Watermelon [
The first principle of producing high-yielding and quality watermelon is to grow healthy seedlings and plants. In the production of vigorous and healthy seedlings, biotic and abiotic factors in the growing environment, genotype, fertilisation, growing conditions of the mother plant of seed, harvest maturity stage of the seed, seed processing techniques, seed moisture content during storage and seed quality are effective factors. In addition, plant growth and vigour can be increased by using varieties or rootstocks with strong roots that provide more water and plant nutrients, synthesise hormones and similar substances that increase plant strength and health (Kovalev and Lisovskaya, 1989; Kovalev, 1990; Ra et al., 1995; Fernández-García and Martínez-Arbelaiz, 2002; Yarşi and Sari, 2006). This can only be achieved either with genotypes with strong roots or by grafting onto suitable rootstocks with a vigorous root system (Yetisir and Sari, 2003; Lee and Oda, 2010).
The grafting in fruit-bearing vegetables is becoming a well-developed practice with many agricultural advantages. The primary starting point for grafting vegetable crops is to prevent damage caused by soil-borne pests and pathogens (Oda, 2002; Yetisir and Sari, 2003). However, in the last few decades, it has also been reported that grafting of vegetable crops improves tolerance to abiotic stresses such as drought, low soil temperature and salinity, the efficiency of water and nutrient use, and fruit yield and quality (Shimada and Nakamura, 1977; Romero et al., 1997; Nisini et al., 2002; Oda, 2002; Rivero et al., 2003; Lee and Oda, 2010; Edelstein et al., 2011). Grafting onto suitable rootstocks can contribute to global food security by enabling the cultivation of watermelon and other fruiting vegetables under stressful environmental and soil conditions.
Although utilisation rates vary, the most common commercial rootstocks for watermelons are
One way to solve the quality problems in grafted watermelon production mentioned earlier could be to use rootstocks developed from the
The most important disadvantage of potential citron genotypes as rootstocks for watermelon is that they have slightly lower plant vigour than
The study was carried out in Kirşehir Ahi Evran University, Agricultural Research and Application Greenhouse. The list of plant materials applied with colchicine is presented in Table 1. Cultivated watermelon (‘Calhoun Gray’) and
List, genotype codes and numbers of plant materials applied with colchicine.
Genotype | Genotype code | Plants used in colchicine application (number) |
---|---|---|
Calhoun Gray ( |
C | 180 |
W1482 ( |
N3 | 210 |
W1832 ( |
N5 | 210 |
W2001 ( |
N7 | 180 |
CxW1482 | CxN3 | 210 |
CxW1832 | CxN5 | 180 |
CxW2001 | CxN7 | 210 |
Total | 1,380 |
The stoma dimension (length and diameter) and density and the number of chloroplasts in guard cells were determined in the lower epidermis of colchicine-treated plant leaves. For this purpose, the fifth and sixth fully developed leaves developed after colchicine application were used. Under a light microscope, the diameter and length of four stomata per leaf were measured magnifying by 40 × 10 objective and oculars, respectively. Obtained values were multiplied by 2.439, a coefficient obtained by adjusting the ocular micrometre, so as to obtain the true length of the stomata. The chloroplast number in each of the two guard cells of stomata was scored under a light microscope. Measurements and counts were performed in two leaves from each genotype and in 10 stomata in two samples from each leaf. The density of stomata was determined as a number of stomata · mm-2. Stomatal measurement and chloroplast count were performed following the procedure described by Sari et al. (1999) and Yetisir and Sari (2003).
Flow cytometry analysis was performed to determine the ploidy levels of the plants found to be different as a result of stomatal observations. Flow cytometry analysis was carried out in the Department of Field Crops, Faculty of Agriculture, University of Tekirdağ. Samples were obtained from plant leaves for flow cytometry analysis, as reported by Tuna et al. (2016). The ploidy levels were examined by using a Partec CyFlow Space (Partec GmbH, Münster, Germany) flow cytometer. Nuclei were isolated from each plants leaves following the protocol described by Tuna et al. (2016). Flow cytometry analyses were performed using a Partec kit as per the manufacturers’ instructions (Aleza et al., 2009; Tuna et al., 2016). Diploid control samples (cell nucleus isolates) were prepared from leaves of original diploid watermelon plants.
Colchicine-applied plants, which were determined to be tetraploid by stomatal measurements and flow cytometry analysis, were planted in Kirşehir Ahi Evran University, Agricultural Research and Application area. Seeds were produced by selfing in each plant grown with regular cultural practices for watermelon. Plants obtained as a result of colchicine application have monoecious flower types, and the fruit set rate of self-fertile flowers is high. Thousand seed weight is the weight of 1,000 seeds in grams.
The seeds used in the germination test were harvested from the fruit produced by selfing in diploids and tetraploids. For each genotypes, 30 uniform seeds were used in the germination test, and the germination rate was determined on the 12th day of incubation. Seeds were placed between two layers of wet filter paper in 11-cm petri dishes and incubated at 24 °C in the dark. The germination response was scored visually as radicle emergence. In 25-day-old seedlings, the cotyledon width (mm), cotyledon length (mm) and hypocotyl diameter (mm) were measured using a digital calliper.
Plant materials used in hydroponic experiments are auto- and tetraploids, original diploid parental lines, commercial rootstocks (RS841 and Argentaio) and watermelon cultivar (Crimson Tide). Commercial
List of genotypes used in hydroponic culture.
Genotype code | Ploidy level | Genotype code | Ploidy level |
---|---|---|---|
M1Calhon Gray | Tetraploid | M1CXN5-1 | Tetraploid |
M1N3 | Tetraploid | M1CXN7-1 | Tetraploid |
M1N5-1 | Tetraploid | M1CXN7-2 | Tetraploid |
M1N5-2 | Tetraploid | M1CXN7-3 | Tetraploid |
M1N5-3 | Tetraploid | M1CXN7-4 | Tetraploid |
M1N5-4 | Tetraploid | M1CXN7-5 | Tetraploid |
M1N5-5 | Tetraploid | Calhoun Gray | Diploid |
M1N5-6 | Tetraploid | CXN3 | Diploid |
M1N7-1 | Tetraploid | CXN5 | Diploid |
M1N7-2 | Tetraploid | CXN7 | Diploid |
M1N7-3 | Tetraploid | N3 | Diploid |
M1N7-4 | Tetraploid | N5 | Diploid |
M1CXN3-1 | Tetraploid | N7 | Diploid |
M1CXN3-2 | Tetraploid | Crimson Tide | Diploid |
M1CXN3-3 | Tetraploid | RS841 | Diploid |
M1CXN3-4 | Tetraploid | Argentario | Diploid |
The seedlings with 2–3 true leaves were transplanted to 136-L plastic pots after cleaning from the growth substrate by washing with tap water on 3rd of March 2021. The upper surface of the pots was covered with Styrofoam, and the plants were placed in the holes drilled on the Styrofoam plate. The cultivation solution was constantly aerated with a pump. A total of 14 plants were grown in each pot. The nutrient solution contained 1,125 mM Ca(NO3)2, 375 mM (NH4)2SO4 750 mM K2SO4, 650 mM MgSO4, 500 mM KH2PO4, 10 mM H3BO32, 0.45 mM MnSO4, 0.45 mM ZnSO4, 20.44mM CuSO43, 0.43 mM MoNa2O4 an4d 80 mM Fe EDD4 HA. The electrical conductivity of the cultivation solution was maintained at 1.50 dS · m-1 and the pH between 6.5 and 7 (Hoagland and Arnon, 1950). The experiment was designed according to the randomised plot design with three replications and three plants in each replication. The study was continued for 21 days under controlled greenhouse conditions (22–24 °C day/16–18 °C night and 60% relative humidity). The experiment was terminated on the 24th of March 2021.
The plant stem diameter (PSD) (mm), plant stem length (cm), and shoot and root fresh and dry weights (g · plant-1) were determined after harvest. The PSD was measured using a digital calliper 1–2 cm below the cotyledons and plant stem length was measured using a tape measure. After harvest, the fresh weights of roots and shoots were determined using a digital balance, with an accuracy of 0.01 (g · plant-1). Their tissues were dried in a forced-air oven at 80 °C for 72 hr for dry biomass determination until a stable weight was achieved. Then, they were weighed on an electronic digital scale (g × plant-1).
The plant RL, RD and RV were measured by using special image analysis software Program WinRHIZO (Win/Mac RHIZO Pro V. 2002c Regent Instruments Inc., Québec, QC G1V 1V4, Canada) in combination with an Epson Expression 11000XL scanner. The root samples (~0.5 g) from each plant were placed in the scanner tray. Water was added using a plastic wash bottle, the roots were homogeneously spread across the tray, and the scanning and analysis were carried out using the WinRHIZO system’s interface on a computer connected to the scanner. The total plant RL, RD and volume were then determined as the ratio of sampled root fresh weight (RFW) to the total RFW (Ulas et al., 2019).
Data from the hydroponic experiment were analysed by one-way analysis of variance (ANOVA) using SPSS version 18.0 at a 5% significance level (IBM, Chicago, IL, USA), and the means were separated using the Duncan test. Classification of genotypes was achieved by principal component analysis (PCA) using XLSTAT software (XLSTAT, New York, USA). Correlation analysis was performed between hydroponic culture parameters and DNA content and stomatal parameters, using SPSS software (IBM SPSS Statistics version 22.0, Chicago, IL, USA).
The survival rate of the seedlings after the application of colchicine was calculated as a percentage and is given in Table 3. In the study, colchicine was applied to a total of 1,380 plants in seven genotypes; 858 of these plants survived, and the average survival rate was 62.17%. Depending on the application of colchicine, the survival rates of the seedlings varied from 52.38% to 87%. The N7 genotype was the least (87.78%) damaged from the negative effects of colchicine application, and the genotype most adversely affected by colchicine application was N5 (52.38%). The low survival rate of the colchicine-treated seedlings can be explained as a negative effect of colchicine. It was reported that colchicine is a toxic chemical, and exposure of young plant cells to high doses of colchicine can be fatal (Oh et al., 2015b). In a study, conducted
Number of plants applied, the number of surviving plants and their ratio (%).
Genotype | Plants applied (number) | Surviving plants (number) | Surviving plants (%) |
---|---|---|---|
C | 180 | 120 | 66.67 |
N3 | 210 | 119 | 56.67 |
N5 | 210 | 110 | 52.38 |
N7 | 180 | 158 | 87.78 |
CXN3 | 210 | 116 | 55.24 |
CXN5 | 180 | 119 | 66.11 |
CXN7 | 210 | 116 | 55.24 |
Total/mean | 1,380 | 858 | 62.17 |
The width and length of guard cells, stomatal density and chloroplast number in guard cells are presented in Table 4. While the stomatal length, stomatal width and number of chloroplasts in guard cells increased in putative tetraploid plants, the number of stomata × mm-2 decreased (Table 4 and Figure 1). Stoma widths, which ranged from 16.09 μm to 18.90 μm in diploids, varied from 20.56 μm to 23.87 μm in putative tetraploids. As the stomatal width, the stoma length increased in putative tetraploid plants. While the minimum and maximum stomatal lengths in diploid plants were 23.3 μm and 26.04 μm, respectively, the minimum and maximum stomatal lengths in tetraploids were 31.42 μm and 34.01 μm, respectively. The stoma density per unit area decreased in putative tetraploids. Minimum and maximum stomatal densities in diploid plants were 627.30 and 927.77 number · mm-2, respectively, while the minimum and maximum stomatal densities in tetraploids were 341.75 and 470.35 number · mm-2, respectively. The number of chloroplasts in stomatal guard cells was significantly affected by colchicine application and increased in putative tetraploid plants. The chloroplast number in guard cells of the diploid plants ranged from 10.18 to 12.03 chloroplasts/stoma, and the chloroplast number in putative tetraploid plants’ guard cells varied from 16.41 to 19.37 chloroplast/stoma.
Stomal diameter and length in diploid (A) and tetraploid (B) plant leaves (magnified 400×).
Mean stomatal diameter, stomatal length, stomatal density and chloroplast number in presumed polyploid and diploid plants.
Stomatal diameter (μm) | Stomatal length (μm) | Stomatal density (number · mm-2) | Chloroplast number (number) | |||||
---|---|---|---|---|---|---|---|---|
Ploidy level | Diploid | Tetraploid | Diploid | Tetraploid | Diploid | Tetraploid | Diploid | Tetraploid |
Maximum | 16.09 | 20.56 | 23.30 | 31.42 | 627.30 | 341.75 | 10.18 | 16.41 |
Minimum | 18.90 | 23.87 | 26.04 | 34.01 | 927.77 | 470.34 | 12.03 | 19.37 |
Mean | 17.50 | 22.22 | 24.67 | 32.72 | 777.54 | 406.05 | 11.11 | 17.89 |
In parallel with our results, it was reported that the average number of stomata per unit area in the leaves of diploid plants is higher than the number of stomata per unit area of leaves of polyploid plants (Chen, 2010; Bae et al., 2020). It was also reported that the stomatal length and width increased in polyploid plants after colchicine application (Yang et al., 2006; Kwon et al., 2015). Consistent with our results, an increase in the number of chloroplasts per guard cell has been reported in tetraploid watermelons (Şimşek et al., 2013; Zhang et al., 2014). A similar increase in the chloroplast number in guard cells from 7.6–8.1 chloroplast/stoma to 17.7–18.8 chloroplast/stoma was also reported by Oh et al. (2015a) in watermelon. It is also known that the number of chloroplasts of guard cells in various plant species is a good characteristic in estimating ploidy levels (Koh, 2002; Oh et al., 2015a).
As a result of stomatal and chloroplast measurements, it was estimated that a total of 84 plants from seven genotypes could be polyploid plants. Morphological parameters, and stomatal and chloroplast measurements are often used as the first primary selection criteria for polyploids, but are often not entirely reliable (Zhang et al., 2010; Guo et al., 2019). It was confirmed that 22 of 84 plants, which were analysed by flow cytometry, were tetraploids. According to the results of flow cytometry, the doubling rate of the chromosome number with colchicine application showed significant variations between genotypes. The highest number of tetraploid plants (6) was obtained in the N5 genotype, while the least number of tetraploid plants (1) was obtained in ‘Calhoun Gray’, N3 and CXN5 genotypes. The success rate of chromosome duplication was 26.19% (Table 5). Flow cytometry analysis, chloroplast number and DNA content are correlated in tetraploid genotypes. It has been reported that the DNA content analysis method with flow cytometry is more reliable, especially in watermelon genome analyses (Jaskani et al., 2005; Oh et al., 2015a). Flow cytometry is an effective method that saves space and time by quickly determining the ploidy level of many plants at the early development stage (Väinölä, 2000; Leus et al., 2009). In a study conducted on the same plant material in
The number and percentage of tetraploid plants obtained as a result of microscope and flow cytometry analyses.
Genotype | Number of tetraploid plants | Flow cytometry analysis percentage of tetraploid plants (%) | |
---|---|---|---|
Stomatal examinations (number) | Flow cytometry analysis | ||
C | 8 | 1 | 12.50 |
N3 | 15 | 1 | 6.67 |
N5 | 11 | 6 | 54.55 |
N7 | 12 | 4 | 33.33 |
CXN3 | 14 | 4 | 28.57 |
CXN5 | 11 | 1 | 9.09 |
CXN7 | 13 | 5 | 38.46 |
Total/mean | 84 | 22 | 26.19 |
While the average nuclear DNA content of 22 tetraploid genotypes after colchicine applications was 1.90 pg/2C, the average DNA content of original diploid plants used as a control was determined as 0.92 pg/2C. The nuclear DNA content of tetraploid plants was approximately twice that of diploid plants (Figure 2). Flow cytometry allows polyploid plants to be analysed at an early stage, saving space and time (Väinölä, 2000). Zhang et al. (2014, 2019) reported that the fluorescence intensity of the main peak of the diploid E46 watermelon genotype is 203.46 pg/2C, and the fluorescence intensity of the main peak of the tetraploid E46 watermelon genotype is about 371.07 pg/2C, which means that the DNA content of cells of tetraploid plants is about twice that of diploid plants. This result is in consensus with our fluorescence intensity results.
Ploidy level of diploid (A) and tetraploid watermelon (B).
Plants estimated to be tetraploid were planted in the field and evaluated in terms of seed weight after seed production by selfing and seed extraction. While the average of 1,000 seed weight of tetraploid plants was 162.67 g, the average of 1,000 seed weight of diploid plants was 144.12 g. When the germination rates of tetraploid and diploid plants were compared, the germination rate of tetraploid plants decreased by 30.59% compared to that of diploid plants. While the cotyledon width of tetraploid seedlings increased by 7.76% compared to that of diploid seedlings, the cotyledon length and stem diameter increased by 12.58% and 20.62% (Table 6 and Figure 3), respectively. Similarly, previous studies have reported significantly increased seed length, width and thickness of tetraploid plants compared to those of diploid plant seeds in watermelon (Oh et al., 2015a; Zhang et al., 2019). The increase in seed size was also reflected in 1,000 seed weights, and the seed weight of tetraploid genotypes was found to be higher than that of diploids. Garber (1972) and Bakulin (1980) reported that auto- or allotetraploid plants generally have larger nuclei and cell size than corresponding diploids. This remarkable increase in the cell volume of polyploids is reflected in the dimensions or organs of their phenotype.
Seedling of diploid (A) CXN5 and tetraploid (B) M1CXN5-1 genotypes, leaf of diploid (C) CXN5 and tetraploid (D) M1CXN5-1 genotypes, male flower of diploid (E) N5 and tetraploid (F) M1N5-1 genotypes and seeds of diploid (G) CXN3 and tetraploid (H) M1CXN3-1 genotypes.
Thousand seed weights, germination rate, cotyledon width, cotyledon length, stem diameter and % change in genome size and 1,000 seed weights.
Ploidy level | % Change | ||
---|---|---|---|
Tetraploid | Diploid | ||
1,000 seed weight (g) | 162.67 | 144.12 | 11.40 |
Germination rate (%) | 65.8 | 94.8 | -30.59 |
Cotyledon width (mm) | 27.92 | 25.89 | 7.76 |
Cotyledon length (mm) | 39.99 | 35.53 | 12.58 |
Hypocotyl diameter (mm) | 3.14 | 2.57 | 20.62 |
Since cell structures of tetraploid plants are larger than those of diploid plants, it has been reported that some vegetative organs of tetraploid plants are quite different from those of diploid plants (Väinölä, 2000; Hiaba and Mohamed, 2009). In this study, diploid and tetraploid M1 plants (the first generation of colchicine-treated plants) were morphologically compared under hydroponic culture. The highest PSD was recorded in RS841 and ‘Argentario’ commercial rootstocks with 9.73 mm and 9.62 mm, respectively. The stem diameter ranged from 2.79 mm to 6.13 mm and did not show a significant variation among watermelon genotypes (diploids and tetraploids). A significant variation (11–115.83 cm) was found among genotypes as regarded to plant length (PL) (Figure 4). The longest plant was observed in ‘Argentario’ (115.83 cm) and RS841 (95.83 cm) commercial rootstocks, followed by M1N7-4 (75.65 cm), M1N5-3 (73.67 cm) and M1N5-4 (70.33 cm) genotypes, while the shortest plant was recorded in ‘Crimson Tide’ (11.00 cm), CXN3 (15.55 cm) and ‘Calhoun Gray’ (17.83 cm) genotypes. As in PL, genotypes showed significant differences in shoot fresh weight (SFW). The highest SFW was recorded in RS841 (84.00 g) and ‘Argentario’ (73.33 g) commercial rootstocks, followed by M1CXN3-2 (58.33 g) and M1CXN7-4 (55.00 g) genotypes, while the lowest SFW was found in commercial watermelon cultivars ‘Crimson Tide’ (2.72 g), CxN3 (3.60 g) and ‘Calhoun Gray’ (5.08 g). Shoot dry weight (SDW) results showed parallelism with SFW results. Similarly, the highest SDW was obtained in RS841 (8.58 g), ‘Argentario’ (7.43 g), M1CXN3-2 (5.93 g) and M1CXN7-4 (5.65 g) genotypes, while the lowest SFW was recorded in Crimson tide (0.39 g), CxN3 (0.41 g) and ‘Calhon Gray’ (0.67 g) genotypes (Table 7). In general, our data showed that auto- and allopolyploid plants produced significantly higher shoot biomass than their corresponding diploids. Polyploid plants have notable differences from diploids in their external morphological characteristics, mainly the shape and size of roots, stems, leaves, flowers and fruits due to chromosome duplication (Zhang et al., 2019), and an increase in DNA content mostly results in increased cell and organ size (Corneillie et al., 2019). Tetra- and hexaploid Arabidopsis plants have a significant increase in stem dry weight compared to diploids (Zhang et al., 2019). Researchers’ general belief that polyploidy increases biomass production is agreement with our results (Głowacka et al., 2010; Li et al., 2012; del Pozo & Ramirez-Parra, 2014; Dudits et al., 2016). When the average of the original diploid genotypes and tetraploids was compared, a 100% increase in autotetraploids and a 156% increase in allotetraploids were determined in shoot biomass production (Table 7)
Diploid N7 (A) and tetraploid M1N7-1 (B) genotypes and diploid CXN3 (C) and tetraploid M1-CXN3-1 (D) genotype plants grown in hydroponic culture for 21 days after transplanting.
PSD, plant height, SFW and SDW of the plants grown in hydroponic culture.
Genotype code | Ploidy level | PSD (mm) | PL (cm) | SFW (g · plant-1) | SDW (g · plant-1) |
---|---|---|---|---|---|
M1Calhon Gray | Tetraploid | 5.82 b–d | 30.83 mn | 12.58 no | 1.42 op |
M1N3 | Tetraploid | 5.61 b–d | 35.53 k–m | 21.37 k–m | 2.30 l–n |
M1N5-1 | Tetraploid | 5.53 b–d | 67.40 c–f | 49.14 de | 4.96 d–f |
M1N5-2 | Tetraploid | 5.57 b–d | 67.67 c–f | 37.50 f–i | 3.92 g–j |
M1N5-3 | Tetraploid | 5.17 b–d | 73.67 cd | 39.17 f–h | 4.08 g–i |
M1N5-4 | Tetraploid | 5.23 b–d | 70.33 cd | 39.17 f–h | 3.97 g–j |
M1N5-5 | Tetraploid | 5.26 b–d | 54.00 e–j | 30.33 h–j | 3.21 i–k |
M1N5-6 | Tetraploid | 4.94 b–d | 51.12 f–k | 30.83 h–j | 3.16 jl |
M1N7-1 | Tetraploid | 5.32 b–d | 49.70 g–l | 23.33 j–m | 2.45 k–n |
M1N7-2 | Tetraploid | 4.88 cd | 65.05 c–g | 25.00 j–m | 2.68 k–m |
M1N7-3 | Tetraploid | 5.19 b–d | 64.25 c–h | 40.83 e–g | 4.21 f–h |
M1N7-4 | Tetraploid | 5.38 b–d | 75.65 c | 43.33 e–g | 4.51 e–h |
M1CXN3-1 | Tetraploid | 6.05 b–d | 46.67 i–m | 30.83 h–j | 3.19 jk |
M1CXN3-2 | Tetraploid | 5.90 b–d | 48.18 h–l | 58.33 c | 5.93 c |
M1CXN3-3 | Tetraploid | 5.77 b–d | 67.67 c–f | 45.00 e–g | 4.68 e–h |
M1CXN3-4 | Tetraploid | 6.13 b–d | 52.02 f–k | 25.83 j–l | 2.69 k–m |
M1CXN5-1 | Tetraploid | 6.48 b–d | 45.47 j–m | 46.33 ef | 4.75 e–g |
M1CXN7-1 | Tetraploid | 6.12 b–d | 64.00 c–h | 44.67 e–g | 4.62 e–h |
M1CXN7-2 | Tetraploid | 5.93 b–d | 34.55 l–n | 40.17 fg | 4.07 g–i |
M1CXN7-3 | Tetraploid | 5.82 b–d | 27.67 no | 36.35 g–i | 3.81 h–j |
M1CXN7-4 | Tetraploid | 6.05 b–d | 60.62 c–j | 55.00 cd | 5.65 cd |
M1CXN7-5 | Tetraploid | 6.53 b–d | 62.17 c–i | 49.33 de | 5.10 d–f |
Calhoun Gray | Diploid | 6.07 b–d | 17.83 o–r | 5.08 op | 0.67 pr |
CXN3 | Diploid | 3.86 d | 15.55 o–r | 3.60 p | 0.41 r |
CXN5 | Diploid | 5.48 b–d | 44.67 j–m | 30.83 h–j | 3.25 i–k |
CXN7 | Diploid | 5.07 b–d | 58.52 d–j | 29.67 k | 3.13 jl |
N3 | Diploid | 4.76 d | 26.22 n–p | 16.52 mn | 1.70 no |
N5 | Diploid | 4.96 b-d | 37.23 k–n | 20.82 mn | 2.26 mn |
N7 | Diploid | 4.11 d | 30.83 mn | 17.33 l–n | 1.81 no |
2.79 d | 11.00 p–r | 2.72 p | 0.39 r | ||
RS841 | 9.73 a | 95.83 b | 84.00 a | 8.58 a | |
Argentario | 9.62 ab | 115.83 a | 73.33 b | 7.43 b |
Values denoted by different letters are significantly different between genotypes within columns at
PL, plant length; PSD, plant stem diameter; SDW, shoot dry weight; SFW, shoot fresh weight.
Significant variations were found in root biomass production and root morphological characteristics among genotypes grown in hydroponic culture for 21 days after transplanting (Table 8). The highest RFW was measured in RS841 (38.17 g), ‘Argentario’ (34.00 g), M1CXN5-1 (33.02 g) and M1CXN3-2 (28.37 g) genotypes, respectively (Figure 1). The lowest RFW was measured in ‘Crimson Tide’ (1.19 g), CXN3 (1.70 g) and ‘Calhoun Gray’ (3.16 g) genotypes. Similar to RFW, RS841 (4.00 g), ‘Argentario’ (3.50 g), M1CXN5-1 (3.41 g) and M1CXN7-4 (3.04 g) produced the highest root dry weights (RDWs), while CXN3 (0.22 g), ‘Crimson Tide’ (0.24 g) and ‘Calhoun Gray’ (0.48 g) produced the lowest root weights. The genotypic variations in RL, volume and diameter were found significant. The genotypes with the highest RL in hydroponic culture were RS841 (11,098.84 cm), ‘Argentario’ (11,000.44 cm), M1CXN5-1 (7,678.59 cm) and M1N7-4 (6,083.45 cm), while genotypes with the shortest RL was commercial ‘Crimson Tide’ watermelon cultivar (148.66 cm). The highest RV was recorded in RS841 (13.04 cm3), followed by M1CXN5-1 (11.09 cm3), while the lowest RV was observed in CxN3 and ‘Crimson Tide’ had (0.27 cm3 and 0.32 cm3), respectively. Root thickness, which showed significant variation among genotypes, ranged from 0.58 mm to 0.34 mm. The highest and lowest RDs were recorded in M1N5-6 and ‘Argentario’ with 0.58 mm and 0.34 mm, respectively. In general, tetraploid genotypes produced more root biomass than diploids. When diploid and tetraploid genotypes were compared in terms of root fresh biomass, an 126% increase in all tetraploids, a 100% increase in autotetraploids and a 180% increase in allotetraploids were found (Table 8 and Figure 4). Similarly, increases in plant biomass due to polyploidisation have been reported in different species in previous studies. It has been reported that polyploid orchids significantly increased in various growth parameters, including fresh weight, dry weight, shoot length, RL and leaf width, compared to diploid orchids (Chung et al., 2017). Polyploid plants showed higher leaf and root growth than diploid plants in
RFW, RDW, RL, RV and RD of the plants grown in hydroponic culture for 21 days after transplanting.
Genotype code | Ploidy level | RFW (g · plant-1) | RDW (g · plant-1) | RL (cm) | RV (cm3 · plant-1) | RD (mm) |
---|---|---|---|---|---|---|
M1Calhon Gray | Tetraploid | 9.81 mn | 1.15 pr | 1,319.16 m | 3.31 l–n | 0.40 g |
M1N3 | Tetraploid | 10.50 l–n | 1.22 o–r | 1,702.86 m | 1.82 o | 0.37 i |
M1N5-1 | Tetraploid | 22.13 fg | 2.26 h–k | 4,818.78 ef | 3.52 k–m | 0.44 f |
M1N5-2 | Tetraploid | 22.94 d–f | 2.46 f–i | 3,570.95 g–k | 3.85 kl | 0.38 i |
M1N5-3 | Tetraploid | 23.61 d–f | 2.53 e–h | 5,175.32 de | 5.92 gh | 0.53 c |
M1N5-4 | Tetraploid | 26.78 c–e | 2.73 d–g | 3,470.66 h–l | 5.25 h–j | 0.44 f |
M1N5-5 | Tetraploid | 20.26 f–h | 2.20 h–k | 3,514.55 h–k | 4.32 l | 0.40 g |
M1N5-6 | Tetraploid | 23.48 d–f | 2.43 f–i | 3,660.05 g–j | 4.48 i–k | 0.58 a |
M1N7-1 | Tetraploid | 13.97 k–m | 1.52 n–p | 4,046.80 f–i | 4.44 i–k | 0.37 i |
M1N7-2 | Tetraploid | 14.51 j–l | 1.63 m–o | 2,764.20 kl | 3.95 kl | 0.55 b |
M1N7-3 | Tetraploid | 20.65 f–h | 2.19 h–k | 3,722.38 g–j | 5.38 h–j | 0.44 f |
M1N7-4 | Tetraploid | 21.48 fg | 2.33 g–j | 6,083.45 c | 2.81 mn | 0.37 i |
M1CXN3-1 | Tetraploid | 15.73 i–k | 1.68 l–n | 2,658.33 l | 4.35 j–l | 0.46 e |
M1CXN3-2 | Tetraploid | 28.37 c | 2.93 de | 4,223.48 f–h | 6.53 fg | 0.46 e |
M1CXN3-3 | Tetraploid | 22.50 fg | 2.43 f–i | 3,333.78 i–l | 6.67 fg | 0.51 d |
M1CXN3-4 | Tetraploid | 18.24 g–j | 1.93 j–n | 2,905.59 j–l | 3.79 k–m | 0.40 g |
M1CXN5-1 | Tetraploid | 33.02 b | 3.41 bc | 7,678.59 b | 11.09 b | 0.44 f |
M1CXN7-1 | Tetraploid | 27.09 cd | 2.86 d–f | 6,001.24 c | 7.40 d–f | 0.40 g |
M1CXN7-2 | Tetraploid | 19.91 f–i | 2.05 i–m | 4,416.07 e–g | 4.50 i–k | 0.35 j |
M1CXN7-3 | Tetraploid | 20.60 f–h | 2.23 h–k | 3,658.58 g–j | 7.28 ef | 0.51 d |
M1CXN7-4 | Tetraploid | 28.94 c | 3.04 c–e | 4,104.75 f–i | 8.21 de | 0.51 d |
M1CXN7-5 | Tetraploid | 22.82 d–f | 2.45 f–i | 5,825.66 cd | 8.29 d | 0.44 f |
Calhoun Gray | Diploid | 3.16 o | 0.48 s | 344.85 n | 0.78 p | 0.44 f |
CXN3 | Diploid | 1.70 o | 0.22 s | 173.10 n | 0.27 p | 0.46 e |
CXN5 | Diploid | 19.29 f–i | 2.09 h–l | 3,645.02 g–j | 4.22 l | 0.40 g |
CXN7 | Diploid | 16.70 h–k | 1.83 k–n | 4,428.47 e–g | 5.51 hi | 0.40 g |
N3 | Diploid | 8.37 n | 0.89 r | 1,454.43 m | 1.82 o | 0.40 g |
N5 | Diploid | 13.90 k–n | 1.57 n–p | 3,591.94 g–k | 4.31 l | 0.40 g |
N7 | Diploid | 10.77 n | 1.16 pr | 1,719.21 m | 2.44 no | 0.44 f |
1.19 o | 0.24 s | 148.66 n | 0.32 p | 0.37 i | ||
RS841 | 38.17 a | 4.00 a | 11,098.84 a | 13.04 a | 0.39 h | |
Argentario | 34.00 b | 3.50 b | 11,000.44 a | 9.70 c | 0.34 k |
Values denoted by different letters are significantly different between genotypes within columns at
RD, root diameter; RDW, root dry weight; RFW, root fresh weight; RL, root length; RV, root volume.
PCA was used for classifying of diploid (D) and tetraploid (T) genotypes based on plant growth parameters in hydroponic culture. According to the analysis, two principle components described 99% of total variation (98% by PC1 and 1% by PC2). When PCA charts were examined, it could be seen that genotypes were separated into four different groups based on measured one feature (Figure 5). The first group is the group containing four of the five diploid genotypes in region III of the graph and is indicated by the blue circle. There is a negative correlation between diploids and biomass parameters. Diploid N5, autotetraploid ‘Calhoun Gray’, and allotetraploids CxN7 and CxN7 formed the second group and are indicated by the red circle between regions II and IV of the graph. This group also showed less vegetative development than the main group. CxN5 is scattered in the far corner of the III region of the graph and is considered group III (green circle). Group IV, with 18 (auto- and allo-) tetraploid and two diploid genotypes, is located in the upper part of the graph (black circle). When group IV is analysed within itself, it was seen that the two diploid genotypes have lower vegetative growth performance than tetraploids. Although there are deviations, in general, tetraploids formed the large main group with higher values, while diploids formed the other group with low vegetative growth performance (Figure 5).
PCA of diploid (D) and tetraploid (T) watermelon genotypes based on hydroponic culture morphological features. PCA, principal component analysis; PL, plant length; PSD, plant stem diameter; RD, root diameter; RDW, root dry weight; RFW, root fresh weight; RL, root length; RV, root volume; SDW, shoot dry weight; SFW, shoot fresh weight.
DNA content was positively correlated with SFW, SDW, RFW, RDW (
Pearson’s correlation coefficients (
PSD | PL | SFW | SDW | RFW | RDW | RL | RV | RD | |
---|---|---|---|---|---|---|---|---|---|
DNA content | 0.33* | 0.48* | 0.60** | 0.60** | 0.60** | 0.61** | 0.45* | 0.47* | -0.02ns |
Stomatal diameter | –0.15ns | –0.49* | –0.56** | –0.56** | -0.58** | -0.58** | -0.53** | -0.44* | 0.26ns |
Stomatal length | 0.26ns | 0.50** | 0.49* | 0.49* | 0.52* | 0.53* | 0.38* | 0.32* | -0.15ns |
Stomatal density | 0.30ns | 0.50** | 0.55** | 0.55** | 0.59** | 0.59** | 0.43* | 0.40* | -0.12ns |
Chloroplast number | –0.19ns | 0.19ns | –0.10 ns | –0.10 ns | 0.02ns | 0.01ns | -0.05ns | -0.24ns | -0.26ns |
respectively; ns, not significant; PL, plant length; PSD, plant stem diameter; RD, root diameter; RDW, root dry weight; RFW, root fresh weight; RL, root length; RV, root volume; SDW, shoot dry weight; SFW, shoot fresh weight.
Correlation analysis between the DNA content and stomatal measurement indicated that stomal dimensions and chloroplast number of guard cells were positively correlated with DNA content. By contrast, a significant negative correlation was found between stomatal density and DNA content in diploid and tetraploid plants (
Pearson’s correlation coefficients (
Stomatal diameter | Stomatal length | Stomatal density | Chloroplast number | |
---|---|---|---|---|
DNA content | 0.96** | 0.90** | -0.79** | 0.88** |
Variable of significance
Polyploidy is a notable approach in the development of high-yielding crops as about half of the crop species are polyploid. While many polyploid plants show higher vigour than their diploid ancestors, they show a feature similar to the heterosis effect by showing a high rate of heterozygosity. Therefore, polyploids show new and useful phenotypic variations. One of these approaches is the generation of auto- or allopolyploids using the polyploidy breeding method. Auto- and allotetraploid