Diploid Watermelon Research Articles

Polyploidization Impact on Plant Architecture of Watermelon (Citrullus lanatus)

Plant architecture includes traits such as plant height, stem diameter, and branching pattern, which have significant impacts on yield and fruit quality. Polyploidization can bring changes in plant architectural traits in different crops along with other agronomic and biochemical attributes; however, the specific physiological and biochemical mechanisms are still unclear. In this study, we utilized five watermelon lines: ‘91E7’, ‘Zhengzhou No. 3’, ‘Fanzu No. 1’, ‘Shenlong’, and ‘Houlv’, along with their corresponding autopolyploid derivatives (diploid, autotriploid, and autotetraploid) to compare plant architecture differences in different polyploidy watermelon plants. The results showed that the growth habits of diploid, triploid, and tetraploid watermelon plants were noticeably different. Triploid and tetraploid watermelon plants had greater stem diameters and larger leaf sizes. The leaf angle was also larger in polyploid watermelons than in their diploid ancestor lines. Although vine length was significantly higher in diploid watermelon, there was no significant difference in node number, indicating that the short vine length was due to the short internodal length. The major differences between diploid and polyploid watermelon plants were found in the branching pattern, as diploid watermelon lines have more branching compared to their polyploid sister lines. Furthermore, we examined the phytohormone content of diploid, triploid, and tetraploid ‘Fanzu No. 1’. The reasons for the selection of this material are its robust growth and profuse branching habit, which cause visible differences among the ploidy levels. Hormone analysis showed distinct variations in abscisic acid in the nodal and stem regions, gibberellin in the auxiliary bud regions, and brassinosteroids in the apical meristematic regions. The correlation coefficient also strongly correlated these hormones with architecture-related traits. Our findings indicated that gibberellin, ABA, and brassinosteroids might be associated with variations in plant architectural traits like branching, vine length, internodal length, stem thickness, and leaf angle among different ploidy levels of watermelon. The exogenous application of GA3 showed a positive effect on branching, whereas ABA showed a negative effect on branching. The application of brassinosteroid at the apical meristem demonstrated its effect on leaf angle, leaf size, and internodal length. The results of this study can provide a theoretical reference and valuable insights into the link between plant architecture and ploidy levels.

Comparative physiological and biochemical mechanisms in diploid, triploid, and tetraploid watermelon (Citrullus lanatus L.) grafted by branches

Seed production for polyploid watermelons is costly, complex, and labor-intensive. Tetraploid and triploid plants produce fewer seeds/fruit, and triploid embryos have a harder seed coat and are generally weaker than diploid seeds. In this study, we propagated tetraploid and triploid watermelons by grafting cuttings onto gourd rootstock (C. maxima × C. mochata). We used three different scions: the apical meristem (AM), one-node (1N), and two-node (2N) branches of diploid, triploid, and tetraploid watermelon plants. We then evaluated the effects of grafting on plant survival, some biochemical traits, oxidants, antioxidants, and hormone levels at different time points. We found significant differences between the polyploid watermelons when the 1N was used as a scion. Tetraploid watermelons had the highest survival rates and the highest levels of hormones, carbohydrates, and antioxidant activity compared to diploid watermelons, which may explain the high compatibility of tetraploid watermelons and the deterioration of the graft zone in diploid watermelons. Our results show that hormone production and enzyme activity with high carbohydrate content, particularly in the 2–3 days after transplantation, contribute to a high survival rate. Sugar application resulted in increased carbohydrate accumulation in the grafted combination. This study also presents an alternative and cost-effective approach to producing more tetraploid and triploid watermelon plants for breeding and seed production by using branches as sprouts.

X-ray Imaging Assessment of Internal Seed Morphology as a Nondestructive Viability Prediction for Triploid Watermelon Seeds

Highlights X-ray imaging techniques were used to assess the internal morphology of triploid watermelon seeds. Structural integrity of triploid watermelon seed was quantified through image-processing and analyzed according to multiple viability classes. Integrity and CNN-based viability prediction models were developed and evaluated for multiple viability criteria. In the integrity analysis and modeling results, there were differences in the correlation between internal seed morphology and viability depending on the condition of the seed lot. Abstract. Watermelon (Citrullus lanatus) is a tropical fruit consumed worldwide in various forms. Triploid watermelons—or seedless watermelons—have remained popular for decades because of the absence of hard seeds and their flavor. However, triploid watermelon seeds have lower viability than diploid watermelon seeds because of their thick seed coats, underdeveloped embryos, and larger internal cavity spaces. This poor viability characteristic of triploid watermelon seed leads to low crop productivity. Therefore, a nondestructive inspection technology is deemed necessary for sorting triploid watermelon seeds. In this study, we assessed the internal morphology of triploid watermelon seeds by applying the X-ray imaging technique to predict seed viability. More specifically, we analyzed the association between the structural integrity and viability of the seeds by X-ray image processing. Furthermore, prediction models based on integrity and convolutional neural networks (CNN) were developed and evaluated for multiple viability criteria and seed lots. As a result, first-grade class seeds were shown to significantly differ from the rest of the classes in terms of integrity. Similarly, the performance of classifying the first-grade class from other classes was the highest among classification criteria in prediction models. Although the CNN model showed better performances than the integrity-based model, seed integrity was considered to be the most important feature even in the CNN model. The CNN model in this study showed accuracies of 73.64%–90.63% depending on the seed lot, suggesting that the correlation between seed internal structure and viability may differ depending on the conditions of the seed lot. Keywords: Deep learning, Seed, Seed integrity, Triploid watermelon, Viability, X-ray.

Comparison on flower, fruit and seed characteristics of tetraploid and diploid watermelons (Citrullus lanatus Thunb. Matsum. and Nakai)

In this study, the characteristics of tetraploid and diploid watermelon’s flowers, fruits, and seeds were examined, and their differences were investigated. As plant material, tetraploid ST101 and ST82; diploid WL92, WL124, WL134, WL216, WL259-B and WL235 were used. Flower (pollen viability, pollen germination, number of anthers and number of pollen per anther and flower); fruit (weight, length, diameter, rind thickness and TSS) and seed (weight of 1000 seed, length, width, thickness, full seed number, seed yield, embryo/seed ratio, germination and emergence) parameters were investigated. In terms of pollen parameters, diploid watermelon has a higher value than tetraploid watermelon. According to research results, average pollen germination was found to be in diploid watermelons at 74.48% and tetraploid watermelons at 71.62%. Pollen viability was determined highest in WL 235 (95.53%). In fruit parameters, tetraploid watermelons had higher values, but fruit length decreased (diploid 19.32 cm; tetraploid 15.33 cm) significantly. Considering the average values of tetraploid watermelons, a significant decrease occurred in terms of seed germination, full seed number, seed yield and embryo/seed ratio (57.22%, 225.48 seed, 6.33 g/fruit, 57.51% respectively in diploids; 37.31%, 57.67 seed, 4.90 g/fruit, 46.42% in tetraploid), and no difference observed in other seed parameters.

A Comparative Study of Morphology, Photosynthetic Physiology, and Proteome between Diploid and Tetraploid Watermelon (Citrullus lanatus L.).

Watermelon is an important fruit that is widely distributed around the world. In particular, the production and consumption of watermelon in China ranks first in the world. Watermelon production is severely affected by a variety of biotic and abiotic stresses during cultivation, and polyploidization can promote stress resistance and yield. However, the morphological and physiological characteristics of tetraploid watermelon and the underlying molecular mechanisms are still poorly understood. In this study, we revealed that the leaves, fruits, and seeds of tetraploid watermelon were significantly larger than those of the diploid genotype. Some physiological characteristics, including photosynthetic rate (Pn) and stomatal conductance (Gs), were greater, whereas the intercellular CO2 concentration (Ci) and transpiration rate (Tr) were lower in tetraploid than in diploid watermelon. Two-dimensional gel electrophoresis combined with tandem mass spectrometry (MALDI-TOF/TOF) was performed to compare proteomic changes between tetraploid and diploid watermelon. A total of 21 differentially expressed proteins were identified; excluding the identical proteins, 8 proteins remained. Among them, four proteins were upregulated and four were downregulated in tetraploid versus diploid genotypes. qRT-PCR results showed inconsistencies in gene expression and protein accumulation, indicating a low correlation between gene expression and protein abundance. Generally, this study extends our understanding of the traits and molecular mechanisms of tetraploid watermelon and provides a theoretical basis for watermelon polyploid breeding.

Expression dynamics of metabolites in diploid and triploid watermelon in response to flooding

Watermelon (Citrullus lanatus) is an economically important cucurbitaceous crop worldwide. The productivity of watermelon is affected by both biotic and abiotic stresses. Flooding has significant impacts on the growth of watermelons by causing oxygen deficiency and a loss of agricultural productivity. Currently, we used the triploid and diploid watermelon Zhengzhou No.3 to study the dynamics of metabolites in response to flooding stress. Quantification of metabolites was performed by UPLC-ESI-MS/MS at different time intervalsi.e., 0, 3, 5 and 7 days under flooding stress. We observed that the activities of oxidants were higher in the diploid watermelon, whereas the higher antioxidant activities in the triploid watermelon makes them more resistant to the flooding stress. We also observed that the root activity and the chlorophyll in the triploid watermelon plants were higher as compared to the diploid watermelon plants. Co-expression network analysis leads to the identification of twenty-four hub metabolites that might be the key metabolites linked to flooding tolerance. Resolving the underlying mechanisms for flooding tolerance and identification of key molecules serving as indicators for breeding criteria are necessary for developing flooding-resistant varieties.

Transcriptome Profiling to Dissect the Role of Genome Duplication on Graft Compatibility Mechanisms in Watermelon.

Simple SummaryTriploid seedless watermelon cultivars have high demand globally, and they are excellent in quality compared to diploid seeded watermelons. A low number of seedlings are produced as a result of grafting in triploid and tetraploid watermelons. In this regard, to understand the influencing factors of genome duplication on graft compatibility, we performed a comparative transcriptome analysis between tetraploid and diploid watermelons grafted on squash rootstock with the splice method. A weighted gene co-expression network analysis (WGCNA) was performed using the common differentially expressed genes (DEGs) between diploid and tetraploid plants of watermelon grafted seedlings and the contents of hormones antioxidants (AOX), sugars, and starch at 0, 3, and 15 days after grafting (DAG). Higher survival rates and contents of hormones, AOX, sugars, and starch were observed in tetraploid grafted seedlings compared to diploid ones. We concluded that genome duplication significantly affected gene expression in the IAA and ZR signal transduction and AOX biosynthesis pathways in the grafted plants, resulting in the regulation of hormone levels’ signal pathways, promoting plant survival. These genes are identified for the first time, and no previous reports about their role or functions in watermelon are available.Watermelon (Citrullus lanatus) is a popular crop worldwide. Compared to diploid seeded watermelon, triploid seedless watermelon cultivars are in great demand. Grafting in triploid and tetraploid watermelon produces few seedlings. To learn more about how genome duplication affects graft compatibility, we compared the transcriptomes of tetraploid and diploid watermelons grafted on squash rootstock using a splicing technique. WGCNA was used to compare the expression of differentially expressed genes (DEGs) between diploid and tetraploid watermelon grafted seedlings at 0, 3, and 15 days after grafting (DAG). Only four gene networks/modules correlated significantly with phenotypic characteristics. We found 11 genes implicated in hormone, AOX, and starch metabolism in these modules based on intramodular significance and RT-qPCR. Among these genes, two were linked with IAA (r2 = 0.81), one with ZR (r2 = 0.85) and one with POD (r2 = 0.74). In the MElightsteelblue1 module, Cla97C11G224830 gene was linked with CAT (r2 = 0.81). Two genes from the MEivory module, Cla97C07G139710 and Cla97C04G077300, were highly linked with SOD (r2 = 0.72). Cla97C01G023850 and Cla97C01G006680 from the MEdarkolivegreen module were associated with sugars and starch (r2 = 0.87). Tetraploid grafted seedlings had higher survival rates and hormone, AOX, sugar, and starch levels than diploids. We believe that compatibility is a complicated issue that requires further molecular research. We found that genome duplication dramatically altered gene expression in the grafted plants’ IAA and ZR signal transduction pathways and AOX biosynthesis pathways, regulating hormone levels and improving plant survival.

Biostimulatory Action of Vegetal Protein Hydrolysate and the Configuration of Fruit Physicochemical Characteristics in Grafted Watermelon

Foliar application of a vegetal-derived protein hydrolysate as a biostimulant was assessed for possible interaction with the ripening of diploid watermelon grafted onto interspecific hybrid rootstock. Assessment encompassed crop performance; fruit morphometric and sensory quality traits; soluble carbohydrates; macrominerals; and bioactive composition at 10, 20, 30, 40, and 50 days post anthesis (dpa). The biostimulant effect on yield components was confounded by the vigorous rootstock effect. Pulp firmness declined precipitously with cell enlargement from 10 to 30 dpa, and the biostimulant phyto-hormonal potential on firmness and rind thickness was masked by grafting. Pulp colorimetry was determined solely by ripening and peaked at 40 dpa. The biostimulant effect reduced lycopene content by 8% compared to the control. Total sugars coevolved with soluble solids content, peaked at 30 dpa, and then stabilized. Fructose and glucose prevailed during rapid fruit growth from 10 to 30 dpa and sucrose prevailed at advanced ripeness between 40–50 dpa, whereas acidity peaked at 20 dpa and then decreased. Potassium, which was the most abundant micromineral, peaked before full ripeness at 30 dpa. The biostimulant effect on the watermelon fruit ripening process is not granted, at least regarding the conditions this study was carried out under. The absence of biostimulant effect might relate to rootstock vigorousness, the grafted watermelon physiology, or the type of biostimulant used.

Diploid, triploid, tetraploid - chromatin organization in polyploid watermelon.

The first half of the 20th century was an important time for the scientific discipline of genetics in Japan (Iida, 2010). Hithoshi Kihara (1893–1986) was one of the pioneering researchers who helped to develop the field. He was the first to define the genome as the minimal set of chromosomes that is required for the fitness of a species and he also discovered sex chromosomes in plants. However, the achievement that made him internationally renowned was the development of seedless watermelon (Kihara, 1951). Kihara realized that triploid plants produce seedless fruits, which could be a desirable trait for certain crops. Therefore, he set out to create a triploid watermelon. To do this, he first obtained a tetraploid plant by treating a normal diploid with colchicine, a technique that was discovered shortly before Kiara’s watermelon experiment (Nebel, 1937). Next, he pollinated the tetraploid with pollen from a diploid. This yielded triploid progeny that did not produce seeds. Nowadays, seedless watermelons are still produced similarly. However, there is still a lot that we do not understand. The tetraploid progenitor of triploid watermelon exhibits many phenotypic differences as compared with their diploid counterparts. As yet, it remains enigmatic what causes these differences. Duplication of the genome might lead to rearrangements of the chromatin, because the nucleus needs to accommodate a doubled number of chromosomes. Although the exact effect of chromatin organization on gene regulation is not fully unraveled, it is clear that transcriptional activity is affected by the way the genome is folded (Doğan and Liu, 2018). Hence, altered chromatin organization might (partly) underlie the phenotypic differences in polyploids. In this issue, Marleny Garcia-Lozano and colleagues investigated the effect of genome doubling on chromatin conformation in watermelon. To understand the effect of doubling the number of chromosomes, the authors compared diploid watermelon with an isogenic tetraploid line. Compared to their diploid counterparts, the tetraploid plants had bigger seeds, bigger leaves, and a thicker stem with more and larger trichomes (Figure 1), phenotypes often seen in polyploids. To investigate how the chromatin is organized in diploid and tetraploid plants, the authors employed the Hi-C chromosome conformation capture technique. This technique crosslinks and ligates interacting chromatin fragments, followed by high-throughput sequencing, and is used to identify long-range physical interactions. They found that the interactions between genomic regions were different: in the tetraploid the chromosomes showed a higher number of interactions than in the diploid, especially between regions from different chromosomes. In addition to the chromatin interaction differences, the Hi-C results showed that the chromatin of tetraploid watermelon was organized differently than the chromatin in diploid plants. In eukaryotes, chromatin is divided into two spatially segregated compartments. The chromatin that occupies the interior nuclear space forms the transcriptionally active A compartment, whereas chromatin that resides at the nuclear periphery forms the less active B compartment. In tetraploid watermelon, several chromosomal regions had switched compartments. The authors found that chromatin organization also differed at lower levels of organization. Within the A and B compartments, chromatin is organized in megabase-sized clusters called topologically associated domains (TADs). TADs are demarcated by boundaries that function as insulators. As a result, DNA sequences within a TAD physically interact with each other more frequently than with sequences outside the TAD. The authors identified the boundaries of TADs in diploid and tetraploid watermelon and found that of 346 boundaries, 93 were differential between the two watermelon lines. Besides improved traits such as larger leaves, fruits, and flowers, polyploids can better deal with stressful environments. Therefore, polyploidy has played a key role in plant breeding for many years, and as climate change continues, polyploid crops might become increasingly important. Garcia-Lozano and colleagues found that the presence of a greater number of chromosomes alters the three-dimensional structure of the genome and affects interactions between genomic regions in watermelon. However, it is unclear how the altered chromatin organization affects the phenotype of watermelon after genome duplication. In addition to chromatin organization differences, the authors observed differences in the transcriptome and methylome between diploid and tetraploid watermelon. Seventy years after Kihara’s discovery, there is still a lot to learn about polyploid watermelon.

Screening and analysis on the differentially expression genes between diploid and autotetraploid watermelon by using of digital gene expression profile.

Synthetic polyploids are key breeding materials for watermelon. Compared with diploid watermelon, the tetraploid watermelon often exhibit wide phenotypic differences and differential gene expression. Digital gene expression (DGE) profile technique was performed in this study to present gene expression patterns in an autotetraploid and its progenitor diploid watermelon, and deferentially expressed genes (DEGs) related to the abiotic and biotic stress were also addressed. Altogether, 4,985 DEGs were obtained in the autotetraploid against its progenitor diploid, and 66.02% DEGs is up-regulated. GO analysis shows that these DEGs mainly distributed in 'metabolic process', 'cell' and 'catalytic activity'. KEGG analysis revealed that these DEGs mainly cover 'metabolic pathways', 'secondary metabolites' and 'ribosome'. Moreover, 134 tolerance related DEGs were identified which cover osmotic adjustment substance, protective enzymes/protein, signaling proteins and pathogenesis-related proteins. This study present the differential expression of stress related genes and global gene expression patterns at background level in autotetraploid watermelons. These new evidences could supplement the molecular theoretical basis for the better resistance after the genome doubling in the gourd family.

Effects of hydropriming and explant origin on in vitro culture and frequency of tetraploids in small watermelons

In vitro culture has the potential to develop micropropagation, genetic transformation, and somaclonal variation in a variety of crops, while hydropriming may promote germination efficiency and seedling growth. In this study, we investigated the effects of hydropriming and explant origin on in vitro culture and the frequency of tetraploids in a small diploid watermelon. Hydropriming statistically reduced germination initiation time, and the time taken for 50% germination. It also enhanced the germination index, and the number of uniform seedlings with enlarged cotyledons increased by 15.5%. Correspondingly, the proximal cotyledons and cotyledonary nodes of hydroprimed seeds produced significantly more explant-producing shoots (24.4% and 17.2%, respectively). The highest level of shoot initiation was seen in hydroprimed cotyledonary nodes (94.7 ± 5.8%), followed by non-primed cotyledonary nodes (77.5 ± 6%), hydroprimed cotyledons (72.4 ± 3.9%), and non-primed cotyledons (48 ± 3.9%). Shoots were not formed from either hydroprimed or non-primed hypocotyls; however, the number of shoots initiated from cotyledonary nodes and cotyledon explants was insignificant, suggesting that both cotyledons and cotyledonary nodes are good sources for the in vitro culture of watermelon. When attempting to produce plants with higher ploidy, choosing explant sources favoring tetraploidy should be considered: in our study, 10.5% of tetraploid regenerants were identified entirely from cotyledon explants. It is possible that cotyledon tissue cells undergo ploidy level changes during culture differentiation. Alternatively, some variations may have already been present in the donor plant tissues. Studying the cytological nature of regenerated plants and the mechanisms leading to tissue culture variation can be useful for inducing future somaclonal variations for crop improvement. Morphological changes in tetraploid regenerants indicated that the altered autopolyploidy trait is genotype-dependent.

Effect of ploidy level on expression of lycopene biosynthesis genes and accumulation of phytohormones during watermelon (Citrullus lanatus) fruit development and ripening

The difference between lycopene and phytohormone levels among diploid, triploid and tetraploid plants of two watermelon cultivars during fruit growth and ripening was studied. The expression pattern of five genes (phytoene synthase (PSY1), phytoene desaturase (PDS), ζ-carotene desaturase (ZDS), carotenoid isomerase (CRTISO), and lycopene β-cyclase (LCYB)) was analyzed in details. In red-fleshed cultivar Mimei, lycopene content increased rapidly from 25 to 35 days after pollination (DAP), and then decreased at 40 DAP. Triploid and tetraploid fruit had higher levels of lycopene than diploid. Moreover, triploid tended to contain more lycopene than tetraploid during fruit growth and ripening stages. However, little amount of lycopene (0–2 mg kg−1 fresh weight (FW)) in yellow-fleshed cultivar Huangmei was found during all fruit development stages. In Mimei, transcript level of PSY1 was generally higher than the other four genes, and LCYB gene expression was the lowest among all five genes being tested. PSY1, CRTISO and LCYB genes showed higher transcript levels in polyploid than in diploid fruit. By contrast, in Huangmei, transcript level of LCYB was not the lowest, but only lower than that of PSY1. PSY1, CRTISO and LCYB genes showed higher expression levels in diploid than in polyploid fruit. In Mimei, the negative correlation between gibberellane (GA) content and lycopene accumulation was determined in all three different ploidy fruits, while a positive correlation was observed between abscisic acid (ABA) content and lycopene accumulation only in diploid watermelon. These results indicated that different lycopene contents in different ploidy watermelons is regulated by the differential transcription expression of the lycopene metabolic genes and phytohormones.

Effect of dry-heat treatment on bacterial fruit blotch and viability of watermelon seeds

Seeds of the diploid watermelon 'Mibao' infected with bacterial fruit blotch caused by Acidovorax citrulli, were dehydrated to 1-7% water content and dry-heated for 24-72 h at 70-80°C. Following germination, seedlings were subjected to vigor tests and a bacterial fruit blotch-bearing test. Test results show that being dry-heated for 72 h at 75°C is a safe and effective treatment for watermelon seeds. However, for treatment at 80°C, seeds should have been previously dehydrated to a water content below 2%, in order to reduce negative effects on seeds.

Respiration during germination of diploid and triploid watermelon

The aim of this work was to determine how differences in lipids and starch content among diploid and triploid watermelon seeds affect respiration and the glyoxylate cycle during germination. In comparison to diploid watermelon seeds, the respiratory quotient (RQ) associated with CO2 release and O2 uptake in triploids was very high initially and declined through four days of germination. The high RQs may indicate unavailability of oxygen due to the thick seed coats of triploids while the lower RQs observed later are consistent with respiration of lipids. Isocitrate lyase (ICL) activity, a marker for the glyoxylate cycle, might be affected by the fatty acid levels, especially high linoleic acids (C18:2) in triploids with low germination. Lower ICL activity in triploid seeds could be physiologically relevant to higher levels of fatty acids, a response to lipid metabolism, and thus contribute to poor germination of triploids.

Phenotypic markers for tetraploid watermelon [Citrullus lanatus (Thunb.) Matsum. et Nakai] following parental exposure to colchicine in T0 generation

The goal of this investigation was to identify phenotypic traits that effectively distinguish tetraploid from diploid watermelon [Citrullus lanatus (Thunb.) Matsum. et Nakai) at various stages of growth. Assays for phenotypic markers were performed on five regular diploid cultivars (WC-8C-2C, WD-2-6K, GW11, GW7, and GW2) exposed to the alkaloid colchicine (0.1 or 0.2%) from January 2010 to August 2011 at Watermelon Experiment Station, Gochang, Jeonbuk, South Korea. Tetraploids were induced using treatment to one of three plant parts: directly on seed (DS), shoot apex (SA) or inverted hypocotyl (IH). Results showed that tetraploid plants exhibit shorter internode length, wider leaf width with high degree of blistering, light green fruit with greyish stripes, and thicker pericarp as compared to the diploid control. In tetraploids, the stamina of the male flower was erect to semi-erect with deep yellow to light green color. No major differences were observed in fruit size and weight between the tetraploid and diploid, and both characteristics were considered unreliable indicators of level of the ploidy during early growth stages of T0 plant. Length, width, and overall size of the seed were remarkably greater in tetraploids. Seeds of tetraploids had broad apical ends and fissures along the longitudinal axis. Number of seeds per fruit and 100 seeds weight of the tetraploid were 51.5 and 4.25 g, respectively. Results identified specific phenotypic traits that could be used to reliably identify tetraploid watermelon in T0 plants in the field. In the future, these traits could potentially be used to develop more efficient watermelon triploid breeding programs.

Selection of Tetraploid of a Yellow Flesh Mini-Watermelon Using Oryzalin

In order to provide parent material for small-type triploid watermelon, this study has been carried out to induce high-quality tetraploid watermelon. We induced tetraploid plants of watermelon by treating the growing points of seedlings of a small-type yellow flesh diploid watermelon with 40, 60 and 100ml/L Oryzalin for different treating time. The autotetraploid plants were selected and identified basing on morphology, determination of the number of chloroplasts in stomatal guard cells, flow cytometry analysis and hybridization. Then we observed a stable autotetraploid material. The results showed that tetraploid watermelons could be obtained under different treatments. The most effective way was extirpating the interior leaves at the 8th day after sowing, then treating the growing points of seedlings with 100mg/L Oryzalin for 6d. The treated seedlings could all survive and the induction frequency of the tetraploid watermelon was 33.33%.

In-row Diploid Watermelon Pollenizer Competition with Triploid Watermelon Based on Four Planting Ratios

Diploid watermelon (Citrullus lanatus) pollenizers are planted within triploid watermelon fields to provide viable pollen for triploid fruit set. In recent years, pollenizer cultivars with desirable characteristics for planting in-row with triploid watermelons have been commercially available. The degree of plant competition from in-row pollenizers grown in the commercially common arrangement where pollenizers are placed equidistant from neighboring triploid plants has not been reported. Field experiments were conducted in 2005, 2006, and 2007 in Quincy, FL, to examine the competitive impact of in-row pollenizers grown equidistant from neighboring triploid plants. Four ratios of pollenizers-to-triploids: 1:1, 1:2, 1:3, and 1:4 were used to provide various levels of pollenizer competition. No significant difference in yield based on the weight or number of fruit per triploid plant resulted from the varied pollenizer ratios. Therefore, pollenizers grown in-row at an equidistant spacing from the neighboring triploid plants had no competitive impact on the yield of the triploid watermelon crop.

Characteristics of storage reserves of triploid watermelon seeds: association of starch and mean germination time

Fatty acid profiles, starch content and germination of watermelon seeds differing in seed vigour were determined for 4 triploid and 2 diploid lines. There were major differences in the fatty acid profiles between diploids and triploids. A major increase in the relative amounts of the unsaturated linoleic acid (C18:2) was found in triploids. Diploids had significantly higher starch levels than triploids. There was a high correlation between starch content and mean germination time. Conversions of seed storage reserves during early germination events may differentially affect seed vigour in triploid and diploid watermelon seeds.

Parthenocarpy of watermelon cultivars induced by γ-irradiation

We found that diploid seedless watermelon can be produced by pollination with partially functional pollen, which was irradiated with γ-rays at the doses of 600 and 800 Gy. The diploid seedless fruits were almost similar to normal fruits in development from pollination to maturity. The number of empty seeds in the diploid seedless fruits varied among the cultivars used. Seedless watermelon cultivars revealed a significant increase in total sugar and carotenoids (lycopene and gb-carotene) contents. The pollen tubes of the pollen subjected to γ-radiation penetrated normally into the synergid, and sperm cells were discharged. Subsequently, the egg nucleus and sperm nucleus became attached to each other in the egg cell and a globular embryo was formed. However, the embryo failed to differentiate the tissues and degenerated. It is suggested that seedless watermelon fruits induced by γ-rays are characterized by increasing yield and better quality due to higher carotenoid and total sugar contents and fruit weight. In some cultivars, there is a tendency in decreasing the thickness of rind.

Induction of parthenocarpy in watermelon ( Citrullus lanatus ) cultivars by gamma irradiation

It was found that diploid seedless watermelon can be produced by pollination with partially functional pollen which was irradiated with gamma rays at doses of 600 and 800 Gray (Gy). The diploid seedless fruit was very similar to normal fruit in days to maturity from pollination and rate of fruit set. The number of empty seeds in the diploid seedless fruit varied for the cultivars used in this study. No correlation was found between the number of empty seeds in seedless fruit and the number of normal seeds in normal fruit. Also, the results indicated that seedless watermelon cultivars have a significant increase in total sugar and carotenoids (lycopene and β-carotene) content, providing an important source of phytonutrients in the diet. The pollen tube of pollen irradiated with gamma radiation penetrated normally into the synergid and sperm cells were discharged. Subsequently, the egg nucleus and sperm nucleus became attached to each other in the egg cell and a globular embryo was formed. However, the embryo failed to differentiate into organ tissues and degenerated. It was suggested that seedless fruit induced by gamma rays had a beneficial effect in increasing the quantity and quality of watermelon yield via increases in the carotenoid, total sugar content and fruit weight. Also, in some cultivars there was a tendency for the thickness of the rind to decrease.