Grafted Watermelon Seedlings Research Articles

Additional far-red light promotes the healing and quality of double-root-cutting grafted watermelon seedlings

Graft healing is an important factor that determines the survival of the double-root-cutting (DRC) grafted plants. Recent studies have shown that adding far-red light (FR) to change the red/far-red (R/FR) ratio plays a crucial role in plant growth and development. However, there have been few studies on how R/FR ratio affects the grafting union healing process of DRC grafted seedling. In this study, we applied four light quality treatments: dark (D), white (R/FR=6.0, W), R/FR ratios of 3 (H) and 0.3 (L). The effects of different ratios of R/FR on the survival rate, photosynthetic fluorescence characteristics, graft union healing and growth of DRC grafted watermelon seedlings during the healing period were analyzed using darkness (D) as a control. The results showed that compared with the control L treatment could significantly improve the survival rate, growth indicators and photosynthetic capacity of grafted seedlings, significantly increased the activities of SOD and POD, and contents of soluble sugar and protein in the graft union, and significantly reduced the accumulation of O2−, H2O2 and MDA, which was conducive to the production of callus cell and the healing of grafted union. Meanwhile, qRT-PCR results showed that the expression levels of graft healing-related genes, ClaIAA, ClaSOD, ClaPOD, ClaWOX4, ClaGH9B14 and ClaGH9B1 were significantly induced L treatment. The current study can contribute to speeding up the development of industrialized production with high-quality watermelon grafted seedlings.

Additional far-red light promotes adventitious rooting of double-root-cutting grafted watermelon seedlings

Root regeneration is an important factor influencing the healing rate of graft union and the survival of double-root-cutting grafting. To date, little information is available on how to enhance root regeneration of rootstock in grafted watermelon (Citrullus lanatus) seedlings. In this study, the effects of different light treatments on root regeneration were determined. This revealed that addition of far-red light (Fr) could significantly expedite root formation in the rootstock. Moreover, the results of transcriptome analysis revealed that plant hormone pathway and auxin-related genes were greatly induced by Fr, especially for auxin-response proteins (including CmIAA11, CmIAA17, and CmAUX28), Small auxin-up RNA genes (including CmSAUR20 and CmSAUR50) and the auxin efflux transporter (CmPIN3). In addition, the expression of Phytochrome Interacting Factor (PIFs), such as CmPIF1, CmPIF3 and CmPIF7, was remarkably increased by Fr. These genes may act together to activate auxin-related pathways under Fr treatment. Based on the results of HPLC-MS/MS analysis, the concentrations of different auxin-types in adventitious root were significantly influenced by Fr. Furthermore, the better growth of rootstock root displayed superior vasculature transport activity of the graft union with Fr treatment, which was determined by the acid magenta dyeing experiment. Therefore, all the results suggested that Fr could induce AR formation in rootstocks, which may be associated with the auxin accumulation by regulating the transcriptional level of auxin-related and PIF genes. The findings of this study demonstrated a practicable way to shorten the healing period of graftings and improve the quality of grafted watermelon seedlings, which will provide a theoretical basis for the speeding development of industrialized seedlings production.

Grafting onto pumpkin alters the evolution of fruit sugar profile and increases fruit weight through invertase and sugar transporters in watermelon

Sweetness is an essential quality trait of watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai), and it depends on both the concentration and composition of sugars. Grafting is a routine technique for watermelon production globally. However, it remains unknown whether rootstock alter the profiles of sugars in watermelon. To address this issue, we grafted watermelon seedlings onto a Cucurbita maxima × Cucurbita moschata rootstock, photosynthesis in leaves, contents of main carbohydrates, activities of invertase and sucrose synthase and expressions of invertase genes and sugar transporters in watermelon fruits were examined. Results showed that grafting could have delayed fruit ripening as fruits from grafted plants had a higher hexose/sucrose ratio (increased concentration of glucose and fructose and decreased concentration of sucrose) compared to fruits from self-grafted plants. These changes were associated with increased vacuolar invertase (VIN) activity. Meanwhile, a watermelon VIN gene (ClVIN2) and two CWIN genes (ClCWIN1 and ClCWIN4) were identified in updated watermelon genome, and ClVIN2 was upregulated accompanied by the elevated activity of VIN. In addition, rootstock grafted plants displayed improved net photosynthesis rate, increased expression of ClAGA2 (coding alkaline alpha-galactosidase), ClVST1 (coding vacuolar sugar transporter) and ClCWIN4 (coding cell wall invertase), and higher activity of cell wall invertase when compared with self-grafted plants, contributing to increased fruit weight. In summary, our results imply that invertase and related sugar transporters might play a role in sugar profiles and fruit weight differentiation observed during fruit maturity evolution.

An analysis of energy use and economic and environmental impacts in conventional tunnel and LED-equipped vertical systems in healing and acclimatization of grafted watermelon seedlings

Uncertain climate changes and increasing energy and food production demands lead to food insecurity, especially for drought-prone areas like the study region, Iran. This study assesses the energy use, economic, and environmental impacts of two different healing and acclimatization systems, the conventional tunnel systems (CTS) and the LED-equipped vertical systems (LVS), for grafted watermelon seedlings in Iran. Life cycle assessment (LCA), cumulative exergy demand (CExD), and life cycle cost analysis (LCCA) approaches are used to assess the impacts of grafted watermelon seedlings. The functional unit is one million grafted watermelon seedlings (MGWS). The top findings of this study indicate that CTS increases energy consumption, damage to human health, ecosystems, and resources compared with the LVS. Further, the economic analysis revealed that the net profit in the multi-floored LVS is 24% higher than that of the CTS. In conclusion, LVS is less energy consumptive and environmentally burdensome yet more profitable than the CTS. Notably, the finding from this study supports recommendations that will be useful for industries or producers who need to develop sustainable grafted watermelon or vegetable production systems in Iran or similar regions. Top recommendations include using organic fertilizers , multi-floor LVS, and most importantly, replacing CTS with LVS to promote a sustainable agricultural production system. • Conventional tunnel systems consume more energy than LED-equipped vertical systems. • LED-equipped vertical systems reduce human health and ecosystem impacts. • LED-equipped vertical systems are more profitable than conventional tunnel systems.

A Light Recipe including Far-Red Wavelength during Healing of Grafted Watermelon Seedlings Enhances the Floral Development and Yield Earliness

Watermelon is widely propagated through grafting, after which seedlings are subjected to healing under controlled conditions including artificial lighting. Light wavelengths, such as blue, red, and far-red, impose considerable effects on seedlings, which possibly carry on to the mature plants. The aim of the present study is to examine whether different light wavelengths during healing of grafted watermelon seedlings impose variable effects during field cultivation. After grafting, seedlings were healed in an environmentally controlled healing chamber under fluorescent (FL) lamps and light-emitting diodes, providing 100% red (R), 100% blue (B), 88/12% R/B (12B), and 12B including 5% far-red (12B + FR). After acclimatization, seedlings were transplanted in the field. Vegetative growth until floral initiation was enhanced by 12B and 12B + FR, as shown by stem diameter and leaf number measurements. Flowering was mainly accelerated by 12B + FR and considerably decelerated by FL and B. The same pattern was followed by fruit yield, which was similar for all treatments at the end of the experiment. Nevertheless, fruit quality was not affected by any of the light treatments. It is concluded that a light recipe, including red, blue and far-red, wavelengths during healing of grafted seedlings enhances the overall growth, and flowering and yield earliness of watermelon crops.

A method for simultaneously monitoring phloem and xylem reconnections in grafted watermelon seedlings

Grafting is an effective way to increase watermelon's tolerances to biotic and abiotic stresses. However, the survival of grafted seedlings largely depends on successful graft formation. Therefore, understanding the graft formation process, particularly vascular reconnection, is of critical importance. This study found that lignin in watermelon stem showed strong auto-fluorescence under blue-light excitation. Consequently, blue-light excited fluorescent tracers (FTs) such as 5(6)-carboxy fluorescein diacetate (CFDA) were unsuitable for assaying vascular connectivity in watermelon. In contrast, UV-light excited esculin and red-light excited acid fuchsin proved to be efficient FTs for monitoring phloem and xylem connectivity, respectively, in self-grafted watermelon. Furthermore, combining esculin application to the scion cotyledon and acid fuchsin to the rootstock root enabled simultaneous monitoring of both phloem and xylem connectivity in individual self-grafted watermelon seedlings. Based on this assay, we found that phloem and xylem reconnections occurred simutaneously in self-grafted watermelon. Moreover, low temperature and removal of the rootstock cotyledons both delayed vascular reconnection in the self-grafted watermelon. In conclusion, this new method provided a convenient, accurate and rapid way to analyze vascular connectivity in watermelon.

Morphological characteristics and quality of grafted watermelon seedlings healing under different light qualities

Morphological characteristics and quality of grafted watermelon seedlings healing under different light qualities

Monitoring of Salinity, Temperature, and Drought Stress in Grafted Watermelon Seedlings Using Chlorophyll Fluorescence.

Chlorophyll fluorescence (CF) is used to measure the physiological status of plants affected by biotic and abiotic stresses. Therefore, we aimed to identify the changes in CF parameters in grafted watermelon seedlings exposed to salt, drought, and high and low temperatures. Grafted watermelon seedlings at the true three-leaf stage were subjected to salinity levels (0, 50, 100, 150, and 200 mM) and temperature [low (8°C), moderate (24°C), and high (40°C)] stresses for 12 days under controlled environmental conditions independently. Eight CF parameters were measured at 2-day intervals using the FluorCam machine quenching protocol of the FluorCam machine. The seedlings were also exposed to drought stress for 3 days independent of salinity and temperature stress; CF parameters were measured at 1-day intervals. In addition, growth parameters, proline, and chlorophyll content were evaluated in all three experiments. The CF parameters were differentially influenced depending on the type and extent of the stress conditions. The results showed a notable effect of salinity levels on CF parameters, predominantly in maximum quantum yield (Fv/Fm), non-photochemical quenching (NPQ), the ratio of the fluorescence decrease (Rfd), and quantum yield of non-regulated energy dissipation in PSII [Y(NO)]. High temperature had significant effects on Rfd and NPQ, whereas low temperature showed significant results in most CF parameters: Fv/Fm, Y(NO), NPQ, Rfd, the efficiency of excitation capture of open photosystem II (PSII) center (Fv′/Fm′), and effective quantum yield of photochemical energy conversion in PSII [Y(PSII)]. Only NPQ and Rfd were significantly influenced by severe drought stress. Approximately, all the growth parameters were significantly influenced by the stress level. Proline content increased with an increase in stress levels in all three experiments, whereas the chlorophyll (a and b) content either decreased or increased depending upon the stressor. The results provided here may be useful for understanding the effect of abiotic stresses on CF parameters and the selection of index CF parameters to detect abiotic stresses in grafted watermelon seedlings.

Light Spectrum Variably Affects the Acclimatization of Grafted Watermelon Seedlings While Maintaining Fruit Quality

In many countries of Europe and Eastern Asia, watermelon production is mainly based on the use of grafted seedlings. Upon grafting, seedlings undergo a period of healing where artificial lighting is provided by light-emitting diodes in controlled chambers in order to accelerate and improve the healing process. The objective of our study was to test the effect of light quality on the final product (i.e., seedlings ready for transplanting) in the nursery, as well as to evaluate the possible implications on fruit quality after field cultivation. Narrow-band blue (B) and red (R) wavelengths, 64–36% R-B (36B), 76–24% R-B (24B), 88–12% R-B (12B), and 83–12% R-B plus 5% far-red (12B+FR) wavelengths were tested. 12B+FR enhanced the root dry weight, root architecture, and maximum photosynthetic rate, while RB combinations generally showed better root system development with increased blue portion. R light induced inferior root dry weight and quality indices (root/shoot and shoot–dry–weight/length ratios), lower gas exchange parameters, and chlorophyll content, but high shoot length and leaf area. B light led to inferior root architecture, lower stem diameter, leaf area, and maximum photosynthetic rate. Both R and B wavelengths showed decreased concentration of macronutrients and trace elements. After field cultivation, fruit quality (i.e., morphology and color), and valuable nutritive characteristics (i.e., phenolics, carotenoids, lycopene, antioxidants) maintained high quality irrespective of light treatments. Overall, 12B+FR performed well in almost all qualitative parameters including the morphology, the root development, and photosynthesis, while also maintaining high fruit quality.

Blue light promotes vascular reconnection, while red light boosts the physiological response and quality of grafted watermelon seedlings

The wound inflicted during grafting of watermelon seedlings requires rapid and sufficient vascular development which is affected by light quality. Our objective was to investigate the effect of light spectra emitted by light-emitting diodes (LEDs) during healing of grafted watermelon (Citrullus lanatus) seedlings on their vascular development, physiological and phytohormonal profile, and root architecture. Three LEDs emitting red (R), blue (B), and RB with 12% blue (12B) were tested in a healing chamber. During the first three days, the photosynthetic apparatus portrayed by PIABS, φP0, ψE0, and ΔVIP was less damaged and faster repaired in B-treated seedlings. B and 12B promoted vascular reconnection and root development (length, surface area and volume). This was the result of signaling cascade between phytohormones such as indole-3-acetic acid and others. After vascular reconnection the seedlings switched lights for 3 more days and the picture was reversed. Seedlings treated with B for the first 3 days and R for days 4 to 6 had better photosynthetic characteristics, root system development, morphological, shoot and root biomass, and quality (i.e. Dickson’s quality index) characteristics. We concluded that blue light is important during the first 3 days of healing, while the presence of red is necessary after vascular reconnection.

Effect of Cold Stress on Growth, Physiological Characteristics, and Calvin-Cycle-Related Gene Expression of Grafted Watermelon Seedlings of Different Gourd Rootstocks

Recently, grafting has been used to improve abiotic stress resistance in crops. Here, using watermelon ‘Zaojia 8424’ (Citrullus lanatus) as scions, three different gourds (Lagenaria siceraria, 0526, 2505, and 1226) as rootstocks, and non-grafted plants as controls (different plants were abbreviated as 0526, 2505, 1226, and 8424), the effect of cold stress on various physiological and molecular parameters was investigated. The results demonstrate that the improved cold tolerance of gourd-grafted watermelon was associated with higher chlorophyll and proline content, and lower malondialdehyde (MDA) content, compared to 8424 under cold stress. Furthermore, grafted watermelons accumulated fewer reactive oxygen species (ROS), accompanied by enhanced antioxidant activity and a higher expression of enzymes related to the Calvin cycle. In conclusion, watermelons with 2505 and 0526 rootstocks were more resilient compared to 1226 and 8424. These results confirm that using tolerant rootstocks may be an efficient adaptation strategy for improving abiotic stress tolerance in watermelon.

Blue Light Improves Photosynthetic Performance during Healing and Acclimatization of Grafted Watermelon Seedlings.

To investigate the importance of light on healing and acclimatization, in the present study, grafted watermelon seedlings were exposed to darkness (D) or light, provided by blue (B), red (R), a mixture of R (68%) and B (RB), or white (W; 35% B, 49% intermediate spectra, 16% R) LEDs for 12 days. Survival ratio, root and shoot growth, soluble carbohydrate content, photosynthetic pigments content, and photosynthetic performance were evaluated. Seedling survival was not only strongly limited in D but the survived seedlings had an inferior shoot and root development, reduced chlorophyll content, and attenuated photosynthetic efficiency. RB-exposed seedlings had a less-developed root system. R-exposed seedlings showed leaf epinasty, and had the smallest leaf area, reduced chlorophyll content, and suppressed photosynthetic apparatus performance. The R-exposed seedlings contained the highest amount of soluble carbohydrate and together with D-exposed seedlings the lowest amount of chlorophyll in their scions. B-exposed seedlings showed the highest chlorophyll content and improved overall PSII photosynthetic functioning. W-exposed seedling had the largest leaf area, and closely resembled the photosynthetic properties of RB-exposed seedlings. We assume that, during healing of grafted seedlings monochromatic R light should be avoided. Instead, W and monochromatic B light may be willingly adopted due to their promoting effect on shoot, pigments content, and photosynthetic efficiency.

Proteomic Analysis of Fusarium oxysporum-Induced Mechanism in Grafted Watermelon Seedlings.

Grafting can improve the resistance of watermelon to soil-borne diseases. However, the molecular mechanism of defense response is not completely understood. Herein, we used a proteomic approach to investigate the molecular basis involved in grafted watermelon leaf defense against Fusarium oxysporum f.sp. niveum (FON) infection. The bottle gourd rootstock-grafted (RG) watermelon seedlings were highly resistant to FON compared with self-grafted (SG) watermelon plants, with a disease incidence of 3.4 and 89%, respectively. Meanwhile, grafting significantly induced the activity of pathogenesis-related proteases under FON challenge. Proteins extracted from leaves of RG and SG under FON inoculation were analyzed using two-dimensional gel electrophoresis. Thirty-nine differentially accumulated proteins (DAPs) were identified and classified into 10 functional groups. Accordingly, protein biosynthetic and stress- and defense-related proteins play crucial roles in the enhancement of disease resistance of RG watermelon seedlings, compared with that of SG watermelon seedlings. Proteins involved in signal transduction positively regulated the defense process. Carbohydrate and energy metabolism and photosystem contributed to energy production in RG watermelon seedlings under FON infection. The disease resistance of RG watermelon seedlings may also be related to the improved scavenging capacity of reactive oxygen species (ROS). The expression profile of 10 randomly selected proteins was measured using quantitative real-time PCR, among which, 7 was consistent with the results of the proteomic analysis. The functional implications of these proteins in regulating grafted watermelon response against F. oxysporum are discussed.

Influence of Light Spectra from LEDs and Scion × Rootstock Genotype Combinations on the Quality of Grafted Watermelon Seedlings.

Grafting is the main means of propagation for watermelon crops. The aim of the present study was to evaluate whether light quality during graft healing variably affects different scion × rootstock genotype combinations. Two watermelon hybrid scions (Sunny Florida F1 and Celine F1) and two interspecific squash rootstocks (Radik and TZ-148) were used, and four scion × rootstock genotype combinations derived. After grafting, we tested seven light-emitting diodes (LEDs), which provided narrow-band red (R) and blue (B); R-B with 36% (36B), 24% (24B), and 12% (12B) blue; 12B with additional far-red (12B+FR); and white (W), in a healing chamber. In three genotype combinations, shoot length, leaf area, and shoot biomass were mainly enhanced under red-blue LEDs, while stem diameter was greater under R. In contrast, dry weight of roots, Dickson’s quality index, and ratio of shoot dry weight/length were variably affected in each genotype combination. From the results, it is concluded that light treatments differentially affected each genotype combination, but some parameters involving biomass production show genotypic dependency.

Supplemental lighting enhances quality of grafted watermelon seedlings

Supplemental lighting enhances quality of grafted watermelon seedlings

Impact of Scion and Rootstock Seedling Quality Selection on the Vigor of Watermelon–Interspecific Squash Grafted Seedlings

Watermelon is mainly grafted onto interspecific squash, and during the season of high demand, seedlings of variable quality are used to cover grafting needs. The objective was to combine watermelon and interspecific squash of different seedling quality categories in order to obtain the optimal combination for the production of high-quality grafted watermelon seedlings. Acceptable seedlings of both species were grouped into quality categories, namely “low”, “optimum”, and “high”. Seedlings of each quality category were combined with each other and grafted seedlings from the nine derived categories were evaluated at two time intervals, at 7 (exit from the healing chamber) and 14 (final product) days after grafting. At both time intervals, watermelon “high” combined with interspecific squash “optimum” exhibited relatively higher shoot length, stem diameter, leaf area, and shoot and root dry weight, as well as shoot dry weight-to-length ratio, which is a quality index. The study shows that watermelon scions should have “high” quality, while interspecific squash rootstocks should have “optimum” quality during grafting for the production of high-quality grafted plants. If possible, “low” to-be-grafted watermelon seedlings should be avoided because the grafted derived seedlings are considered low quality.

Effect of Supplementary Lighting Duration on Growth and Activity of Antioxidant Enzymes in Grafted Watermelon Seedlings

Insufficient exposure to light in the winter may result in a longer production periods and lower quality of seedlings in greenhouses for plug growers. Supplementary artificial lighting to plug seedlings may be one solution to this problem. The objective of this study was to assess the effects of the duration of the supplementary light on the growth and development of two watermelon cultivars, ‘Speed’ and ‘Sambok Honey’ grafted onto ‘RS-Dongjanggun’ bottle gourd rootstocks (Lagenaria siceraria Stanld). Seedlings were grown for 10 days in a glasshouse with an average daily natural light intensity of 340 μmol·m−2·s−1 photosynthetic photon flux density (PPFD) and daily supplementary lighting of 8, 12 or 16 h from mixed LEDs (W1R2B1, chip ratio of white:red:blue = 1:2:1) at a light intensity of 100 μmol·m−2·s−1 PPFD, a group without supplementary light was set as the control (CK). The culture environment in a glasshouse had 25/15 °C day/night temperatures, an 85 ± 5% relative humidity, and a natural photoperiod of 8 h. The results showed that all the growth and development parameters of seedlings grown with supplementary light were significantly greater than those without supplementary light (CK). The 12 and 16 h supplementary light resulted in greater growth and development parameters than the 8 h supplementary light did. The same trend was also found with the indexes that reflect the quality of the seedlings, such as the dry weight ratio of the shoot and root, total biomass, dry weight to height ratio of scions, and specific leaf weight. The 12 h and 16 h light supplements resulted in greater Dickson’s quality indexes compared to the 8 h supplementary light, and the 12 h supplementary light showed the greatest use efficiency of the supplementary light. 16 h of daily supplementary light significantly increased the H2O2 content and the antioxidant enzyme activities in seedlings compared to the other treatments. This indicated that 16 h of supplementary light led to certain stresses in watermelon seedlings. In conclusion, considering the energy consumption, 12 h of supplementary light was the most efficient in improving the quality of the two cultivars of grafted watermelon plug seedlings.

Effects of ozonated water irrigation on the quality of grafted watermelon seedlings

Ozonated water is an important postharvest sanitizer and an interesting alternative to keep nursery crops sanitized. Ozonated water (OW, 750 mV) and electrolyzed water (EW, 495 mV) were compared to a control (CTRL, water without sanitizer treatment), applied as overhead micro sprinkler irrigation, in grafted watermelon seedling plants grown under greenhouse conditions. As results we found a reduction in micronutrients (Fe, Mn, Cu, Zn and B) and macronutrients (Ca and Mg) in grafted watermelon leaves treated with OW, although the OW did not affect the photosynthesis rate or plant development. Additionally, EW reduced the vitamin C content at days 45 and 57 compared to the OW and CTRL samples. OW and EW showed higher total phenolic content (TPC) than the CTRL at days 45 and 49. However, no significant differences were observed in TPC and antioxidant capacity among treatments at day 57. On the other hand, catalase activity increased in OW samples after days 49 and was maintained at day 57, but no significant changes in lipid peroxidation was observed among treatments. As main conclusion, OW caused a moderate stress in grafted watermelon seedlings increasing the oxidative status to balance the redox system that could provide plants with higher bioactive compounds.

Bichromatic red and blue LEDs during healing enhance the vegetative growth and quality of grafted watermelon seedlings

Watermelon is an economically important crop that is exclusively established through the use of grafted seedlings. Grafting procedure and the period of healing are critical for the production of high quality seedlings. During healing, grafted seedlings are grown in a chamber with controlled conditions, including supplementary lighting. The aim of the present study was to evaluate the impact of commonly used fluorescent (FL, control) lamps or light-emitting diodes (LEDs) with varying red (R) and blue (B) proportions [100 % R (R), 12 % B and 88 % R (12B), 24 % B and 76 % R (24B), 36 % B and 64 % R (36B) or 100 % B (B)] employed in the healing chamber on the quality of grafted watermelon seedlings. Seedlings under FL and B performed poorly in almost all tested parameters compared to the other LEDs. However, monochromatic B led to the greatest rates of photosynthesis (Pmax), stomatal conductance (g) and transpiration (E). On the contrary, R promoted the seedling length, fresh and dry weight (FW and DW) of shoots and roots, and root-to-shoot ratio (R/S) but led to inferior gas exchange and photosynthetic efficiency (Fv/Fm). B addition to R light (12B and 24B) enhanced the morphological and growth characteristics tested at least as much as R light or even more (leaf area, shoot DW). It should be noted that the entire root system of the seedlings was cut off during the grafting procedure and its re-growth was highly promoted by dichromatic LEDs (R plus B). Altogether, the above results demonstrate that R light with addition of low proportion of B light (12–24%) enhances the production of high quality grafted watermelon seedlings.

Assessing Quantitative Criteria for Characterization of Quality Categories for Grafted Watermelon Seedlings

Vegetable grafting is a practice employed worldwide since it helps prevent biotic and abiotic disorders, and watermelon is one of the most important species grafted. The objective of this study was to set critical limits for the characterization of quality categories for grafted watermelon seedlings. Specifically, watermelon (scion) seedlings were grafted onto squash (rootstock) seedlings, moved into a healing chamber for 7 days, and then transferred into a greenhouse for seven more days. At 7 and 14 days after grafting, experienced personnel assessed grafted seedling quality by categorizing them. The categories derived were Optimum and Acceptable for both time intervals, plus Not acceptable at 14 days after grafting. Optimum seedlings showed greater leaf area, and shoot and root fresh and dry weights at both time intervals. Moreover, they had greater stem diameter, root-to-shoot ratio, shoot dry weight-to-length ratio and Dickson’s quality index compared to the other category at 14 days after grafting. Therefore, Optimum seedlings would likely develop into marketable plants of high quality, with better establishment in the field. Not acceptable seedlings showed considerably inferior development, while Acceptable seedlings were between the other categories, but were still marketable.