Photosynthetic pigments, growth, and production of cherry tomato under salt stress and hydrogen peroxide¹

Pigmentos fotossintéticos, crescimento, e produção de tomate cereja sob estresse salino e peróxido de hidrogênio

ABSTRACT

Excess of salts in water and/or soil stands out as one of the stresses that compromise the development of crops, including cherry tomato, requiring the use of strategies that reduce salt stress effects, such as foliar application of hydrogen peroxide. Thus, the objective of this study was to evaluate the effect of foliar application of H₂O₂ on the contents of photosynthetic pigments, growth, and production of cherry tomato under irrigation water salinity. The design used was randomized blocks, in a 5 × 5 factorial scheme, with five values of electrical conductivity of water - ECw (0.3, 1.0, 1.7, 2.4, and 3.1 dS m^-1) and five concentrations of hydrogen peroxide - H₂O₂ (0, 15, 30, 45, and 60 μM). Application of hydrogen peroxide at concentration of 60 μM attenuated the deleterious effects of salt stress on the growth and number of leaves of cherry tomato up to ECw of 3.1 dS m^-1. Hydrogen peroxide concentration of 45 μM increased root dry mass, synthesis of chlorophyll b and total chlorophyll under electrical conductivity of water of 0.3 dS m^-1 and synthesis of chlorophyll a up to ECw of 0.8 dS m^-1. Foliar application of 30 μM reduced the effects of salt stress on leaf, shoot and total dry mass accumulation up to ECw of 3.1 dS m^-1. Electrical conductivity of water from 1.41 dS m^-1 reduced the production of cherry tomato.

Key words:
Solanum lycopersicum L.; acclimatization; elicitor; salinity

RESUMO

O excesso de sais na água e/ou no solo se destaca como um dos estresses que compromete o desenvolvimento das culturas, dentre elas o tomate cereja, sendo necessário o uso de estratégias que reduzam o efeito do estresse salino, como à aplicação foliar de peróxido de hidrogênio. Assim, o objetivo deste estudo foi avaliar o efeito da aplicação foliar de H₂O₂ sobre o teor de pigmentos fotossintéticos, crescimento e produção de tomate cereja sob salinidade da água de irrigação. O delineamento utilizado foi o de blocos casualizados, em esquema fatorial 5 × 5, sendo cinco valores de condutividade elétrica da água - CEa (0,3; 1,0; 1,7; 2,4 e 3,1 dS m^-1) e cinco concentrações de peroxido de hidrogênio - H₂O₂ (0; 15; 30; 45 e 60 µM). A aplicação de peróxido de hidrogênio na concentração de 60 µM atenuou o efeito deletério do estresse salino no crescimento em altura de plantas e no número de folhas de tomate cereja até a CEa de 3,1 dS m^-1. A concentração de 45 µM de peróxido de hidrogênio aumentou a fitomassa seca de raiz, a sintese de clorofila b e total sob água de condutividade elétrica de 0,3 dS m^-1 e de clorofila a até a CEa de 0,8 dS m^-1. A aplicação foliar de 30 µM reduziu o efeito do estresse salino no acúmulo de fitomassa seca de folhas, da parte aérea e total até a CEa de 3,1 dS m^-1. A condutividade elétrica da água a partir de 1,41 dS m^-1 reduziu a produção de tomate cereja.

Palavras-chave:
Solanum lycopersicum L.; aclimatação; elicitor; salinidade

HIGHLIGHTS:

Foliar application of H₂O₂ attenuates the effects of salt stress on cherry tomato growth under ECw of up to 3.1 dS m^-1.

H₂O₂ concentration of 45 µM increases chlorophyll contents in cherry tomato leaves.

Electrical conductivity of water above 1.41 dS m^-1 reduces cherry tomato production.

Introduction

The semi-arid region of the Brazilian Northeast is characterized by scarcity of water resources in terms of both quality and quantity, with irregular rainfall and high rates of evapotranspiration. Thus, the use of irrigation is a necessity of producers, who in many cases use water with high levels of salts, compromising crop development (Andrade et al., 2022).

Salt stress triggers a series of deleterious effects on plants, due to osmotic effects that limit their capacity to absorb water, ionic effects that result in specific ion toxicity and nutritional imbalance, and oxidative stress that leads to the formation of reactive oxygen species and degradation of enzymes and photosynthesizing pigments (Ramos et al., 2022a; Nóbrega et al., 2023).

Given the deleterious effects caused by salt stress on most cultivated species, there is a growing search for strategies capable of mitigating salt stress effects by inducing crop tolerance, among which the exogenous application of hydrogen peroxide (H₂O₂) stands out (Silva et al., 2021; Lacerda et al., 2022). In plants subjected to stress conditions, H₂O₂ application can induce cross-tolerance, through the signaling and modulation of antioxidant defense mechanisms, increasing the plant’s tolerance to salt stress (Santos et al., 2019; Veloso et al., 2022; Silva et al., 2024).

Cherry tomato (Solanum lycopersicum L.) is a crop of high potential for exploitation and commercialization in the Brazilian Northeast, being widely used in the ornamentation of dishes and appetizers (Roque et al., 2022). The beneficial effect of foliar application of H₂O₂ on cherry tomatoes was observed by Guedes et al. (2023), who reported that foliar application of up to 25 µM attenuated the effect of salinity on the number and quality of fruits produced in a hydroponic system. Thus, it is necessary to develop strategies that enable cultivation with saline waters under the semi-arid conditions of northeastern Brazil. Given this context, the objective of this study was to evaluate the effect of foliar application of H₂O₂ on the contents of photosynthetic pigments, growth, and production of cherry tomato under irrigation water salinity.

Material and Methods

The experiment was conducted under field conditions from July 28 to October 27, 2022, at the Centro de Ciência e Tecnologia Agroalimentar (CCTA) of the Universidade Federal de Campina Grande (UFCG), located in the municipality of Pombal, Paraíba, Brazil, at the geographical coordinates 6º 46’13” S and 37°48’06” W, at an altitude of 193 m. The climate of the region is hot and dry semi-arid, with average annual evaporation of 2,000 mm and average annual rainfall of approximately 750 mm, according to Köppen’s climate classification adapted to Brazil (Alvares et al., 2013). The data of maximum and minimum temperature, relative humidity, and precipitation during the experimental period are shown in Figure 1. Data were obtained daily with the aid of a digital thermo-hygrometer located in the center of the experimental area.

Figure 1
Data of maximum and minimum air temperature, relative air humidity, and precipitation during the experimental period (from July 27 to October 27, 2022)

A randomized block design was used, in a 5 × 5 factorial scheme, whose treatments consisted of the combination of two factors: five values of electrical conductivity of irrigation water - ECw (0.3, 1.0, 1.7, 2.4, and 3.1 dS m^-1) and five concentrations of hydrogen peroxide - H₂O₂ (0, 15, 30, 45, and 60 μM), with three replicates. The electrical conductivity values were based on a study carried out by Roque et al. (2022) with the cherry tomato crop (Solanum lycopersicum var. Cerasiforme), while the H₂O₂ concentrations were adapted from the study carried out by Dantas et al. (2022) with zucchini (Cucurbita pepo L.).

The seedlings were grown in polyethylene trays and transplanted into 20 L pots adapted as drainage lysimeters when they reached 10 cm in height. The lysimeters were filled with a 0.5 kg layer of crushed stone, followed by 20 kg of material from a sandy loam Neossolo Regolítico (Entisol - Psamment). The lysimeters were perforated at the base and connected to a 15-mm-diameter drain, positioned at the bottom of the lysimeter, wrapped with a non-woven geotextile (Bidim OP 30) to avoid clogging by soil material. Each drain was connected to a plastic bottle to collect drained water and determine water consumption by the plants. The soil used in the experiment came from the rural area of São Domingos de Pombal, PB, 0-20 cm layer, and its physical and chemical characteristics were obtained according to methodologies of Teixeira et al. (2017), as shown in Table 1.

Table 1
Chemical and physical attributes of the soil (0-20 cm depth) used in the experiment, before the application of the treatments

Chemical attributes
pH (H2O)		OM		P		K+		Na+		Ca2+		Mg2+		Al3+		H+
(1:2.5)		(g kg-1)		(mg kg-1)		(cmolc kg-1)
8.53		3.10		77.30		0.56		0.20		5.08		5.11		0		0
Chemical attributes							Physical attributes
ECse	CEC		SARse		ESP		Particle-size fraction (g kg-1)						Moisture (dag kg-1)
(dS m-1)	(cmolc kg-1)		(mmol L-1)0.5		(%)		Sand		Silt		Clay		33.42 kPa1		1519.5 kPa2
0.46	10.95		1.02		1.83		775.70		180.90		43.40		12.45		5.00

• pH - Hydrogen potential, OM - Organic matter: Walkley-Black Wet Digestion; Ca²⁺ and Mg²⁺ extracted with 1 M KCl at pH 7.0; Na⁺ and K⁺ extracted with 1 M NH4OAc at pH 7.0; Al³⁺+H⁺ extracted with 0.5 M CaOAc at pH 7.0; EC_se - Electrical conductivity of saturation extract; CEC - Cation exchange capacity; SAR_se - Sodium adsorption ratio of saturation extract; ESP - Exchangeable sodium percentage; ^1,2 referring to moisture contents in the soil corresponding to field capacity and permanent wilting point

Fertilization with NPK was carried out according to the recommendation of Trani et al. (2015) for the cultivation of table tomatoes, using urea as nitrogen source, with application of 38.9 g per plant (19.74 g of N), monoammonium phosphate as phosphorus source, with application of 20.35 g (12.44 g of P₂O₅ per plant), previously discounting the N supplied by this source, and potassium chloride as potassium source, with application of 65.94 g (39.56 g of K₂O per plant), starting at 12 days after transplanting, performed weekly via irrigation water.

The irrigation water of different electrical conductivity - ECw were prepared by dissolving sodium chloride (NaCl) in public-supply water of Pombal - PB, considering the relationship between ECw and salt concentration (Richards, 1954), according to Eq. 1:

$$C\left(mg L^{-1}\right)\approx 640\times ECw$$ (1)

where:

C - concentration of salts in irrigation water (mg L^-1); and

ECw - electrical conductivity of water (dS m^-1).

Prior to transplanting, the volume of water needed to raise soil moisture to the value corresponding to field capacity was determined. After transplanting, irrigation was performed daily at 5 p.m., applying in each lysimeter the volume corresponding to that obtained by the water balance, determined by Eq. 2:

$$VI-\frac{\left(Va-Vd\right)}{\left(1-LF\right)}$$ (2)

where:

VI - volume of water to be used in the irrigation event (mL);

Va - volume applied in the previous irrigation event (mL);

Vd - volume drained in the previous irrigation event (mL); and

LF - leaching fraction of 0.15, applied every 15 days.

The desired concentrations of H₂O₂ were obtained by dilution in deionized water and applied by foliar spraying in the late afternoon (from 5 p.m.), performed manually with a spray bottle and fully wetting the leaves (abaxial and adaxial sides). The applications began 72 hours before the beginning of the application of saline water and were subsequently performed at 15-day intervals, until the plants began to flower. During H₂O₂ spraying, a plastic structure was used to prevent the solution from drifting onto neighboring plants, and an average volume of 15 mL was applied per plant.

At 45 days after transplanting (DAT), the contents of photosynthetic pigments and plant growth were evaluated. Contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids were determined according to the methodology of Arnon (1949), using plant extracts collected from the blade of the third mature leaf from the apex, quantifying the values with a spectrophotometer at the absorbance wavelength (ABS) (470, 647 and 663), according to Eqs. 3, 4, 5, and 6:

$$Chlorophyll a=\left(12.25\times AB{S}_{663}\right)-\left(2.79\times AB{S}_{647}\right)$$ (3)

$$Chlorophyll b=\left(21.5\times AB{S}_{647}\right)-\left(5.1\times AB{S}_{663}\right)$$ (4)

$$Total chlorophyll=\left(7.15\times AB{S}_{663}\right)+\left(18.71\times ABS\right)$$ (5)

$$Carotenoids=\frac{\left[\left(1000\times AB{S}_{470}\right)-\left(1.82\times Chl a\right)-\left(85.02\times Chl b\right)\right]}{198}$$ (6)

The values obtained for the contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids were expressed in mg g^-1 of fresh matter (FM).

Growth variables evaluated were the number of leaves (NL), determined by counting fully formed leaves; plant height (PH), obtained by taking as reference the distance from the plant collar to the insertion of the apical meristem; stem diameter (SD), measured at 5 cm from the plant collar with a digital caliper; and the height/diameter ratio of cherry tomato plants.

The production components of cherry tomato were determined by evaluating the number of fruits per plant (NFP), total fruit fresh mass (TFFM), and average fruit weight (AFW). NFP was obtained by counting all fruits produced per plant. TFFM was determined on a precision balance. AFW was determined as the ratio between TFFM and NFP. Harvest was carried out when the fruits showed color varying from light green to bright red (Monteiro et al., 2018) and began at 45 DAT, extending to 75 DAT.

At the end of the experiment at 75 DAT, the plants were removed from the lysimeters and separated into roots, stem, and leaves, which were placed in kraft paper bags and dried in a forced air circulation oven at 65 ºC until reaching constant weight. Then, the samples were weighed on a balance with 0.01 g precision to obtain root dry mass, stem dry mass and leaf dry mass. Shoot dry mass was obtained by summing stem dry mass and leaf dry mass, while the total dry mass of cherry tomato was determined by summing all the biomass values.

The data obtained were subjected to the normality test (Shapiro-Wilk) and then to analysis of variance by the F test at p ≤ 0.01 and p ≤ 0.05. Polynomial regression analysis was applied, and trend lines were presented only for the variables with coefficient of determination (R²) > 0.6, for prognostic purposes. The statistical program Sisvar^® version 5.6 was used to perform the analysis (Ferreira, 2019).

Results and Discussion

The interaction between irrigation water electrical conductivity values and H₂O₂ concentrations significantly (p ≤ 0.01) affected the contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids of cherry tomato plants (Table 2).

Table 2
Summary of the analysis of variance for chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Chl T) and carotenoids (Car) of cherry tomato plants, at 45 days after transplanting subjected to electrical conductivity of irrigation water (ECw) values and hydrogen peroxide (H₂O₂) concentrations

Variation sources	DF	Mean squares
		Chl a	Chl b	Chl T	Car
ECw values (ECw)	4	0.0052**	0.0079**	0.020**	0.00014**
Linear regression	1	0.000083ns	0.00032ns	0.00029ns	0.00044**
Quadratic regression	1	0.0050**	0.0014*	0.0023ns	0.000001ns
Hydrogen peroxide (H2O2)	4	0.00037ns	0.0025**	0.0048**	0.00017**
Linear regression	1	0.000021ns	0.00016ns	0.00036ns	0.00037**
Quadratic regression	1	0.00085ns	0.00009ns	0.000017ns	0.000086*
Interaction (ECw × H2O2)	16	0.00038**	0.0029**	0.012**	0.00012**
Blocks	2	0.00021ns	0.00012ns	0.0043**	0.000025ns
Residual	48	0.00030	0.00028	0.00075	0.000014
CV (%)		5.59	10.9	5.79	5.62

• DF - Degrees of freedom; CV - Coefficient of variation; (**) significant at p ≤ 0.01; (*) significant at p ≤ 0.05; (ns) not significant

Application of H₂O₂ reduced the effect of salt stress on the synthesis of photosynthetic pigments of cherry tomato. For the chlorophyll a contents (Figure 2A), the highest estimated value (0.35 mg g^-1 FM) was obtained in plants subjected to ECw of 0.8 dS m^-1 and 45 μM of H₂O₂. In plants grown under ECw of 3.1, 2.3 and 0.3 dS m^-1, the maximum estimated values of 0.33, 0.32 and 0.33 mg g^-1 FM were achieved under foliar application of 0, 15 and 30 μM of H₂O₂, respectively. On the other hand, in plants subjected to electrical conductivity of water of 1.9 dS m^-1 the maximum value (0.32 mg g^-1 FM) was achieved under application of 60 μM of H₂O₂ (y = 0.2780 + 0.0454**x - 0.0117**x², R² = 0.56). The beneficial effect of H₂O₂ at adequate concentrations on chlorophyll a contents is associated with its physiological role in signaling defense mechanisms and cellular homeostasis in plants subjected to stress conditions (Veloso et al., 2022).

Figure 2
Contents of chlorophyll a, chlorophyll b, total chlorophyll (A, B, and C, respectively), and carotenoids (D) of cherry tomato plants, at 45 days after transplanting as a function of electrical conductivity of irrigation water - ECw and hydrogen peroxide concentrations

Chlorophyll b and total chlorophyll contents were higher (0.20 and 0.59 mg g^-1 FM) in plants subjected to irrigation water electrical conductivity of 0.3 dS m^-1 and H₂O₂ concentration of 45 μM, respectively (Figure 2B and 2C). The increase in chlorophyll contents occurs due to the metabolic changes triggered by H₂O₂, stimulating the activity of antioxidant enzymes that reduce the degradation of photosynthetic pigments (Ashraf et al., 2015). However, it was observed that the increase in H₂O₂ concentration of 60 μM led to the lowest values (0.10 and 0.36 mg g^-1 FM) in plants irrigated with water of 0.3 dS m^-1. The occurrence of this effect may be due to the fact that H₂O₂ is a reactive species of oxygen, which in excess can cause oxidative stress and even intensify the damaging effect of salinity. This fact has been observed by Andrade et al. (2022) in yellow passion fruit (Passiflora edulis f. flavicarpa Dreneger) and by Capitulino et al. (2023) in soursop (Annona muricata L.).

The H₂O₂ concentration of 15 μM (y = 0.0609 + 0.0069*x - 0.0020*x², R² = 0.57) attenuated the effect of electrical conductivity of water on carotenoid contents, with the highest value (0.10 mg g^-1 FM) obtained under electrical conductivity of 3.1 dS m^-1 (Figure 2D). On the other hand, irrigation with ECw of 0.3 dS m^-1 and foliar application of 45 μM resulted in the lowest value of carotenoids (0.05 mg g^-1 FM). At H₂O₂ concentrations of 0 and 60 μM, the highest values of carotenoids (0.073 and 0.072 mg g^-1 FM) were obtained in plants subjected to ECw of 3.1 dS m^-1, whereas the H₂O₂ concentrations of 30 and 45 μM resulted in values of 0.072 and 0.074 mg g^-1 FM under ECw of 1.9 and 2.2 dS m^-1, respectively. This behavior indicates that H₂O₂ application induced the production of carotenoids in cherry tomato plants, standing out as a mechanism to prevent photoinhibition due to salt stress, improving the acclimatization of plants and reducing oxidative stress (Andrade et al., 2022).

The occurrence of beneficial effect of H₂O₂ application on the synthesis of photosynthetic pigments in plants under salt stress conditions has been reported in other species, such as passion fruit, for which Ramos et al. (2022a) found that the application of 15 μM of H₂O₂ attenuated the effect of electrical conductivity up to 3.0 dS m^-1 and increased the contents of chlorophylls and carotenoids. Aragão et al. (2023) also found that the concentration of 15 μM increased the synthesis of photosynthetic pigments in bell pepper plants up to ECw of 1.4 dS m^-1.

The interaction between electrical conductivity of water and H₂O₂ concentrations significantly influenced (p ≤ 0.01) all growth variables analyzed (Table 3).

Table 3
Summary of the analysis of variance for plant height (PH), stem diameter (SD), number of leaves per plant (NL), plant height/stem diameter ratio (PH/SD), root (RDM), stem (STDM), leaf (LDM), shoot (SHDM), and total (TDM) dry mass per plant of cherry tomato, at 45 days after transplanting subjected to electrical conductivity of irrigation water (ECw) values and hydrogen peroxide (H₂O₂) concentrations

Variation sources	DF	Mean squares
		PH	SD	NL	PH/SD	RDM	STDM	LDM	SHDM	TDM
ECw values (ECw)	4	618.23**	0.58ns	36.18**	8.99**	26.61**	13.38**	3.84**	12.32**	69.34**
Linear regression	1	816.66**	1.60*	34.56**	2.33ns	35.11**	38.99**	4.81**	16.39**	99.51**
Quadratic regression	1	7.24ns	0.20ns	47.61**	0.83ns	60.96**	12.32**	3.00*	27.50**	170.37**
Hydrogen peroxide (H2O2)	4	93.29**	0.34ns	17.75**	3.99ns	8.63**	8.67**	10.45**	32.12**	64.37**
Linear regression	1	81.40*	0.007ns	52.80**	1.22ns	6.00**	15.81**	0.039ns	14.27**	38.79**
Quadratic regression	1	15.74ns	0.15ns	0.23ns	2.82ns	12.40**	12.25**	29.98**	80.58**	156.22**
Interaction (SL × H2O2)	16	381.69**	2.10**	28.32**	20.22**	4.43**	6.74**	19.25**	35.66**	41.01**
Blocks	2	43.22ns	0.44ns	6.09ns	3.17ns	0.078ns	1.38ns	1.20ns	1.60ns	1.01ns
Residual	48	20.12	0.28	3.02	2.28	0.51	0.57	0.61	1.39	1.66
CV (%)		5.96	8.71	8.95	12.0	22.3	10.2	10.0	7.80	7.44

• DF - Degrees of freedom; CV - Coefficient of variation; (**) significant at p ≤ 0.01; (*) significant at p ≤ 0.05; (ns) not significant

Hydrogen peroxide application increased the growth in height of cherry tomato plants, with the highest value of 88 cm obtained under irrigation with ECw of 3.1 dS m^-1 and H₂O₂ concentration of 60 μM, while the lowest value (66.4 cm) was obtained under 30 μM of H₂O₂ and electrical conductivity of 3.1 dS m^-1. At H₂O₂ concentrations of 0 and 15 μM (y_{15 μM} = 60.4981 + 15.6292^*x - 3.7901*x², R² = 0.56), the highest estimated values of 81.7 and 76.6 cm were reached in plants subjected to ECw of 3.1 and 2.1 dS m^-1, respectively. For the concentrations of 30 μM (y_{30 μM} = 67.4138 + 11.3300*x - 3.7609*x², R² = 0.51) and 45 μM, the highest values of 76.0 and 87.0 cm were obtained in plants subjected to ECw of 1.5 dS m^-1 (Figure 3A).

Figure 3
Plant height (A), stem diameter (B), number of leaves (C), and plant height/stem diameter ratio (D) of cherry tomato plants, at 45 days after transplanting as a function of electrical conductivity of irrigation water (ECw) values and hydrogen peroxide (H₂O₂) concentrations

Thus, it is possible to highlight that the H₂O₂ concentrations of 45 and 60 μM promoted the highest growth in height of cherry tomato plants under water salinity conditions, possibly because H₂O₂ is involved in the mechanisms of enzymatic defense and contributes to reducing osmotic and ionic effects, enabling greater absorption of water and nutrients by plants, in addition to reducing the accumulation of reactive oxygen species, avoiding oxidative stress (Capitulino et al., 2023).

For stem diameter (Figure 3B), the largest increase occurred in plants subjected to ECw of 1.6 dS m^-1 and H₂O₂ concentration of 0 μM (control), with the maximum estimated value of 7.12 mm. However, as the ECw increased, reductions were observed, with the lowest value of 5.16 mm in plants grown under irrigation water electrical conductivity of 3.1 dS m^-1 and H₂O₂ concentration of 0 μM. At H₂O₂ concentrations of 15 and 60 μM, the highest values (6.7 mm for both) occurred in plants subjected to ECw of 3.1 dS m^-1. At concentrations of 30 and 45 μM, the highest values (7.08 and 7.0 mm) were obtained under ECw of 0.3 and 1.9 dS m^-1, respectively. This behavior indicates that H₂O₂ application accentuated the effect of salt stress, reducing stem diameter when compared to plants that did not receive H₂O₂ application. This reduction in diameter caused by salt stress occurs due to changes in the physiological processes of the plant, including cell expansion and elongation (Nóbrega et al., 2022).

The number of leaves was higher in plants that received H₂O₂ application at concentrations of 45 μM and ECw value of 2.1 dS m^-1, and 60 μM under the ECw values of 0.3 and 3.1 dS m^-1, with 23 leaves in both cases (Figure 3C). Hydrogen peroxide concentrations of 0, 15 and 30 μM promoted the maximum estimated values of 22 and 20 leaves in plants subjected to ECw of 3.1 and 1.6 dS m^-1, respectively. Contrary to what was observed for the growth in stem diameter (Figure 3B), the increase in the number of leaves is an indication that the application of H₂O₂ mitigated the effect of salt stress, probably due to its function in the signaling of enzymes that regulate the plant’s defense system, increasing tolerance to salt stress (Aragão et al., 2023).

The highest plant height/stem diameter ratio (16.1) occurred in plants subjected to water salinity of 2.0 dS m^-1 and H₂O₂ concentration of 30 μM (Figure 3D). At concentrations of 0 and 15 μM, the highest values (12.9 and 12.6) were obtained in plants subjected to irrigation water electrical conductivity of 1.4 dS m^-1. At H₂O₂ concentrations of 45 μM (y_45μM = 13.6169 + 1.1620*x - 0.5758*x², R² = 0.52) and 60 μM, the highest values of PH/SD ratio (14.2 and 13.0) were obtained under ECw of 1.0 and 0.3 dS m^-1, respectively. The increase in plant height/stem diameter ratio promoted by H₂O₂ concentrations is an indication that its application improves the tolerance of cherry tomato probably due to the contribution of metabolites and antioxidants (Silva et al., 2024).

Beneficial effect of exogenous application of H₂O₂ on plant growth under salt stress conditions has also been reported by other authors, such as Santos et al. (2019), who evaluated melon under concentration of 15 mM. Capitulino et al. (2023) found that the concentration of 30 μM attenuates the effects of salinity on soursop, and Aragão et al. (2023), in bell pepper, observed a mitigating effect at the concentration of 15 μM.

The dry mass production of cherry tomato plants was stimulated by H₂O₂ application under salt stress conditions. For root dry mass (Figure 4A), the highest value (8.07 g per plant) was obtained in plants subjected to ECw of 0.3 dS m^-1 and H₂O₂ concentration of 45 μM, with a reduction of 46% when compared with the values obtained in plants cultivated under ECw of 3.1 dS m^-1. At the other H₂O₂ concentrations, the highest RDM values were also observed under the lowest ECw (0.3 dS m^-1), with reductions of 21.7, 39.6, 37.2, and 13.7% compared to plants irrigated with water of highest electrical conductivity (3.1 dS m^-1) at H₂O₂ concentrations of 0, 15, 30, and 60 μM, respectively. Hydrogen peroxide is a signaling molecule of the defense system, which induces the production of organic compounds and proteins, reducing the oxidative effect of reactive oxygen species (Khan et al., 2018), which may have enabled the development of the root system of cherry tomato plants.

Figure 4
Root (A), stem (B), leaf (C), shoot (D) and total (E) dry mass of cherry tomato plants, at 75 days after transplantation as a function of electrical conductivity of irrigation water (ECw) values and hydrogen peroxide (H₂O₂) concentrations

For stem dry mass (Figure 4B), the highest estimated values were reached in plants grown under ECw of 0.3 dS m^-1 and H₂O₂ concentrations of 15, 30 and 45 μM (10.6, 9.23 and 9.31 g per plant). Foliar application of 60 μM of H₂O₂ promoted the maximum value (9.0 g per plant) in plants grown under estimated ECw of 0.9 dS m^-1, whereas plants grown under foliar application of 0 μM obtained the maximum value (6.59 g per plant) under irrigation with water of electrical conductivity of 1.2 dS m^-1. When comparing the maximum values obtained, it is possible to observe increments of 37.8, 28.6, 29.2, and 26.8% at the concentrations of 15, 30, 45, and 60 μM, respectively, compared to the control (0 μM), indicating that H₂O₂ promoted greater growth of cherry tomato plants subjected to salt stress. It is noteworthy that H₂O₂ concentration of 15 µM caused a marked reduction in plants subjected to ECw of 1.7 dS m^-1. The fact that H₂O₂ acts on the antioxidant defense mechanisms of plants, from the signaling of enzymes, induces tolerance to salinity (Lacerda et al., 2022), allowing greater capacity to promote cell expansion and division, resulting in increased stem biomass.

For leaf, shoot, and total dry mass of cherry tomato plants (Figures 4C, 4D and 4E), the highest values (13.4, 22.1, and 26.8 g per plant) were obtained under irrigation with water of electrical conductivity of 3.1 dS m^-1 and H₂O₂ concentration of 30 μM, whereas the lowest values (4.23, 9.22, and 11.1 g per plant, respectively) were obtained in plants subjected to ECw of 3.1 dS m^-1 and H₂O₂ concentration of 60 μM. The increase in biomass accumulation may be associated with the fact that H₂O₂ acts in the regulation of plant growth under stress conditions, increasing cell wall strength and resistance, and favoring cell expansion processes (Ramos et al., 2022b).

There was significant effect of the interaction between water electrical conductivity values and H₂O₂ concentrations for the average fruit weight (p ≤ 0.05), while water salinity significantly (p ≤ 0.05) influenced the number of fruits per cherry tomato plant (Table 4). Total fruit fresh mass was significantly affected by the single factors electrical conductivity values (p ≤ 0.01) and H₂O₂ concentrations (p ≤ 0.05).

Table 4
Summary of the analysis of variance for number of fruits per plant (NFP), average fruit weight (AFW), and total fruit fresh mass (TFFM) of cherry tomato, harvested in the period from 45 to 75 days after transplanting subjected to electrical conductivity of irrigation water (ECw) values and hydrogen peroxide (H₂O₂) concentrations

Variation sources	DF	Mean squares
		NFP	AFW	TFFM
ECw values (ECw)	4	55.05*	11.75**	4028.02**
Linear regression	1	63.37*	37.88**	3971.99**
Quadratic regression	1	90.02*	3.38ns	105.88ns
Hydrogen peroxide (H2O2)	4	11.38ns	3.80ns	1704.91*
Linear regression	1	6.61ns	6.00ns	1573.47*
Quadratic regression	1	0.86ns	7.59ns	717.09ns
Interaction (ECw × H2O2)	16	17.44ns	4.24*	638.01ns
Blocks	2	13.48ns	0.65ns	648.25ns
Residual	48	11.06	2.00	392.29
CV (%)		35.7	23.1	32.4

• DF - Degrees of freedom; CV - Coefficient of variation; (**) significant at p ≤ 0.01; (*) significant at p ≤ 0.05; (ns) not significant

The number of fruits per plant was described by the quadratic model, with the highest value (12 fruits per plant) obtained in plants grown under ECw of 1.4 dS m^-1 (Figure 5A), followed by decreases with increasing salinity, reaching 36.2% when compared with the values obtained at ECw of 3.1 dS m^-1. It should be noted that the values obtained in this study are well below the average values of the crop’s production capacity, which is due to the environmental conditions during the flowering and fruiting stages, when high temperatures associated with low relative humidity may have intensified the effect of salinity, causing the abortion of flowers and fruits, as highlighted by Roque et al. (2022) in a study with cherry tomato.

Figure 5
Number of fruits per plant of cherry tomato as a function of electrical conductivity of irrigation water (ECw) (A), average fruit weight as a function of the interaction between ECw and hydrogen peroxide (H₂O₂) concentrations (B), and total fruit fresh mass (C and D) as a function of ECw (C) and H₂O₂ concentrations (D), for fruits harvested in the period from 45 to 75 days after transplantation

For average fruit weight (Figure 5B), the highest values (8.28 and 8.26 g per fruit) were achieved in plants subjected to irrigation water electrical conductivity of 1.8 dS m^-1 and H₂O₂ concentrations of 0 and 15 μM, respectively (Figure 5A). Plants grown under foliar application of 45 μM (y_45μM = 4.1593 + 1.6449*x - 0.3834*x², R² = 0.58) obtained the highest value (5.92 g per fruit) under ECw of 2.1 dS m^-1. The AFW data of plants subjected to H₂O₂ concentrations of 30 and 60 μM were not satisfactorily described by any regression model tested (y_30μM = 5.8603 + 0.4579^*x - 0.0948*x², R² = 0.35; y_60μM = 5.7631 - 0.6668^*x + 0.2259*x², R² = 0.36), respectively.

From the results it is possible to verify that H₂O₂ application accentuated the effect of salt stress on the production of cherry tomato, reducing the average fruit weight when plants were subjected to different concentrations and compared to the control (0 μM). By intensifying the deleterious effect of salinity, H₂O₂ causes oxidative stress due to accumulation of reactive oxygen species, reducing plant production (Dantas et al., 2022).

For the total fruit fresh mass, it is possible to observe that the salinity of irrigation water caused reductions, with the highest estimated value (71.4 g per plant) obtained in plants subjected to ECw of 1.1 dS m^-1, reaching a reduction of 43.5% (31.03 g per plant), when compared with the values obtained under irrigation water electrical conductivity of 3.1 dS m^-1 (Figure 5C). This effect is an indication that salt stress caused a reduction in the number of fruits and in their size, resulting in low values of total fruit fresh mass. Reduction in cherry tomato production due to salt stress was also found by Agius et al. (2022), but the authors point out that salinity promoted improvements in the physicochemical quality of the fruits.

Regarding the effect of H₂O₂ concentrations on the total fresh mass of cherry tomato fruits (y = 50.9429 + 0.7023*x - 0.0081*x², R² = 0.58), it is possible to highlight that the highest value (66.2 g per plant) was obtained in plants subjected to a concentration of 43 μM, representing an increase of 23% when compared to the values of plants that did not receive foliar application of H₂O₂. This effect may be associated with a positive effect of H₂O₂ on the development and biomass production of shoots, increasing the availability of organic solutes to the fruits, resulting in an increase in the total fresh mass of cherry tomato fruits. This was observed in potato production by Elhady et al. (2021), who found that H₂O₂ application promoted increments in water productivity and tuber yield.

Conclusions

1. Electrical conductivity of irrigation water above 1.4 dS m^-1 compromises the growth, photosynthetic pigments, and production of cherry tomatoes.

2. Application of hydrogen peroxide at concentration of 60 μM attenuates effects of salt stress on the growth in plant height and number of leaves of cherry tomato up to the electrical conductivity of 3.1 dS m^-1, at 45 days after transplanting.

3. Foliar application of hydrogen peroxide up to 45 μM increases dry mass production and chlorophyll synthesis under water salinity of 0.3 and 0.8 dS m^-1, respectively. The production of carotenoids is stimulated by the application of 15 μM of hydrogen peroxide up to electrical conductivity of irrigation water of 3.1 dS m^-1.

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• ¹ Research developed at Universidade Federal de Campina Grande, Centro de Ciências e Tecnologia Agroalimentar, Pombal, PB, Brazil

Edited by

Editors: Ítalo Herbet Lucena Cavalcante & Walter Esfrain Pereira

Publication Dates

• Publication in this collection
  29 Mar 2024
• Date of issue
  June 2024

History

• Received
  26 June 2023
• Accepted
  17 Jan 2024
• Published
  20 Feb 2024