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Article

Two Genotypes of Tomato Cultivated in Gobi Agriculture System Show a Varying Response to Deficit Drip Irrigation under Semi-Arid Conditions

by
Xuemei Xiao
1,2,
Xiaoqi Liu
3,
Ning Jin
1,
Yue Wu
1,
Zhongqi Tang
1,
Khuram Shehzad Khan
4,
Jian Lyu
1 and
Jihua Yu
1,2,*
1
College of Horticulture, Gansu Agricultural University, Lanzhou 730070, China
2
State Key Laboratory of Aridland Crop Science, Gansu Agricultural University, Lanzhou 730070, China
3
Agricultural Science Research Institute, The Sixth Division of Xinjiang Production and Construction Corps, Wujiaqu 831301, China
4
College of Agronomy, Gansu Agricultural University, Lanzhou 730070, China
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(9), 2133; https://doi.org/10.3390/agronomy14092133
Submission received: 9 August 2024 / Revised: 31 August 2024 / Accepted: 16 September 2024 / Published: 19 September 2024
(This article belongs to the Section Water Use and Irrigation)
Browse Figures
Versions Notes

Abstract

:
Water-saving irrigation is of extraordinary importance for tomato production in semi-arid areas of northwest China. For this purpose, we conducted a two-season trial in a solar greenhouse of two tomato genotypes named ‘181’ and ‘Mao Fen 802’ and cultivated with substrate, under four irrigation regimes, i.e., well-watered (WW), low (LWD, 80% WW), moderate (MWD, 60% WW) and high (HWD, 40% WW) water deficit. The substrate water content of WW treatment was 75%θf to 90%θf (where θf is the field capacity). The study results showed that the single fruit weight and yield of tomato were significantly declined with an increasing water deficit degree. Compared to WW treatment, the fruit weight and yield were decreased about 34.45% and 20.35% for ‘181’ and ‘Mao Fen 802’ under HWD treatment, respectively. Conversely, water deficit treatment led to an obvious promotion of WUE and showed an upward trend as the water deficit level increased. In addition, compared to WW treatment, the water deficit significantly decreased the total flavonoids of the ‘181’ tomato by 24.4–93.1%, whereas there was no significant impact on that of ‘Mao Fen 802’. Nonetheless, different individual polyphenols were increased by suitable deficit irrigation for two tomato cultivars. Gallic acid, 3,4-dihydroxybenzoic acid, and naringin of ‘181’tomato were increased by 128.4–195.2%, 8.6–43.7%, and 31–73-fold, respectively, under water deficit compared to WW treatment. Further, under water deficit treatment, p-coumaric acid, benzoic acid, and 3,4-dihydroxybenzoic acid of ‘Mao Fen 802’ were increased by 36.2–49.2%, 59.1–189.7%, and 36.3–106.4% compared to WW treatment. As the main carotenoid component, the lycopene content of tomato fruit exhibited a significant rise of 7.84–20.02% and 20.55–32.13% for ‘181’ and ‘Mao Fen 802’ under three degrees of water deficit compared to WW treatment. Linear regression showed a significantly positive relationship between irrigation amounts and yield, and total polyphenols, whereas there was a significantly negative relationship between irrigation amounts and WUE, and total carotenoids. Based on correlation and PCA, WW and LWD, and MWD and HWD, were gathered together for ‘181’, while LWD, MWD, and HWD, were gathered, and only WW scattered for ‘Mao Fen 802’, along the PC1 direction. It was proposed that ‘Mao Fen 802’ was more sensitive to water deficit than the ‘181’ tomato. In conclusion, water deficit is conductive to water-saving cultivation of the greenhouse tomato and the tomato genotypes, and water deficit level is a key factor necessary for consideration.

1. Introduction

Water has become a limited resource across the world, particularly in semi-arid and arid regions [1]. In China, about 58.74% of the land area belongs to the arid and semi-arid regions [2]. It is a major agricultural challenge for developing regions because of the vast water consumption in agricultural production. As we all know, the tomato is a high-economic horticultural crop and a nutrient-rich variety that is necessary for human health. Based on this information, the tomato is widely cultivated around the world, exceeding 4.8 million hectares [3]. However, a previous study demonstrated that tomato growth highly relied on water, and water shortages resulted in a decrease in photosynthesis and fruit production [4]. For tomato agricultural production, it is urgent to adopt effective water-saving irrigation strategies, such as regulated deficit irrigation (RDI), and drip irrigation [5,6]. RDI is generally defined as an irrigation practice of watering a crop with a lower irrigation amount than the optimal requirement for plant growth [5]. Extensive studies demonstrated that moderate water deficit not only increased water use efficiency (WUE), and saved water consumption [7,8,9] but also improved fruit quality and flavor with a slightly depressed yield [10,11]. Consequently, learning how to maximize the promotion of deficit irrigation on WUE and fruit quality is worthy of further investigation by scholars and agronomists.
In arid and semi-arid environments, there are large areas of “Gobi land” (defined as non-arable land), including 1.95 million ha of desert land in the six provinces of Northwestern China [12]. China’s diligent efforts to build this Gobi land for food production includes using an innovative cropping system called “Gobi agriculture”. Herein we define this cultivation system as “a cultivation system with a cluster of locally constructed, solar-powered plastic greenhouse with drip irrigation system-like cultivation units for the production of high-yielding, high-quality fresh produce (vegetables, fruits, and ornamentals) in an effective, efficient and economical manner” [13]. Previous studies reported that the efficient water-saving potential of Gobi agriculture was observed more than in traditional cultivation patterns, which might be due to the controlled water supply, subsurface drip irrigation, and useful mulching methods [14,15]. In the Gobi land cultivation system, tomatoes are considered main vegetables, which need an adequate water supply throughout the growing season. Furthermore, in order to blindly pursue high yield for farmers, excess irrigation still happens in greenhouse tomato cultivation, which not only causes the waste of water resources [16] but also decreases WUE and nutrient use efficiency, as well as fruit quality deterioration [17,18]. Although there are many studies focused on the application of water deficit on tomatoes to save water and improve WUE [18,19,20], the literature seldomly reported on tomatoes grown in ‘Gobi agriculture’ in response to deficit drip irrigation. This cultivation pattern of tomatoes was carried out in the present study.
Despite abundant landraces and cultivars of tomato, a few modern genotypes were given more attention due to increased yield rates, but less quality and flavor followed [21]. Several studies demonstrated that the long shelf-life (LSL) and thick skin of the tomato fruit showed more drought tolerance [22,23]. However, because of the lack of characteristic tomato flavor and good taste, LSL tomatoes have little place in the fresh tomato market. Due to the increasing demand by consumers for flavor and taste, the high-quality (“flavor varieties”) genotypes rich in bioactive compounds of tomato were bred by breeding scientists [24,25]. Nevertheless, these tomatoes always exhibited a weak resistance to adversity and sensitivity to pathogeny [24]. A recent study confirmed that different cultivars (landraces and modern genotypes) and fruit types (processing, big size, long shelf-life, and cherry) of tomatoes showed varying response to different degrees of water deficit [22]. Thus, it is necessary to understand the effect of deficit irrigation on high-quality and common genotypes of tomatoes.
Polyphenols and carotenoids, as crucial bioactive compounds, are recognized as conductive ingredients for human health [26,27]. It is well known that tomato is a good source of these two bioactive compounds, which play a vital role in the prevention of cardiovascular diseases and cancer [28]. Moreover, polyphenols and carotenoids comprise various components, such as flavonoids, phenolic acids, lycopene, and β-carotene. Each component appears to play a specific function on human health. In addition, polyphenols and carotenoids are important antioxidants, which play a vital role in resisting adverse environmental conditions, including water shortage. Previous studies reported that appropriate water deficit improves the accumulation of polyphenols and carotenoids in tomato fruit [23,29]. Also, several studies concentrated on total polyphenols and carotenoids in response to deficit irrigation, while studies on various components of polyphenols and carotenoids were rare.
Therefore, in this study, the following two research questions were proposed: What is the optimal water deficit strategy for the tomato in Gobi agriculture system? Is the response of two tomato varieties (“flavor varieties” and “common varieties”) of tomato to water deficit the same? To solve these questions, the yield, WUE, 16 polyphenols, and 4 carotenoids of tomato fruit were investigated for two genotypes of tomato, cultivated in Gobi agriculture over two consecutive growing seasons, under four irrigation regimes. The objectives of this study are to: (1) explore the impact of deficit drip irrigation on two genotypes of tomato from the perspective of yield, WUE, and bioactive compounds; (2) evaluate the response of two tomato cultivars to different water deficit levels based on a multivariate statistical analysis; (3) and obtain the optimum water deficit strategy for tomatoes grown in the ‘Gobi agriculture’ system.

2. Materials and Methods

2.1. Experimental Site and Growth Conditions

This experiment was conducted in a solar greenhouse located in Yuzhong County, Lanzhou city, Gansu Province, China (35°87′ N, 104°09′ E) from November 2021 to May 2022. A tank culture with a length of 9 m, a width of 0.4 m, and a depth of 0.25 m was used. The substrate of 1 m3 was filled in each tank culture, which was purchased from Gansu Lvnengriqi Agricultural Technology Co., Ltd., Wuwei, China. The averaged substrate bulk density was 0.584 g/cm3, and the field capacity was 76.55%. The main substrate sources were various planting and breeding waste such as livestock manure and crop straw after fermentation. The experimental site daily mean maximum and minimum substrate temperature were 31.8 °C and 10.4 °C, the daily mean maximum and minimum air temperature was 21.6 °C and 16.3 °C, and the daily mean maximum and minimum air relative humidity was 93.7% and 41.7%, respectively (Figure 1).
The tomato plants were arranged in two lines of each culture tank, with spacing between plants and rows of 0.45 × 0.2 m. Drip irrigation of integral control of water and fertilization were used in this experiment. The system consisted of a water reservoir, a water and fertilizer-integrated machine, and a water meter and irrigation pipe. The irrigation pipe was arranged along the length of culture tank, with a water dropper at a 10 cm distance from the tomato plant. The photographs of tomato growth periods including seedling, transplanting, blooming, and fruit setting are shown in Figure S1. Before transplanting, 6000 kg of commercial organic fertilizer (organic matter >40%, N 1.60%, P2O5 0.52%, and K2O 1.11%), 180 kg ha−1 N, 207 kg ha−1 P2O5, and 187.5 kg ha−1 K2O were used as base fertilizer. At the flowering stage of the tomato, top dressing with 90 kg ha−1 N, 70 kg ha−1 P2O5, and 94 kg ha−1 K2O was used at an interval of every two weeks to meet the demand of tomato growth. The remaining farm operations were the same for all treatments.

2.2. Experimental Design

A greenhouse experiment based on a randomized block design with four replicates and one culture tank as one replicate was used. The experimental layout is shown in Figure 2. Two varieties ‘181’ and ‘Mao Fen 802’ of tomato were selected as the test plant. The ‘181’ and ‘Mao Fen 802’ belong to high sugar fruits (Hsf) and common sugar fruits (Csf) based on soluble sugar content. The low (LWD), moderate (MWD), and high water deficit (HWD) treatments were set when the rate of the first fruit set reached 80% on the first ear of fruit, with a well-watered (WW) as a control treatment. According to a previous study, the suitable substrate water content (SWC) was from 75%θf to 90%θf (where θf is the field below 75%θf, irrigation capacity) [30]. Therefore, under WW treatment, when the SWC was performed until the SWC reached 90%θf. The water deficit treatments were irrigated at the same time. The irrigation amounts of LWD, MWD, and HWD were 80%, 60%, and 40% of that of WW, respectively. The variations in corresponding irrigation upper and lower limits are shown in Figure 3. At the end of the tomato harvesting stage, the irrigation upper and lower limits of LWD, MWD, and HWD were 66%θf–58%θf, 59%θf–54%θf, and 54%θf–49%θf. The exact irrigation amount in different treatments is shown in Table 1.

2.3. Meteorological Factors

The data of air temperature, soil temperature, and relative air humidity were recorded every 30 min using an automatic IoT equipment named ‘Tianlinrunyu’ (Tianlin Water Saving Irrigation Technology Development Co., Ltd., Lanzhou, China).

2.4. Substrate Water Content

The vertical substrate water content profile over the 20 cm-deep substrate layer was measured using a TRIME PICO 32 TDR (IMKO Ltd., Ettlingen, Germany). The data of substrate volumetric water content were recorded one time for every 10 min. The substrate mass water content was obtained using volumetric water content divided by bulk density.

2.5. Fruit Number, Yields, and WUE

At the fruiting period of the tomato, we randomly selected six plants in each tank to record the number of fruits and single fruit weight. The yield was calculated based on the single plant yield and planting density. Further, the water use efficiency (WUE) was calculated as follows [31].
WUE = Y/ETc,
where Y is the yield (kg·hm−2), and ETc is the evapotranspiration (m3·hm−2).
Because the experiment was conducted in tank culture with substrate under solar greenhouse, there was no rainfall, recharge of underground water, deep percolation, and runoff. Therefore, the irrigation amount was equal to the evapotranspiration in the WUE equation.

2.6. Polyphenols Content Analyses

2.6.1. Extraction of Polyphenols

Three mature tomato fruits for one replication were taken in different water deficit treatments and four replications for one treatment. Samples were divided into blocks of one-centimeter squares, mixed, frozen in liquid nitrogen, and lyophilized to powder by vacuum freeze drier. The extraction of polyphenols was conducted following the procedure of Vallverdú-Queralt et al. [32] and Xiao et al. [33] with some modifications. Tomato powder (0.1 g) was weighed and homogenized with methanol (2 mL). The homogenates were kept at room temperature for 1 h and centrifugated (8000 rpm, 4 °C) for 10 min. The extraction was repeated and combined two parts of supernatants. The supernatant was filtered through a 0.22 μm polytetrafluoroethylene (PTFE) filter and stored at −20 °C until analysis.

2.6.2. HPLC/DAD Quantitative Analyses for Polyphenols

The content of sixteen kinds of polyphenols (4 flavonols and 12 phenolic acids) were determined by the RP-HPLC method. The liquid chromatography equipment was an ACQUITY Arc Waters HPLC instrument (Waters, MA, USA) equipped with a 1525 pump, a 2998 photodiode array detector, and an autosampler. Separation of polyphenols was performed with a HPLC Symmetry C18 column (250 mm × 4.6 mm, 5 μm, Waters, MA, USA). The mobile phase consisted of methanol (solvent A) and 1% acetic acid (solvent B). The injection volume was 10 μL, the flow rate was 1.1 mL·min−1, and the column oven was 30 °C. Separation was carried out in 60 min under the following procedure: 0–30 min, 5% A and 95% B; 31–40 min, 30% A and 70% B; 41–45 min, 40% A and 60% B; 46–50 min, 50% A and 50% B; 51–55 min, 40% A and 60% B; and 56–60 min, 5% A and 95% B. The detection wavelength was 240 nm for p-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, quercetin, chlorogenic acid and rutin, and 280 nm for trans-cinnamic acid, p-coumaric acid, gallic acid, naringin, and benzoic acid, and 322 nm for sinapic acid, caffeic acid, cynarin, kaempferol, ferulic acid and 3,4-dihydroxybenzoic acid. The external standard method was used to quantify the polyphenols. The content of polyphenols was expressed in μg g−1 of dry tomato power. The total flavonoid and phenolic acids contents were obtained by the sum of each corresponding individual polyphenol.

2.7. Carotenoids Content Analyses

2.7.1. Extraction of Carotenoids

The samples were taken and prepared the same as the polyphenols. The extraction of carotenoids was collected by following the procedure of Londoño-Giraldo et al. [34] with some modifications. Tomato powder (0.5 g) was weighed and homogenized with petroleum ether and acetone (2:1, 50 mL). The homogenates were extracted under ultrasonic conditions for 15 min and collected the extracting solution in an amber bottle. We repeated the above operation until the residue left no color. Then, the combined extracting solution was transferred to a separating funnel and washed twice with 250 mL of distilled water. After the aqueous phase was discharged, anhydrous sodium sulfate was added to remove the remaining water. The extracting solution was evaporated to dryness by a rotary evaporation at <45 °C. Finally, the residue was redissolved with the solution of acetonitrile: methylene chloride: methanol (55:20:25) up to 25 mL, filtered through 0.22 μm polytetrafluoroethylene (PTFE) filter and stored at −20 °C until analysis.

2.7.2. HPLC/DAD Quantitative Analyses for Carotenoids

The content of lutein, lycopene, β-carotene, and violaxanthin were determined by the RP-HPLC method. The liquid chromatography equipment was an ACQUITY Arc Waters HPLC instrument (Waters, MA, USA) equipped with a 1525 pump, 2998 photodiode array detector, and an autosampler. Carotenoids were separated using a HPLC Symmetry C18 column (250 mm × 4.6 mm, 5 μm, Waters, MA, USA). The elution solution was acetonitrile: methylene chloride: methanol (55:20:25). The operating conditions were the following: column temperature, 25 °C; injection volume, 10 L; flow rate, 1.2 mL·min−1; and detection wavelength, 450 nm. Separation was carried out in 15 min. The quantitation of carotenoids was performed by the external standard method. The content of carotenoids was expressed in μg g−1 of dry tomato power.

2.8. Statistical Analyses

The results are presented as mean value ± standard error. A statistical variance analysis and Pearson correlation were performed using SAS software (version 8.1). All the treatment means were compared by a least significant difference test (LSD, p < 0.05). The line chart, column diagram, and regression analysis between the irrigation amount and yield, WUE, total polyphenols, and carotenoids was made by SigmaPlot software (10.0). Heatmap visualizations of polyphenols data were performed using Heml 1.0.3.7 software. The PCA loading plot was plotted by OriginPro 2018 (OriginLab Corporation, Northampton, MA, USA) software.

3. Results

3.1. Fruit Yield and Water Use Efficiency

According to the single fruit weight, we know the ‘Hsf’ tomato belongs to medium size and ‘Csf’ belongs to a big size of fruit (Table 2). The single fruit weight, number of fruits per plant, and yield declined as the degree of water deficit increased both for ‘Hsf’ and ‘Csf’. However, the variation in specific index depended on the varieties and degree of water deficit. For the ‘Hsf’ tomato, compared with WW, the HWD treatment significantly decreased the single fruit weight and number of fruits per plant by 17.2% and 21.1% (p < 0.05). In contrast, the fruit yield per plant and total yield under MWD and HWD treatments were significantly lower than that under WW treatment (p < 0.05). For the ‘Csf’ tomato, the MWD and HWD treatments significantly reduced the single fruit weight by 10.8% and 14.6% (p < 0.05), whereas non-significant changes were observed for a number of fruits per plant (p > 0.05). Similarly, the moderate and high water deficit resulted in a decrease in the fruit yield per plant and total yield by 12.6%–20.5% and 12.7%–20.3% (p < 0.05). On the contrary, WUE was improved by the water deficit. The MWD and HWD treatments markedly increased WUE for ‘Hsf’ by 25.8%–40.0% and for ‘Csf’ tomato by 35.3%–70.0% (p < 0.05). Particularly for ‘Csf’ tomato, WUE was significantly increased by 14.6% under the LWD treatment (p < 0.05).

3.2. Polyphenols Content

As shown in Figure 4, the water deficit treatment had a different effect on polyphenol content of two varieties of tomato. No significant difference in total phenolic acids was found between WW and water deficit treatment for the ‘Hsf’ tomato (p > 0.05), whereas the low water deficit treatment significantly increased the total phenolic acid content by 12.3% (p < 0.05) for ‘Csf’ tomato, compared with WW treatment. Differently, the total flavonoid content of ‘Hsf’ tomato was markedly decreased by 24.4%, 48.4%, and 93.1% under the LWD, MWD, and HWD treatments (p < 0.05). The total flavonoid content of the ‘Csf’ tomato was not significantly influenced by water deficit (p > 0.05). From Figure 4C, we know that different kinds of polyphenols showed varying response to water deficit for both tomato cultivars. There were 13 polyphenols detected in the ‘Hsf’ tomato except cinnamic acid. Further, the gallic acid, 3,4-dihydroxy benzoic acid, benzoic acid, and naringin contents of the ‘Hsf’ tomato were accumulated under all water deficit degrees. Besides, the p-coumaric acid and rutin were increased by low water deficit treatment while decreased by moderate and high water deficit treatment. Three kinds of polyphenols including sinapic acid, p-hydroxybenzoic acid, and quercetin were reduced by all degrees of water deficit. For the ‘Csf’ tomato, 14 polyphenol components were detected. Compared with WW, different degrees of water deficit treatments increased the p-coumaric acid, benzoic acid, 2,5-dihydroxy benzoic acid, ferulic acid, 3,4-dihydroxy benzoic acid, p-hydroxybenzoic acid, and naringin content, especially developed the ferulic acid and naringin from nothing. Conversely, all water deficit treatments led to a decrease in cynarin, caffeic acid, cinnamic acid, and quercetin. Only the rutin content was positively affected by low water deficit while negatively affected by moderate and high water deficit.

3.3. Carotenoid Content

The effect of water deficit on lutein, lycopene, β-carotene, and violaxanthin content of ‘Hsf’ and ‘Csf’ tomatoes under substrate cultivation is shown in Figure 5. Compared with WW, the moderate and high water deficit significantly increased lutein content of ‘Hsf’ tomato by 7.72% and 9.91% (p < 0.05). However, there were no significant changes in lutein content under all water deficit treatments for the ‘Csf’ tomato (p > 0.05). All water deficit treatments resulted in a significant increase in lycopene content (p < 0.05), with an increase by 7.84–20.02% for ‘Hsf’ tomato and 20.55–32.13% for the ‘Csf’ tomato. In contrast, no significant difference in β-carotene content was observed for the ‘Hsf’ tomato under all water deficit treatments (p > 0.05), whereas a significant 7.84% increase was obtained for ‘Csf’ tomato under HWD treatment than WW treatment (p < 0.05). Surprisingly, the HWD treatment reduced the violaxanthin content by 15.71% for the ‘Hsf’ tomato, reaching a significant level (p < 0.05). However, water deficit showed no significant effect on violaxanthin content for the ‘Csf’ tomato (p > 0.05).

3.4. Relationships of Irrigation Amount vs. Yield, WUE, Polyphenols and Carotenoids

The relationship irrigation amount vs. yield, WUE, polyphenols, and carotenoids of tomato is shown in Figure 6. The linear relation showed the same trend for two varieties of the ‘Hsf’ and ‘Csf’ tomato. Positive relationships were described between irrigation amount, yield, and polyphenol content. It indicates that yield and polyphenol content tend to increase as the irrigation amount increase. Further, an extremely significant (p < 0.01) and significant (p < 0.05) relationship of irrigation amount and yield were observed for the ‘Csf’ and ‘Hsf’ tomato, respectively. The slope of a linear equation from the irrigation amount and polyphenol content of the ‘Hsf’ tomato was higher than that of the ‘Csf’ tomato. It indicated that the effect of water deficit on polyphenol content of the ‘Hsf’ tomato was more intense than the ‘Csf’ tomato. Inversely, significantly negative relationships were obtained between irrigation amounts and carotenoids in both tomato varieties.

3.5. Comprehensive Evaluation of Two Varieties Tomato Response to Water Deficit Based on PCA

The correlation analysis showed that there was a close relationship among the index detected in this study (Figure 7). As shown in Figure 7A, a significant (p < 0.05) or extremely significant (p < 0.01) positive correlation was observed between yield and total flavonoids (r = 0.991, p < 0.01), between total flavonoids and violaxanthin (r = 0.979, p < 0.05), and between xanthophyll and lycopene (r = 0.982, p < 0.05). On the contrary, a significant (p < 0.05) or extremely significant (p < 0.01) negative correlation between yield and WUE (r = −0.998, p < 0.01), between WUE and total flavonoids (r = −0.997, p < 0.01), and violaxanthin (r = −0.964, p < 0.05), between total flavonoids and xanthophyll (r = −0.971, p < 0.05), and lycopene (r = −0.961, p < 0.05) was obtained. From Figure 7B, we found that a significant positive or negative correlation existed between many polyphenol components. P2 had a significant positive correlation with P13, and P3 had a significant or extremely significant negative correlation with P6 and P8 but a positive correlation with P9. Further, P6 showed a significant positive correlation with P8 but negative correlation with P9. Interestingly, P7 showed an opposite trend compared with P6. In addition, there was a significant negative correlation between P5 and P11, and between P8 and P9, while a significant positive correlation between P10 and P12. These results indicate that an inherent relationship might exist between parameters and play a similar role in response to water treatment. Therefore, we further evaluated the combined effect of water deficit using a principal component analysis.
A principal component analysis revealed that water deficit degrees produced different effects on two tomato varieties (Figure 8). For variety ‘181’, two main principal components explained 84.20% of the total variance, of which PC1 accounted for 61.50% of the total variance, and PC2 accounted for 22.70% of the total variance (Figure 8A). There was a positive response value toward PC1 for WW and LWD treatments but negative for MWD and HWD treatments. However, for variety ‘Mao Fen 802’, the first two components PC1 and PC2 explained 71.82% and 21.81% of the total variance, respectively (Figure 8B). Further, three water deficit treatments of LWD, MWD, and HWD were gathered along the PC1 positive direction, while WW scattered in the PC1 negative direction. It indicated that variety ‘Mao Fen 802’ was more sensitive to water deficit than variety ‘181’. In addition, we found that varying parameters made the main contribution in two principal components for two tomato varieties. The yield, quercetin, and total flavonoids showed a main contribution to the PC1, and total phenolic acid and ferulic acid showed a main contribution to the PC2 for variety ‘181’. Unlike this, the ferulic acid, p-coumaric acid, and lycopene mainly played a role in PC1, and rutin played a role in PC2 for variety ‘Mao Fen 802’.

4. Discussion

In this study, two genotypes of tomato (different sugar contents and fruit sizes) were selected, and the impact of four water irrigations on tomato yield and fruit quality was assessed. Similar studies were carried out in open-field and greenhouse cultivation under soil conditions [18,23] but rarely found under substrate culture as the present study. It was found that moderate water deficit (MWD, 60% WW) and high water deficit (HWD, 40% WW) significantly decreased the single fruit weight and yield of both tomato cultivars (Table 2). This is in accordance with the previous studies [18,35]. Surprisingly, no significant difference in the number of fruits per plant was observed for ‘Mao Fen 802’ tomato, regardless of the treatment, whereas that of the ‘181’ tomato significantly declined under HWD treatment. It was proposed that the yield decrease in the ‘Mao Fen 802’ tomato was ascribed to the diminishment of fruit size, while the combined action of fruit size and fruit number was ascribed to the ‘181’ tomato. Moreover, the reduction rate of yield was different between two cultivars of tomato, with a 34.45% and 20.35% decrease in ‘181’ and the ‘Mao Fen 802’ tomato, under HWD treatment. This is consistent with the previous studies, possibly due to the genotypes, growing conditions, and irrigation deficit degrees [19,22,36]. In contrast to the tomato yield, the WUE was markedly stimulated by the water deficit condition and showed an upward trend as the irrigation deficit increased. This result is consistent with the study of [22,37,38], who reported increased WUE related to lower yields.
Polyphenols, consisting of phenolic acids and flavonoids, play a vital role in human disease protection due to their antioxidant capacity. In the present study, we found that the total phenolic acids and flavonoids of ‘181’ were more than that of the ‘Mao Fen 802’ tomato fruit, meaning the difference depending on genotype. This agrees with other studies [29,38]. In accordance with findings by Martí et al. [39], the present study also found that a suitable water deficit significantly increased phenolic acids of tomato fruit, and the impact level depending on genotype, fruit position, or growth period [29,40,41]. Unexpectedly, the total flavonoids of the ‘181’ tomato declined when watered scarcely, which was different from most research reported by other authors. We speculate that the flavonoid biosynthesis of this genotype tomato is more sensitive to deficit irrigation. The definite reason needs to be further studied. In addition, the polyphenols components were investigated in the present study, and individual polyphenol showed various responses to different degrees of water deficit. It can be obtained that p-coumaric acid, p-hydroxy benzoic acid, ferulic acid, and naringin were accumulated regardless of water deficit, compared to full irrigation. This result is consistent with previous studies [29,39,41]. Nevertheless, other individual polyphenols exhibited a reduction or a fluctuating trend, with the intensity of different water deficit degrees.
Carotenoid is another key bioactive substance in tomato fruit, with a health-promoting role. Previous studies have confirmed that lycopene and β-carotene are two of the most abundant carotenoids in tomato fruit [42,43]. Consistent results were obtained in the present study. Notably, lycopene, β-carotene, and lutein of the ‘181’ tomato fruit was significantly higher than that of ‘Mao Fen 802’, reconfirming that the ‘181’ tomato is a high-quality genotype. Plenty of studies reported that water stress can stimulate the synthesis of antioxidant substances including carotenoids, in turn improving fruit or vegetable quality [41,44,45]. In accordance with these results, we also found that carotenoid levels were risen significantly under water deficit treatments, especially for lycopene content, with a 1.2–1.3-fold increase. Moreover, two genotypes of tomato showed a similar upward trend during deficit drip irrigation. Thus, regulated water deficit could be an effective approach of producing high-quality tomatoes.
In order to make clear the relation of water deficit degree with tested tomato index, and whether the response of two tomato varieties to water deficit is consistent, the linear regression, correlation analysis, and PCA were conducted in the present study. Linear regression showed a positive relationship between water deficit and WUE, and carotenoids, whereas a negative relationship was shown between water deficit and yield. A similar finding was also reported by Patanè et al. [23]. Controversially, the relationship between water deficit and polyphenols was negative, although many studies in the literature support this finding [29,39,46]. Still, some studies reported that a water deficit limited the accumulation of polyphenols [41,47], which could be attributed to the genotype and cultivation condition. In the present study, based on the correlation and PCA, a different response to water deficit degrees of two tomato varieties were observed. This result was consistent with that of Fullana-Pericàs et al. [22], who reported that landraces had a better performance than modern improved genotypes of tomato in terms of minimizing yield reduction and increasing fruit quality under water deficit. Likewise, to receive a more comprehensive and accurate evaluation over water deficit treatment, the correlation and PCA was also adopted in recent studies [48,49,50]. The present study suggests an optimal water deficit strategy on two genotypes of tomato cultivated in Gobi agriculture from the perspective of yield, WUE, and polyphenols and carotenoids, which can be applied under substrate cultivation where soil cultivation is not possible. However, the underlying molecular mechanism needs to be clarified in future studies.

5. Conclusions

In the present study, a novel cultivation mode of planting tomatoes with substrate using a drip irrigation system in a solar greenhouse was used to assess the impact of different degrees of water deficit on two tomato genotypes. It was concluded that appropriate deficit drip irrigation remarkedly improved the water use efficiency of tomatoes, with a decrease in yield. Despite a slight decrease in total polyphenol content under water deficit, some individual polyphenols including benzoic acid, 3,4-dihydroxybenzoic acid, and naringin, were accumulated regardless of tomato cultivar and treatments. Moreover, the water deficit treatment led to rising levels of carotenoids in both tomato cultivars, especially for lycopene and β-carotene. The correlation and PCA suggest that two genotypes of tomato have a varying response to water deficit, indicating more sensitivity for the ‘181’ than ‘Mao Fen 802’ tomato. It may be explained by the result of a more antioxidant substance of ‘181’ than that of the ‘Mao Fen 802’ tomato obtained. This study can provide a reference for setting out rational irrigation regimes for greenhouse tomatoes under Gobi agriculture.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy14092133/s1, Figure S1: Photograph of tomato growth periods.

Author Contributions

Conceptualization, X.X. and J.Y.; Methodology, X.X., X.L. and N.J.; Software, X.X. and N.J.; Validation, X.X. and X.L.; Investigation, Y.W.; Resources, Z.T. and J.Y.; Data curation, X.L., N.J. and K.S.K.; Writing—original draft, X.X.; Writing—review & editing, K.S.K., J.L. and J.Y.; Visualization, X.X.; Supervision, J.L. and J.Y.; Project administration, Y.W. and Z.T.; Funding acquisition, X.X. and J.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (No. 32160703), Key Research and Development Project of Gansu Province (23YFNA0021), Top Leading Talent Plan of Gansu Province (GSBJLJ-2021-14), Major Science and Technology Project of Gansu Province (23ZDNA008).

Data Availability Statement

The original contributions presented in the study are included in the article/Supplementary Materials, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Maximum (Tmax) and minimum (Tmin) daily substrate temperature, and air temperature (A), and air relative humidity (B) during growing period of tomato.
Figure 1. Maximum (Tmax) and minimum (Tmin) daily substrate temperature, and air temperature (A), and air relative humidity (B) during growing period of tomato.
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Figure 2. The layout of experimental design and irrigation and fertilization system. WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit.
Figure 2. The layout of experimental design and irrigation and fertilization system. WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit.
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Figure 3. Substrate water content under different water deficit degrees in different growth stages.
Figure 3. Substrate water content under different water deficit degrees in different growth stages.
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Figure 4. Effect of different water deficit degrees on total phenolic acids (A), total flavonoids (B), and 14 components of polyphenols (C) of tomato fruit. Different letters above column indicate values that are significantly different at the p < 0.05 level. Error bars represent standard errors (n = 3). Hsf and Csf mean high sugar fruits of variety ‘181’ and common sugar fruits of variety ‘Mao Fen 802’. WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit. P1–P14 represent p-coumaric acid, gallic acid, benzoic acid, 2,5-dihydroxy benzoic acid, cynarin, caffeic acid, ferulic acid, sinapic acid, 3,4-dihydroxybenzoic acid, trans-cinnamic acid, p-hydroxybenzoic acid, quercetin, naringin, and rutin. Red, green, and black mean high content, low content, and not detected, respectively.
Figure 4. Effect of different water deficit degrees on total phenolic acids (A), total flavonoids (B), and 14 components of polyphenols (C) of tomato fruit. Different letters above column indicate values that are significantly different at the p < 0.05 level. Error bars represent standard errors (n = 3). Hsf and Csf mean high sugar fruits of variety ‘181’ and common sugar fruits of variety ‘Mao Fen 802’. WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit. P1–P14 represent p-coumaric acid, gallic acid, benzoic acid, 2,5-dihydroxy benzoic acid, cynarin, caffeic acid, ferulic acid, sinapic acid, 3,4-dihydroxybenzoic acid, trans-cinnamic acid, p-hydroxybenzoic acid, quercetin, naringin, and rutin. Red, green, and black mean high content, low content, and not detected, respectively.
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Figure 5. Effect of different water deficit degrees on the lutein (A), lycopene (B), β-carotene (C), and violaxanthin (D) of tomato fruit. Different letters above column indicate values that are significantly different at the p < 0.05 level. Error bars represent standard errors (n = 3). Hsf and Csf mean high sugar fruits of variety ‘181’ and common sugar fruits of variety ‘Mao Fen 802’. WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit.
Figure 5. Effect of different water deficit degrees on the lutein (A), lycopene (B), β-carotene (C), and violaxanthin (D) of tomato fruit. Different letters above column indicate values that are significantly different at the p < 0.05 level. Error bars represent standard errors (n = 3). Hsf and Csf mean high sugar fruits of variety ‘181’ and common sugar fruits of variety ‘Mao Fen 802’. WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit.
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Figure 6. Linear regression of irrigation amount vs. yield (A), WUE (B), polyphenols (C), and carotenoid content (D) in tomatoes. Linear equation, correlation coefficient square (R2), and significance (* and ** indicate significant difference at the p < 0.05 and p < 0.01 level) are shown. Hsf and Csf mean high sugar fruits of variety ‘181’ and common sugar fruits of variety ‘Mao Fen 802’.
Figure 6. Linear regression of irrigation amount vs. yield (A), WUE (B), polyphenols (C), and carotenoid content (D) in tomatoes. Linear equation, correlation coefficient square (R2), and significance (* and ** indicate significant difference at the p < 0.05 and p < 0.01 level) are shown. Hsf and Csf mean high sugar fruits of variety ‘181’ and common sugar fruits of variety ‘Mao Fen 802’.
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Figure 7. Correlation matrix based on Pearson’s correlation coefficient between yield, WUE, and functional components (A) or polyphenol components (B). Different intensity of colors means different correlativity. Positive correlations are shown in red, and negative correlations are shown in green. * and ** indicate significant difference at the p < 0.05 and p < 0.01 level. P1–P14 are defined as Figure 4.
Figure 7. Correlation matrix based on Pearson’s correlation coefficient between yield, WUE, and functional components (A) or polyphenol components (B). Different intensity of colors means different correlativity. Positive correlations are shown in red, and negative correlations are shown in green. * and ** indicate significant difference at the p < 0.05 and p < 0.01 level. P1–P14 are defined as Figure 4.
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Figure 8. Loading plot of 4 water deficit degrees and 22 parameters for the high sugar fruits of variety ‘181’ (A) and common sugar fruits of variety ‘Mao Fen 802’ (B) based on principal component analysis (PCA). WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit. V1–V22 represent yield, WUE, p-coumaric acid, gallic acid, benzoic acid, 2,5-dihydroxy benzoic acid, cynarin, caffeic acid, ferulic acid, sinapic acid, 3,4-dihydroxybenzoic acid, trans-cinnamic acid, p-hydroxybenzoic acid, total phenolic acids, quercetin, naringin, rutin, total flavonoids, xanthophyll, lycopene, β-carotene, and violaxanthin.
Figure 8. Loading plot of 4 water deficit degrees and 22 parameters for the high sugar fruits of variety ‘181’ (A) and common sugar fruits of variety ‘Mao Fen 802’ (B) based on principal component analysis (PCA). WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit. V1–V22 represent yield, WUE, p-coumaric acid, gallic acid, benzoic acid, 2,5-dihydroxy benzoic acid, cynarin, caffeic acid, ferulic acid, sinapic acid, 3,4-dihydroxybenzoic acid, trans-cinnamic acid, p-hydroxybenzoic acid, total phenolic acids, quercetin, naringin, rutin, total flavonoids, xanthophyll, lycopene, β-carotene, and violaxanthin.
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Table 1. Irrigation amount of different treatments.
Table 1. Irrigation amount of different treatments.
TreatmentsThe Base of Irrigation AmountIrrigation Amount
(L Tank−1 Time−1)		TimesTotal Irrigation Amount
(m3 hm−2)
WW75%θf–90%θf (where θf is the field capacity)72.41183622
LWD80% WW57.93182897
MWD60% WW43.45182173
HWD40% WW28.96181449
WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit.
Table 2. Yield and WUE of tomato response to different degrees of water deficit.
Table 2. Yield and WUE of tomato response to different degrees of water deficit.
CultivarTreatmentSingle Fruit Weight (g Plant−1)Number of Fruits per PlantFruit Yield per Plant (kg)Total Yield (t hm−2)WUE (kg m−3)
HsfWW117.70 ± 3.32 a25.71 ± 1.06 ab3.02 ± 0.13 a79.99 ± 3.54 a22.05 ± 0.98 c
LWD106.86 ± 6.04 ab27.14 ± 1.40 a2.85 ± 0.04 a75.44 ± 0.98 a25.29 ± 0.33 bc
MWD105.40 ± 2.82 ab23.43 ± 1.32 bc2.45 ± 0.11 b64.95 ± 2.81 b27.74 ± 1.20 ab
HWD97.45 ± 4.92 b20.29 ± 0.81 c1.98 ± 0.14 c52.43 ± 3.69 c30.87 ± 2.18 a
CsfWW250.78 ± 12.62 a19.43 ± 0.72 a4.83 ± 0.12 a127.68 ± 3.18 a35.20 ± 0.88 d
LWD241.29 ± 9.08 ab19.00 ± 0.65 a4.55 ± 0.08 a120.43 ± 2.25 a40.35 ± 0.75 c
MWD223.71 ± 3.63 bc18.86 ± 0.46 a4.22 ± 0.10 b111.50 ± 2.67 b47.62 ± 1.14 b
HWD214.05 ± 6.50 c18.00 ± 0.53 a3.84 ± 0.13 c101.70 ± 3.40 c59.87 ± 2.00 a
Values are the mean ± standard error (n = 7). The same lower-case letters show that the mean values among water treatments within one cultivar of tomato are not significantly different at p < 0.05 (LSD’s test). Hsf and Csf mean high sugar fruits of variety ‘181’ and common sugar fruits of variety ‘Mao Fen 802’. WW: well-watered; LWD: low water deficit; MWD: moderate water deficit; HWD: high water deficit.
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MDPI and ACS Style

Xiao, X.; Liu, X.; Jin, N.; Wu, Y.; Tang, Z.; Khan, K.S.; Lyu, J.; Yu, J. Two Genotypes of Tomato Cultivated in Gobi Agriculture System Show a Varying Response to Deficit Drip Irrigation under Semi-Arid Conditions. Agronomy 2024, 14, 2133. https://doi.org/10.3390/agronomy14092133

AMA Style

Xiao X, Liu X, Jin N, Wu Y, Tang Z, Khan KS, Lyu J, Yu J. Two Genotypes of Tomato Cultivated in Gobi Agriculture System Show a Varying Response to Deficit Drip Irrigation under Semi-Arid Conditions. Agronomy. 2024; 14(9):2133. https://doi.org/10.3390/agronomy14092133

Chicago/Turabian Style

Xiao, Xuemei, Xiaoqi Liu, Ning Jin, Yue Wu, Zhongqi Tang, Khuram Shehzad Khan, Jian Lyu, and Jihua Yu. 2024. "Two Genotypes of Tomato Cultivated in Gobi Agriculture System Show a Varying Response to Deficit Drip Irrigation under Semi-Arid Conditions" Agronomy 14, no. 9: 2133. https://doi.org/10.3390/agronomy14092133

APA Style

Xiao, X., Liu, X., Jin, N., Wu, Y., Tang, Z., Khan, K. S., Lyu, J., & Yu, J. (2024). Two Genotypes of Tomato Cultivated in Gobi Agriculture System Show a Varying Response to Deficit Drip Irrigation under Semi-Arid Conditions. Agronomy, 14(9), 2133. https://doi.org/10.3390/agronomy14092133

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