One Plant-Based Biostimulant Stimulates Good Performances of Tomato Plants Grown in Open Field ^†

Abstract

Most agricultural practices have evolved towards biological and sustainable systems. The purpose of modern agriculture is to reduce inputs without reducing yield and quality. This objective can be achieved through the identification of organic molecules capable of activating plant metabolism. Biostimulants contain a wide range of mostly still unknown bioactive compounds. These products are generally able to improve a plant’s nutrient utilization efficiency and increase tolerance to biotic and abiotic stresses. The aim of this study was to determine biometric measurements and metabolic profiling of two tomato genotypes grown in open field and treated or not with a plant-derived biostimulant named CycoFlow (Agriges). The application of the biostimulant stimulated growth (plants up to 55.06% higher) and yield per plant (up to 111.66%). In plants treated with the biostimulant, ascorbic acid and carotenoids contents in fruit were higher compared to non-treated plants. In particular, the content of β-carotene increased after treatments with the biostimulant. The present study proves that the effect of the biostimulant was dependent on genotype. Altogether, we demonstrated that the application of a plant-derived biostimulant can increase tomato performance in the field and that results are maximized on the appropriate genotype.

1. Introduction

There are many works in the literature that aimed to find alternative management practices able to improve the growth, productivity and quality of crops and that are also environmentally friendly [1]. For these reasons, in modern agriculture, the use of biostimulants is increasingly becoming an interesting and widespread option [2]. Biostimulants typically do not include nutrients; however, they promote nutrient uptake by stimulating root growth and function [3,4]. According to Traon [5], “A biostimulant is any substance or microorganism, in the form in which it is supplied to the user, applied to plants, seeds or the root environment with the intention of stimulating the natural processes of plants for the benefit of efficiency, the use of nutrients and/or tolerance to abiotic stress, regardless of its nutrient content, or any combination of such substances and/or microorganisms intended for this use”. Biostimulant treatment may differentially affect not only plant growth and yield, but also product quality. A critical indicator of crop quality is the content of antioxidant compounds determining high-added value [3,4]. These secondary metabolites protect from several external stressors and limit many diseases in humans. Among antioxidants, carotenoids and phenolic compounds are of particular interest due to their strong potential to reduce stress events both at cellular and organismal levels. In the wide range of biostimulants, particular attention has been given to compounds of plant origin whose effects is linked to their involvement in the metabolism, signaling and hormonal regulation of the growth and development of a plant [1,6,7,8,9]. Tomato (Solanum lycopersicum L.) is one of the most consumed vegetables worldwide, also owing to the development of products such as soups, juices, purees, and sauces [10]. Tomato is an essential component of the Mediterranean diet and of other traditional diets, and its consumption has been related to the prevention of many diseases. This positive effect has been associated with different molecules, including carotenoids and ascorbic acid, that are important health-promoting agents.

Given the key role of this crop, research aimed at improving yield and internal tomato quality could contribute to global food production. To verify this hypothesis, we used a plant-based biostimulant named CycoFlow (Agriges), and we performed biometric measurements and biochemical analyses on two different tomato genotypes grown in open field and treated or not with this novel plant-based biostimulant.

2. Methods

Experiments were carried out at an agronomy farm located in Apollosa, (Benevento), Italy (latitude 41°5′42″36 N; longitude 14°42′22″32 E) on a clay–loam soil. Four weeks following seeding, after the third true leaf was fully expanded, tomato plants (genotype E42, available at the University of Naples, Department of Agricultural Sciences and genotype LA3120, Tomato Genetics Resource Centre, TGRC, University of California, Davis, CA, USA) were transplanted into an open field in May 2020. Tomato plants were grown following the standard agronomical practices. The experimental design consisted of a completely randomized design with three replicates per treatment and ten plants per each biological replication. There were two different groups: one control, which did not receive any biostimulant, and one that was treated with the biostimulant. The biostimulant was applied at the moment of transplanting and thereafter every 15 days, until the end of the cultivation cycle for a total of four applications, by fertigation with a 3 g per liter solution. CycoFlow is a plant-extracts-based biostimulant produced by the Agriges company (Benevento, Italy), which is rich in glutamic acid (including glutamine) and glycine betaine, peptides, nucleotides, vitamins B, trace elements, and other growth factors. Its chemical composition contains total nitrogen of 4.5% and organic carbon of 19.5%. The biostimulant has a pH of 5.0, a density of 1200 kg/m³, and an EC value of 15 dS/m [11]. Pollen viability was analyzed using five flowers per plant sampled from three different plants per replicate with DAB test according to Dafni et al. [12]. Harvesting started at the beginning of August 2020. Six plants per treatment were collected for biomass determination and plant height. Plant height was measured from the root-to-shoot junction to the apical meristem. Shoot biomass was calculated as the sum of aerial vegetative plant parts (leaves + stems) and fruit were counted and weighted. Plant material was put in a stove at 85 °C for 24 h and the dry weight of the shoot was measured. Samples of freshly harvested, fully ripened fruit were collected from each plot to determine antioxidant and pigments content via a colorimetric assay on freeze-dried and finely ground sub-samples. The evaluation of total carotenoids, lycopene, and β-carotene was carried out according to the method reported by Wellburn and by Zouari et al., as modified by Rigano et al. [13,14,15]. Measurements of the content of reduced ascorbic acid (AsA) were carried out by using a colorimetric method [16], with modifications reported by Rigano et al. [17,18]. Total phenolic compounds were evaluated by using the Folin–Ciocalteu assay with modifications reported by Rigano et al. [17]. Hydrophilic antioxidant activity (HAA) determination was carried out according to the 2,20-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) method [19]. Data were analyzed via ANOVA, and means were compared using Tukey’s test.

3. Results and Discussion

As reported in Figure 1, the application of a plant-based biostimulant named CycoFlow (Agriges) resulted in higher height and higher fresh and dry biomass of the vegetative plant parts only in the genotype E42 compared to non-treated plants (Figure 1A–C). Marketable yield (Figure 1F) and its components, fruit number (Figure 1E) and average fruit weight (Table S1), were significantly affected by biostimulant treatment according to ANOVA analyses (

Table 1. Analyses of variance for all measurements in fruit of two tomato genotypes treated with the biostimulant CycoFlow.

	Significance
	G	B	GxB
Height (cm)	***	***	***
Pollen viability	**	ns	ns
Shoot FW (g)	**	**	*
Shoot DW (g)	ns	*	*
N° fruit	***	***	*
Yield (kg/pt)	ns	***	ns
Ascorbic acid (mg/100 g FW)	***	***	***
Carotenoids (mg/100 g FW)	***	ns	**
β-carotene (mg/100 g FW)	***	**	***
Lycopene (mg/100 g FW)	***	ns	ns
Phenols (mg/100 g FW)	***	***	ns
HAA Abts (µmol TE/100 g FW)	***	***	***

G = genotype, B = biostimulant; * = p ≤ 0.05; ** = p ≤ 0.01; *** = p ≤ 0.001.

). On the contrary, biostimulant application had no effect on pollen viability (Figure 1D, Table 1). In both genotypes, the application of the biostimulant resulted in significantly higher yields compared to non-treated control plants (+111.67% in E42 and +43.37% in LA3120) (Figure 1F). The observed effect may be due to the physiological mechanisms triggered in tomato plants after biostimulant application and linked to an increased content of signaling molecules, which are the main components of this biostimulant of plant origin [11]. Accordingly, it has been reported that plant growth, fruit set, and yield can be improved by the cytokinin-like activity of the biostimulant applied [11]. Biostimulant application likely increased plant development and yield by stimulating cell proliferation by signaling molecules, such as specific amino acids linked to nitrogen metabolism (i.e., glutamic and aspartic acids) and soluble peptides.

Fruit vegetables, and in particular tomato, are considered good sources of antioxidant molecules such as lycopene, ascorbic acid, and polyphenols; for this reason, a key aspect of biostimulant use is the increase in the content of these health-promoting compounds. The influence of biostimulant application on antioxidant activities and bioactive compounds is reported in Figure 2. The treatment with the biostimulant only increased the content of ascorbic acid in the genotype E42 (Figure 2A). The content of ascorbic acid increased by 28.59% in fruit from E42-treated plants, while it decreased by 14.36% in fruit from LA3120-treated compared to non-treated plants (Figure 2A). Only in the LA3120-treated plants there was a significant decrease in phenol content equal to 17.47% (Figure 2B). Moreover, a significantly higher antioxidant activity HAA (up to 1.82%) was demonstrated in fruit from E42 plants treated with the biostimulant (Figure 2C). These results are in agreement with results obtained in soybean seeds, Verbascum arcturus and Origanum microphyllum, even if the reported effects depended on the kind of biostimulant applied and on the number and method (foliar/root) of applications. [3,4,19,20]. According to ANOVA analyses, the application of biostimulant did not have a significant effect on either the carotenoid or the lycopene content (Table 1). Similar results were obtained by Chehade et al. [21] in tomato. On the contrary, Rouphael et al. [22] demonstrated that in tomato, foliar applications of a legume-derived protein hydrolysate, had an effect also on lycopene content. On the other hand, the β-carotene content is not influenced by the application of the biostimulant in the LA3120 genotype, but in the E42-treated plants, there was an increase in the β-carotene content, as shown in Figure 2E. In particular, a 13.63% higher content of β-carotene was registered in fruits from E42 treated with the biostimulant compared to the respective non-treated control. Altogether, the biostimulant had a greater effect on the content of ascorbic acid compared to the other compounds measured.

4. Conclusions

From the research conducted on two different tomato genotypes, the positive effects of the application of a biostimulant based on plant extracts on fruit yield, nutritional and functional attributes emerged. In general, the genotypic components remain decisive in the response obtained in the two tomato genotypes to the biostimulant, and the positive effects were only evident in the genotype E42. The fact that the effect of biostimulants may only be evident when the appropriate genotype is selected highlight the importance of performing pilot cultivation trails. Altogether, the present study demonstrated that the application of biostimulants may contribute to the creation of a sustainable, conventional tomato cultivation system.