroponic lettuce plants significantly reduced the severity of the diseases caused by important soil-borne pathogens such as Fusarium oxysporum f. sp. lactucae, suggesting the possibility of using this element to improve the efficiency of soilless crops.
Conclusion
The results show an increase in vegetative growth greater than 10% in all of the plants and a significant increase in the thickness of the plant cuticles.
Additionally, in the case of lettuce plants, the increase in cuticle thickness caused by the use of Si in the nutrient solution provides protection against fungal penetration by B. cinerea through the cuticle and slows the progression of the disease inside the leaves of lettuce, tomato, and pepper plants.
It is recommended to use nutrient solutions with a Si concentration of at least 0.65 mm for all of the studied plants.
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