An applied study to improve Le-Conte pear productivity and quality using potassium humate with hydrogen peroxide or irradiated licorice extract

Pears (Pyrus communis L.), which belongs to the Rosaceae family, are among the most significant, well-known, and lucrative fruits in the world. In terms of production, it is the fifth-ranked deciduous fruit crop worldwide, with a total production of 23.73 million tons from 1.4 million hectares in 2019¹. According to the most recent market data, Egypt has consistently produced an annual pear production of approximately 75,000 metric tons with a harvested area of about 5600 hectares and an average yield of 13 tons per hectare. This reflects a minor drop of 1.8% from the prior year². This kind of fruit is cultivated mainly for its high usability, it is initially enjoyed as a popular fresh fruit and, because of its high content of “primary and secondary metabolites,” which are crucial for human nutrition and health, can also be processed into a wide range of products³. The primary pear cultivar grown in Egypt is the Le-Conte pear which is a hybrid of Pyrus communis and Pyrus serotina. However, over the previous few decades, the cultivated area of pears varied significantly due to the fire blight outbreak⁴. Fire blight, caused by the pathogenic bacteria Erwinia amylovora, is the most destructive factor that greatly affects the growth, productivity, and quality of pear trees. These bacteria infect pears as well as most other members of the Rosacea family and are currently found in more than 50 countries, including Egypt⁵. Recently, environmental challenges have attracted attention because they have a major impact on fire blight infection and fruit quality. Natural products are viewed as an alternative to many synthetic materials used as plant nutrition because of their accessibility, affordability, and minimal potential for causing pollution or degrading soil and land⁶.

It has been established that humic acid (HA), an organically charged biostimulant, has a positive impact on every aspect of agriculture. Beginning with the soil, humic acid addition enhances the soil’s chemical, biological, and physical characteristics⁷. Additionally, Canellas and Olivares⁸ reported that HA improved a number of physiological processes in plants, such as enhancing permeability of cell membranes, nutrient absorption, triggering the synthesis of chlorophyll pigment, and facilitating the assembly of sugars, amino acids, and enzymes. One of HA’s unique qualities is that it makes plants more disease-resistant, which improves plant health. Additionally, it greatly reduces the stresses of high salinity and temperature that can lead to toxicity, which gives the plant a degree of resistance and benefits the continuation of essential processes^9,10. Apart from these benefits, some research has demonstrated that HA spraying improved fruit size, weight, total soluble solids, and vitamin C contents, as demonstrated in guava¹¹ and apricots¹².

In recent decades, interest in hydrogen peroxide (H₂O₂), the most stable reactive oxygen species with a relatively long half-life, has grown significantly as a critical regulator of numerous physiological and biochemical processes in plants, both under stress and under normal circumstances¹³. The plant is sensitive to H₂O₂, and while a high concentration can stress the plant to the point of death, low and normal concentrations aid in the plant’s ability to withstand a variety of stresses¹⁴. Low-concentration foliar application of H₂O₂ not only promotes plant growth, enzymatic antioxidant activities, fruit yield, and quality¹⁵, but it also plays a vital role in combating plant pathogens like wheat leaf rust¹⁶ and barley net blotch disease¹⁷. Furthermore, non-host resistance mechanisms in cereal and legume plants against incompatible pathogens greatly depend on an early increase in H₂O₂¹⁸.

Plant extracts are one kind of biostimulant that agriculture has recently adopted on a large scale. Licorice root (glycyrrhiza glabra), a member of the Leguminoseae family of plants that grows widely throughout the world, including Egypt, could be used as a safe substitute for chemical growth regulators¹⁹. More than 100 necessary substances, such as flavonoids, phenolic compounds, minerals, proteins, amino acids, monosaccharaides, several vitamins, lignin, tannins, and mevalonic acid that is involved in the synthesis of gibberellins, are found in licorice root extract²⁰. Because of all these components, licorice helps with most of the essential functions of the plant, including promoting cell division and cellulose enzyme activity, which in turn promotes plant growth. Additionally, it improves the plant’s capacity to reduce rates of transpiration and water loss, preserving cell tension²¹. Spraying potato plants²² and pear trees⁴ with foliar licorice root extract enhanced the plants’ growth and leaf mineral contents, ultimately increasing their marketable yield.

Ionizing radiation exposure, including electron beam, X-rays, and gamma rays, is one feasible method of reducing the microbiological load of medicinal herbs²³. However, depending on the radiation dose and herb type, the effect of radiation varies from negligible to minimal on the volatile oil content and overall yield of herbal extracts^24,25 and may result in a significant increase in some bioactive ingredients²⁶. Licorice exposed to gamma radiation showed a significant increase in the total yield of volatile compounds²⁷, as well as in the concentration of maltose and glycyrrhezinic acid in the resultant solutions²⁸.

Therefore, the purpose of this study was to evaluate the feasibility of foliar application of potassium humate, hydrogen peroxide, and gamma-irradiated licorice extract to improve production, quality, and fire blight infection control of Le-Conte pear. We hypothesize that, foliar spraying Le-Conte pear trees with potassium humate, hydrogen peroxide, and gamma-irradiated licorice extract will boost fruit quality and yield while reducing fire blight. The novel aspect of this study is the application of hydrogen peroxide, potassium humate, and gamma-irradiated licorice extract as eco-friendly foliar treatments. This report is the first to look at the use of environmentally friendly compounds to improve the fruit quality and productivity of pear trees in Egypt and prevent fire blight.

Fruit physical characteristics

All treatments enhanced the Le-Conte pear fruits’ diameter, length, firmness, and size as compared to the control (Table 1). The foliar application of potassium humate, hydrogen peroxide, or irradiated licorice extract alone or in combination greatly raised the previously stated parameters. When those treatments were taken at the higher level, their effects became noticeably stronger. In comparison to hydrogen peroxide, the increment effect of irradiated licorice extract was greater. The highest values of fruit size, length, diameter, and firmness were obtained when high level of potassium humate combined with a high level of irradiated licorice extract or hydrogen peroxide. Sole foliar application of the high level of potassium humate and hydrogen peroxide as well as irradiated licorice extract greatly improved the fruit shape index. While all combined treatments resulted in a notable increase in the fruit shape index, high levels of irradiated licorice extract and hydrogen peroxide had the greatest increase. The greatest improvement was found when combining potassium humate with either hydrogen peroxide or irradiated licorice extract at their high levels.

Yield characteristics

The findings presented in Table 2 demonstrated a significant increase in Le-Conte pear fruit number/tree, fruit weight, and yield/tree upon foliar application of potassium humate, hydrogen peroxide, or irradiated licorice extract in comparison to the control. The enhancement effect became stronger when the level of these treatments increased. Either hydrogen peroxide or irradiated licorice extract produced a more favorable impact than potassium humate, with irradiated licorice extract being chosen in most cases. Also, the aforementioned characteristics were greatly boosted by all combined foliar sprays. The combinations of hydrogen peroxide or irradiated licorice extract with potassium humate at their high levels were better than their low levels. The highest rate of increment in fruit number and yield were obtained by combined high levels of potassium humate and hydrogen peroxide treatment (43.9% and 85.3%, respectively) while the highest rate of increment in fruit weight was obtained by combined high level of potassium humate and irradiated licorice treatment (30.1%). The number of fire blighted fruits and, hence, the percentage of fire blighted fruits were dramatically decreased when potassium humate, hydrogen peroxide, or irradiated licorice extract were sprayed individually compared to the control. Hydrogen peroxide, in particularly at the high level where the proportion of fire-blighted fruits was 1.30% and 1.28% in both seasons, respectively, proved to be the most successful solitary application. All combined sprays resulted in a significant decrease in the number of fire-blighted fruits, particularly for sprays with a high concentration of hydrogen peroxide. When potassium humate at the high level was combined with hydrogen peroxide at the high level, the lowest percentage of fire-blighted fruits was obtained (1.02% and 0.94% for both seasons, respectively). This was followed by potassium humate at the low level combined with hydrogen peroxide at the high level (1.14% and 1.05% for both seasons, respectively).

Fruit chemical characteristics

Table 3 showed how the TSS, acidity, TSS/acid ratio, and vitamin C content of Le-Conte pear fruit were affected by foliar application of potassium humate, hydrogen peroxide, or irradiated licorice extract. The foliar application of potassium humate, hydrogen peroxide, or irradiated licorice extract individually resulted in a considerable rise in fruit TSS, TSS/acid ratio, and vitamin C content compared to the control except potassium humate’s low level, which had no apparent effect on the TSS/acid ratio. As the level of the foliar-sprayed treatments— potassium humate, hydrogen peroxide, or irradiated licorice extract— increased, the rate of increment in the previously mentioned characteristics increased. In addition, it was discovered that foliar spraying of irradiated licorice extract had the greatest rate of improvement (13.77, 13.40; 35.94, 36.92; 3.22, 3.24 for both seasons for TSS, TSS/acid ratio, and vitamin C content, respectively), followed by hydrogen peroxide and potassium humate. The TSS, TSS/acid ratio, and vitamin C content all significantly increased as a result of the combination sprays; sprays with high treatment levels were more effective over those with lower levels, and irradiated licorice extract was preferred over hydrogen peroxide and potassium humate. Foliar spraying of different treatments and levels, either individually or in combination, led to a significant reduction in the acidity when compared to the control. Once more, when the level of foliar spray treatments increases, so does the rate of decrease in acidity. Additionally, the highest reduction in acidity was observed with irradiated licorice extract-containing sprays, which was followed by hydrogen peroxide and potassium humate.

The impact of foliar application of potassium humate, hydrogen peroxide, and irradiated licorice extract on total, reduced, and non-reduced sugar content of Le-Conte pear fruits was illustrated in Table 4. Foliar application of potassium humate, hydrogen peroxide, and irradiated licorice extract, either separately or in combination, had a favorable effect on the total and reduced sugar content compared to the control. Irradiated licorice extract was associated with higher increases in total and reduced sugar content among sole applications. Foliar spraying of potassium humate and irradiated licorice extract had a higher positive impact on total and reduced sugar content compared to potassium humate and hydrogen peroxide. For non-reduced sugars, it showed a significant reduction when potassium humate, hydrogen peroxide, or irradiated licorice extract was foliar applied individually or in combination as compared to the control.

The results in Table 5 demonstrate the effects of spraying potassium humate, hydrogen peroxide, and irradiated licorice extract on the potassium, zinc, and iron levels of Le-Conte pears. The K% in Le-Conte pear fruits was dramatically increased by each individual foliar spraying with potassium humate, hydrogen peroxide, and irradiated licorice extract. The irradiated licorice extract or the high hydrogen peroxide level showed a significant, superior effect over the others. For combination sprays, potassium humate combined with hydrogen peroxide or irradiated licorice extract significantly raised the fruit K%. Spraying potassium humate at the high level with either of the irradiated licorice extract levels, the high hydrogen peroxide level, or potassium humate at the low level with the high irradiated licorice extract level produced the greatest K% values. All foliar treatments, whether sprayed singly or in combination, significantly increased the Zn and Fe content compared to the control. Sole foliar spraying of irradiated licorice extract led to a more notable increase in Zn and Fe content, followed by hydrogen peroxide, then potassium humate, with a preference for the high level of each substance over the low one. The fruit content of Zn and Fe increased significantly as a result of all combined sprays, while the ones containing potassium humate and irradiated licorice extract were preferred over the others. When high levels of irradiated licorice extract and potassium humate were sprayed, the greatest values for Zn and Fe content were achieved (41.0, 42.0, 141.0, and 141.3 for Zn and Fe in both seasons, respectively).

Research on Le-Conte pear production and fire blight treatments is essential given the increasing demand for new standards for environmentally friendly farming techniques globally due to climate change and future plans for sustainable fruit farming to improve fruit quality and productivity. Two of the risk factors for Erwinia amylovora infection are climatic: rainfall during warm periods and temperatures above 15°C during flowering, which enhance the pathogen’s capacity to multiply to infection-causing levels²⁹. In order to improve absorption of the sprayed treatments, foliar spraying of hydrogen peroxide and irradiated licorice extract was selected for February and March, when buds start to appear. Additionally, April and May were selected because rising temperatures encourage the spread of fire blight.

Our study discovered that foliar spraying Le-Conte pear trees with potassium humate improved the physical and chemical properties of the fruits as well as their yield qualities, while also dramatically reducing the proportion of fire-blighted pears. Accordingly, Mosa et al.³⁰ discovered that applying 5% or 4% HA to Le-Conte pear trees significantly increased the fruits’ size, length, diameter, firmness, and weight, but had little effect on the fruit shape index. There was a noticeable rise in the ratio of TSS to acidity, total sugars, and soluble solids. Furthermore, 4% HA produced the greatest reduction in fruit acidity, whereas 5% HA significantly raised the quantity of reducing and non-reducing sugars in pear fruits. Likewise, the physical attributes of the fruit, such as its size, length, diameter, and firmness, as well as the quantity and weight of fruits produced, improved when NPK humate was applied to Le-Conte pear trees, especially at a high rate. Moreover, fruit juice’s total sugar content, soluble solids content, and soluble solids content/acid ratio all increased as acidity dropped³¹. When commercial humic substances were sprayed foliar on table grapes, Ferrara and Brunetti³² and Sánchez-Sánchez et al.³³ observed a comparable response. Both the chlorophyll content and vegetative growth had significantly improved, according to their reports. Moreover, the yield increased significantly due to a significant increase in the berry and bunch weight and length. Titratable acidity fell as total soluble solids and the total soluble solids/acid ratio rose. Following the application of humate, they observed that the trees’ absorption of mineral nutrients—which are critical for fruit production and result in larger fruit—was most likely the source of the increase in fruit size. Moreover, humic acids enhance plant growth by improving photosynthesis, root development, and cell membrane permeability, facilitating the uptake of essential nutrients^34,35. The possible hormone-like activity of the humic substances—which could include auxins, gibberellins, and cytokinins—should also be taken into account³⁶. Gibberellin also improves fruit firmness by increasing the number of cells in the fruit, which increases the ratio of cell wall to cell volume. Potassium is necessary for many fundamental physiological functions, such as the synthesis of proteins, the generation of sugars and starches, cell division and development, and the flavor and color of fruits. Applying potassium humate helps enhance the absorption of potassium³⁷.

Regarding the advantages of H₂O₂ spraying for Le-Conte pear fruits and the incidence of fire blight, Hafez et al.⁵ discovered that spraying H₂O₂ on Le-Conte pear trees greatly enhanced the fruit’s diameter, firmness, weight, length, and yield per tree. H₂O₂ foliar application not only markedly decreased the incidence percentage of fire blight in flowers or leaves and fruits of pear trees compared to control treatment but also improved the fruit quality in terms of higher fruit total soluble solids and reduced fruit acidity. Khandaker et al.³⁸ connected the increased growth of wax apple trees sprayed with H₂O₂ to a significant increase in photosynthesis rates, stomatal conductance, and leaf transpiration. This growth was observed in terms of leaf dry matter and chlorophyll content, as well as a marked increase in fruit size, total soluble solids, and total sugar content, and yield. The greater yield is also ascribed to the function of H₂O₂ as a signaling molecule, which regulates photosynthesis, respiration, translocation, and transpiration³⁹. The reduced incidence of fire blight may be related to H₂O₂‘s capacity to slow down the rate of bacterial growth⁴⁰. Also, plants produce reactive oxygen species (ROS) as a defense mechanism against bacteria such as Erwinia amylovora⁴¹. Hydrogen peroxide, one of the most significant and harmful of these free radicals, is distinguished by its high stability, capacity to pass through cell membranes and walls, and high reactivity with proteins, lipids, and nucleic acids⁴². The bacteria also promote the synthesis of specific enzymes that counteract these free radicals⁴³. Erwinia amylovora and plants interact in one of two ways: either the plant cells detect the bacterial cells and react with an oxidative burst and a hypersensitive response, which lowers the pathogen populations and stops tissue colonization⁴⁴, or the bacterial cells are able to avoid or reduce both the release of ROS and the hypersensitive response, which kills plant cells and advances within host tissues, resulting in the characteristic necrosis of fire blight disease⁴⁵. As a result, applying hydrogen peroxide externally may strengthen the plant’s resistance to bacteria. The presence of H₂O₂ in the fruits, which accelerates the ripening process, and its ability to support cellular development and regulate cell expansion may account for the improved chemical properties of the pear fruits⁴⁶.

The stimulating effect of spraying irradiated licorice extract on Le-Conte pear fruit characteristics was also found by Abd El–Hamied and El-Amary⁴ who discovered that applying licorice extract to Le-Conte “pear” substantially boosted the fruit’s total soluble solids, total sugar, vitamin C content, and fruit length, diameter, volume, weight, and number per tree. On the other hand, such treatments significantly decreased the number and percentage of fire blight infected fruits as well as fruit juice total acidity. Similar findings were reported in the studies conducted by Hasan and Kader⁴⁷ on Sawa, Anbhu et al.⁴⁸ on Bhagwa, and Nooruldeen et al.⁴⁹ on Salemy pomegranate cultivars. Pomegranate trees were sprayed with licorice extract at varying rates, which significantly improved the fruit’s yield characteristics as well as its physical and chemical characteristics. Spraying irradiated licorice extract enhanced the benefits of reducing the percentage of sunburned and cracked fruits and boosting vegetative development, nutritional status, fruit physical and chemical properties, leaf yield, and nutritional content. This improvement was comparable to that of Ahmed et al.⁵⁰, who found that irradiated licorice extract sprayed on red globe grapevine significantly improved vegetative growth as well as the percentages of NPK and total chlorophyll in the leaves. Moreover, it reduced the number of sunburned bunches and the percentage of berry acidity while increasing berry volume, weight, TSS%, anthocyanin content, bunch weight, and yield.

The improved physical and yield characteristics are due to the magic ingredient, mevalonic acid. Mevalonic acid stimulates the synthesis of gibberellin, which promotes increased cell division and expansion in the fruit, increasing its weight, size, and yield. Additionally, it is rich in growth phytohormones, minerals, vitamins, amino acids, carbohydrates, and salts. These nutrients support root and vegetative growth in addition to cell division and elongation. These elements, in addition to the fruits’ enhanced ability to take in water and nutrients from the soil, raise the yield parameters^51,52. A possible explanation for the observed decrease in fire blight following the application of irradiated licorice extract is an increase in the synthesis of phenolic compounds. These compounds are known to impede the proliferation of pathogens and reinforcing the plant cell wall, enabling plants to respond promptly to pathogen assaults^53,54. Furthermore, licorice extract enhances the plant’s resistance to infections by altering the plant’s responses to the threat through the use of salicylic acid and ethylene⁵⁵. The reduced total acidity, however, can result from acid exhaustion in numerous physiological functions, such as respiration. The increased fruit total soluble solids after foliar licorice spraying may be due to increased leaf area and chlorophyll content, which in turn improved the uptake of soil nutrients and the synthesis of carbohydrates⁵⁶.

When it comes to medicinal plants, radiation is a delicate process because different radiation doses have different effects on plants and asymmetric effects on the same plant in terms of content, especially volatile components, making some components disappear and others appear. In the case of licorice, gamma-irradiation with 10 kGy does not cause any volatile compounds to disappear; instead, it causes the appearance of new compounds like benzaldehyde and a noticeable increase in the amount of many other compounds like indole. Once more, licorice exposed to a 10 kGy dose of radiation showed a 12% increase in the maximum yield of its volatile compounds and the highest content of all the compounds present when compared to non-irradiated licorice²⁷.

The study was conducted throughout two consecutive seasons in 2022 and 2023 on fifteen-year-old Le-Conte pear trees that were uniformly vigorous, budded on Pyrus communis rootstock, and planted in a private orchard at a distance of 70 km from Cairo on the Cairo Alexandria desert road, Egypt (30° 13′ 31.4″ N 30° 39′ 09″ E). The owner of the farm granted us permission to conduct the study, and we did so in compliance with local laws. The trees were grown using a drip irrigation system, and the planting space was 4 × 4 m. The trees were uniform in vigor and received common horticultural practices with the addition of half the amount of potassium sulfate fertilization. The tested trees were sprayed to drip point with potassium humate at (0, 1, and 2%) in 21 February, 21 March, 21 April, 21 May, and 31 June, while hydrogen peroxide at (0, 1, 2 ml/L) and gamma-irradiated licorice at (0, 4, 8 g/L) were sprayed at 15 February, 1^st March, 15 March, 15 April, and 15 May for both seasons. The method used for extracting dried licorice root was as described by Ahmed et al.⁵⁰. Licorice extract was irradiated with a 10 KGy dosage at the Egyptian Atomic Energy Authority’s National Centre for Radiation Research and Technology in Cairo, Egypt, using a Gamma Cell (60Co) at dose rate 0.773 and 0.678 for February 2022 and 2023, respectively. The irradiated licorice extract constituents were as follow total phenols (23.2%), total flavonoids (15.7%), amino acids (9.3%), N (2.7%), P (2.5%), K (1.89%), Fe (50 ppm), Zn (63 ppm), and Mn (7 ppm). The physical and chemical properties of the soil during two seasons (2022 and 2023) were shown in Table 6. It was sandy loam soil, which is good for pear tree growth. The pH of the soil was 8 in both seasons, which is near the pH range of 6–7 that is ideal for raising productivity. Notably, soil properties improved slightly in 2023 compared to 2022, with a decrease in soil salinity (EC, Cl⁻, and Na) and an increase in certain nutrients like calcium and potassium, indicating improved soil quality for agriculture.

This experiment used a fully randomized block design with 15 treatments and three replicates of three trees each. To eliminate surface tension, each tree got 3 L of the applied solution plus 5 cm per liter of 20, except for the control treatment, which received water and 5 cm per liter of 20. The trial contained the following fifteen treatments: Control (no foliar spray), K1 (potassium humate at 1%), K2 (potassium humate at 2%), H1 (hydrogen peroxide at 1 ml/L), H2 (hydrogen peroxide at 2 ml/L), L1 (gamma-irradiated licorice at 4 g/L), L2 (gamma-irradiated licorice at 8 g/L), K1H1, K1H2, K1L1, K1L2, K2H1, K2H2, K2L1, and K2L2.

Fruit quality parameters

1. 1-

   Fruit physical characteristics: size (cm³), height (cm), diameter (cm), shape index, and firmness (N; Newton) were measured on 15 fruits harvested from each duplicate tree.

2. 2-

   Yield characteristics: harvesting achieved on (15th August for each season), fruit weight (g), fruit number, and yield (Kg/tree) were recorded. In March and April of each season, a visual inspection of pear fruits was conducted, during which the number of fruits affected by fire blight was recorded, and the corresponding percentages were calculated.

Fruit chemical properties: according to AOAC⁵⁷, the Abbe digital refractometer was used to measure the percentage of total soluble solids (TSS). According to AOAC⁵⁷, total acidity was calculated as citric acid by titration with a 0.1 N. NaOH solution and phenolphthalein as an indicator. The values were computed as grams per 100 milliliters of juice. The total soluble solids/acid ratio was obtained using the following equation: Total soluble solids/acid ratio = TSS/ total acidity. The method described in AOAC⁵⁷ was used to determine the total juice sugar: total sugars (g/100 g FW). This involved naturalizing 25 ml of juice sample to a pH of 7.5 to 8.0 with 1 N NaOH, adding 2 ml of lead acetate and a few drops of potassium oxalate, and diluting the mixture. Then, 5 g of citric acid was added to the filtrate, neutralized using phenolphthalein as an indicator, and neutralized with 20% NaOH until a pink hue was achieved. The titration’s end point was colorless. Sugars were calculated using the previously described methodology by Ali et al.⁵⁸. To turn non-reducing sugars into reducing sugars, a sample of fruit pulp treated with 25% lead acetate and 20% potassium oxalate was hydrolyzed with HCl and left overnight. The aliquot that had been hydrolyzed by HCl was then titrated against Fehling solutions after being neutralized with 0.1 N NaOH. The fruits’ potassium content was determined by flame photometry, and their zinc and iron contents were determined by atomic absorption spectrometry⁵⁹.

Statistical analysis

This study employed a randomized full-block design with three replicates. The current data was statistically analyzed by Snedecor and Cochran⁶⁰. The new L.S.D. values were used to compare averages at the 5% level. According to McLain⁶¹, the MSTAT program was used to compute the collected data.

1. FAOSTAT. (2020). (accessed 26 March 2021). http://www.fao.org/faostat/en/#data/QC (2020).

2. INDEXBOX. Egypt: Pear Market Overview and Forecast. https://www.indexbox.io/search/production-pear-egypt/ (2004).

3. Milošević, T., Milošević, N. & Mašković, P. Phenolic compounds and antioxidant capacity of pear as affected by rootstock and cultivar. Mitt. Klosterneubg. 70(4), 308–319 (2020).

   Google Scholar 

4. Abd El-Hamied, S. A. & El-Amary, E. I. Improving growth and productivity of “pear” trees using some natural plants extracts under north sinai conditions. J. Agric. Vet. Sci. 8(1), 1–9. https://doi.org/10.9790/2380-08110109 (2015).

   Article  Google Scholar 

5. Hafez, Y. M. et al. Exogenous application of Bacillus subtilis and H2O2 mitigated fire pear blight bacterial dis-ease incidence in correltaed with yield and fruit quality improvement. Fresenius Environ. Bull. 29(07A), 6315–6327 (2020).

   Google Scholar 

6. Phiri, C. Influence of Moringa oleifera leaf extracts on germination and early seedling development of major cereals. Agric. Biol. J. N. Amer. 1(5), 774–777. https://doi.org/10.5251/abjna.2010.1.5.774.777 (2010).

   Article  Google Scholar 

7. Li, Y. Research progress of humic acid fertilizer on the soil. J. Phys: Conf. Ser. 1549(2), 022004. https://doi.org/10.1088/1742-6596/1549/2/022004 (2020).

   Article  Google Scholar 

8. Canellas, L. P. & Olivares, F. L. Physiological responses to humic substances as plant growth promoter. Chem. Biol. Technol. Agric. 1, 3. https://doi.org/10.1186/2196-5641-1-3 (2014).

   Article  Google Scholar 

9. Abdellatif, I. M. Y., Abdel-Ati, Y. Y., Abdelmageed, T. & Hassan, M. M. Effect of humic acid on growth and productivity of tomato plants under heat stress. J. Hort. Res. 25(2), 59–66. https://doi.org/10.1515/johr-2017-0022 (2017).

   Article  Google Scholar 

10. Mindari, W., Sasongko, P. E., Kusuma, Z., Syekhfani, S. & Aini, N. Efficiency of various sources and doses of humic acid on physical and chemical properties of saline soil and growth and yield of rice. AIP Conf.Proc. 2019(1), 030001. https://doi.org/10.1063/1.5061854 (2018).

    Article  Google Scholar 

11. da Rocha, L. F. et al. Fruit production and quality of guava ‘Paluma’as a function of humic substances and soil mulching. Afr. J. Biotechnol. 15(36), 1962–1969. https://doi.org/10.5897/AJB2016.15587 (2016).

    Article  Google Scholar 

12. Fatma, K. M. S., Morsey, M. M. & Thanaa, S. M. Influence of spraying yeast extract and humic acid on fruit maturity stage and storability of” Canino” apricot fruits. Int. J. Chem. Tech. Res. 8, 530–543 (2015).

    Google Scholar 

13. Ralmi, N. H. et al. Influence of rhizopheric H₂O₂ on growth, mineral absorption, root anatomy and nematode infection of Ficus deltoidea. Agronomy 11(4), 704. https://doi.org/10.3390/agronomy11040704 (2021).

    Article  Google Scholar 

14. Cheeseman, J. M. Hydrogen peroxide concentrations in leaves under natural conditions. J. Exp. Bot. 57(10), 2435–2444. https://doi.org/10.1093/jxb/erl004 (2006).

    Article  PubMed  Google Scholar 

15. Orabi, S. A., Dawood, M. G. & Salman, S. R. Comparative study between the physiological role of hydrogen peroxide and salicylic acid in alleviating the harmful effect of low temperature on tomato plants grown under sand-ponic culture. Sci. Agri. 9(1), 49–59. https://doi.org/10.15192/PSCP.SA.2015.1.9.4959 (2015).

    Article  Google Scholar 

16. Omara, R. I., Kamel, S. L., Hafez, Y. M. & Morsy, S. Z. Role of non-traditional control treatments in inducing resistance against wheat leaf rust caused by Puccinia triticina. Egypt. J. Biol. Pest. Cont. 25(2), 335–344 (2015).

    Google Scholar 

17. Abdelaal, Kh. et al. Nano silver and non-traditional compounds mitigate the adverse effects of net blotch disease of barley in correlation with up-regulation of antiox idant enzymes. Pak J. Bot. 52(3), 1065–1072. https://doi.org/10.30848/PJB2020-3(13) (2020).

    Article  MathSciNet  Google Scholar 

18. Hafez, Y. M. Early accumulation of reactive oxygen species has a pivotal role in non-host resistance mechanisms in legume and cereal plants to the incompatible pathogens. J. Plant Protec. Pathol. 6(3), 455–472. https://doi.org/10.21608/jppp.2015.53306 (2015).

    Article  Google Scholar 

19. Vlaisavljević, S. et al. Chemical composition, antioxidant and anticancer activity of licorice from Fruska Gora locality. Ind. Crops Prod. 112, 217–224. https://doi.org/10.1016/j.indcrop.2017.11.050 (2018).

    Article  Google Scholar 

20. Hussein, S. A., Noori, A. M., Lateef, M. A. & Ismael, C. R. Effect of foliar spray of seaweed (Alga300) andlicorice extracts on growth, yield and fruit quality of pomegranate trees Punica granatum L. Cv. Salimi. IOP Conf. Ser: Earth Environ. Sci. 761(1), 012037. https://doi.org/10.1088/1755-1315/761/1/012037 (2021).

    Article  Google Scholar 

21. Peng, T. et al. Alterations of the rhizosphere soil microbial community composition and metabolite profiles of Angelica sinensis seedlings by co-application of nitrogen fixing bacteria and amino acids. Plant Soil 493(1), 535–554. https://doi.org/10.1007/s11104-023-06248-4 (2023).

    Article  Google Scholar 

22. Matar, H. M., Mahmood, S. A. & Ramadan, A. F. Effect of the treatment by gibberelic acid and liquorice extract on growth and yield of potato. Diyala Agric. Sci. J. 4(1), 220–234 (2012).

    Google Scholar 

23. Molnár, H. et al. The effect of different decontamination methods on the microbial load, bioactive components, aroma and colour of spice paprika. Food Contr. 83, 131–140. https://doi.org/10.1016/j.foodcont.2017.04.032 (2018).

    Article  Google Scholar 

24. Gouvêa, M. M. et al. Decontamination of Mikania glomerata leaves by gamma irradiation: coumarin determination by HPLC-DAD, microbiological control and genotoxicological studies. Planta Med. 84(1), 65–72. https://doi.org/10.1055/s-0043-116630 (2018).

    Article  PubMed  Google Scholar 

25. Huang, M. et al. Effects of electron beam irradiation on microbial load and physicochemical qualities of Ligusticum chuanxiong. Hort. Radiat. Phys. Chem. 217, 111508. https://doi.org/10.1016/j.radphyschem.2023.111508 (2024).

    Article  Google Scholar 

26. Khawory, M. H. et al. Effects of gamma radiation treatment on three different medicinal plants: Microbial limit test, total phenolic content, in vitro cytotoxicity effect and antioxidant assay. Appl. Radiat. Isot. 157, 109013. https://doi.org/10.1016/j.apradiso.2019.109013 (2020).

    Article  PubMed  Google Scholar 

27. Gyawali, R. et al. Effect of γ-irradiaton on the volatile compounds of licorice (Glycyrrhiza uralensis Fischer). Eur. Food Res. Technol. 226, 577–582. https://doi.org/10.1007/s00217-007-0591-2 (2008).

    Article  Google Scholar 

28. Al-Bachir, M., Al-Adawi, M. A. & Al-Kaid, A. Effect of gamma irradiation on microbiological, chemical and sensory characteristics of licorice root product. Rad. Phys. Chem. 69(4), 333–338. https://doi.org/10.1016/j.radphyschem.2003.08.002 (2004).

    Article  ADS  Google Scholar 

29. Taylor, R. K., Hale, C. N., Henshall, W. R., Armstrong, J. L. & Marshall, J. W. Effect of inoculum dose on infection of apple (Malus domestica) flowers by Erwinia amylovora. N Z J Crop. Hortic. Sci. 31(4), 325–333. https://doi.org/10.1080/01140671.2003.9514268 (2003).

    Article  Google Scholar 

30. Mosa, W. F. A. et al. Foliar applications of citric acid, gibberellic acid and humic acid improve growth and fruit quality of ‘Le Conte’ pear (Pyrus communis L.). Hortic. 8(6), 507. https://doi.org/10.3390/horticulturae8060507 (2022).

    Article  Google Scholar 

31. Shalan, A. M. Effect of bio-stimulant and soil amendment on vegetative growth, yield and fruit quality of Pyrus communis cv. “Le Conte” pear trees. J. Plant Prod. 5(12), 1973–1987. https://doi.org/10.21608/jpp.2014.64760 (2014).

    Article  Google Scholar 

32. Ferrara, G. & Brunetti, G. Foliar applications of humic acids in Vitis vinifera L. cv Italia. J. Int. Sci. Vigne. Vin. 42, 79–87 (2008).

    Google Scholar 

33. Sànchez-Sànchez, A., Sànchez-Andreu, J., Juàrez, M., Jordà, J. & Bermúdez, D. Improvement of iron uptake in table grape by addition of humic substances. J. Plant Nutrit. 29(2), 259–272. https://doi.org/10.1080/01904160500476087 (2006).

    Article  Google Scholar 

34. Chen, Q. et al. Humic acid modulates growth, photosynthesis, hormone and osmolytes system of maize under drought conditions. Agric. Water Manag. 263, 107447. https://doi.org/10.1016/j.agwat.2021.107447 (2022).

    Article  Google Scholar 

35. Jung, H., Kwon, S., Kim, J. H. & Jeon, J. R. Which traits of humic substances are investigated to improve their agronomical value?. Molecules 26(3), 760. https://doi.org/10.3390/molecules26030760 (2021).

    Article  PubMed  PubMed Central  Google Scholar 

36. Souza, A. C., Olivares, F. L., Peres, L. E., Piccolo, A. & Canellas, L. P. Plant hormone crosstalk mediated by humic acids. Chem. Biol. Technol. Agric. 9(1), 29. https://doi.org/10.1186/s40538-022-00295-2 (2022).

    Article  Google Scholar 

37. Abbas, F. & Fares, A. Best management practices in citrus production. Tree For Sci Biotech. 3, 1–11 (2008).

    Google Scholar 

38. Khandaker, M. M., Boyce, A. N. & Osman, N. The influence of hydrogen peroxide on the growth, development and quality of wax apple (Syzygium samarangense, [Blume] Merrill & LM Perry var. jambu madu) fruits. Plant Physiol. Biochem. 53, 101–110. https://doi.org/10.1016/j.plaphy.2012.01.016 (2012).

    Article  PubMed  Google Scholar 

39. Slesak, I., Libik, M., Karpinska, B., Karpinski, S. & Miszalski, Z. The role of hydrogen peroxide in regulation of plant metabolism and cellular signalling in response to environmental stresses. Acta Biochim Pol. 54(1), 39–50 (2007).

    Article  PubMed  Google Scholar 

40. Macarisin, D., Droby, S., Bauchan, G. & Wisniewski, M. Superoxide anion and hydrogen peroxide in the yeast antagonist–fruit interaction: a new role for reactive oxygen species in postharvest biocontrol?. Postharvest Bio. Technol. 58, 194–202. https://doi.org/10.1016/j.postharvbio.2010.07.008 (2010).

    Article  Google Scholar 

41. Kashmiri, Z. N. & Mankar, S. A. Free radicals and oxidative stress in bacteria. Int. J. Curr. Microbiol. Appl. Sci. 3(9), 34–40 (2014).

    Google Scholar 

42. Linley, E., Denyer, S. P., McDonnell, G., Simons, C. & Maillard, J. Y. Use of hydrogen peroxide as a biocide: new consideration of its mechanisms of biocidal action. J. Antimicrob. Chemother. 67(7), 1589–1596. https://doi.org/10.1093/jac/dks129 (2012).

    Article  PubMed  Google Scholar 

43. Yu, S. C., Fen, S. Y., Chien, C. L. & Wong, H. C. Protective roles of katG-homologous genes against extrinsic peroxides in Vibrio parahaemolyticus. FEMS Microbiol. Lett. 363(6), 038. https://doi.org/10.1093/femsle/fnw038 (2016).

    Article  Google Scholar 

44. Venisse, J. S., Barny, M. A., Paulin, J. P. & Brisset, M. N. Involvement of three pathogenicity factors of Erwinia amylovora in the oxidative stress associated with compatible interaction in pear. FEBS Lett. 537(1–3), 198–202. https://doi.org/10.1016/S0014-5793(03)00123-6 (2003).

    Article  PubMed  Google Scholar 

45. Abdollahi, H., Ghahremani, Z., Erfaninia, K. & Mehrabi, R. Role of electron transport chain of chloroplasts in oxidative burst of interaction between Erwinia amylovora and host cells. Photosynth. Res. 124, 231–242. https://doi.org/10.1007/s11120-015-0127-8 (2015).

    Article  PubMed  Google Scholar 

46. Geros, H., Chaves, M. & Delrot, S. The Biochemistry of the Grape Fruit 304 (Bentham Science Publishers, USA, 2012).

    Google Scholar 

47. Hasan, D. M. & Kader, J. S. Response of pomegranate trees cv. Sawa to foliar application with NPK fertilizer and licorice root extract. Kirkuk Univ. J. Agric. Sci. 13(3), 202–216 (2022).

    Google Scholar 

48. Anbhu, A. V., Rajangam, J., Premalakshmi, V. & Venkatesan, K. Influence of bioextracts on improving the yield and quality of pomegranate (Punica granatum L.) var. Bhagwa. Biol. Forum Int. J. 14(3), 230–234 (2022).

    Google Scholar 

49. Nooruldeen, N., Assi, B. K. & Al-Hadethi, M. E. A. Effect of some organic treatment on yield characteristics of pomegranate. Ind. J. Ecol. 49(19), 103–108 (2022).

    Google Scholar 

50. Ahmed, M. F., Eliwa, N. E. & Ismail, H. M. Ameliorative effect of yeast and gamma irradiated licorice extracts on growth, yield, fruit quality and nutrient content of red globe grapevine. Egypt. J. Rad. Sci. Applic. 36(1), 61–70. https://doi.org/10.21608/ejrsa.2023.239705.1162 (2023).

    Article  Google Scholar 

51. Pérez, F. J. & Gómez, M. Possible role of soluble invertase in the gibberellic acid berry-sizing effect in Sultana grape. Plant Growth Regul. 30(2), 111–116. https://doi.org/10.1023/A:1006318306115 (2000).

    Article  Google Scholar 

52. Zadeh, J. B., Kor, Z. M. & Goftar, M. K. Licorice (Glycyrrhiza glabra Linn) as a valuable medicinal plant. Int. J. Adv. Biol. Biomed. Res. 1, 1281–1288 (2013).

    Google Scholar 

53. Schenk, S. T. et al. N-acyl-homoserine lactone primes plants for cell wall reinforcement and induces resistance to bacterial pathogens via the salicylic acid/oxylipin pathway. Plant Cell 26(6), 2708–2723. https://doi.org/10.1105/tpc.114.126763 (2014).

    Article  PubMed  PubMed Central  Google Scholar 

54. Scherf, A., Treutwein, J., Kleeberg, H. & Schmitt, A. Efficacy of leaf extract fractions of Glycyrrhiza glabra L. against downy mildew of cucumber (Pseudoperonospora cubensis). Eur. J. Plant Pathol. 134, 755–762. https://doi.org/10.1007/s10658-012-0051-0 (2012).

    Article  Google Scholar 

55. Hermann, S. et al. Biocontrol of plant diseases using Glycyrrhiza glabra leaf extract. Plant Dis. 106(12), 3133–3144. https://doi.org/10.1094/PDIS-12-21-2813-RE (2022).

    Article  PubMed  Google Scholar 

56. Alsalhy, B. F. J. & Aljabary, A. M. A. O. Effect of moringa leaves extracts and licorice roots on some growth characteristics and yield of grape (Vitis vinifera L.) Cv. Halawany. Plant Arch. 20(2), 2616–2623 (2020).

    Google Scholar 

57. A. O. A. C. Association of Official of Analytical Chemists 14th edn. (A.O.A.C, Washington DC, USA, 2006).

    Google Scholar 

58. Ali, M. M. et al. Plant growth and fruit quality response of strawberry is improved after exogenous application of 24-epibrassinolide. J. Plant Growth Regul. 41(4), 1786–1799. https://doi.org/10.1007/s00344-021-10422-2 (2022).

    Article  Google Scholar 

59. Chapman, H. D. & Pratt, P. F. Methods of analysis for soils. Plants Waters. Soil Sci. 93(1), 68. https://doi.org/10.1097/00010694-196201000-00015 (1962).

    Article  Google Scholar 

60. Snedecor, G. W. W. & Cochran, W. G. Statistical Methods 177–195 (Iowa State University Press, Ames, 1980).

    Google Scholar 

61. McLain, D. L. The MSTAT-I: a new measure of an individual’s tolerance for ambiguity. Educ. Psychol. Measur. 53(1), 183–189. https://doi.org/10.1177/0013164493053001020 (1993).

    Article  Google Scholar 

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Authors and Affiliations

1. Natural Products Department, National Centre for Radiation Research and Technology, Egyptian Atomic Energy Authority, Cairo, Egypt

   Mohamed Farouk Ahmed & Noha Eid Eliwa

2. Biochemistry Department, Faculty of Agriculture, Al Azhar University, Cairo, Egypt

   Radwan Mohamed Ali

3. Agronomy Department (Chemistry Branch), Assiut Faculty of Agriculture, Al Azhar University, Assuit, Egypt

   Medhat Ibrahim A. Omar

Contributions

M.F.A. made the conceptualization, M.F.A., N.E.E. and R.M.A. made the methodology, M.F.A. and M.I.O. made the formal analysis and investigation, M.F.A. and N.E.E. wrote the original draft, R.M.A. and M.I.O. reviewed and edited the manuscript and all authors read and approved the final manuscript.

Corresponding author

Correspondence to Mohamed Farouk Ahmed.

Competing interests

The authors declare no competing interests.

Consent for publication

Publication was permitted by Egyptian Atomic Energy Authority, Cairo, Egypt.

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