Air temperature and relative humidity recorded during the healing and hardening process of grafted transplants.
Real-time air temperature and relative humidity inside the greenhouse.
Real-time growing media temperature and water content at a depth of 2 cm.
Effect of grafting and cultivar on the soil plant analysis development value of tomato. Vertical bar represents the SE. Dissimilar letters on the line graph show statistical differences, the same letters show statistical similarities according to Tukey’s honest significant difference test at P < 0.05. NonGra-Vel = nongrafted ‘Velocity F1’; Gra-Vel = grafted ‘Velocity F1’; NonGra-Sig = non-grafted ‘Sigma F1’; Gra-Sig = grafted ‘Sigma F1’. ** Significant at P < 0.01.
Effects of grafting and cultivar on the transpiration rate (A), assimilation rate (B), intercellular CO2 (C), and stomatal conductance (D) of tomato. Vertical bar represents the SE. Dissimilar letters on the line graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05. NonGra-Vel = nongrafted ‘Velocity F1’; Gra-Vel = grafted ‘Velocity F1’; NonGra-Sig = nongrafted ‘Sigma F1’; Gra-Sig = grafted ‘Sigma F1’. **, * Significant at P < 0.01 and P < 0.05, respectively.
Effects of grafting and cultivar on electrolyte leakage of tomato. Vertical bar represents the SE. Dissimilar letters on the line graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05. NonGra-Vel = nongrafted ‘Velocity F1’; Gra-Vel = grafted ‘Velocity F1’; NonGra-Sig = nongrafted ‘Sigma F1’; Gra-Sig = Grafted ‘Sigma F1’. ** Significant at P < 0.01.
Effects of grafting and cultivar on days required to first flower (A), days required to 50% flower (B), flower drop (C), and fruit set (D) of tomato. Vertical bar represents the SE. Dissimilar letters on the bar graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05.
Effects of grafting and cultivar on pollen viability of tomato. Vertical bar represents the SE. Dissimilar letters on the bar graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05.
Effects of grafting, cultivar, and plant density on marketable fruit yield of tomato. Vertical bar represents the SE. Dissimilar letters on the bar graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05.
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Hot and humid conditions create challenges for tomato production under a controlled environment. Low tomato productivity is related to the lack of stress tolerance of existing cultivars and their ability to maximize fruit set and yield. The aim of this study was to evaluate the effectiveness of three management strategies, cultivar selection, grafting, and plant density, for the growth and production efficiency of organically grown hydroponic tomatoes under adverse environmental conditions in Qatar. The experiment used a split-split plot design with ‘Velocity F1’ and ‘Sigma F1’ as the main plot treatments and a factorial arrangement of grafting combinations and planting densities (3.5 and 5.5 plants/m2) as subplots. Tomato cultivar Velocity F1 grafted on Maxifort F1 resulted in greater vegetative growth and improved phenological attributes than nongrafted Velocity F1. Grafted ‘Velocity F1’ plants grown at 3.5 plants/m2 had an increase in leaf photosynthetic rates (18%), less transpiration loss (16%), and less electrolyte leakage (15%) while maintaining stomatal conductance and intercellular CO2 concentrations. At 9 weeks after transplanting, canopy growth was higher (24%) and flowering occurred earlier (3 days) with grafted ‘Velocity F1’ transplants than with nongrafted transplants. Higher fruit sets (20%), pollen viability (22%), and fewer flower drops (17%) were also observed for grafted ‘Velocity F1’ transplants than for nongrafted transplants. Marketable fruit yields were higher (26%) with grafted ‘Velocity F1’ grown at 3.5 plants/m2 than with nongrafted ‘Velocity F1’. Both grafted ‘Velocity F1’ and ‘Sigma F1’ fruits retained acceptable fruit color (L*, a*, b*, C*, °h), firmness, °Brix, titratable acidity, weight, and prolonged shelf life by 4 additional days than nongrafted ones. We conclude that grafted tomato ‘Velocity F1’ grown at a plant density of 3.5 plants/m2 was the best management strategy for enhancing seedlings quality, plant growth, and postharvest quality and alleviating abiotic stresses under this protected environment and hydroponic system.
Adverse climatic conditions, water scarcity, and lack of arable lands and fertile soils preclude growing enough vegetables to satisfy the domestic demand of Qatar. This situation forces Qatar to import most of its produce from abroad. In Qatar, tomato is a high-value crop that is cultivated both in the open field (312 ha) and under greenhouse conditions (153 ha), ensuring more than 31,800 tons of production in 2020 in Qatar (AS-Agricultural Statistics 2020). Because of the growing population, amplified food demand, and rapid economic growth, Qatar’s agricultural sector has expanded. Now, agriculture is considered an emerging sector that contributed 0.2% of Qatar’s gross domestic product in 2019. During that year, it was reported that self-sufficiency, a prerequisite for ensuring food security, increased by 28% for vegetables (Karanisa et al. 2021). During the last decade (2010–19), the consumed vegetable production (32–66 tons) in open fields and greenhouses increased by 110% in Qatar (AS-Agricultural Statistics 2020). Currently, local farms are adopting hydroponics techniques to increase vegetable production in controlled environment systems. Growing vegetables hydroponically is a viable alternative option for maximizing outputs from crop cultivation in arid climatic conditions (Grand View Research 2021; Velazquez-Gonzalez et al. 2022). Hydroponics not only reduces the demand for resources such as water, soil, and space but also results in higher yields during a comparatively shorter time than open-field cultivation (Cammarano et al. 2020; Sambo et al. 2019).
It is very common to use breeding and biotechnological approaches both in public and private sectors to develop plants that can sustain adverse climatic conditions, although the process is tedious and time-consuming. Grafting could be considered a suitable alternative to developing a composite plant that can maintain the proper growing schedule and mitigate unfavorable environments without losing the yield potential (Kumar et al. 2017). For tomato, the grafting technique has been widely used to minimize the negative effects of abiotic stresses caused by low- and high-temperature stress (Venema et al. 2008) and water stress (Bhatt et al. 2015) conditions. Boosting crop production using grafting techniques, especially for Solanaceous and Cucurbitaceous vegetables, has become a common practice in many countries (Lee et al. 2010). Grafted tomatoes exhibit potentiality against soil-borne diseases (Fusarium wilt, bacterial wilt, and verticillium wilt) and reduce the use of pesticides (methyl bromide) under protected farming systems (Mcavoy et al. 2012). In terms of nutrition, grafted tomatoes exhibited a higher nitrogen efficiency mechanism under low-nitrogen conditions, increased yield, and crop productivity and an improvement in fruit quality compared with nongrafted tomatoes (Barrett et al. 2012; Zhang et al. 2021). Tomato yield varied significantly (35%) between grafted and nongrafted tomato plants, as reported by Grieneisen et al. 2018.
Research has suggested that both the scion and the rootstock play key roles in improving the fruit yield and quality of tomatoes (Sora et al. 2019). Therefore, it is very important to select appropriate rootstock and scion combinations to confirm the proper growth, yield, and quality of fruits (Aloni et al. 2010; Nguyen and Yen 2018). In North America, ‘Maxifort’ is broadly used as a rootstock because ‘Maxifort’-grafted tomatoes showed vigorous growth, suppressed soil-borne diseases, and improved the yield of tomatoes both in greenhouse and field conditions (Kubota et al. 2008). Additionally, the use of ‘Maxifort’ rootstock increased marketable fruit yield by more than 50% compared with the nongrafted plants (Djidonou et al. 2017).
Optimizing plant density in a production system is crucial for increasing yield and fruit quality. It facilitates proper plant growth through effective light interception, thereby increasing photosynthesis (Maboko and du Plooy 2018) and assimilating translocation to fruits (Heuvelink 1997). Higher or lower plants per unit area can result in less yield, decreased quality, and low profits for growers. Plants compete for nutrients, water, and light when plant density is higher than optimum. Dense foliage caused by high plant density leads to light deficiency in the lower canopy and decreased photosynthesis (Jiang et al. 2017). Crop yield is greatly impacted by planting densities because this strategy regulates the canopy structure, shade effect, and competition among the plants (Heuvelink et al. 2007). A linear relationship was observed between tomato yield and planting densities, and the yield improved as planting densities increased (Maboko et al. 2011). Plant density is one of the important agronomic management factors that significantly modulate the productivity of tomatoes (Amare and Gebremedhin 2020). For example, it was reported that a high-density planting boosted tomato yield by 39% under greenhouse conditions (Ayarna et al. 2021).
It has been proven that grafted tomatoes could mitigate abiotic stress to improve plant growth, yield, and fruit quality in arid climatic conditions in Riyadh, Saudi Arabia, under a controlled polyethylene greenhouse (Al-Harbi et al. 2017). However, the combination of grafting and plant density has not been tested in hydroponic systems. Limited information exists regarding how further increases in plant density affect fruit size and yield of indeterminate tomato varieties grown hydroponically under the climatic conditions of Qatar. Therefore, the main goal of this study was to evaluate the effectiveness of three management strategies, cultivar selection, grafting, and plant density, on improving growth, production efficiency, yield, quality, and abiotic stress mitigation of organically grown hydroponic tomatoes under adverse environmental conditions.
Hybrid Velocity F1 and Sigma F1 (Semillas Fito; Barcelona, Spain) tomato cultivars were grafted onto an interspecific hybrid rootstock Maxifort (Solanum lycopersicum × Solanum habrochaites). Tomato seeds were sown in polystyrene 50-cell trays (4.8 × 3.8 × 5.8 cm, 80 cm3 cell volume; XQ50 model; Wilson Garden Co. Ltd., Zhengzhou, China) filled with growing media consisting of 90% cocopeat and 10% compost (Hortalan Group; Live Plant Biotec, Cordoba, Spain), and trays were irrigated and incubated at 24 °C and 80% relative humidity for 72 h in an insulated cold room. ‘Maxifort F1’ (Johnny’s Selected Seeds, Fairfield, ME, USA) tomato seeds were sown 4, 7, and 10 d earlier than ‘Velocity F1’ and ‘Sigma F1’ to match stem diameters between the rootstock and scion.
The seedlings were grown in a propagation unit for 40 d until the stem diameter reached the target size (2.5 mm) for grafting. The trays were fertilized at 3-d intervals using organic nitrogen (N), phosphorous (P), and potassium (K) fertilizer (N20–P10–K30; 200 mg⋅L−1 of N) and trace elements (iron, zinc, bromine, molybdenum, copper, manganese; 10 mg⋅L−1) (Yara; Hortalan Group, Madrid, Spain) beginning 24 d after seedling emergence.
The seedlings were cut below the cotyledon, and the splice method of grafting was followed. The graft union was attached tightly using a 2.5-mm-diameter silicone graft clip (Johnny’s Selected Seeds). The grafted seedlings were immediately transferred to a healing chamber for acclimatization at 21 to 23 °C and relative humidity of 85% to 96% (Fig. 1). The dark condition was maintained for 3 d, a dim light-emitting diode light was added outside of the chamber on the fourth day, and the relative humidity was decreased gradually until the 10 d of acclimation. Afterward, the grafted seedlings were transferred to the main propagation unit for 6 d of hardening. Then, they were transferred to the grow bags (1.0 × 0.2 × 0.1 m) filled with cocopeat growing media (Polydime; Kirulapone, Colombo, Sri Lanka) in the greenhouse.
Citation: HortScience 58, 10; 10.21273/HORTSCI17249-23
The experiment was performed using a split-split plot design with ‘Velocity F1’ and ‘Sigma F1’ as main plot treatments with a factorial arrangement of grafting combinations and planting densities (3.5 and 5.5 plants/m2) as subplots with four replications. Each experimental unit consisted of 12 plants. The greenhouse air temperature (°C) and relative humidity (%) were monitored continuously during the experiments (Ambient weather; model: WS80BN; Chandler, AZ, USA) (Fig. 2). Growing media temperatures (°C) and water content (m3⋅m−3) were recorded using data loggers at a depth of 2 cm (HOBO® MX; MX2307; Onset, Bourne, MA, USA) (Fig. 3). The plants were irrigated daily between 8:00 am and 4:00 pm with a drip irrigation system (flow rate, 0.3 L emitter−1⋅h−1) and fertilized weekly with N20–P10–K30 fertilizer (200 mg⋅L−1of N).
Citation: HortScience 58, 10; 10.21273/HORTSCI17249-23
Citation: HortScience 58, 10; 10.21273/HORTSCI17249-23
Starting from 30 d after planting, the canopy area (cm2) was measured weekly, and the image was taken from the top of the plants (Nikon AF-S DX Nikkor; D5500 DSLR; Nikon, Bangkok, Thailand) and analyzed using ImageJ software (version 1.53e; Laboratory for Optical and Computational Instrumentation, Madison, WI, USA), as mentioned by Martin et al. (2020). Soil plant analysis development (SPAD) (chlorophyll index) values were recorded using a portable chlorophyll meter (SPAD-502 Plus; Konica Minolta, Tokyo, Japan). The SPAD values were measured from the third expanded leaf from the top, and four SPAD values from each experimental unit were averaged to represent one reading and used for analysis. Gas exchange data [transpiration rate (E), assimilation rate (A), intercellular CO2 (Ci), stomatal conductance to water vapor (gs)] were measured from the third expanded leaf from the top using a portable photosynthesis system (LI-6800; LI-COR Inc., Lincoln, NE, USA) between 10:00 AM and 1:00 PM and exposed to a flow rate of 500 mmol⋅s−1, reference CO2 of 400 mmol⋅mol−1, fan speed of 10,000 rpm, fluorometer set point of 100 μmol⋅m−2⋅s−1, and aperture size of 6 cm2. The gas exchange data were measured at 15 d, starting from 30 d after planting. Electrolyte leakage (EL) was calculated according to Mukherjee et al. (2023). The following formula was used to calculate EL: [1] where EC1 was recorded (Cond 6+ conductivity meter; Oakton Instruments, Bunker Court, Vernin Hills, IL, USA) initially after keeping the leaf discs (six) in a test tube filled with deionized water for 20 h. Thereafter, the samples were boiled for 15 min and cooled; then, the final EC2 reading was recorded.
Flowering (days to first and 50% flowering) was evaluated by keeping a record of the number of days from planting to the first and 50% flower opening from each experimental unit. To assess the flower drop and fruit set performance against abiotic stresses, five mature flower clusters (containing 5–12 flowers) were tagged per plot and the existing information was collected regularly. Pollen viability was evaluated according to Sulusoglu and Cavusoglu (2014). The iodine potassium iodide (IKI) staining test was used to evaluate the pollen viability. During this process, 1 g potassium iodide and 0.5 g iodine were dissolved in 100 mL distilled water to obtain the IKI solution. Pollen viability counts were performed 5 min after pollen was placed in the IKI solution. Pollen grains stained dark (dark red or brown color) were counted as alive, and an evaluation was performed under the microscope (DM 2700M; Leica Microsystems Inc., Deerfield, IL, USA).
Fully ripe marketable fruits were harvested each alternative day, and the total yield was calculated. Different postharvest quality parameters (shelf life, fruit weight, firmness, color attributes, acid, °Brix) were evaluated for stored fruits. The harvested fruits were stored immediately at the laboratory (169E; Mechanical Engineering Department, Texas A&M University, Doha, Qatar) in ambient environments (temperature, 23 °C; relative humidity, 75%) to determine the postharvest quality of tomatoes. A digital force gauge (DFS3 Chatillon force measurement instrument; Ametek, Largo, FL, USA) was used to assess the firmness of storage fruits (2 mm probe). The force was calculated in N/cm2. The storage fruit color attributes (L* a*, b*, C*, °h) were recorded using a portable chromometer (CR 410; Konica Minolta, Inc., Chiyoda City, Tokyo, Japan). The percentages of Brix and acid in tomato juice (1:50 dilution ratio) were evaluated from the reading performed using the pocket Brix-Acidity meter (PAL-BXIACID3; Atago Co. Ltd., Shiba-Koen, Minato-ku, Tokyo, Japan).
A three-factor split-split plot design was used for this experiment. The collected data were analyzed using Origin 2020 (version 9.6.5; OriginLab Corporation, Northampton, MA, USA). The data were subjected to a three-way analysis of variance to determine the statistical differences among the treatments, and pairwise mean comparisons were estimated using Tukey’s honest significant difference test at P ≤ 0.05.
Canopy growth was significantly higher in grafted ‘Velocity F1’ plants than in nongrafted plants, resulting in 24% higher vegetative growth. Similarly, grafted ‘Sigma F1’ plants had a 22% higher canopy growth than nongrafted plants. Both grafted ‘Velocity F1’ and ‘Sigma F1’ grown at a plant density of 3.5 plants/m2 had higher canopy growth than when grown at a plant density of 5.5 plants/m2. Initially, plant density had no significant effect on canopy growth, but the difference was noticeable over time with grafted ‘Velocity F1’ and ‘Sigma F1’ grown at 3.5 plants/m2, showing an increase of 16% to 22% in canopy growth compared to those grown at 5.5 plants/m2 after 9 weeks of planting (data not shown).
Grafted ‘Sigma F1’ had significantly higher SPAD (chlorophyll index) values than nongrafted plants over time (Fig. 4). There were significant cultivar × grafting interactions, and grafted ‘Sigma F1’ had a greater increase (10%) in the SPAD value than nongrafted plants. Grafted ‘Velocity F1’ showed a 9% increase in the SPAD value compared with the nongrafted plants, but it showed a 3% decrease in the SPAD value compared with grafted ‘Sigma F1’. However, there were no plant density effects on SPAD values.
Citation: HortScience 58, 10; 10.21273/HORTSCI17249-23
Leaf transpiration (E) was significantly higher in nongrafted plants than in grafted plants (Fig. 5A). The results showed that grafted plants conserved water, with significantly lower transpiration loss (16%) than nongrafted plants. Furthermore, the assimilation rate (A) was significantly higher for grafted plants than for nongrafted plants (Fig. 5B). Grafted ‘Velocity F1’ plants exhibited an increase in leaf assimilation rates (18%) compared with nongrafted plants. A comparison of cultivars showed that grafted Velocity F1 exhibited a 9% higher net assimilation rate than grafted Sigma F1 plants. There were no plant density effects on the net assimilation rate. Similarly, grafted ‘Velocity F1’ plants maintained an intercellular CO2 (Ci) concentration that was significantly higher than that of nongrafted plants (Fig. 5C). Similar to the Ci, stomatal conductance of water vapor (gs) was significantly higher in grafted ‘Velocity F1’ plants than in nongrafted plants (Fig. 5D). Grafted ‘Velocity F1’ plants had a 13% higher gs than nongrafted plants. Plant density effects were not statistically significant for gs. Grafted ‘Velocity F1’ reduced lower electrolyte leakage (15%) compared with nongrafted ones (Fig. 6).
Citation: HortScience 58, 10; 10.21273/HORTSCI17249-23
Citation: HortScience 58, 10; 10.21273/HORTSCI17249-23
There were significant cultivar × grafting interactions for phenological attributes for which the effect of grafting on days required to first flower differed with those of nongrafted plants (Fig. 7A). Flowering occurred 3 d earlier with grafted ‘Velocity F1’ plants than with nongrafted plants. A similar trend was observed for 50% flowering, with a delay in the flowering of more than 3 d for nongrafted plants than for grafted plants, regardless of the cultivar (Fig. 7B). However, plant density had no significant effect on days required to first and 50% flowering (not shown). Grafted plants for both cultivars also showed fewer flower drops compared with nongrafted plants (Fig. 7C), with no differences between the cultivars. Additionally, grafted plants exhibited higher fruit sets compared with nongrafted plants (Fig. 7D). Higher fruit sets (20%) were also detected for grafted ‘Velocity F1’ transplants than for nongrafted transplants. Additionally, grafted ‘Sigma F1’ unveiled a similar trend of fruit sets (20%) compared with nongrafted plants. Cultivars had no significant effect on flower sets. Furthermore, grafted ‘Velocity F1’ exhibited higher pollen viability (22%) compared with nongrafted plants (Fig. 8).
Citation: HortScience 58, 10; 10.21273/HORTSCI17249-23
Citation: HortScience 58, 10; 10.21273/HORTSCI17249-23
Marketable fruit yield was significantly influenced by the three-way interaction among the tomato cultivars, grafting combinations, and plant densities (P < 0.05). Grafted ‘Velocity F1’ grown at 3.5 plants/m2 had 26% higher marketable fruit yields than nongrafted ‘Velocity F1’ grown at 5.5 plants/m2 (Fig. 9). Similarly, grafted ‘Sigma F1’ had 21% more marketable fruit yields when grown at 3.5 plants/m2 compared with nongrafted ‘Sigma F1’ grown at 5.5 plants/m2. Both grafted ‘Velocity F1’ and ‘Sigma F1’ exhibited higher fruit production efficiency compared with the nongrafted plants.
Citation: HortScience 58, 10; 10.21273/HORTSCI17249-23
Grafted ‘Velocity F1’ maintained postharvest quality and fruits had more than 4 d of storage shelf life than nongrafted ones (Table 1). The results revealed that at the end of the storage period, grafted ‘Velocity F1’ had 34% higher fruit weight compared with the nongrafted ones. Fruit firmness is a vital indicator of the quality attributes of tomatoes during storage. Grafted ‘Velocity F1’ maintained a significantly higher firmness level (33%) than the fruits from nongrafted plants. However, grafted ‘Sigma F1’ fruits showed maximum firmness values compared with other fruits. There were no significant differences in Brix and acid levels attributable to grafting. At the end of storage life, grafted ‘Velocity F1’ had a higher surface color, as indicated by 30% more redness (a*) than that of the nongrafted ones. Additionally, those fruits collected from grafted ‘Velocity F1’ illuminated better lightness (L*) with less proportion of yellowness (b*), good color purity or chroma value (C*), and better color tone or hue angle (°h) than those of others.
Tomato plant growth, physiology, phenology, yield, and postharvest storage quality greatly influenced the management practices evaluated during the current controlled environment hydroponic study. Both grafted (‘Velocity F1’ and ‘Sigma F1’) plants enhanced growth and protected plants against abiotic stresses, consistent with the results of previous studies. Albacete et al. (2015) reported that grafting improved nutrient uptake efficiency and resulted in higher plant vigor and increased yield potential of elite varieties. Singh et al. (2020) stated that grafted plants alleviated high-temperature stress and water deficit conditions and had better plant growth than nongrafted plants. Meimandi and Kappel (2020) described that grafted tomato plants had stronger root systems, which correlated with more resistance to abiotic and biotic stresses and improved physiological responses. Several other studies have reported that grafting commercially viable cultivars onto resistant rootstocks could mitigate the harmful effects of abiotic and biotic stresses and maintain proper plant growth (Penella et al. 2017; Rouphael et al. 2018). Poudyala et al. (2015) illustrated that a widespread deep root system of rootstock for tomatoes amplified the drought resistance in the grafted plants compared with nongrafted ones. Additionally, the exudation of strigolactone compounds from the rootstock could regulate the branching architecture and development pattern of the scion in grafted grapevine plants, as reported by Cochetel et al. (2018).
Increasing tomato productivity by focusing on plant density is a common approach in vegetable production systems. We speculate that at the density of 3.5 plants/m2, plants had more effective light interception, thereby increasing the net assimilation rate and ensuring vigorous plant growth compared with the 5.5 plants/m2. Grafting and the plant density combination foster tomato plant growth. The result could be explained by the higher growth of grafted plants grown with 3.5 plants/m2, which was also observed by Maboko and du Plooy (2018). Amare and Gebremedhin (2020) reported that the interaction effects of inter-row and intra-row spacing remarkably affected plant growth and marketable fruit number, fruit diameter, and marketable fruit yield of tomatoes. The 20-cm intra-row and 60-cm inter-row plant density may have had a significant role in the improvements of the availability of moisture, nutrients, light, and air movements, causing vigorous plant growth and development of ‘Weyno’ tomato.
During the present study, it was observed that one cultivar showed a higher SPAD value than the other. It is possible that genetic differences between two cultivars in terms of chlorophyll content resulted in a higher SPAD value for grafted ‘Sigma F1’. Oliveira et al. (2022) reported that the leaf chlorophyll index (SPAD) value varied among the 12 tomato cultivars and Onix, Maestrina, Shanty, Pizzadoro, Sheena, and Santa Clara had higher SPAD values that could be used to select tomato genotypes for a multi-trait breeding program. During a previous study, SPAD values varied among growth stages of tomato plants under water stress conditions and during the flowering stage, with tomato leaves exhibiting a 7% higher leaf chlorophyll index value (54.0) compared with the early fruiting stage leaf chlorophyll index (48.0) value as reported by Nemeskeri et al. (2019). Huang et al. (2015) stated that the increase in the chlorophyll content by grafting could supply more substrate for the continuous vigorous growth of tomato plants, which supports the present findings. Additionally, significantly higher SPAD values (chlorophyll index) were observed in grafted plants than in nongrafted ones during the current study. A similar response of grafting was found for the chlorophyll content, with ‘Ikram’ × ‘Maxifort’-grafted and ‘Ikram’ × ‘Unifort’-grafted plants exhibiting better responses than the nongrafted ones (Kumar et al. 2015). Furthermore, the higher performance of grafted plants was associated with a higher chlorophyll content and photosynthetic pigment concentrations in leaves, which were linked with better nutrient translocation and availability in leaves.
During the current study, grafted tomato plants reduced the transpiration loss compared with nongrafted plants. It may be possible that grafted plants had a greater ability to operate stomata more efficiently under stress conditions. A vital challenge for water stress mitigation is modulating transpiration through stomata (Biasuz and Kalcsits 2022). Marguerit et al. (2012) reported that rootstock controlled the transpiration rate under water deficit conditions through independent genetic controls because no specific quantitative trait loci for these effects were recognized on the grapevine. During our study, grafted (‘Maxifort F1’ × ‘Velocity F1’) transplants exhibited a higher assimilation rate than nongrafted transplants. The increase in the net assimilation rate using grafted transplants was expected because our intention was to improve stomatal conductance and intercellular CO2 in leaves to protect transplants from stresses. Previous research claimed that grafted tomatoes provided greater protection against heat stress as indicated by a higher assimilation rate than that of nongrafted ones. Additionally, grafting appears to preserve cell membrane functions, as reported by Kumar et al. (2015) for tomato grafting combinations of ‘Ikram’ × ‘Unifort’ and ‘Ikram’ × ‘Maxifort’, who speculated that the cell membrane stability is increased by calcium uptake and both ‘Unifort’ and ‘Maxifort’ rootstocks facilitated a fast uptake and translocation of calcium in the tomato plants. Mauro et al. (2020a) stated that the grafting combination (‘Dreamer’ × ‘Maxifort’) presented dominancy for plant growth and reduced leaf electrolyte leakage compared with the nongrafted or self-grafted ones, especially under root hypoxia conditions.
During our study, grafted tomato plants accelerated the time to flowering. It is possible that grafted plants reduced the negative effect of transplanting shock established early through the robust root systems and enabled more nutrients from the growing media compared with the nongrafted plants. Penella et al. (2017) reported that grafted plants resulted in faster nutrient accumulation than that nongrafted ones. A previous study by Meyer et al. (2017) showed that grafting and a 50% leaf removal combination resulted in a higher flower count compared with nongrafted tomato plants. The results suggested that grafting and a 50% leaf removal combination may influence the timing of flowering of tomatoes. Grafting tomatoes on tobacco plants resulted in earlier flowering by 11 d and significantly higher total flower numbers (10%–39%) per plant than self-grafting or nongrafted plants (Yasinok et al. 2009). A previous study claimed that grafted tomato plants required 4 d less for a flower than nongrafted plants (Mahbou et al. 2022). Gisbert et al. (2011) reported that grafted plants may establish faster by mitigating environmental stresses and accelerating physiological activities, resulting in early flowering. However, plant spacing had no effects on days to 50% flowering of tomatoes under the Shewarobit condition of Ethiopia (Amare and Gebremedhin 2020), which is consistent with our findings. In contrast with the present study, other results indicated that onset and 50% flowering were significantly earlier in wider spacing (Ismail and Mousa 2014).
It is well-established that abiotic stresses reduce the pollen viability of tomatoes and other crops. Viable pollen is an important indicator that measures a plant’s ability to experience a series of flowering events encompassing pollination, fertilization, and seed and fruit development (Halo et al. 2023). Borghi and Fernie (2020) stated that anther and pollen are adversely affected by heat stress, resulting in failure of sexual reproduction and significantly reduced fruit sets. Similarly, Muller and Rieu (2016) revealed that high temperatures decreased pollen viability. Several physiological and biochemical events of plants are disrupted because of extreme heat, leading to flower drop, poor flower set, and poor fruit yield (Osei-Bonsu et al. 2022). Extreme heat stress negatively affected pollen grain, impaired pollen germination and impaired pollen tube development (Raja et al. 2019). High temperatures cause abortion of male gametophytes and reduce the fruit set; the overall checked crop productivity decreased when the atmospheric temperature was raised by 1.5 to 11 °C (Reddy and Kakani 2007). Heat stress could stimulate flower abortion and decrease fruit yield, as reported by Camejo et al. (2005). Alsamir et al. (2021) described that extremely high temperatures not only reduce flower and fruit sets but also affect fruit development and maturity. Latifah et al. (2023) revealed that grafted ‘Cervo’ and ‘Timoty’ tomatoes on selected eggplant rootstock produced more flowers and higher fruit sets compared with the nongrafted ones. It is possible that grafted plants with strong root systems could improve levels of plant hormones, resulting in a higher physiological response by tomato plants (Som and Madhava 2013). Improved flower and fruit setting and lower flower drop and higher pollen viability from grafted plants suggested that grafted plants performed well, thus alleviating abiotic stresses and allowing the continuation of proper growth and development.
The finding that grafted tomato plants improved fruit yield compared with nongrafted ones are in agreement with those of previous studies. When the ‘Belladonna F1’ tomato was grafted onto the rootstock ‘M82’, an 11% higher fruit production compared to self-grafted ones was reported by Kalozoumis et al. (2021). Rigano et al. (2016) described that regardless of stress conditions, the total fruit yield of tomatoes improved for grafted plants (‘Belladonna F1’ × ‘M82’), which corroborates our study results. The mean tomato fruit weight is greatly influenced by grafting, as stated by Schwarz et al. (2013) and Kyriacou et al. (2017). The effect of rootstock or rootstock × scion combination influenced the average fruit weight of cherry tomatoes (Mauro et al. 2020b). Another study also reported that fruit size and weight increased significantly when using grafted tomato transplants (Riga 2015), although those responses depend on the grafting combinations (Schwarz et al. 2013). Schwarz et al. (2013) stated that when ‘Piccolino’ cherry tomato was grafted onto commercial rootstock ‘Maxifort’, plant growth was modulated, resulting in larger fruits. Grafted tomatoes showed vigorous growth, suppressed soil-borne diseases, and improved the yield of tomatoes in both greenhouse and field conditions (Kubota et al. 2008). Additionally, the use of ‘Maxifort’ rootstock improved the marketable fruit yield by more than 50% compared with the nongrafted plants (Djidonou et al. 2017). However, it is vital to select appropriate rootstock and scion combinations to maximize the growth, yield, and quality of fruits (Aloni et al. 2010). Tomato yield was increased by 45% when grafted seedlings (‘TMS-150’ × ‘0301111’) were used compared with the nongrafted seedlings (Zhang et al. 2021), which is consistent with the conclusion of Kunwar et al. (2017). Similarly, Fu et al. (2022) reported that the grafted tomato plants produced 17% and 15% more yield when ‘Mingzhi88’ scion was grafted on ‘Cheong Gang’ and ‘TMS150’ rootstocks, respectively, than those of nongrated plants. In an organic management system, grafting enhanced fruit weight (12%), fruit number (22%), and marketable fruit yield (43%) more than nongrafting (Moreno et al. 2019). Latifah et al. (2023) also revealed that grafted tomato ‘Cervo’ and ‘Timoty’ yielded 30% more marketable fruits than nongrafted ones.
During our study, grafting significantly impacted the postharvest quality of tomatoes. Ilic et al. (2020) conveyed that the external and internal quality of tomato fruit could be influenced by grafting, although they are triggered by the rootstock and scion combination. Abu Glion et al. (2019) described that the fruit shelf life and other quality parameters were better for the ‘Lorka’ × ‘Register’ tomato grafting combination than those of other groups. As previously indicated by Aloni et al. (2010), this response was likely caused by the proper selection of scion and rootstock combinations that resulted in better stimulation of the hormonal balance within the plant, thereby improving source/sink relationships of fruits. Fruits collected from grafted ‘Cervo’ and ‘Timoty’ tomato plants showed 10% longer shelf life and more total soluble solids compared with nongrafted plants (Latifah et al. 2023). Additionally, fruits exhibited 16% more red color intensity (a*) and 20% more firmness than nongrafted ones; these data support the findings of the present study. Larger fruits, more soluble solids, and increased storage life were observed for grafted tomato (‘Cyndia’ × ‘Charlotte F1’) plants compared with nongrafted ones (Balliu et al. 2008). The grafting (‘Maxifort’ × ‘Optima F1’) and shading (50%) combination helped boost marketable tomato yields and maintain quality during storage, and it especially increased micronutrients (Fe, Zn) and macronutrients (Ca), resulted in a higher malic acid content and lower sugar content, and increased firmness (Milenkovic et al. 2020). After 21 d of storage, tomato fruits collected from grafted plants had a higher firmness value than fruits collected from nongrafted plants (Ozturk and Ozer 2019), thus supporting the present findings. Grafted tomato plants grown in a greenhouse had less impact on the titratable acidity (TA) content; however, the TA content increased when the grafted plants were grown in an open field environment. The results suggested that growing conditions are more important than grafting for the TA contents of tomato fruits (Khah et al. 2006). Aloni et al. (2010) informed that not only shading but also grafting modulate the TA content of tomato fruits. The TA content of tomato fruits was increased by 9% when the plants were grafted (‘Maxifort’ × ‘Classy’) and maintained proper shade (50%), as reported by Krumbein and Schwarz (2013); these results are in contrast to those of the current study, but the acid content did not vary because of grafting. The soluble solids content varied among grafted (‘Maxifort’ × ‘Optima F1’) and nongrafted fruits, with the main differences in the fructose and glucose contents or their in fruits (Milenkovic et al. 2020). Previous studies claimed that the grafting (‘Maxifort’ × ‘Florida 47’; ‘Multifort’ × ‘Florida 47’; ‘Beaufort’ × ‘Florida 47’) combination could affect fruit quality attributes such as texture, total soluble solids, fruit color, and aroma profile (Djidonou et al. 2017). Similarly, fruits collected from grafted (‘Strain B’ × ‘Edkawy’) plants exhibited higher total soluble solid contents than nongrafted ones, as mentioned by Sayed et al. (2022). However, the grafting combination (rootstock and scion) might play a key role in determining fruit quality. Similarly, for watermelon, fruit quality is greatly influenced by variations in grafting (‘TZ148’ × ‘Pegasus’) combinations (Kyriacou et al. 2016).
Adverse climatic conditions preclude growing enough vegetables to meet the domestic demand of Qatar and other countries facing similar challenges. It is quite clear from previous reports that, to ensure food security for growing populations, hydroponically vegetable production could be one of the most suitable options to maximize outputs in arid climatic conditions. If the hydroponics system is managed in the correct way using suitable grafted (‘Maxifort F1’ × ‘Velocity F1’) tomato plants and proper plant density (3.5 plants/m2), then it can significantly enhance productivity, thus providing opportunities to meet food demand and contribute Qatar’s gross domestic product. The present approach of hydroponics management systems is a new method of enriching the agricultural sector, especially for organic farmers seeking to increase their long-term farm income, and setting an example for other hydroponic organic farms.
Air temperature and relative humidity recorded during the healing and hardening process of grafted transplants.
Real-time air temperature and relative humidity inside the greenhouse.
Real-time growing media temperature and water content at a depth of 2 cm.
Effect of grafting and cultivar on the soil plant analysis development value of tomato. Vertical bar represents the SE. Dissimilar letters on the line graph show statistical differences, the same letters show statistical similarities according to Tukey’s honest significant difference test at P < 0.05. NonGra-Vel = nongrafted ‘Velocity F1’; Gra-Vel = grafted ‘Velocity F1’; NonGra-Sig = non-grafted ‘Sigma F1’; Gra-Sig = grafted ‘Sigma F1’. ** Significant at P < 0.01.
Effects of grafting and cultivar on the transpiration rate (A), assimilation rate (B), intercellular CO2 (C), and stomatal conductance (D) of tomato. Vertical bar represents the SE. Dissimilar letters on the line graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05. NonGra-Vel = nongrafted ‘Velocity F1’; Gra-Vel = grafted ‘Velocity F1’; NonGra-Sig = nongrafted ‘Sigma F1’; Gra-Sig = grafted ‘Sigma F1’. **, * Significant at P < 0.01 and P < 0.05, respectively.
Effects of grafting and cultivar on electrolyte leakage of tomato. Vertical bar represents the SE. Dissimilar letters on the line graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05. NonGra-Vel = nongrafted ‘Velocity F1’; Gra-Vel = grafted ‘Velocity F1’; NonGra-Sig = nongrafted ‘Sigma F1’; Gra-Sig = Grafted ‘Sigma F1’. ** Significant at P < 0.01.
Effects of grafting and cultivar on days required to first flower (A), days required to 50% flower (B), flower drop (C), and fruit set (D) of tomato. Vertical bar represents the SE. Dissimilar letters on the bar graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05.
Effects of grafting and cultivar on pollen viability of tomato. Vertical bar represents the SE. Dissimilar letters on the bar graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05.
Effects of grafting, cultivar, and plant density on marketable fruit yield of tomato. Vertical bar represents the SE. Dissimilar letters on the bar graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05.
Contributor Notes
This study was financially supported by the Qatar National Research Fund and the Ministry of Municipality and the Environment through a grant (MME01-0923-190060). AGRICO provided in-kind support for the study.
P.K.D. is the corresponding author. E-mail: prosanta.dash@qatar.tamu.edu.
Air temperature and relative humidity recorded during the healing and hardening process of grafted transplants.
Real-time air temperature and relative humidity inside the greenhouse.
Real-time growing media temperature and water content at a depth of 2 cm.
Effect of grafting and cultivar on the soil plant analysis development value of tomato. Vertical bar represents the SE. Dissimilar letters on the line graph show statistical differences, the same letters show statistical similarities according to Tukey’s honest significant difference test at P < 0.05. NonGra-Vel = nongrafted ‘Velocity F1’; Gra-Vel = grafted ‘Velocity F1’; NonGra-Sig = non-grafted ‘Sigma F1’; Gra-Sig = grafted ‘Sigma F1’. ** Significant at P < 0.01.
Effects of grafting and cultivar on the transpiration rate (A), assimilation rate (B), intercellular CO2 (C), and stomatal conductance (D) of tomato. Vertical bar represents the SE. Dissimilar letters on the line graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05. NonGra-Vel = nongrafted ‘Velocity F1’; Gra-Vel = grafted ‘Velocity F1’; NonGra-Sig = nongrafted ‘Sigma F1’; Gra-Sig = grafted ‘Sigma F1’. **, * Significant at P < 0.01 and P < 0.05, respectively.
Effects of grafting and cultivar on electrolyte leakage of tomato. Vertical bar represents the SE. Dissimilar letters on the line graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05. NonGra-Vel = nongrafted ‘Velocity F1’; Gra-Vel = grafted ‘Velocity F1’; NonGra-Sig = nongrafted ‘Sigma F1’; Gra-Sig = Grafted ‘Sigma F1’. ** Significant at P < 0.01.
Effects of grafting and cultivar on days required to first flower (A), days required to 50% flower (B), flower drop (C), and fruit set (D) of tomato. Vertical bar represents the SE. Dissimilar letters on the bar graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05.
Effects of grafting and cultivar on pollen viability of tomato. Vertical bar represents the SE. Dissimilar letters on the bar graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05.
Effects of grafting, cultivar, and plant density on marketable fruit yield of tomato. Vertical bar represents the SE. Dissimilar letters on the bar graph show statistical differences, whereas the same letters show statistically similarities according to Tukey’s honest significant difference test at P < 0.05.
