The experiment was conducted during two successive seasons 2016 and 2017 on sweet pepper plants to study the effect of foliar application of some natural extracts (fulvic acid at 2, 4 and 6% or algae at 1, 2 and 4 g.L-1) were applied three times along each season (after 2, 4 and 6 weeks of planting). The influence was evaluated through the response of vegetative growth, and some physical and chemical characteristics of sweet pepper fruits. The results obtained showed that the algae extract at 1 g.L-1 in most cases was better than the other spray treatments investigated to improve most fruit characteristics (length, diameter and yield of fruits), vegetative growth, and chemical properties followed by 6% fulvic acid. With regard to organic acids, malic and citric acids are the main organic acids found in sweet pepper. Malic, succinic and glutaric acids were higher in 1 g.L-1 algae extract treatment, but the concentration of citric acid was higher in 6% fulvic acid treatment. Therefore, algae extract and fulvic acid could be safely recommended as a natural biostimulants application for improving most desirable characteristics of sweet pepper grown under the same experimental condition.
Sweet pepper is one of the most important vegetable crops as well as important exportable crops in Egypt and it is considered an excellent source of bioactive nutrients. Vitamin C, carotenoids and phenolic compounds are the main antioxidant components (
Evaluation of the effect of foliar application of some natural extracts (fulvic acid and algae) on vegetative growth, and some fruit physical and chemical characteristics of sweet pepper.
The experiment was conducted during the two seasons 2016 and 2017 where the sweet pepper seeds (
Physical and chemical properties of experimental soil in 2016 and 2017 seasons.
Soil properties | Experimental year | |
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2016 | 2017 | |
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pH (1:1) | 7.32 | 7.31 |
EC (1:1) dS.m-1 | 2.2 | 1.8 |
Soluble anions (meq.L-1) | ||
CO3= | 1.5 | 1.3 |
HCO3- | 4.5 | 3.6 |
Cl- | 8.0 | 5.9 |
SO4= | 11.7 | 9.8 |
Soluble cations (meq.L-1) | ||
Ca++ | 10.5 | 9 |
Mg++ | 3.5 | 2 |
K+ | 0.50 | 0.4 |
Na+ | 11.2 | 9.2 |
Sand (%) | 57.3 | 58.4 |
Silt (%) | 21.2 | 18.2 |
Clay (%) | 21.5 | 23.4 |
Texture class | Sandy clay loam | Sandy clay loam |
The effect of the differential investigated spray treatments was evaluated through the response of the following measurements.
After 90 days from transplanting, four plants per replicate were randomly chosen to measure, plant height (cm), root length (cm) and branches/plant.
Mature pepper fruits were harvested manually at full colour stage. Fruit length, fruit diameter and fruit yield/plant (kg) were determined.
Chlorophyll a, chlorophyll b and carotenoids were determined in leaves (
Ascorbic acid was measured as described by (
Sample (0.5 g) from each treatment were homogenized in 100 mM pre-chilled sodium phosphate buffer (pH 7.0) containing 0.1 mM EDTA and 1% polyvinyl pyrrolidone (PVP) (w/v) at 4 ºC. The extraction ratio was 4.0 mL buffer for each one gram of sample. The homogenate was centrifuged at 15.000 x g for 15 min at 4 ºC. Supernatant was used to estimate the activities of peroxidase and polyphenol oxidase. Proteins content was determined in the enzymes extract (
Peroxidase was assayed following method the method of
Polyphenol oxidase was assayed following method the method of
The fruits of sweet pepper were freeze dried (Virtis model 10-324) and ground. The ground samples were extracted using ethanol 80% and used in chemical analyses. Phenolic content was determined (
Power reduction was determined by
Metal chelating activity was consequently evaluated by 0.1 mM FeSO4 (0.2 mL) and 0.25 mM ferrozine (0.4 mL) in 0.2 mL of samples (
Organic acids were separated by high performance liquid chromatography (HPLC) Knauer, Germany, flow rate was set at 0.6 mL.min-1, UV detector set at λ = 214 nm, column oven temperature kept constant at 65 °C. The column used was Rezex@ column for organic acids analysis, mobile phase was 0.005 M H2SO4, data integration by clarity-chrom software.
All the statistical analyses were performed using an ANOVA, and Duncan’s multiple range tests (
Table
Effect of fulvic acid and algae extracts spraying on growth parameters of sweet pepper plants during the first and second seasons.
Treatments | Plant height (cm ± |
Root length (cm ± |
Branches/plant ± |
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Fulvic acid | Cont (Zero) | 101.0±0.954 |
11.67±0.268 |
26.00±0.306 |
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2% | 105.0±0.814 |
18.47±0.277 |
30.33±0.493 |
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4% | 113.7±1.26 |
20.00±0.178 |
34.33±0.794 |
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6% | 124.7±0.252 |
22.07±0.378 |
38.00±0.517 |
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Algae extract | 1g.L-1 | 132.6±0.458 |
25.70±0.265 |
43.00±0.379 |
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2g.L-1 | 104.7±0.802 |
15.00±0.225 |
27.00±0.755 |
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4g.L-1 | 103.7±0.208 |
13.00±0.187 |
26.67±0.631 |
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Fulvic acid | Cont (Zero) | 102.0±2.08 |
11.67±0.764 |
25.33±1.02 |
|
2% | 107.3±1.80 |
18.67±0.697 |
29.67±0.862 |
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4% | 115.4±1.16 |
21.67±0.289 |
33.33±0.603 |
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6% | 126.5±1.89 |
22.70±0.289 |
36.67±0.751 |
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Algae extract | 1g.L-1 | 133.8±0.764 |
24.50±0.904 |
44.33±0.854 |
|
2g.L-1 | 106.7±0.289 |
16.00±0.297 |
28.67±0.802 |
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4g.L-1 | 104.7±0.812 |
14.33±0.404 |
26.67±1.01 |
Note: Values are mean of three replications ± standard deviation. Different letters indicate statistically significant differences at
Data presented in Table
Effect of fulvic acid and algae extracts spraying on physical characteristics of sweet pepper fruits during the first and second seasons.
Treatments | Fruit length (cm ± |
Fruit diameter (cm ± |
Fruit yield/plant (kg ± |
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Fulvic acid | Cont (Zero) | 9.00±0.577 |
8.83±0.305 |
0.8950±0.021 |
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2% | 10.17±0.631 |
9.83±0.681 |
1.700±0.011 |
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4% | 10.50±0.584 |
10.17±0.513 |
1.900±0.01 |
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6% | 11.67±0.543 |
11.00±0.608 |
2.183±0.013 |
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Algae extract | 1g.L-1 | 12.17±0.601 |
11.50±0.304 |
2.550±0.21 |
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2g.L-1 | 9.67±0.325 |
9.17±0.255 |
1.583±0.10 |
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4g.L-1 | 9.17±0.275 |
8.93±0.413 |
1.200±0.009 |
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Fulvic acid | Cont (Zero) | 8.37±0.231 |
8.00±0.152 |
0.8467±0.031 |
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2% | 10.33±0.0.312 |
9.50±0.254 |
1.500±0.044 |
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4% | 10.90±0.415 |
9.87±0.274 |
1.800±0.032 |
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6% | 11.50±0.502 |
10.67±0.159 |
2.000±0.0521 |
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Algae extract | 1g.L-1 | 11.67±0.344 |
11.00±0.312 |
2.467±0.0458 |
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2g.L-1 | 9.60±0.218 |
9.33±0.321 |
1.417±0.021 |
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4g.L-1 | 8.50±0.140 |
8.33±0.173 |
1.167±0.0252 |
Note: Values are mean of three replications ± standard deviation. Different letters indicate statistically significant differences at
The stimulatory effects of fulvic acid are directly related to increase uptake of nutrient such as nitrogen, phosphorus, potassium and micronutrients (
Therefore, their use on plants will improve the vegetative growth of plants in addition to the physical and chemical properties of fruits, which will be reflected in increased productivity. Fulvic acid and humic acid when used with a concentration of 40 mg.kg-1 increased flowering and growth parameters such as shoots number, plant diameter, flowers number and root length compared to control plants in impatiens walleriana (
Fulvic acids and algae extracts applications affected fruit chlorophyll content during both two seasons (Figure
Effect of fulvic acid and algae extracts spraying on chlorophyll content (mg.g-1 FW) of sweet pepper fruits during the first (A) and second (B) seasons. Note: Vertical bars show standard deviation (n = 3). Different letters indicate statistically significant differences at
Results indicate that fruits chlorophyll content increased with most of treatments. The highest content of fruit chlorophyll was obtained from algae extract (1 g.L-1), followed by fulvic acid (6%).
Seaweed extracts contain cytokinins that stimulate physiological activities (such as activation of some enzymes that involved in photosynthesis), increased total chlorophyll in the plant and photosynthesis activity that will be positively reflected on shoot characteristics (
The effect of spray treatments with fulvic acids and algae extracts on ascorbic acid content, depends on the concentration used (Figure
Effect of fulvic acid and algae extracts spraying on ascorbic acid content (mg.g-1 FW)) of sweet pepper fruits during the first and second seasons. Vertical bars show standard deviation (n = 3). Different letters indicate statistically significant differences at
The results in Figure
Effect of fulvic acid and algae extracts spraying on peroxidase (POX) and polyphenol oxidase (PPO) activities (unit min-1 mg-1 protein) of sweet pepper fruits during the first (A) and second (B) seasons. Vertical bars show standard deviation (n = 3). Different letters indicate statistically significant differences at
It is clear from Figure
Effect of fulvic acid and algae extracts spraying on phenolic content (mg.g-1 DW) of sweet pepper fruits during the first and second seasons. Vertical bars show standard deviation (n = 3). Different letters indicate statistically significant differences at
The organic fertilizer applications significantly affected total phenolic content. Plants cannot allocate resources for growth and defence at the same time, and there is competition between proteins and phenols in plants for common precursors involved in their biosynthesis (
Figures
Effect of fulvic acid and algae extracts spraying on metal chelating activity % of sweet pepper fruits during the
first and second seasons. Vertical bars show standard deviation (n = 3). Different letters indicate statistically significant
differences at
Effect of fulvic acid and algae extracts spraying on reducing power (at 700 nm) of sweet pepper fruits during
the first and second seasons. Vertical bars show standard deviation (n = 3). Different letters indicate statistically
significant differences at
Organic fertilizers increased the antioxidant activity (
Organic acids have sour and fresh taste that impart unique flavour to the food (
Effect of fulvic acid and algae extracts spraying on organic acids (μg.mg-1 DW) of sweet pepper fruits during the first and second seasons.
Organic acid (μg.mg-1DW) | Control | Fulvic acid | Algae extract | ||||
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2% | 4% | 6% | 1 g.L-1 | 2 g.L-1 | 4 g.L-1 | ||
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Oxalic acid | 7.15 | 8.61 | 8.66 | 6.75 | 6.66 | 7.02 | 5.32 |
Citric acid | 15.64 | 20.64 | 24.33 | 29.54 | 28.97 | 27.64 | 22.30 |
Malic acid | 50.31 | 4764 | 52.64 | 60.31 | 66.43 | 67.5 | 51.97 |
Succinic acid | 13.23 | 18.34 | 20.33 | 18.88 | 21.70 | 18.42 | 17.02 |
Glutaric acid | 2.35 | 2.13 | 2.50 | 2.11 | 3.65 | 3.89 | 2.75 |
Propionic acid | 0.02 | 0.005 | Nd | Nd | Nd | Nd | Nd |
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Oxalic acid | 6.01 | 7.03 | 7.27 | 5.50 | 5.03 | 5.66 | 3.27 |
Citric acid | 13.67 | 19.55 | 26.75 | 38.05 | 36.04 | 30.31 | 23.23 |
Malic acid | 45.60 | 41.20 | 45.83 | 52.94 | 73.70 | 52.82 | 45.49 |
Succinic acid | 11.99 | 15.55 | 19.14 | 17.35 | 19.29 | 15.47 | 13.05 |
Glutaric acid | 3.17 | 2.46 | 3.21 | 1.88 | 5.68 | 3.90 | 3.41 |
Propionic acid | 0.013 | 0.02 | 0.014 | 0.014 | 0.013 | 0.01 | Nd |
Note: Nd = Not detected.
The use of plant biostimulants has positive effects on growth and bioactive compounds in sweet pepper plants, especially when used at appropriate concentrations. Fulvic acid and algae extracts improved most fruit characteristics (length and diameter of fruits), vegetative growth, and chemical properties. With regard to organic acid, malic and citric acids are the main organic acids found in sweet peppers malic, succinic and glutaric acids were higher in 1 g.L-1 algae extract treatment, but the concentration of citric acid was higher in 6% fulvic acid treatment. The results of the current study showed that the best treatment is algae extract at 1 g.L-1 which gave the best value in most results followed by 6% fulvic acid so that it can be safely recommended as a natural biostimulants.
The authors would like to thank the Egyptian Atomic Energy Authority for supporting and funding this study. Also, the authors would like to thank the journal editorial board and the reviewers for their counteractive observations and comments that contributed to improve this study.