Key findings:

Increasing concentrations of plant extracts improved seed germination and plant growth traits. Licorice root extract at 20 g/L achieved the highest seed germination rate of 92.67%. Additionally, increased extract concentrations enhanced plant height, root length, number of leaves, number of branches, and leaf area, with licorice extract showing the greatest improvement.

What is known and what is new?

Plant extracts such as Glycrrhiza glabra L. (licorice root), Nigella sativa L. (black seed), and banana peel have been used to promote seed germination and plant growth. Higher concentrations of these extracts are generally associated with improved plant development traits. This study specifically identifies that licorice root extract at a concentration of 20 g/L significantly enhances seed germination (92.67%) and improves various plant growth traits, such as plant height, root length, number of leaves, number of branches, and leaf area, more effectively than other extracts and concentrations.

What is the implication, and what should change now?

The study suggests that using licorice root extract, especially at higher concentrations, can significantly enhance seed germination and overall plant growth. This offers a natural and effective alternative to synthetic growth promoters, potentially leading to more sustainable agricultural practices. Agricultural practices should consider integrating licorice root extract, particularly at 20 g/L, into seed treatment and plant growth protocols. 

Vigna radiate L. is one of the important crops in most countries that produce it, especially in developing countries in Asia, Africa and Latin America, and because it contains high levels of vitamins, proteins and mineral elements, people have consumed its soft green pods, dry seeds and leaves, whether as food for it or as fodder for animals. Increasing soil fertility through nitrogen fixation [1]. This plant is characterized by its suitability to the Iraqi environment, so attention must be paid to expanding its cultivation and studying the factors that may increase growth and yield per unit area. Due to its importance, it has become necessary to study its growth requirements in an extensive study. Researchers have tended to use modern technical methods and methods for the purpose of adopting them in processing plants with nutrients. Which it needs for the purpose of its growth and improving its productivity, by reducing the obstacles faced by the nutrients in the soil and thus reducing its readiness for the plant. One of these methods is the adoption of foliar feeding methods by spraying solutions of plant extracts on the plant, which is one of the methods that have proven effective in delivering nutrients directly plant, The world is currently tending to use natural plant extracts that do not pollute the soil and avoid chemicals that have negative effects on the soil, plants and yield [2]. Therefore, many alternatives were used for this purpose, including the root extract of Glycrrhiza glabra L., which is a perennial wild herbaceous plant that grows Its presence in Iraq, as its roots are characterized by the presence of Glycyrrhizin sweet substances, which are found in the form of calcium or potassium salts of Glycyrrhizic acid.This substance is characterized by being similar to the work of the gibberellins. In addition to the fact that the extract contains tannin, sugars, and many elements, including iron, manganese, copper, potassium, and zinc, and it also contains mevalonic acid, which has a role in building gibberellic acid [3].

 (Naggar, 2003) [4] indicated that Nigella sativa L. seeds contain flavonoids, which are antioxidants that play an important role in regulating the activity of the natural hormone, indol acitic acid, which stimulates cell division and elongation at low concentrations, and this is consistent with the opinion of [5]. (Al-Rubaie, 2009) [6] Soaking eggplant seeds in Nigella sativa L. seed extract led to significant increases in the percentage, duration and speed of plant growth compared to the treatment of soaking in distilled water.

As for the banana peel extract, fruit peels generally accumulate daily and in large quantities, and they are rich in macro and micro nutrients important for plant growth. Banana peels have been used as fertilizers to enhance soil fertility because of the nutrients they contain necessary for plant growth (Singh et al., 2017) [7], and banana peels are rich in some elements (Br, Ca, K, Fe, Na, Mn [8].

Preparation of extracts

A quantity of Glycrrhiza glabra L. roots, Nigella sativa L. seeds, and dried banana peels were ground and soaked (5, 10, 20)g separately of extracts in one liter of distilled water and left for 24 hours, then the solutions were filtered using filter paper., Finally , each extract was put in own vial.

Seed germination experiment

The seeds Vigna radiate L. (local variety) were sterilized using sodium hypochloride at a concentration of 5% for 5 minutes, then washed with tap water for several times, and then washed with running water. two filler papers put with 100 seeds and distributed in to four dishes, with 25 seeds in each dish, then (7) cm of distilled water was added for the control treatment and 7 cm of different concentrations of the three extracts with concentrations (5, 10, 20) g / L, on respectively.

    After 10 days of germination, the number of growing seeds was calculated and the percentage of germination was calculated through the following equation.

Germination percentage = X 100

Soil preparation 

The soil was brought from the nursery and purified from impurities by sieving it with a sieve with a capacity of 1 mm and mixed with animal manure at a ratio of (1:2) based on volume and packed in pots.A 10 seeds were planted and divided in to three replicates for each concentration and watered with distilled water until the seedlings grow, then it was diluted to five plants. In each pot and at the stage of (4-5) leaves, it was sprayed with extract concentrations once a week on the shoot until complete wetness. Manual sprayers with a capacity of ( 1 L) were used, in addition to spraying the control plants with distilled water only until the end of the experiment period, the lengths of the shoot and root were measured. With the metric tape and the number of leaves , branches and the rates of leaf areas were calculated

Leaf area (cm²)

Leaf area was calculated by selecting one leaf from each repetition and measuring the length and width of the selected leaves according to the following equation:

Leaf area (cm2) = leaf length x width x 0.75

 (Abdel, 1994)

Statistical analysis

The growth properties were analyzed statistically according to the randomized complete block design with three replications, where the experiment included two factors, the plant extracts and their concentrations, and the comparison between the averages was done using the Least Significant Difference L.S.D test with a probability level of 0.05.

Germanation 

Table (1) shows the effect of spraying plant extracts and their concentrations on the germination percentage of Vigna radiate L. The results of the statistical analysis indicate that there are no significant differences between the germination percentage rates of the three extracts. As for the effect of different concentrations of plant extracts on the rate of germination percentages, a significant increase was observed between their rates with an increase in the concentrations of those extracts, as the treatment (20) g / L had the highest rates,  reached (91.22), while it was the lowest in the control treatment,  reached (83.67). And there were significant differences between the concentrations, but no significant differences were observed between the two concentrations (0,5) g / L. It was noted that there were significant differences between the percentage rates of germination due to the effect of the interaction of two factors, the plant extracts and their concentrations, where the control treatment recorded the lowest rates and reached (83.67), while the treatment of 20 g / L of licorice root extract had the highest and reached (92.67).This may be due to the fact that the extract of the licorice plant contains many chemical compounds, as it is characterized by the presence of chemical compounds with a sweet taste, as it contains Glycyrrhejel, Liquoric acid, and flavonoid compounds, including Glabridin, Glabrin, and others. (Al-Ajili, 2005) [3] and that Glycyrrizin and Glycyrrizic acid are the two most important components in Glycrrhiza glabra L., as they have an effectiveness similar to the activity of plant hormones that lead to an increase in the formation of proteins, so it increases the rate of seed growth (Al-Mohammadi, 2010) [9] the results agree with (Al-Waeli, 2016) [10] who explained that Licorice extract has an effect similar to that of gibberellin in the germination of Citrus aurantium  and Citrus limonus  seeds.

The results observed that the percentage of germination percentages increased with increasing concentrations of the Nigella sativa L. extract, and the germination percentages reached (83.67, 84.00, 88.67, 91.67), respectively, at concentrations (0, 5, 10, 20) g /L  and there were Significance differences between treatment of control and concentrations, he reason may be due to the Nigellone compounds, led to an increased in the speed of cell divisions, the Dithymoquinene compound, which acts as an antioxidant to hormones and enzymes and prevent their decomposition, and the Thymoquinene compound, which works to prevent the oxidation of proteins, amino acids and fatty acids, in addition to the accompanying decomposition of nutrients stored in the seed such as sugars and soluble proteins. As well as the content of seeds of DNA, which doubles at each cell division, and then the transmission of these products to the main growth areas in the embryonic axis, where these products are used to build new materials that contribute to stimulating germination and increasing the strength of seedlings [11]. (Naggar, 2003) [4] also indicated that the seeds of Nigella sativa L. contain flavonoids, which has a high antioxidants that play an important role in regulating the activity of the natural hormone, indol acitic acid, which stimulates cell division and elongation at low concentrations, and this is consistent  [12,13].

In addiation , the results the banana peel extract, showed a significant increase in the germination percentage when treated with 20 g / L banana peel extract , it reached 89.33. This may be due to the fact that fruit peels in general are of value to the plant, as when used in combination with fertilizer, they provide the plant with many macro and micro nutrients. Banana peels are contain( Br, Ca ,K , Fe, Na , Mn) [8]. Potassium,     important for seed germination, as seeds, when lacking, may fail to fully develop.

Table (1) Effect of plant extracts on the percentage of germination of Vigna radiate L. seeds

Plant height

Table (2) shows the effect of spraying plant extracts and their concentrations on the plant height rates of Vigna radiate L. The results of the statistical analysis indicate that there are no significant differences between the plant height rates of licorice and black seed extracts. As for the effect of different concentrations of plant extracts on the rate of plant height, a significant increase was observed between their rates with an increase in the concentrations of those extracts, as the treatment (20) g / L had the highest rates, reached (47.55) cm, while it was the lowest in the control treatment, reached (28.66). cm, and there were significant differences between the concentrations, but no significant differences were observed between the two concentrations (0.5) g/L.

It was noted that there were significant differences between the plant height rates due to the effect of the interaction of  two factors, the plant extracts and their concentrations, where the control treatment recorded the lowest rates and reached (28.66), while the treatment of 20 g / L of licorice root extract had the highest and reached (50.33) cm.. The increase may be attributed to the role of the extract similar to the role of gibberellic acid in stimulating the vegetative growth of the plant due to its association with gibberellic acid in the intermediate compound Mevalonic acid, the initiator of gibberellic biosynthesis, and this constitutes a catalyst in the processes of cell division and elongation (Al-Ajili, 2005) [3] in addition to the fact that the extract contains many terpene compounds Thus, the behavior of the gibberellic has taken its effect in increasing the vegetative growth, elongation and cell division, and the plant cells may have been able to absorb part of the extract sugars and benefit from them in their vital requirements, and then increase the plant height [14].

It was observed in Table (2) a significant increase in plant height when the two treatments (10 and 20) g/L reached (49.66, 42.66) cm. Cellular such as Nigellone and some antioxidants of amino acids and proteins such as Thmoquinene and antioxidants of carbohydrates such as Hydrothymoquinene. All these substances lead to the increase and growth of the vegetative part of the plant [15,11,16]. It is clear from the results, Table (2), that the treatment of 20 g / liter of banana peel extract showed a significant increase in plant height, which reached (42.66) cm, compared to the control treatment, which amounted to (28.66) cm. This may be due to the fact that the banana peel is rich in many nutritional components such as amino acids, proteins, dietary fiber, potassium, and unsaturated fatty acids (Emaga et al., 2007) [17], all of them are substances that promote plant growth, whether they are mixed with fertilizer or foliar spray, and this is consistent with the findings of (Guevara et al., 2005; Anwar et al., 2011) [18,19], where they noticed that banana peel increases plant growth for many plant species, and (Nguyen et al., 2003) [20] confirmed that banana peel extract contains high levels of vitamin C and some amino acids, especially tryptophan, as well as high levels Of vitamin A such as beta-carotene in addition to carbohydrates, protein, macro and micro nutrients, fats, fiber and phenolic compounds.

Table (2) Effect of plant extracts on Plant height of Vigna radiate L.

Number of leaves

Table (3) shows the effect of spraying plant extracts and their concentrations on the number of leaves of Vigna radiate L. The results of the statistical analysis indicate that there are no significant differences between the rates of number of leaves for extracts of licorice and black seed.

As for the effect of the different concentrations of plant extracts on the average number of leaves, a significant increase was observed between the rates with an increase in the concentrations of those extracts, as the treatment (20) g /  L had the highest rates,   reached (26.78), while it was the lowest in the control treatment,  reached (16.67). There were significant differences between the concentrations, but no significant differences were observed between the two concentrations (0.5) g/l.

It was noted that there were significant differences between the number of leaves  rates due to the effect of the interaction of  two factors, the plant extracts and their concentrations, where the control treatment recorded the lowest rates and reached (16.67), while the treatment of 20 g / L of licorice root extract had the highest and reached (29.33)

Table (3 ) the effect of plant extracts on the number of leaves in Vigna radiate L.

Leaf area

Table (4) shows the effect of spraying plant extracts and their concentrations on leaf area of Vigna radiate L. The results of the statistical analysis indicate that there are no significant differences between the mean leaf area of licorice and black seed extracts. As for the effect of different concentrations of plant extracts on the leaf area rates , a significant increase was observed between their rates with an increase in the concentrations of those extracts, as the treatment (20) g/L had the highest rates, reached (383.20) cm ²,  it was the lowest in the control treatment, reached (118.31). cm², and there were significant differences between all concentrations. It was noted that there were significant differences between the leaf area rates due to the effect of the interaction of two factoes , the plant extracts and their concentrations, where the control treatment recorded the lowest rates and reached (118.31), while the treatment of 20 g / L of licorice root extract had the highest and reached to (421.94) cm ².

Table (4) Effect of plant extracts on the leaf area of Vigna radiate L.

Number of  branches

It is noted from Table (5) the effect of spraying plant extracts and their concentrations on the number of branches of Vigna radiate L. The results of the statistical analysis indicate that there are no significant differences between the rates of the number of branches of the three extracts. As for the effect of the different concentrations of plant extracts on the average number of branches, a significant increase was observed between their rates with an increase in the concentrations of those extracts, as the treatment (20) g / L had the highest rates, reached  (6.55), while it was the lowest when the control treatment reached (3.33), There were significant differences between the concentrations, but no significant differences were observed between the two concentrations (0,5) g/l and the two treatments (10,20) g/l.  It was noted that there were significant differences between the rates of the number of branches due to the effect of the interaction of  two factors, the plant extracts and their concentrations, where the control treatment recorded the lowest rates and reached (3.33),  the treatment of 20 g / L of licorice root extract had the highest and reached (7.33).

Table (5) Effect of plant extracts on the number of branches in Vigna radiate L.

The extract of Glycrrhiza glabra L root worked on increasing plant height, number of leaves, leaf area and  number of  branchesbecause it contains the intermediate compound Mevalonic acid, the bio-initiator of endogenous gibberellin, which leads to improving vegetative growth and contains a high concentration of carbohydrates. Its behavior is similar to the behavior of gibberellins in its stimulation of the enzymes necessary to convert complex compounds into simple compounds and exploit them in supplying the plant with energy and accelerating the division and elongation of cells [21,22]. The results also indicate an increase in the number of leaves, and this is consistent with all of Al-Abdali (2002) [23] on Dianthus caryophllus and Al-Jawari (2002) [24] on Capsicum annum L.

The extract of Glycrrhiza glabra L., in addition to being similar to gibberellin, contains many growth-promoting substances such as minerals, vitamins, sugars, flavonoids, saponins, sterols, amino acids, starch, and some nutrients such as potassium, phosphorus, zinc, iron, and magnesium [21]. The high percentage of nitrogen in Nigella sativa L. extract gives an increase in the number of branches as a result of the increase in photosynthesis and the processes of building protoplasm. The calcium present in Nigella sativa L.extract reduces the heat stress that the plant is exposed to, and this helps to improve vegetative growth and increase the number of branches and the number of leaves [24]. As for the banana peel extract, it contains many compounds that promote growth, such as some vitamins, flavonoids, proteins and amino acids. The results agree with (Nguyen et al.,2003 [20]; Guevara et al.,2005 ; Anwar et al., 2011) [18,19].

Table (6) the effect of plant extracts on root length of Vigna radiate L.

It is noted from Table (6) the effect of spraying plant extracts and their concentrations on the root length of Vigna radiate L. The results of the statistical analysis indicate that there are no significant differences between the root length rates of the three extracts.As for the effect of the different concentrations of plant extracts on the average root length, a significant increase was observed between their rates with an increase in the concentrations of those extracts, as the treatment (20) g / L had the highest rates reaching (21.15)cm, while it was the lowest when the control treatment reached (12.60)cm, and there were significant differences between the concentrations, but no significant differences were observed between the two concentrations (0, 5) g/l and the two treatments (10, 20) g/l. It was noted that there were significant differences between the root length rates due to the effect of the interaction of  two factors, the plant extracts and their concentrations, where the control treatment recorded the lowest rates and reached (12.60) cm, while the treatment of 20 g / L of licorice root extract had the highest and reached (23.50)cm .The reason may be due to the role of Glycrrhiza glabra L. extract, which increased the root length as it led to the accumulation of nutrients and thus increased the strength of vegetative growth and its transfer to the roots leading to increased growth in the root system [25]. The increase in the number of roots relative to the increase in the number of branches is due to the hormonal balance between the growth of roots and the growth of branches, as when a number of branches grows, a number of roots grows against it in order to balance plant growth, As the number of branches increases, an increase in the supply of raw materials obtained by the plant from the roots is required to supply the roots with auxins resulting from the growing apices of the branches, while the roots produce in their growing apices an amount of cytokines that are transmitted by wood to the growing apices of the branches, which leads to an increase in cell division and an increase in the number of The branches and these results are consistent with the findings of [26,27].

Conflict of Interest: The authors declare that they have no conflict of interest.

Funding: No funding sources 

Ethical approval: The study was approved by the Institutional Ethics Committee of Universitas Negeri Makassar

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