Enhancing milk quality assessment with watermelon (Citrullus lanatus) urease immobilized on VS2-chitosan nanocomposite beads using response surface methodology

An eco-friendly hydrothermal method synthesized VS2 nanosheets. Several spectroscopic and microscopic approaches (TEM) were used to characterize the produced VS2 nanosheet microstructure. VS2, Chitosan, and nanocomposite were used to immobilize watermelon (Citrullus lanatus) urease. Optimization using the Response Surface Methodology and the Box-Behnken design yielded immobilization efficiencies of 65.23 %, 72.52 %, and 87.68 % for chitosan, VS2, and nanocomposite, respectively. The analysis of variance confirmed the mathematical model's validity, enabling additional research. AFM, SEM, FTIR, Fluorescence microscopy, and Cary Eclipse Fluorescence Spectrometer showed urease conjugation to the matrix. During and after immobilization, FTIR spectra showed a dynamic connectivity of chemical processes and bonding. The nanocomposite outperformed VS2 and chitosan in pH and temperature. Chitosan and VS2-immobilized urease were more thermally stable than soluble urease, but the nanocomposite-urease system was even more resilient. The nanocomposite retained 60 % of its residual activity after three months of storage. It retains 91.8 % of its initial activity after 12 reuse cycles. Nanocomposite-immobilized urease measured milk urea at 23.62 mg/dl. This result was compared favorably to the gold standard p-dimethylaminobenzaldehyde spectrophotometric result of 20 mg/dl. The linear range is 5 to 70 mg/dl, with a LOD of 1.07 (±0.05) mg/dl and SD of less than 5 %. The nanocomposite's ksel coefficient for interferents was exceptionally low (ksel < 0.07), indicating urea detection sensitivity. Watermelon urease is suitable for dairy sector applications due to its availability, immobilization on nanocomposite, and reuse.

Phytochemical identification and in silico elucidation of interactions of bioactive compounds from Citrullus lanatus with androgen receptor towards prostate cancer treatment

Androgen receptor (AR) is known to play a crucial role in the development and progression of prostate cancer, and compounds that inhibit its activity are regarded as promising for the development of drugs to treat the disease. This study aimed to investigate the AR-inhibiting potential of Citrullus lanatus fruit compounds for prostate cancer drug development. Following HPLC identification, the binding energies, molecular interactions, and pharmacological potentials of the compounds against AR were elucidated using in silico techniques such as, molecular docking, induced-fit docking, molecular dynamics simulation, and ADMET prediction. Some of the compounds found to be present in Citrullus lanatus fruit included flavonoids such as proanthocyanin, naringin, flavan 3 ol, flavonones, naringenin, epicatechin, citrulline, and catechin. Naringenin exhibited the highest docking score in the molecular docking analysis, followed by resveratrol, ribalinidine, and epicatechin. These compounds share a common AR binding site with the standard ligand, dihydrotestosterone (DHT). Some of the compounds showed favorable ADMET profiles, while others showed at least one toxicity potential. The induced-fit docking of naringenin with AR yielded a higher docking score than the initial score obtained from standard docking while preserving stable molecular contacts with the interacting amino acids. Consistent hydrogen bond interactions of naringenin with PHE 764, ASN 705, and THR 877 of AR, including a persistent pi-pi stacking contact with PHE 764, were observed from the molecular dynamic simulation. The Citrullus lanatus compounds, particularly naringenin, may therefore be considered for further research towards the development of drugs for prostate cancer therapy.

Identification of a novel locus C2 controlling canary yellow flesh color in watermelons

The flesh color of watermelon is an important trait that is determined by carotenoid composition and affects consumers' fruit desirability. Although a complete dominant control by C locus (Cllcyb) for canary yellow flesh (CY) over red flesh has been reported, red and CY colors frequently appear as a mixed pattern in the same flesh (incomplete canary yellow, ICY) in F1 and inbred lines carrying dominant C alleles. Therefore, we examined the genetic control of the mixed color pattern in ICY using whole-genome resequencing of three ICY (ICY group) and three CY inbred lines (CY group), as well as genetic linkage mapping of an F2 population. The segregation pattern in 135 F2 plants indicated that CY is controlled by a single locus (named C 2) dominant over ICY. The whole-genome resequencing of ICY and CY inbred lines revealed an ICY/CY-specific region of approximately 27.60-27.88 Mb on Chr. 2 that was polymorphic between the ICY and CY groups. Our genetic map, using nine cleaved amplified polymorphic sequence markers developed based on the single-nucleotide polymorphisms from the ICY/CY-specific region, confirmed that C 2 is located on Chr. 2 and cosegregated with the marker (M7) derived from a non-synonymous single-nucleotide polymorphism of the pentatricopeptide repeat (PPR) gene (ClPPR, Cla97C02G039880). Additionally, 27 watermelon inbred lines of ICY, CY, and red flesh were evaluated using previously reported Cllcyb (C locus)-based markers and our C 2 locus-linked ClPPR-based marker (M7). As a result, dominant alleles at the C 2 locus were required to produce CY, in addition to dominant alleles at the C locus, while a recessive homozygous genotype at the C locus gave the red flesh irrespective of the genotype at the C 2 locus. Using a ClPPR-based cleaved amplified polymorphic sequence developed in this study and Cllcyb-based markers, watermelon cultivars with CY, ICY, and red flesh could be successfully discerned, implying that the combined use of these markers will be efficient for marker-assisted selection of flesh color in watermelon breeding.

Valorization of Waste Watermelon Rinds as a Bio-adsorbent for Efficient Removal of Methylene Blue Dye from Aqueous Solutions

Nature-based solutions (NBSs) for remediation of various emerging contaminants have gained impetus during the last few decades. In the current study, watermelon (citrullus lanatus), a highly consumed seasonal fruit, was used as a feedstock waste biomass for biochar synthesis through valorization of watermelon rinds. The watermelon biochar (WM-BC) was synthesized through slow pyrolysis at 550°C under anoxic conditions. Langmuir model with R²>99, was found to best fit the adsorption isotherm, and the adsorption kinetics was best described by the pseudo-second-order model. Various characterization tools including FTIR, SEM, BET, XRD, and TEM were used to evaluate the surface morphology of the biochar. The removal efficiency increased from 35% (dosage = 0.4 g), to 81% at WM-BC dosage of 2 g. A maximum adsorption capacity of 115.61 mg/g was found. The results from kinetic and isotherm model model suggested that the adsorption was favorable and multilayer adsorption can be considered. The adsorption mechanism was found to be governed by the co-existing factors such as hydrogen bonding, electrostatic interactions, and aromatic interactions. Results suggest that WM-BC has high potential to be employed as an adsorbent for efficient remediation of methylene blue dyes from aqueous solutions.

Mineral, Nutritional, and Phytochemical Composition and Baking Properties of Teff and Watermelon Seed Flours

Demonstrated limitations in the mineral and nutritional composition of refined flours have led to calls for the possibility of enriching them with health-promoting supplements, such as high-value non-cereal seeds. Teff and watermelon seeds have been found suitable for the production of gluten-free flour, but so far, their potential to enrich conventional baking flours has not been comprehensively studied. Hence, the present study aimed at farinographic evaluation of dough based on refined wheat flour with additions of whole white teff (TF) and watermelon seed (WSF) and pomace (DWSF) flours (tested levels 10%, 20%, and 30%), as well as possibly extensive chemical characterization of the plant material tested, including LC-MS/MS, GC-MS, total phenolics, flavonoids, melatonin, and antioxidant potential. Most of the rheological traits were improved in the flour mixtures compared to the base white flour: development time and quality number (above 1.6-fold increase), softening and stability time (up to 1.3-fold change), and water absorption (up to 6%). Overall, the best results were achieved after the addition of watermelon seed pomace. The DWSF material was characterized by the highest levels of P, Mg, Na (7.5, 1.7, 0.4 g/kg, respectively), and Fe and Zn (124 and 27 mg/kg), while TF was the richest in Ca (0.9 g/kg) and Mn (43 mg/kg). Protein and fat levels were significantly higher in watermelon seeds compared to teff (about double and up to 10-fold, respectively). Phytochemical analyses highlighted the abundance of phenolics, especially flavones, in TF, WSF and DWSF flours (244, 93, and 721 mg/kg, respectively). However, the value of total polyphenols was low in all materials (<2 mg GAE/g), which also correlates with the low antioxidant potential of the samples. Watermelon seed pomace was characterized by significantly higher melatonin concentration (60 µg/kg) than teff (3.5 µg/kg). This study provides new information on the chemical composition and application opportunities of teff and watermelon seeds.

Identification of chromosome region and candidate genes for canary-yellow flesh (Cyf) locus in watermelon (Citrullus lanatus)

Genetic control of fruit flesh color in watermelon is complex, and significant knowledge gaps still exist. In the present study, we investigated the genetic basis of canary-yellow flesh color in watermelon inbred line PI 635597 using a segregating population derived from a cross between PI 635597 and another inbred line, Cream of Saskatchewan (pale yellow flesh color). We showed that a single dominant gene controls the canary-yellow flesh color for the Cyf (canary-yellow flesh) trait. Bulk segregant analysis (BSA) and fine genetic mapping narrowed down the Cyf locus to a 79.62-kb region on chromosome 6, which harbors 10 predicted genes. Sequence variation analysis in the promoter and coding regions and gene expression analysis in both parental lines and selected watermelon accessions with diverse fruit flesh colors support Cla97C06G122050 (unknown protein) and Cla97C06G122120 (pentatricopeptide repeat) as predicted candidate genes for the Cyf locus. Marker-assisted selection and sequence alignment showed that the Cyf locus could differentiate canary-yellow flesh and pale-yellow flesh. Our results indicate that the Cyf locus might be responsible for canary-yellow flesh color and carotenoid accumulation levels.

Comparative bioinformatics analysis and abiotic stress responses of expansin proteins in Cucurbitaceae members: watermelon and melon

Watermelon and melon are members of the Cucurbitaceae family including economically significant crops in the world. The expansin protein family, which is one of the members of the cell wall, breaks down the non-covalent bonds between cell wall polysaccharides, causing pressure-dependent cell expansion. Comparative bioinformatics and molecular characterization analysis of the expansin protein family were carried out in the watermelon (Citrullus lanatus) and melon (Cucumis melo) plants in the study. Gene expression levels of expansin family members were analyzed in leaf and root tissues of watermelon and melon under ABA, drought, heat, cold, and salt stress conditions by quantitative real-time PCR analysis. After comprehensive searches, 40 expansin proteins (22 ClaEXPA, 14 ClaEXPLA, and 4 ClaEXPB) in watermelon and 43 expansin proteins (19 CmEXPA, 15 CmEXPLA, 3 CmEXPB, and 6 CmEXPLB) in melon were identified. The greatest orthologous genes were identified with soybean expansin genes for watermelon and melon. However, the latest divergence time between orthologous genes was determined with poplar expansin genes for watermelon and melon expansin genes. ClaEXPA-04, ClaEXPA-09, ClaEXPB-01, ClaEXPB-03, and ClaEXPLA-13 genes in watermelon and CmEXPA-12, CmEXPA-10, and CmEXPLA-01 genes in melon can be involved in tissue development and abiotic stress response of the plant. The current study combining bioinformatics and experimental analysis can provide a detailed characterization of the expansin superfamily which has roles in growth and reaction to the stress of the plant. The study ensures detailed data for future studies examining gene functions including the roles in plant growth and stress conditions.

Identification of the GAPDH gene family in Citrullus lanatus and functional characteristics of ClGAPC2 in Arabidopsis thaliana

Members of the GAPDH family play important roles in plant growth and development, as well as in stress responses. Our aim was to identify stress resistance genes through systematic analysis of the GAPDH family in watermelon. This could not only provide genetic resources for stress resistance breeding, but also form a basis for the study of plant stress resistance mechanisms. Eight GAPDHs representing four types of plant GAPDH in watermelon were identified (ClGAPA/B, ClGAPC1-3, ClGAPCp1-2 and ClGAPN). A comprehensive analysis of physicochemical properties, chromosome distribution, evolutionary relationships, exon-intron structure and conserved motifs of watermelon GAPDHs was performed using bioinformatics. Expression characteristics were assessed by RT-qPCR. Based on RT-qPCR results, ClGAPC2 was screened as a candidate for subcellular localization analysis and functional verification in Arabidopsis thaliana. Eight GAPDHs were classified into four subfamilies. GAPDHs in each subgroup were generally conserved and shared similarities in structure and conserved motifs. ClGAPDHs had notable tissue specificity and different expression patterns in response to H₂ O₂ , chilling, salt, osmotic stress, heat, salicylic acid, gibberellin, brassinosterol, ethylene and abscisic acid treatments. Three ClGAPC genes, especially ClGAPC2, were markedly induced by several treatments. ClGAPC2 was located in the nucleus and cytoplasm of tabacum epidermal cells. The ClGAPC2 transgenic Arabidopsis showed enhanced tolerance to salinity at the germination stage. We suggest that ClGAPC2 plays important roles in the adaptation of watermelon to salinity. Our findings provided candidate genes for further improving the salt tolerance of watermelon.

Ascophyllum nodosum and Silicon-Based Biostimulants Differentially Affect the Physiology and Growth of Watermelon Transplants under Abiotic Stress Factors: The Case of Salinity

Salinization of cultivated soils is a global phenomenon mainly caused by agricultural practices and deteriorates plant production. Biostimulants are products which can be applied exogenously to enhance the plants' defense mechanism and improve their developmental characteristics, also under abiotic stresses. We studied the potential of two biostimulants, Ascophyllum nodosum (Asc) seaweed and a silicon-based (Si), to alleviate the saline conditions endured by watermelon transplants. Three salinity (0 mM, 50 mM, and 100 mM NaCl) treatments were applied in watermelon seedlings transplanted in pots, while the two biostimulants were sprayed in the foliar in the beginning of the experiment. Relative water content was improved by Asc in the high salinity level. The plant area, leaf number, and shoot dry weight deteriorated in relation to the salinity level. However, the root system (total root length and surface area) was enhanced by 50 mM salt, as well as Asc in some cases. The OJIP transient of the photosynthetic apparatus was also evaluated. Some OJIP parameters diminished in the high salinity level after Asc application. It is concluded that after salt stress Asc provoked a positive phenotypic response, while Si did not alleviate the salinity stress of transplanted watermelon.

Effect of Structural Differences in Naringenin, Prenylated Naringenin, and Their Derivatives on the Anti-Influenza Virus Activity and Cellular Uptake of Their Flavanones

Vaccines and antiviral drugs are widely used to treat influenza infection. However, they cannot rapidly respond to drug-resistant viruses. Therefore, new anti-influenza virus strategies are required. Naringenin is a flavonoid with potential for new antiviral strategies. In this study, we evaluated the antiviral effects of naringenin derivatives and examined the relationship between their cellular uptake and antiviral effects. Madin-Darby canine kidney (MDCK) cells were infected with the A/PR/8/34 strain and exposed to the compound-containing medium for 24 h. The amount of virus in the supernatant was calculated using focus-forming reduction assay. Antiviral activity was evaluated using IC₅₀ and CC₅₀ values. Cells were exposed to a constant concentration of naringenin or prenylated naringenin, and intracellular uptake and distribution were evaluated using a fluorescence microscope. Prenylated naringenin showed strong anti-influenza virus effects, and the amount of intracellular uptake was revealed by the strong intracellular fluorescence. In addition, intracellular distribution differed depending on the position of the prenyl group. The steric factor of naringenin is deeply involved in influenza A virus activity, and prenyl groups are desirable. Furthermore, the prenyl group affects cellular affinity, and the uptake mechanism differs depending on its position. These results provide important information on antiviral strategies.

Prioritizing pollinators over pests: wild bees are more important than beetle damage for watermelon yield

Insect pests and pollinators can interact directly and indirectly to affect crop production; however, impacts of these interactions on marketable yield are little known. Thus, the evaluation of interactions between pests and pollinators are needed to best prioritize management efforts. Over 2 years, we evaluated the impact of pollinator visitation and/or beetle (Acalymma vittatum) infestation on fruit set and yield in seedless watermelon production. In 2020, we tested the main effect of pollinator visitation: two or eight honeybee visits, two wild bee visits, hand pollinated and open pollinated. In 2021, we crossed wild and managed pollinator visitation (two or four honeybee visits, two or four wild bee visits, hand pollinated and open pollinated) with varying beetle infestation levels (0, 3, 6 and 9 beetles/plant). In both years, wild bees contributed significantly to high fruit yields, and exclusive visitation from wild bees increased yield by a factor of 1.5-3 compared to honeybees. In 2021, pollination was the only significant factor for fruit set and marketable yield even when compared to the varying beetle infestation levels. These data advocate for a reprioritization of management, to conserve and protect wild bee pollination, which could be more critical than avoiding pest damage for ensuring high yields.

Antispasmodic activity of the ethanol extract of Citrullus lanatus seeds: Justifying ethnomedicinal use in Pakistan to treat asthma and diarrhea

ETHNOPHARMACOLOGICAL RELEVANCE

Citrullus lanatus (Thunb.) belongs to the ground family, Cucurbitaceae, known for edible fruit. Besides nutritional benefits, the traditional herbal practitioners in Pakistan and India used their seeds to treat gastrointestinal, respiratory, and urinary disorders. In Northern Sudan, its seeds are often used as a laxative. Its root is laxative and emetic at a high dose. Its seeds are also used to treat bedwetting and urinary tract obstruction.

AIM OF THE STUDY

This study aimed to elucidate the multi-target mechanisms of Citrullus lanatus seeds to treat asthma and diarrhea. The pharmacological experiments were designed and conducted, along with the pharmacology network and molecular docking predictions, to verify the seeds biopotency for antispasmodic and bronchodilator properties.

METHODS

LC ESI-MS/MS were performed to identify the potentially active compounds in hydroethanolic extract of Citrullus lanatus seeds, then to quantify them by HPLC. The quantified bioactive compounds of Citrullus lanatus, i.e., stigmasterol, quinic acid, malic acid, epicatechin, caffeic acid, rutin, p-coumaric acid, quercetin, ferulic acid, scopoletin, apigenin, and kaempferol were subjected to in silico studies for molecular docking. The hydroethanolic extract of Citrullus lanatus seeds was examined on isolated rabbit tissue, i.e., jejunum, trachea, and urinary bladder. The antiperistalsis, antidiarrheal and antisecretory studies were also performed in animal models.

RESULTS

In silico studies revealed that bioactive compounds of C. lanatus seeds interfere with asthma and diarrhea-associated target genes, which are a member of calcium mediate signaling, regulation of cytosolic calcium concentration, smooth muscle contraction, and inflammatory responses. It was also found that rutin, quercetin, kaempferol, and scopoletin were stronger binding to voltage-gated calcium channels, calcium/calmodulin-dependent protein kinase, myosin light chain kinase, and phosphoinositide phospholipase C, thus, exerting calcium channel blocker activity. The hydroethanolic extract of C. lanatus seeds exerted a concentration-dependent relaxant response for the spasmolytic response on isolated jejunum and trachea preparations and caused relaxation of spastic contraction of K⁺ (80 mM). Furthermore, it caused a non-parallel rightward shift with suppression of calcium concentration-response curves. In animal models, the Cl.EtOH showed antiperistalsis, antidiarrheal and antisecretory response.

CONCLUSION

Thus, we confirm Citrullus lanatus seeds have some medicinal effects by regulating the contractile response through target proteins of calcium mediates signaling and can be a promising component in the medical treatment for asthma and diarrhea.

Plant hormone signals regulate trehalose accumulation against osmotic stress in watermelon cells

Trehalose, one of the most chemically stable sugars, can effectively improve the tolerance of various plants against abiotic stress by protecting and stabilizing protein and cell membranes. However, the signaling pathway in trehalose biosynthesis triggered by abiotic stresses is still unclear. In the study, it can be shown that exogenous trehalose can alleviate the inhibitory effect of osmotic stress on cell growth, suppress extracellular alkalization, ROS burst, and maintain the integrity of the microtubular cytoskeleton. Trehalose-6-phosphate synthase (TPS) is the key limiting enzyme for trehalose synthesis and is encoded by 7 ClTPS genes, located in 7 different chromosomes of the watermelon genome. Expression analysis by qRT-PCR indicated that osmotic stress could upregulate the expression of all the family members of ClTPS and promote the accumulation of trehalose in watermelon cells accordingly. Exogenous methyl jasmonate (MeJA), ethephon (ETH), abscisic acid (ABA), or salicylic acid (SA) induced trehalose accumulation, with MeJA being the most effective treatment. When fluridone (FL), an ABA biosynthesis inhibitor, was pre-perfused into the cells before osmotic stress, trehalose accumulation and packed cell volume were suppressed significantly, whereas inhibition of ethylene biosynthesis could even restore cell growth. Moreover, inhibition of trehalose hydrolysis could also increase the tolerance against osmotic stress. This study shows that trehalose biosynthesis is phytohormone-dependent and the hydrolysis of trehalose is involved in osmotic tolerance regulation.

seeds in isoproterenol induced myocardial infraction

BACKGROUND

Cardiovascular diseases (CVDs) are a significant cause of morbidity and death in the current world, posing a challenge to both developing and industrialized nation's health systems. Citrullus lanatus (Thunb.) Matsum. & Nakai. seeds have long been utilized to supplement and enhance health and treat cardiovascular illnesses. However, its treatments for CVDs are still unknown. More research is required to fully comprehend the impact of C. lanatus seeds on vasorelaxation and myocardial infractions.

PURPOSE

Therefore, an integrated metabolomics profiling technique was used to investigate possible pathways of C. lanatus in isoproterenol (ISO)-induced myocardial infarction (MI). Isoproterenol causes long-term cardiac hypertrophy by causing cardiomyocyte compensatory loss, eventually leading to heart failure.

METHODS

In vitro models of vasoconstriction, atrium, and in vivo models of invasive blood pressure measurement and isoproterenol (ISO) induced cardiac hypertrophy in rats were used to understand underlying mechanistic by LC-MS/MS based dynamic metabolomics analysis of the serum and heart samples to be investigated the effect of ethanolic extract of C. lanatus (Cl.EtOH).

RESULTS

Cl.EtOH exhibited vasorelaxant, negative chronotropic, and inotropic effects in in-vitro models whereas, a potent hypotensive effect was observed in normotensive rats. The Cl.EtOH protected the animals from ISO-induced myocardial infarction (MI) with therapeutic interventions in left ventricular thickness, cardiomyocyte hypertrophy, mRNA gene expression, biochemical assays, and metabolomic profiling of serum and heart tissues.

CONCLUSIONS

For the first time, our study confirmed that C. lanatus seeds (Cl.EtOH) possess significant antihypertensive and prevent ISO-induced myocardial infarction. These findings comprehensively demonstrated mechanistic insights of Cl.EtOH in vasorelaxation and myocardial infarction. The current study provides evidence for further mechanistic studies and the development of C. lanatus seeds as a potential therapeutic intervention for patients with cardiovascular disorders.

Free Amino Acids and Volatile Aroma Compounds in Watermelon Rind, Flesh, and Three Rind-Flesh Juices

Watermelon rind is treated as agricultural waste, causing biomass loss and environmental issues. This study aimed to identify free amino acids and volatiles in watermelon rind, flesh, and rind-flesh juice blends with ratios of 10%, 20%, and 30%. Among the 16 free amino acids quantified, watermelon rind alone contained higher total amino acids (165 mg/100 g fresh weight) compared to flesh alone (146 mg/100 g). The rind had significantly higher (1.5×) and dominant amounts of citrulline and arginine (61.4 and 53.8 mg/100 g, respectively) than flesh. The rind, however, contained significantly lower amounts of essential amino acids. Volatile analysis showed that watermelon rind total volatiles (peak area) comprised only 15% of the flesh volatiles. Of the 126 volatiles identified, the rind alone contained 77 compounds; 56 of these presented in all five samples. Aldehydes and alcohols were most prevalent, accounting for >80% of the total volatiles in all samples. Nine-carbon aldehyde and alcohol compounds dominated both the flesh and rind, though the rind lacked the diversity of other aldehydes, alcohols, ketones, terpenes, terpenoids, esters and lactones that were more abundant in the watermelon flesh. Watermelon rind was characterized by the major aroma compounds above their thresholds, including 17 aldehydes and six unsaturated nine-carbon alcohols. This study demonstrated the potential for rind as a food or beverage supplement due to its key features such as concentrated citrulline and arginine, relatively low odor intensity, and valuable volatiles associated with fresh, green, cucumber-like aromas.

First report of fusarium wilt disease caused by Fusarium equiseti on grafted watermelon in Korea

In Korea, most of the grafted watermelons are a fusion of bottle gourd (Lagenaria siceraria) as a rootstock and watermelon (Citrullus lanatus) as a scionstock (Lee et al., 2010). Currently, we have collected several samples from grafted watermelon displaying symptoms of yellowing, withered and wilting leaves. When the symptomatic stem was excised, browning vascular tissues were observed due to the colonization of fungal pathogen. From the samples obtained, 25 fungal isolates were identified as species of Fusarium. Among 25 isolates, 18 were identified as Fusarium oxysporum, four as Fusarium solani, and three as Fusarium equiseti (F. equiseti) . Initial assessment showed that one of the F. equiseti isolates (NIHHS 16-126) was highly virulent to rootstock. Interestingly, this is the first time F. equiseti has been identified pathogenic to grafted watermelon. NIHHS 16-126 isolate was collected from watermelon cultivation field around Buyeo-gun (36.25951°N, 126.92044°E) county. Disease incident was estimated to infect approximately 10% of the watermelon plants cultivated in this area. NIHHS 16-126 isolate was examined to confirm its identity. On potato dextrose agar, colonies appeared yellowish-brown while the aerial mycelium was whitish to peach in color. Macroconidia were relatively long (20.21 - 51.13 × 2.30 - 4.5 μm, n=50), comprise of 3-6 septa, curvature shape and its conidiophores were with monophialides. However, microconidia formation was not observed. These morphological characteristics resemble F. equiseti characters as described by Hyun (2019). For molecular identification, an internal transcribed spacer of ribosomal DNA (ITS-rDNA), elongation factor-1α (EF-1α), and beta-tubulin (β-tub) genes were sequenced using primer pairs of ITS1/ITS4 (White et al., 1990), EF1-728F/EF1-986R (Glass and Donaldson 1995), and Bt2a/Bt2b (Carbone and Kohn 1999). BLASTN analysis revealed that ITS-rDNA (LC648248), EF-1α (LC648250), and β-tub (LC648249) sequences were 99-100% identical to F. equiseti reference sequences (KF515650, KF747331, and KF747330) infected Avicennia marina in China (Lu 2014). Phylogenetic analysis of concatenated ITS-rDNA, EF-1α and β-tub sequences showed that this isolate clustered in the same clade as F. equiseti, confirming its identity as F. equiseti. For the inoculation, roots of 12-days-old seedlings (watermelon and bottle gourd, n=10 each) were dipped in the conidia suspension (1x106 conidia/µL) for 30 min. Inoculated seedlings were planted in the soil before being transferred to the greenhouse (temperature; 30°C, daylight; 14 hours). Control plants were inoculated with sterile water. Results showed that after 21 days post-inoculation, all inoculated bottle gourd seedlings (n=10) wilted and eventually died. In contrast, none of the inoculated watermelons or control seedlings were affected. Re-isolation of three fungal isolates (infected root) showed that their morphology and gene markers sequence were identical to the original isolates thus fulfilled Koch's postulates. Bottle gourd is the most preferred rootstock for grafted watermelons among Korean farmers due to its ability to resist Fusarium spp. infection. Therefore, the identification of F. equiseti as a fungal that is pathogenic to rootstock is crucial information to manage fusarium wilt disease among grafted watermelon. To our knowledge, this is the first report confirming F. equiseti infection in grafted watermelon plants in Korea.

Scientific basis for medicinal use of Citrullus lanatus (Thunb.) in diarrhea and asthma: In vitro, in vivo and in silico studies

BACKGROUND

Citrullus lanatus (Thunb.) is a member of the Cucurbitaceae family, commonly farmed as an edible vegetable around the globe. It has been used in traditional therapies in addition to nutritional advantages. Traditional herbal practitioners employ C. lanatus seeds to treat gastrointestinal, respiratory, and urinary diseases in Pakistan and India. However, more investigation is needed to understand the effect of C. lanatus seeds on treating gastrointestinal, respiratory, and urinary disorders.

PURPOSE

This research aimed to use network pharmacology and molecular docking to understand multi-target mechanisms of C. lanatus seeds against asthma and diarrhea and to validate its effects using biological tests to investigate antispasmodic and bronchodilator capabilities.

METHODS

The ground seeds of C. lanatus were extracted in hexane, dichloromethane, ethanol, and aqueous for sequential extracts. The bioactive components in sequential extracts of C. lanatus seeds were identified using LC ESI-MS/MS, and specific compounds were quantified using HPLC. The quantified bioactive compounds of C. lanatus were subjected to in silico studies for network pharmacology and molecular docking to elucidate their role in antispasmodic and bronchodilator properties. The sequential extracts were tested on isolated rabbit tissue, i.e., jejunum, trachea, and urinary bladder. The antiperistalsis, antidiarrheal and antisecretory studies were also performed in animal models.

RESULTS

In silico studies indicate that bioactive chemicals from sequential extracts of C. lanatus seeds interfere with asthma and diarrhea-associated pathogenic genes. Those are members of calcium mediate signaling, cholinergic synapse, regulation of cytosolic calcium concentration, smooth muscle contraction, and inflammatory responses. It was also found that rutin, quercitrin, stearic acid, umbelliferone, and kaempferol were stronger binding to voltage-gated calcium channels and muscarinic M3 receptor, thus exerting calcium channel blocker activity and cholinergic receptor stimulant response. On isolated jejunum, trachea, and urinary preparations, sequential extracts of C. lanatus seeds elicited the spasmolytic response and showed the relaxation of spastic contractions of K+ (80 mM) and carbachol (1 µM). Furthermore, it induced a non-parallel rightward shift in calcium concentration-response curves with suppression. In animal models, C. lanatus seed extracts exhibited partially or completely antiperistalsis, antidiarrheal, and antisecretory effects.

CONCLUSION

Thus, Citrullus lanatus had therapeutic benefits by modulating the contractile response through calcium-mediated signaling target proteins, hence exerting bronchodilator and antidiarrheal properties. The current study provides evidence for further mechanistic studies and the development of C. lanatus seeds as a potential therapeutic intervention for patients with gastrointestinal, respiratory, and urinary disorders.

Broad Resistance to Post-Harvest Fruit Rot in USVL Watermelon Germplasm Lines to Isolates of Phytophthora capsici Across the United States

Watermelon is an important cucurbit vegetable crop grown in most of the United States. Phytophthora fruit rot of watermelon caused by Phytophthora capsici has been a major factor, limiting production for the past 15 years in the southeastern United States. The U.S. Department of Agriculture, Agricultural Research Service released five Phytophthora fruit rot-resistant germplasm lines for use in breeding programs. These lines were developed by phenotyping using a local isolate of P. capsici from South Carolina. The present study was undertaken to determine if these resistant lines had broad resistance to diverse P. capsici isolates collected from different states and crops. Five resistant germplasm lines (USVL020-PFR, USVL203-PFR, USVL782-PFR, USVL489-PFR, and USVL531-MDR) and two susceptible cultivars, Sugar Baby and Mickey Lee, used as checks were grown in a field in 2014 and 2015 to produce fruit for evaluation. Mature fruit were harvested and placed in a walk-in growth chamber and inoculated with 20 different P. capsici isolates. The chamber was maintained at 26 ± 2°C and high relative humidity (>95%) using a humidifier. All five resistant germplasm lines were significantly more resistant than the two susceptible checks to all 20 P. capsici isolates. Among the five resistant germplasm lines, USVL020-PFR, USVL782-PFR, and USVL531-MDR had broad resistance. Some P. capsici isolates induced minor lesions and rot on USVL489-PFR compared with the other resistant lines. Variation in virulence and genetic diversity among the 20 P. capsici isolates was also observed. The five watermelon germplasm lines will be useful for developing commercial watermelon cultivars with broad resistance to P. capsici.

Physiological responses and production of mini-watermelon irrigated with reject brine in hydroponic cultivation with substrates

The scarce availability of good quality water for irrigation in semi-arid regions leads to the reuse of waters, such as reject brine. Associated with this, the use of alternatives, such as hydroponic cultivation in substrates suitable for the development of profitable crops, such as watermelon, a species considered moderately sensitive to salinity, will allow new opportunities for communities assisted by desalination plants. An experiment was conducted in a plastic greenhouse to evaluate the growth, physiological responses, yield, and fruit quality of 'Sugar Baby' mini-watermelon cultivated in a hydroponic system with reject brine from desalination plants and different substrates. The experimental design was randomized blocks, with treatments arranged in a 5 × 4 factorial scheme, corresponding to five mixtures of reject brine (9.50 dS m^-1) and tap water (0.54 dS m^-1) applied to mini-watermelon plants, in an open hydroponic system, with four types of substrate and four replicates, with two plants per plot. Mini-watermelon plants grown in coconut fiber substrate showed the best growth and production. On the other hand, washed sand was the substrate that most hampered the development of plants in all mixtures. The use of reject brine to prepare the nutrient solution reduced the growth and production of mini-watermelon, mainly in mixtures with salinity above 4.00 dS m^-1. The changes in gas exchange caused by salt stress in mini-watermelon were of stomatal nature. Mini-watermelon has high energy stability under conditions of salt stress.

Application of boron reduces vanadium toxicity by altering the subcellular distribution of vanadium, enhancing boron uptake and enhancing the antioxidant defense system of watermelon

Vanadium (V) is the fifth most abundant transition metal, elevated levels of V are hazardous to plants. Boron (B) is an essential micronutrient for plants and can mitigate heavy metal toxicity. However, the mechanism used by B to promote tolerance to vanadium is unknown. In this study, a combination of physiological and gene expression analysis was used to explain mechanism of B (75 µM) induced V (40 mg L^-1) stress tolerance in watermelon. V stress severely reduced root and shoot growth and increased the accumulation of ROS. B application improved tolerance to V by enhancing the expression of B transporter genes (ClaNIP5;1-1, ClaNIP5;1-2, ClaBOR4) that facilitated B uptake and transport while restricting V transport in plant tissues. At cellular level, the higher V retention in leaves was achieved by cell wall chelation, whereas, the higher V exclusion in vacuole of root cell was driven by elevated vacuolar H⁺-ATPase, H⁺-PPase activities, and transcript level of ClaVHP1;1, ClaPDR12-1 and ClaPDR12-2 genes facilitated by B application. Moreover, B application reduced tissue ROS cascade by enhancing antioxidant enzymatic activity and expression of superoxide dismutase (ClaCSD1-1, ClaCSD1-2, ClaCSD3, ClaMSD1) and catalase (ClaCAT2-1, ClaCAT2-2) genes that enhanced the defense mechanism of the V treated plants, improved root and shoot growth and tolerance index of watermelon. In conclusion, we demonstrate that ameliorative effect of B in tolerance to V of watermelon was based on B homeostasis and improved antioxidant defense system. These findings might help to increase watermelon production in V polluted soils.

Integrated Transcriptome Analysis and Single-Base Resolution Methylomes of Watermelon (Citrullus lanatus) Reveal Epigenome Modifications in Response to Osmotic Stress

DNA methylation plays an important role against adverse environment by reshaping transcriptional profile in plants. To better understand the molecular mechanisms of watermelon response to osmotic stress, the suspension cultured watermelon cells were treated with 100mM mannitol, and then a methylated cytosines map was generated by whole genome bisulfite sequencing (WGBS). Combined with transcriptome sequencing, the effects of osmotic stress on differentially methylated expressed genes (DMEGs) were assessed. It was found that genes related to plant hormone synthesis, signal transduction, osmoregulatory substance-related and reactive oxygen species scavenging-related enzyme could rapidly respond to osmotic stress. The overall methylation level of watermelon decreased after osmotic stress treatment, and demethylation occurred in CG, CHG, and CHH contexts. Moreover, differentially methylated expressed genes (DMEGs) were significantly enriched in RNA transport, starch and sucrose metabolism, plant hormone signal transduction and biosynthesis of secondary metabolites, especially in biosynthesis of osmolytes synthase genes. Interestingly, demethylation of a key enzyme gene Cla014489 in biosynthesis of inositol upregulated its expression and promoted accumulation of inositol, which could alleviate the inhibition of cell growth caused by osmotic stress. Meanwhile, a recombinant plasmid pET28a-Cla014489 was constructed and transferred into Escherichia coli BL21 for prokaryotic expression and the expression of ClMIPS protein could improve the tolerance of E. coli to osmotic stress. The effect of methylation level on the expression properties of inositol and its related genes was further confirmed by application of DNA methylation inhibitor 5-azacytidine. These results provide a preliminary insight into the altered methylation levels of watermelon cells in response to osmotic stress and suggest a new mechanism that how watermelon cells adapt to osmotic stress.

Comparative Transcriptome Analysis in Homo- and Hetero-Grafted Cucurbit Seedlings

Watermelon (Citrullus lanatus) is a valuable horticultural crop with nutritional benefits grown worldwide. It is almost exclusively cultivated as grafted scions onto interspecific squash rootstock (Cucurbita maxima × Cucurbita moschata) to improve the growth and yield and to address the problems of soilborne diseases and abiotic stress factors. This study aimed to examine the effect of grafting (homo- and hetero-grafting) on the transcriptome level of the seedlings. Therefore, we compared homo-grafted watermelon (WW) with non-grafted watermelon control (W), homo-grafted squash (SS) with non-grafted squash control (S), hetero-grafted watermelon onto squash (WS) with SS, and WS with WW. Different numbers of differentially expressed genes (DEGs) were identified in each comparison. In total, 318 significant DEGs were detected between the transcriptomes of hetero-grafts and homo-grafts at 16 h after grafting. Overall, a significantly higher number of downregulated transcripts was detected among the DEGs. Only one gene showing increased expression related to the cytokinin synthesis was common in three out of four comparisons involving WS, SS, and S. The highest number of differentially expressed (DE) transcripts (433) was detected in the comparison between SS and S, followed by the 127 transcripts between WW and W. The study provides a description of the transcriptomic nature of homo- and hetero-grafted early responses, while the results provide a start point for the elucidation of the molecular mechanisms and candidate genes for the functional analyses of hetero-graft and homo-graft systems in Cucurbitaceae and generally in the plants.

Frequency of parasitic infections in Arachishypogaea L (groundnuts), Citrulluslanatus seeds (watermelon seeds), and Ziziphusspina-christi (nabag) sold by street vendors in Khartoum State, Sudan: a cross-sectional study

Background: Plant products, including seeds are an important source of vitamins, minerals, proteins, and energy. This study aimed to assess parasitic contaminations in roasted groundnuts, nabag, and tasali (watermelon seeds) sold by street vendors in Khartoum State, Sudan. Methods: The frequency of parasitic contaminations among all crop products was detected by washing the plants with saline, and then conducting an examination using a formal ether concentration technique (FECT), followed by a saturated sugar floatation technique. Results: The detected parasites belonged to two species: Entamoeba histolytica (33.3%) and Giardia lamblia (15.6%). No helminthic parasites were detected. Mixed contamination of the mentioned parasites was also observed (11.1%). The most contaminated crop was nabag, followed by groundnut, and finally tasali. Conclusion: No relation was established between the positivity of samples for parasites and crop type, Khartoum State city, or  seller sex. FECT was more sensitive than the saturated sugar floatation technique as a detection method.

Watermelon Reduces the Toxicity of Cisplatin Treatment in C57BL/6 Mice with Induced Melanoma

An alternative to reduce the undesirable effects of antineoplastic agents has been the combination of classical treatments with nutritional strategies aimed at reducing systemic toxicity without decreasing the antitumor activity of already used drugs. Within this context, this study evaluated the possible reduction of toxicity when cisplatin treatment is combined with watermelon pulp juice supplementation in C57BL/6 mice with melanoma. Watermelon is a fruit rich in vitamins, minerals, proteins, lycopene, carotene, and xanthophylls, which has shown effectiveness in the treatment of cardiovascular diseases, weight loss, urinary infections, gout, hypertension, and mutagenicity. The following parameters were analyzed: animal survival, bone marrow genotoxicity, serum creatinine and urea, histopathological features of the tumor tissue, tumor weight and volume, and weight of non-tumor tissues (kidney, liver, spleen, heart, and lung). The results showed that watermelon had no antitumor effect but reduced the toxicity of cisplatin, as demonstrated by an increase in the number of bone marrow cells and a decrease in serum creatinine and urea levels. The data suggest that watermelon pulp juice can be an alternative for reducing the side effects of antineoplastic agents.

Genome wide analysis of kinesin gene family in Citrullus lanatus reveals an essential role in early fruit development

BACKGROUND

Kinesin (KIN) as a motor protein is a versatile nano-machine and involved in diverse essential processes in plant growth and development. However, the kinesin gene family has not been identified in watermelon, a valued and nutritious fruit, and yet their functions have not been characterized. Especially, their involvement in early fruit development, which directly determines the size, shape, yield and quality of the watermelon fruit, remains unclear.

RESULTS

In this study, we performed a whole-genome investigation and comprehensive analysis of kinesin genes in C. lanatus. In total, 48 kinesins were identified and categorized into 10 kinesin subfamilies groups based on phylogenetic analysis. Their uneven distribution on 11 chromosomes was revealed by distribution analysis. Conserved motif analysis showed that the ATP-binding motif of kinesins was conserved within all subfamilies, but not the microtubule-binding motif. 10 segmental duplication pairs genes were detected by the syntenic and phylogenetic approaches, which showed the expansion of the kinesin gene family in C. lanatus genome during evolution. Moreover, 5 ClKINs genes are specifically and abundantly expressed in early fruit developmental stages according to comprehensive expression profile analysis, implying their critical regulatory roles during early fruit development. Our data also demonstrated that the majority of kinesin genes were responsive to plant hormones, revealing their potential involvement in the signaling pathways of plant hormones.

CONCLUSIONS

Kinesin gene family in watermelon was comprehensively analyzed in this study, which establishes a foundation for further functional investigation of C. lanatus kinesin genes and provides novel insights into their biological functions. In addition, these results also provide useful information for understanding the relationship between plant hormone and kinesin genes in C. lanatus.

Suitability of food resources for Proprioseiopsis mexicanus, a potentially important natural enemy in eastern USA agroecosystems

The phytoseiid Proprioseiopsis mexicanus has been collected from a wide range of plants in the western hemisphere, including many cucurbit agroecosystems in South Carolina, USA. Our aim was to characterize the lifestyle of P. mexicanus and its potential as a natural enemy of Tetranychus urticae, a common pest in cucurbits. We determined developmental time, pre-oviposition time, and fecundity of females on pollen-only diets from a commercial Typha spp. supplement source, Citrullus lanatus, Cucurbita maxima, Cucurbita moschata, Cucurbita pepo, Delosperma cooperi, Trifolium incarnatum, and on T. urticae and a combination of T. urticae and Typha spp. pollen. Female development time differed based on diet-development was fastest on C. lanatus and D. cooperi diets (ca. 3 days) and slowest on Typha pollen diet (ca. 5 days). Pre-oviposition time was shorter for females fed C. lanatus and T. incarnatum (1.6 days) and longest when fed Typha pollen (3.1 days). Citrullus lanatus, T. incarnatum, and D. cooperi pollen diets resulted in more eggs/day compared to other diets. Cucurbita moschata pollen resulted in the lowest oviposition rate (0.69 eggs/day). Because these pollens varied in size, we examined pollen size as a factor in developmental and reproductive success. With the exception of Typha pollen, small-pollen diets (C. lanatus, D. cooperi, and T. incarnatum) resulted in faster development, shorter pre-oviposition time, and higher fecundity than large-pollen diets (Cucurbita spp.). We concluded that P. mexicanus is a generalist predator that may require pollen for survival and reproduction, but alone this species may not be an effective predator of T. urticae.

Transcriptome regulation of carotenoids in five flesh-colored watermelons (Citrullus lanatus)

BACKGROUND

Fruit flesh color in watermelon (Citrullus lanatus) is a great index for evaluating the appearance quality and a key contributor influencing consumers' preferences. But the molecular mechanism of this intricate trait remains largely unknown. Here, the carotenoids and transcriptome dynamics during the fruit development of cultivated watermelon with five different flesh colors were analyzed.

RESULTS

A total of 13 carotenoids and 16,781 differentially expressed genes (DEGs), including 1295 transcription factors (TFs), were detected in five watermelon genotypes during the fruit development. The comprehensive accumulation patterns of carotenoids were closely related to flesh color. A number of potential structural genes and transcription factors were found to be associated with the carotenoid biosynthesis pathway using comparative transcriptome analysis. The differentially expressed genes were divided into six subclusters and distributed in different GO terms and metabolic pathways. Furthermore, we performed weighted gene co-expression network analysis and predicted the hub genes in six main modules determining carotenoid contents. Cla018406 (a chaperone protein dnaJ-like protein) may be a candidate gene for β-carotene accumulation and highly expressed in orange flesh-colored fruit. Cla007686 (a zinc finger CCCH domain-containing protein) was highly expressed in the red flesh-colored watermelon, maybe a key regulator of lycopene accumulation. Cla003760 (membrane protein) and Cla021635 (photosystem I reaction center subunit II) were predicted to be the hub genes and may play an essential role in yellow flesh formation.

CONCLUSIONS

The composition and contents of carotenoids in five watermelon genotypes vary greatly. A series of candidate genes were revealed through combined analysis of metabolites and transcriptome. These results provide an important data resource for dissecting candidate genes and molecular basis governing flesh color formation in watermelon fruit.

Modelling the Extraction of Pectin towards the Valorisation of Watermelon Rind Waste

Watermelon is the second largest fruit crop worldwide, with great potential to valorise its rind waste. An experimental design was used to model how extraction parameters (temperature, pH, and time) impact on the efficiency of the process, purity, esterification degree, monosaccharide composition and molar mass of watermelon rind pectin (WRP), with an insight on changes in their structural properties (linearity, branching degree and extraction severity). The models for all responses were accurately fitted (R2 > 90%, lack of fit p ≥ 0.05) and experimentally validated. At optimum yield conditions, WRP yield (13.4%), purity (540 µg/g galacturonic acid) and molar mass (106.1 kDa) were comparable to traditional pectin sources but showed a higher branching degree with longer galactan side chains and a higher protein interaction. Harsher conditions (pH 1) generated purer homogalacturonan fractions with average molar masses (80 kDa) at the expense of yield, while mild extraction conditions (pH ≥ 2) produced highly branched entangled pectin structures. This study underlines novel compositional features in WRP and the possibility of producing novel customized pectin ingredients with a wider potential application scope depending on the targeted structure.

Protective effects of Citrullus lanatus seed ethanol extract on aluminum chloride-induced testosterone, testicular and hematological changes in an experimental male rat model

The study was done to ascertain the protective potentials of ethanol seed extract of Citrullus lanatus on aluminum chloride-induced reproductive and hematological toxicities. Thirty mature male rats were used for the study. They were assigned into five groups (n = 6). Group 1 was treated daily with aluminum chloride (100 mg kg^-1) per os for 8 weeks. Group 2 was treated with aluminum chloride (100 mg kg^-1) and C. lanatus seed extract (CLSE) 200 mg kg^-1 per os simultaneously for 8 weeks. Group 3 was served as a normal control and given distilled water as a placebo per os daily for 8 weeks. Group 4 was only treated with CLSE (200 mg kg^-1) for eight weeks. Group 5 was only treated with aluminum chloride (100 mg kg^-1) per os for 8 weeks and then treated with CLSE (200 mg kg^-1) per os for another 4 weeks. Testosterone level, testicular weight, sperm motility, gonadal sperm, and extragonadal sperm reserves showed significant increases in group 2 compared to groups 1 and 5. Optimum histoarchitectural protection of the seminiferous tubules was observed in group 2, which did not differ from normal ones. For the hematological parameters, optimum protection was also observed in group 2 compared to other groups. From the results, ethanol seed extract of C. lanatus demonstrated protective potentials against aluminum's harmful effects on the male reproductive system and hematology in an experimental male rat model.

Cell Wall Polysaccharide Composition of Grafted 'Liberty' Watermelon With Reduced Incidence of Hollow Heart Defect

Grafting watermelon scions to interspecific squash hybrids has been found to increase fruit firmness. Triploid (seedless) watermelon are prone to hollow heart (HH), an internal fruit disorder characterized by a crack in the placental tissue expanding to a cavity. Although watermelon with lower tissue firmness tend to have a higher HH incidence, associated differences in cell wall polysaccharide composition are unknown. Grafting "Liberty" watermelon to "Carnivor" (interspecific hybrid rootstock, C. moschata × C. maxima) reduced HH 39% and increased tissue firmness by 3 N. Fruit with and without severe HH from both grafted and non-grafted plants were analyzed to determine differences in cell wall polysaccharides associated with grafting and HH. Alcohol insoluble residues (AIR) were sequentially extracted from placental tissue to yield water soluble (WSF), carbonate soluble (CSF), alkali soluble (ASF), or unextractable (UNX) pectic fractions. The CSF was lower in fruit with HH (24.5%) compared to those without HH (27.1%). AIRs were also reduced, hydrolyzed, and acetylated for GC-MS analysis of monosaccharide composition, and a portion of each AIR was methylated prior to hydrolysis and acetylation to produce partially methylated alditol acetates for polysaccharide linkage assembly. No differences in degree of methylation or galacturonic and glucuronic acid concentrations were found. Glucose and galactose were in highest abundance at 75.9 and 82.4 μg⋅mg^-1 AIR, respectively, followed by xylose and arabinose (29.3 and 22.0 μg⋅mg^-1). Mannose was higher in fruit with HH (p < 0.05) and xylose was highest in fruit from grafted plants (p < 0.05). Mannose is primarily found in heteromannan and rhamnogalacturonan I side chains, while xylose is found in xylogalacturonan or heteroxylan. In watermelon, 34 carbohydrate linkages were identified with galactose, glucose, and arabinose linkages in highest abundance. This represents the most comprehensive polysaccharide linkage analysis to date for watermelon, including the identification of several new linkages. However, total pectin and cell wall composition data could not explain the increased tissue firmness observed in fruit from grafted plants. Nonetheless, grafting onto the interspecific hybrid rootstock decreased the incidence of HH and can be a useful method for growers using HH susceptible cultivars.

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.

Stability enhancement of lycopene in Citrullus lanatus extract via nanostructured lipid carriers

Lycopene is one of naturally occurring carotenoids in plants including watermelon (Citrullus lanatus). Heat, light, and oxygen effect on lycopene isomerization and degradation. Nanostructured lipid carriers (NLCs) are drug delivery system which can enhance the stability of active compound. Therefore, this study aimed to develop watermelon extract loaded in NLCs for lycopene stability improvement. The NLCs were prepared using a hot homogenization technique. Cocoa butter was used as solid lipid. Grape seed oil was used as liquid lipid. Span® 80 and Plantasens® HE20 were used as an emulsifier. The selected unloaded NLCs contained solid lipid to liquid lipid at the ratio of 3:1 and 10% (w/w) of total lipid. The particle size of watermelon extract-loaded NLCs (WH-loaded NLCs) was 130.17 ± 0.72 nm with low PDI and high zeta potential. It also presented high entrapment efficiency. For stability study, the WH-NLC3 could enhance stability and maintain lycopene content after stability test. It exhibited the highest values of lycopene content (83.26 ± 2.30%) when stored at 4°C. It also possessed a prolonged release pattern over 48 hr. Therefore, the NLCs could improve stability and release profile of lycopene from watermelon extract.

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.

Anti-atherogenic properties of Kgengwe (Citrullus lanatus) seed powder in low-density lipoprotein receptor knockout mice are mediated through beneficial alterations in inflammatory pathways

Kgengwe fruits are commonly consumed in sub-Saharan countries. Recent reports indicated low coronary artery disease rates in those regions. To investigate anti-atherogenic properties and potential mechanisms of action of Kgengwe seed powder (KSP), male low-density lipoprotein receptor knockout (LDL-r-KO) mice were fed with an atherogenic diet supplemented with (treated, n = 10) or without (controls, n = 10) 10% (w/w) KSP for 20 weeks. Proximate analysis revealed that KSP contained 38% fibre and 15% lipids. KSP supplementation was not associated with significant changes in body weight gain rate, food intake, and plasma lipid levels. However, the average atherosclerotic lesion size in the aortic roots in the KSP-treated group was 58% smaller than that in the control group (0.26 vs 0.11 mm2, p < 0.05). This strong anti-atherogenic effect was associated with significant increases in the average plasma levels of certain cytokines such as IL-10 (6 vs 13 pg/mL, p < 0.05), GM-CSF (0.1 vs 0.2 pg/mL, p < 0.05), and EPO (7 vs 16 pg/mL, p < 0.05) along with reductions in the average levels of plasma MCP-1 (19 vs 14 pg/mL, p < 0.05) and MIP-2 (28 vs 13 pg/mL, p < 0.05). Except for relatively high levels of saturated fatty acids, KSP possesses balanced nutrient compositions with strong anti-atherogenic properties, which may be mediated through alterations in inflammatory pathways. Additional studies warrant confirmation and mechanism(s) of action of such effects. Novelty: Kgengwe seeds prevent atherogenesis in LDL-r-KO mice. Kgengwe seeds increase circulating levels of IL-10 and EPO. No reduction in plasma total cholesterol levels.

Evaluating Cucurbit Rootstocks to Prevent Disease Caused by Pythium aphanidermatum and P. myriotylum on Watermelon

Pythium species cause root and stem rot in watermelon (Citrullus lanatus), but cucurbit rootstocks used to graft watermelon have not been evaluated for resistance. P. aphanidermatum and P. myriotylum were inoculated onto 15 nongrafted watermelon, citron (Citrullus amarus), bottle gourd (Lagenaria siceraria), and interspecific hybrid squash (Cucurbita maxima × C. moschata) cultivars in a growth chamber. Watermelon was more susceptible than bottle gourd and interspecific hybrid squash at 20 and 30°C. Twenty-one cultivars were inoculated in a field with an equal blend of both Pythium species. Interspecific hybrid squash was less susceptible than bottle gourd and watermelon in 2018 and 2019. Seedless watermelon cultivar Tri-X 313 was grafted to one citron, one bottle gourd, and three interspecific hybrid squash rootstocks. Plants were inoculated in the field as described. Grafting to interspecific hybrid squash rootstocks reduced disease incidence compared with nongrafted controls in 2018 and 2019. Mefenoxam and propamocarb applied at transplanting did not affect disease compared with non-fungicide-treated plots. Grafting to interspecific hybrid squash Camelforce significantly increased total and marketable fruit numbers and total weight in 2019 compared with the nongrafted control. In summary, interspecific hybrid squash was consistently resistant to Pythium, demonstrating resistance and utility in watermelon grafting.

Pumpkin rootstock improves the growth and development of watermelon by enhancing uptake and transport of boron and regulating the gene expression

Boron (B) is an essential trace element that plays a vital role in metabolic and physiological functions of higher plants. The adequate supply of B is important for plant growth and development. Grafting is a technique used to improve the ion uptake and plant growth. In this study, a commercial watermelon cultivar "Zaojia 8424" [Citrullus lanatus (Thunb.) Matsum. and Nakai.] was grafted onto pumpkin (Cucurbita maxima × Cucurbita moschata) rootstock cv. "Qingyan Zhenmu No.1" with an aim to investigate the response of grafted plants to different levels of B supply (0.25 μM, 25 μM and 75 μM B) in the nutrient solution. Self-grafted watermelon plants were used as control. Pumpkin rootstock improved the plant growth, chlorophyll and carotenoid contents, photosynthetic assimilation, stomatal conductance, transpiration rate, B accumulation and up-regulated the expression of NIP5;1, NIP6;1 and B transporter (BOR2, BOR4) genes in the roots and leaves at 25 μM B compared with self-grafted watermelon plants. Moreover, pumpkin rootstock reduced the oxidative stress and cell damage by reducing H₂O₂ and MDA contents, and down-regulating the expression of PDCD2-1, PDCD2-2 genes. Moreover, it enhanced the antioxidant activity of watermelon by up-regulating the expression of SOD1, SOD2, CAT2-1, and CAT2-2 genes. Based on these observations, we concluded that pumpkin rootstock has ability to improve the plant growth of watermelon by enhancing the B uptake. This study may help adjust the B concentration in the nutrient medium for watermelon production where pumpkin grafted plants are utilized.

Metabolite Profiles of Red and Yellow Watermelon (Citrullus lanatus) Cultivars Using a 1H-NMR Metabolomics Approach

Watermelon, a widely commercialized fruit, is famous for its thirst-quenching property. The broad range of cultivars, which give rise to distinct color and taste, can be attributed to the differences in their chemical profile, especially that of the carotenoids and volatile compounds. In order to understand this distribution properly, water extracts of red and yellow watermelon pulps with predominantly polar metabolites were subjected to proton nuclear magnetic resonance (1H-NMR) analysis. Deuterium oxide (D2O) and deuterated chloroform (CDCl3) solvents were used to capture both polar and non-polar metabolites from the same sample. Thirty-six metabolites, of which six are carotenoids, were identified from the extracts. The clustering of the compounds was determined using unsupervised principal component analysis (PCA) and further grouping was achieved using supervised orthogonal partial least squares discriminant analysis (OPLS-DA). The presence of lycopene, β-carotene, lutein, and prolycopene in the red watermelon plays an important role in its differentiation from the yellow cultivar. A marked difference in metabolite distribution was observed between the NMR solvents used as evidenced from the PCA model. OPLS-DA and relative quantification of the metabolites, on the other hand, helped in uncovering the discriminating metabolites of the red and yellow watermelon cultivars from the same solvent system.

Antidiabetic activity of watermelon (Citrullus lanatus) juice in alloxan-induced diabetic rats

Introduction

Watermelon is one of the commonly eaten fruit in most homes in Nigeria and has been used in the management of diabetes mellitus traditionally. This study was carried out to explore the antidiabetic potential of watermelon (Citrullus lanatus) juice in alloxan-induced diabetic rats.

Methods

Watermelon juice was used for the determination of in vitro parameters such as 1,1-diphenyl-2-picryl-hydrazil (DPPH), nitric oxide and ferric reducing antioxidant potential (FRAP) as well as phytochemicals such as total phenol, total flavonoids. In vitro, α-glucosidase and α-amylase inhibitory activities were also accessed using standard procedures. Diabetes was induced in the rats by a single intraperitoneal (I.P) injection of freshly prepared alloxan (150 mg/kg body weight). The animals were randomly grouped into five groups of normal control, untreated diabetic control, diabetic rats administered 200 mg/kg body weight of metformin, diabetic rats administered 500 mg/kg body weight of watermelon (Citrullus lanatus) juice and diabetic rats administered 1000 mg/kg body weight of watermelon juice. The rats were sacrificed on the 14th day of the experiment and various in vivo biochemical parameters were also evaluated in the serum and tissue homogenates of diabetic rats.

Results

The watermelon juice exhibits anti-oxidant properties and inhibitory activities against α-glucosidase and α-amylase in a dose-dependent manner. Added to this, the administration of different doses of the watermelon juice significantly (p < 0.05) reduced the fasting blood glucose level, serum lipid profile, glucose-6-phosphatase, lipid peroxidation and anti-inflammatory activities in alloxan-induced diabetic rats. There was a significant (p < 0.05) increase in antioxidant enzyme activities, hexokinase activity as well as glucose transporters (GLUT 2 and GLUT 4) levels in diabetic rats administered different doses of Citrullus lanatus.

Conclusion

Taken together, this study demonstrates that watermelon (Citrullus lanatus) juice exhibits its antidiabetic potential in experimental diabetic animal model via multiple pathways involving modulation of glucose transporters, anti-inflammatory activities as well as antioxidant defense system and inhibition of α-glucosidase and α-amylase. This suggests that the watermelon (Citrullus lanatus) juice may have a useful clinical application in the management of diabetes mellitus and its metabolic complications if developed as adjuvant therapy.

A rapid fluorescence-based real-time isothermal assay for the detection of Cucurbit yellow stunting disorder virus in squash and watermelon plants

Cucurbit yellow stunting disorder virus (CYSDV) is a single-stranded positive-sense RNA virus that produces devastating disease in watermelon and squash. Foliar symptoms of CYSDV consist of interveinal yellowing, brittleness, and thickening of older leaves leading to reduced plant vigor. A rapid diagnostic method for CYSDV would facilitate early detection and implementation of best viral-based management practices. We developed a rapid isothermal reverse transcription-recombination polymerase amplification (exo RT-RPA) assay for the detection of CYSDV. The primers and a 6-fluorescein amidite (6-FAM) probe were developed to target the nucleocapsid gene. The real-time assay detected CYSDV at 2.5 pg purified total RNA extracted from CYSDV-infected leaf tissue and corresponded to 10 copies of the target molecule. The assay was specific and did not cross-react with other common cucurbit viruses found in Florida and Georgia. The performance of the exo RT-RPA was evaluated using crude extract from 21 cucurbit field samples and demonstrated that the exo RT-RPA is a rapid procedure, thus providing a promising novel alternative approach for the detection of CYSDV.

Data on the derived mesoporous based catalyst for the synthesized of fatty acid methyl ester (FAME) from ternary oil blend: An optimization approach

This work presents datasets on fatty acid methyl ester (FAME) synthesized from the ternary blend of Cucurbita pepo-chrysophyllum albidum -papaya mix oils via methanolysis of mesoporous CaO heterogeneous catalyst derived from the mixture of Citrullus lanatus and Musa acuminate peels. The oils were extracted from the milled powdered using the solvent extraction method. Ternary oil mixed ratio of 33:33:34 with low acid value and density was achieved using simplex lattice design software. Characterization of the mixed calcined catalyst powder (MCCP) at 700 °C for 4 h was carried out using scanning electron microscopy (SEM), energy dispersive spectroscope (EDS), X-ray diffraction analysis (XRD), and BET analysis. The thermal decomposition of mixed calcined catalyst powder (MCCP) produced 78.74% CaO with a strong basic site of 143 (μmole.g⁻¹). Fatty acid methyl ester (FAME) was synthesized through the based catalyst transesterification of a derived catalyst by considering four variables data (reaction time, reaction temperature, catalyst amount and methanol/oil molar ratio) using response surface methodology (RSM). The maximum experimental FAME data of 94.29 (wt. %) was achieved at run 16, but the central composite design (CCD) software predicted value of 98.00 (wt. %) at a reaction time of 70 min, reaction temperature of 80 °C, catalyst amount of 5.0 (wt.) and methanol to oil molar ratio (MeOH/OMR) of 6.97, at the desirability of 97.90%. This was validated in triplicate, and the average FAME data obtained was 93.45 (wt. %). The produced FAME properties dataset meets the standard recommended value of ASTM and EN14214.

Comparative analysis of primary metabolites and transcriptome changes between ungrafted and pumpkin-grafted watermelon during fruit development

Grafting has been reported as a factor that influences fruit quality. However, a comprehensive study of the metabolic profile related to fruit quality and the underlying molecular mechanism in grafted watermelon has not been carried out. Metabolomics and transcriptome analysis were performed on both pumpkin-grafted watermelon and ungrafted watermelon at different developmental stages. In total, 56 primary metabolites were identified with either high or low abundance between ungrafted and pumpkin-grafted watermelon. The results indicated that ornithine, arginine, lysine (amino acids), glucose, sucrose, glucosamine (sugars), malic acid, fumaric acid and succinic acid (organic acids) were among the dominant metabolites influencing fruit quality. Additionally, comparative RNA sequence analysis on grafted and ungrafted watermelon yielded 729, 174, 128 and 356 differentially expressed genes at 10, 18, 26 and 34 days after pollination (DAP), respectively. Functional annotations of these genes indicated that grafting significantly altered the biological and metabolic processes related to fruit quality. Our comparative metabolomics and transcriptome analysis revealed that FBA2, FK, SuSy, SPS, IAI, AI and sugar transporter gene (SWT3b) might play a central role in the accumulation of glucose and sucrose, whereas higher malic acid content was attributed to high down regulation of ALMT13 and ALMT8 in pumpkin-grafted watermelon. Changes in the ornithine, glutamine, alanine, tyrosine, valine, asparagine, phenylalanine, arginine and tryptophan contents were consistent with the transcript level of their metabolic genes such as NAOD, GS, AGT, TaT, aDH1, OGDH, aDC, 4CL 1, PaL, CaT and two nitrate transporter genes (NRT1) in pumpkin-grafted watermelon. This study provides the basis for understanding the graft-responsive changes in the metabolic profile and regulatory mechanism related to fruit quality.

Inside and Beyond Color: Comparative Overview of Functional Quality of Tomato and Watermelon Fruits

The quali-quantitative evaluation and the improvement of the levels of plant bioactive secondary metabolites are increasingly gaining consideration by growers, breeders and processors, particularly in those fruits and vegetables that, due to their supposed health promoting properties, are considered "functional." Worldwide, tomato and watermelon are among the main grown and consumed crops and represent important sources not only of dietary lycopene but also of other health beneficial bioactives. Tomato and watermelon synthesize and store lycopene as their major ripe fruit carotenoid responsible of their typical red color at full maturity. It is also the precursor of some characteristic aroma volatiles in both fruits playing, thus, an important visual and olfactory impact in consumer choice. While sharing the same main pigment, tomato and watermelon fruits show substantial biochemical and physiological differences during ripening. Tomato is climacteric while watermelon is non-climacteric; unripe tomato fruit is green, mainly contributed by chlorophylls and xanthophylls, while young watermelon fruit mesocarp is white and contains only traces of carotenoids. Various studies comparatively evaluated in vivo pigment development in ripening tomato and watermelon fruits. However, in most cases, other classes of compounds have not been considered. We believe this knowledge is fundamental for targeted breeding aimed at improving the functional quality of elite cultivars. Hence, in this paper, we critically review the recent understanding underlying the biosynthesis, accumulation and regulation of different bioactive compounds (carotenoids, phenolics, aroma volatiles, and vitamin C) during tomato and watermelon fruit ripening. We also highlight some concerns about possible harmful effects of excessive uptake of bioactive compound on human health. We found that a complex interweaving of anabolic, catabolic and recycling reactions, finely regulated at multiple levels and with temporal and spatial precision, ensures a certain homeostasis in the concentrations of carotenoids, phenolics, aroma volatiles and Vitamin C within the fruit tissues. Nevertheless, several exogenous factors including light and temperature conditions, pathogen attack, as well as pre- and post-harvest manipulations can drive their amounts far away from homeostasis. These adaptive responses allow crops to better cope with abiotic and biotic stresses but may severely affect the supposed functional quality of fruits.

Economic injury levels and sequential sampling plans for control decision-making systems of Bemisia tabaci biotype B adults in watermelon crops

BACKGROUND

Decision-making systems are essential parts of integrated pest management programs. The whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is a major pest of many crops, including watermelon (Citrullus lanatus), the second most consumed fruit worldwide. However, there are still no studies on decision-making systems for B. tabaci on this crop. Thus, we aim to determine a decision-making system to control B. tabaci biotype B on watermelon crops.

RESULTS

The highest densities of B. tabaci biotype B reduced the yield of watermelon crops by up to 56%. Watermelon plants were more susceptible to the pest at the vegetative stage than at the reproductive stage. The economic injury levels of B. tabaci biotype B when watermelon prices were low, average, and high were respectively, 0.52, 0.21 and 0.13 adults leaf^-1 at the vegetative stage, and 1.69, 0.69 and 0.44 adults leaf^-1 at the reproductive stage. The sequential plans reached the same decisions as the conventional plan, and reduced the time and cost of sampling by up to 92.68%.

CONCLUSION

The decision-making systems determined in this study enable an expedited and proper decision to be made for controlling B. tabaci, biotype B and can be used in different price situations for watermelon and in crops at different phenological stages. © 2018 Society of Chemical Industry.

and Nakai] Juice Improves Swimming Performance in Rats

Nutritional intervention of fruit juice supplementation is able to maximize exercise performance. Watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] contains high L-citrulline content and consumption of watermelon juice may promote ergogenic effects. The aim of the present study was to investigate the role of 100% flesh watermelon juice and 100% rind watermelon juice supplementation for 14 days on swimming performance in rats. Twenty four male Sprague-Dawley rats were randomly divided into four groups: Cx group of rats supplemented with filtered tap water (negative control), L-cit group of rats supplemented with L-citrulline (positive control), FR group of rats supplemented with 100% flesh watermelon juice, and RR group of rats supplemented with 100% rind watermelon juice. Each group was supplemented for 14 days ad libitum prior to swimming exercise protocol. The rats were performed swimming exercise for 3 days and swimming time until exhaustion was measured. Plasma samples were collected to measure lactate concentration, ammonia concentration, and nitric oxide production. Rats supplemented with 100% flesh watermelon juice demonstrated significantly prolonged of swimming time until exhaustion, reduction of lactate and ammonia concentrations, and increased of nitric oxide production compared to Cx and L-cit groups (P<0.05). These findings postulate that supplementation with 100% flesh watermelon juice improves endurance in swimming performance.

Two new phenolic glycosides from the seeds of Citrullus lanatus

Two new phenolic glycosides, named lanatusosides C (1) and D (2), together with four known compounds (3-6), were isolated from the seeds of Citrullus lanatus. Among them, compounds 3 and 4 were isolated from Cucurbitaceae for the first time, and compound 5 was reported from this plant for the first time. Their structures were elucidated by means of extensive spectral analysis, including HR-ESI-MS, ¹H and ¹³C NMR techniques. The isolated new compounds were evaluated for cytotoxic activity against HepG2 cell line, of which compound 1 demonstrated weak cytotoxicity against the tested cell line.

Chromosomal Locations and Interactions of Four Loci Associated With Seed Coat Color in Watermelon

Different species of edible seed watermelons (Citrullus spp.) are cultivated in Asia and Africa for their colorful nutritious seeds. Consumer preference varies for watermelon seed coat color. Therefore, it is an important consideration for watermelon breeders. In 1940s, a genetic model of four genes, R, T, W and D, was proposed to elucidate the inheritance of seed coat color in watermelon. In this study, we developed three segregating F₂ populations: Sugar Baby (dotted black seed, RRTTWW) × plant introduction (PI) 482379 (green seed, rrTTWW), Charleston Gray (dotted black seed, RRTTWW) × PI 189225 (red seed, rrttWW), and Charleston Gray (dotted black seed, RRTTWWdd) × UGA147 (clump seed, RRTTwwDD) to re-examine the four-gene model and to map the four genes. In the dotted black × green population, the dotted black seed coat color (R_) is dominant to green seed coat color (rr). In the dotted black × red population, the dominant dotted black seed coat color and the recessive red seed coat color segregate for the R and T genes, where the R gene is dominantly epistatic to the T gene. However, the inheritance of the T locus did not fit the four-gene model, thus we named it T¹ . In the dotted black × clump population, the clump seed coat color and the dotted black seed coat color segregate for W and D, where D is recessively epistatic to W. The R, T¹ , W, and D loci were mapped on chromosomes 3, 5, 6, and 8, respectively, using QTL-seq and genotyping-by-sequencing (GBS). Kompetitive Allele Specific PCR (KASP™) assays and SNP markers linked to the four loci were developed to facilitate maker-assisted selection (MAS) for watermelon seed coat color.

Genome-Wide Analysis of Watermelon HSP20s and Their Expression Profiles and Subcellular Locations under Stresses

Watermelon (Citrullus lanatus L.), which is an economically important cucurbit crop that is cultivated worldwide, is vulnerable to various adverse environmental conditions. Small heat shock protein 20s (HSP20s) are the most abundant plant HSPs and they play important roles in various biotic and abiotic stress responses. However, they have not been systematically investigated in watermelon. In this study, we identified 44 watermelon HSP20 genes and analyzed their gene structures, conserved domains, phylogenetic relationships, chromosomal distributions, and expression profiles. All of the watermelon HSP20 proteins have a conserved the α-crystallin (ACD) domain. Half of the ClHSP20s arose through gene duplication events. Plant HSP20s were grouped into 18 subfamiles and a new subfamily, nucleo-cytoplasmic XIII (CXIII), was identified in this study. Numerous stress- and hormone-responsive cis-elements were detected in the putative promoter regions of the watermelon HSP20 genes. Different from that in other species, half of the watermelon HSP20s were repressed by heat stress. Plant HSP20s displayed diverse responses to different virus infections and most of the ClHSP20s were generally repressed by Cucumber green mottle mosaic virus (CGMMV). Some ClHSP20s exhibited similar transcriptional responses to abscisic acid, melatonin, and CGMMV. Subcellular localization analyses of six selected HSP20- green fluorescence protein fusion proteins revealed diverse subcellular targeting. Some ClHSP20 proteins were affected by CGMMV, as reflected by changes in the size, number, and distribution of fluorescent granules. These systematic analyses provide a foundation for elucidating the physiological functions and biological roles of the watermelon HSP20 gene family.

Glycinebetaine Biosynthesis in Response to Osmotic Stress Depends on Jasmonate Signaling in Watermelon Suspension Cells

Glycinebetaine is an important non-toxic osmoprotectant, which is accumulated in higher plants under various stresses. The biosynthesis of glycinebetaine achieved via is a two-step oxidation from choline and betaine aldehyde, catalyzed by choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH), respectively. Up-regulated gene expression of BADH and CMO induced by stress is clearly observed, but the signal transduction is poorly understood. Here, glycinebetaine accumulation in response to osmotic stress and growth recovery induced by exogenous glycinebetaine were observed in a watermelon cell line. When tracing back to the genome sequence of watermelon, it shows that there exists only one member of ClCMO or ClBADH corresponding to glycinebetaine biosynthesis. Both genes harbor a CGTCA-motif in their promoter region which is involved in methyl jasmonate (MeJA)-responsiveness. Amongst MeJA, Ethephon, abscisic acid (ABA), and salicylic acid (SA), MeJA was most effective in gene inducing the expression of ClCMO and ClBADH, and the accumulation of glycinebetaine could also reach an amount comparable to that after osmotic stress by mannitol. Moreover, when ibuprofen (IBU), a JA biosynthesis inhibitor, was pre-perfused into the cells before osmotic stress, glycinebetaine accumulation was suppressed significantly. Interestingly, newly grown cells can keep a high content of glycinebetaine when they are sub-cultured from osmotic stressed cells. This study suggests that osmotic stress induced glycinebetaine biosynthesis occurs via JA signal transduction and not only plays a key role in osmotic stress resistance but also contributes to osmotic stress hardening.

Genome-wide expression profiling of leaves and roots of watermelon in response to low nitrogen

BACKGROUND

Nitrogen (N) is a key macronutrient required for plant growth and development. In this study, watermelon plants were grown under hydroponic conditions at 0.2 mM N, 4.5 mM N, and 9 mM N for 14 days.

RESULTS

Dry weight and photosynthetic assimilation at low N (0.2 mM) was reduced by 29 and 74% compared with high N (9 mM). The photochemical activity (Fv/Fm) was also reduced from 0.78 at high N to 0.71 at low N. The N concentration in the leaf, stem, and root of watermelon under low N conditions was reduced by 68, 104, and 108%, respectively compared with 9 mM N treatment after 14 days of N treatment. In the leaf tissues of watermelon grown under low N conditions, 9598 genes were differentially expressed, out of which 4533 genes (47.22%) were up-regulated whereas, 5065 genes (52.78%) were down-regulated compared with high N. Similarly in the root tissues, 3956 genes were differentially expressed, out of which 1605 genes were up-regulated (40.57%) and 2351 genes were down-regulated (59.43%), compared with high N. Our results suggest that leaf tissues are more sensitive to N deficiency compared with root tissues. The gene ontology (GO) analysis showed that the availability of N significantly affected 19 biological processes, 8 cell component metabolic pathways, and 3 molecular functions in the leaves; and 13 biological processes, 12 molecular functions, and 5 cell component metabolic pathways in the roots of watermelon. The low affinity nitrate transporters, high affinity nitrate transporters, ammonium transporters, genes related with nitrogen assimilation, and chlorophyll and photosynthesis were expressed differentially in response to low N. Three nitrate transporters (Cla010066, Cla009721, Cla012765) substantially responded to low nitrate supply in the root and leaf tissues. Additionally, a large number of transcription factors (1365) were involved in adaptation to low N availability. The major transcription factor families identified in this study includes MYB, AP2-EREBP, bHLH, C2H2 and NAC.

CONCLUSION

Candidate genes identified in this study for nitrate uptake and transport can be targeted and utilized for further studies in watermelon breeding and improvement programs to improve N uptake and utilization efficiency.

Chemical, sensory, and functional properties of whey-based popsicles manufactured with watermelon juice concentrated at different temperatures

The effects of the concentration of watermelon juice at different temperatures (45, 55, or 65 °C) on the physicochemical and sensory characteristics, antioxidant capacity, and volatile organic compounds (VOCs) of whey-based popsicles were investigated. Total phenolic content, lycopene, citrulline, VOCs, melting rate, instrumental colour, antioxidant capacity, and the sensory characteristics (hedonic test and free listing) were determined. The temperature led to a significant decrease in bioactive compounds (total phenolics, lycopene, and citrulline). The popsicle manufactured with reconstituted watermelon juice concentrated to 60 °Brix at 65 °C presented higher antioxidant capacity and was characterized by the presence of alcohols, aldehydes and ketones and presented a similar acceptance to the untreated popsicle (except for flavour). It is possible to combine whey and concentrated watermelon juice for the manufacture of bioactive-rich popsicles, using the concentration temperature of 65 °C as a suitable processing condition for potential industrial applications.