Watermelon Plants Research Articles

Effects of Watermelon Cropping Management on Soil Bacteria and Fungi Biodiversity

Watermelons grown in sandy soil are rich in trace elements, particularly selenium, and are therefore also known as selenium-rich sand watermelons. However, continuous watermelon cultivation in the same sandy field decreases soil fertility and degrades the ecosystem, ultimately resulting in low-quality watermelons. Introducing different crops into the crop pattern could alleviate the problems posed by continuous cropping. A field experiment was conducted to explore the effects of different crop patterns on soil microbial communities and soil properties via standard techniques. The results showed that 14,905 bacterial and 2150 fungal operational taxonomic units were obtained and assigned to eight bacterial and five fungal phyla, respectively. Soil bacterial communities primarily comprised Proteobacteria, Planctomycetes, Actinobacteria, and Acidobacteria, and the soil fungal community was dominated by Ascomycota, Chytridiomycota, and Basidiomycota. Different crop patterns had a significant effect on the Chao and ACE indexes of fungal communities in the soil. The rotation of six years of watermelon and one year of wheat had the highest richness indexes of all the rotations. Different crop patterns had significant effects on soil properties, such as organic matter (OM), total nitrogen (TN), total potassium (TK), available phosphorus (AP), available K, nitrate nitrogen (NN), and pH. The soil OM, TN, NN, and pH of six years of watermelon and one year of wheat cultivation were significantly higher than those of the other three crop patterns. In addition, the soil TK and AP of the continuous watermelon planting treatment were significantly higher than those of the other three crop patterns. Redundancy analysis results revealed many complex relationships between soil properties and soil bacterial or fungal communities. Employing different crop patterns plays an important role in the effective regulation of soil microbial diversity and properties.

Active Sugar Accumulation and Water Status of Watermelon Fruit Grown under Different Nutrient Concentrations in Hydroponic Culture

We investigated sugar (solute) accumulation in watermelon [Citrullus lanatus (Thunb.) Matsum. et Nakai] fruits at the immature stage. Watermelon plants were grown hydroponically in a nutrient solution with an electric conductivity (EC) of 1.2 S⋅m−1 (EC 1.2 regime); then, fruits were harvested 21 days after anthesis. The flesh of each fruit was divided into seven different parts to measure the sugar concentration and water status. The results indicated that the sugar concentration was higher in the center of the fruit flesh than in the other parts, such as around the pericarp. Moreover, the lowest osmotic potential was observed in the center of the fruit flesh, indicating solute accumulation. Concurrently, when the transport of photosynthates in the fruit was investigated using the 13CO2 isotope, the active solute accumulation in the center of the fruit flesh was observed, supporting the observed sugar accumulation in this part. Consequently, this active solute accumulation and distribution occurred in the center of the watermelon fruit, as demonstrated by the data of osmotic pressure and sugar concentration and supported by the observed active photosynthate accumulation. Additionally, we investigated these measurements by increasing the nutrient solution concentration 14 days after anthesis. As a result, fruit growth was slightly inhibited using the EC 3.0 regime, and 13C translocation was also inhibited in the fruit, especially in its center. Even though the sugar concentration and osmotic pressure of the fruit flesh were not clearly affected by high nutrient solution concentrations, the cell turgor of the central flesh of the fruit grown using the EC 2.0 and 3.0 regimes was lower than that of the fruit grown using the EC 1.2 regime. Treatments with higher nutrient concentrations might have negative effects on immature watermelon fruits.

Estado nutricional de melancia irrigada com água salobra em diferentes sistemas de plantio

ABSTRACT Watermelon is cultivated in practically all Brazilian states; however, there are still disagreements as to the best way to propagate it. In addition, the Northeast region, the main producing region in the country, is increasingly facing the scarcity of low-salinity water. Given this context, this study aimed to evaluate the morphophysiology and mineral contents of the watermelon crop subjected to irrigation water of different electrical conductivities, using seedlings or direct seeding. A randomized block experimental design with split plots was used, with four replications. The plot was formed by the electrical conductivities of the irrigation water (0.3, 1.5, 3.0, and 4.5 dS m-1) and the subplot by the planting methods - DS = direct seeding, TP1 = transplanting of the seedling produced with water of moderate salinity (1.5 dS m-1), and TP2 = transplanting of the seedling produced with water of low salinity (0.3 dS m-1). The highest biomass accumulation was obtained in the direct seeding method. Salt stress increases the intrinsic water use efficiency in watermelon plants. The TP1 and TP2 planting methods led to the highest contents of P and K in the leaf. The increase in the salinity level increases the content of S and reduces the content of Cu and Mn.

Exogenous Brassinosteroid Enhances Zinc tolerance by activating the Phenylpropanoid Biosynthesis pathway in Citrullus lanatus L

ABSTRACT Zinc (Zn) is an important element in plants, but over-accumulation of Zn is harmful. The phytohormone brassinosteroids (BRs) play a key role in regulating plant growth, development, and response to stress. However, the role of BRs in watermelon (Citrullus lanatus L.) under Zn stress, one of the most important horticultural crops, remains largely unknown. In this study, we revealed that 24-epibrassinolide (EBR), a bioactive BR enhanced Zn tolerance in watermelon plants, which was related to the EBR-induced increase in the fresh weight, chlorophyll content, and net photosynthetic rate (Pn) and decrease in the content of hydrogen peroxide (H2O2), malondialdehyde (MDA), and Zn in watermelon leaves. Through RNA deep sequencing (RNA-seq), 350 different expressed genes (DEG) were found to be involved in the response to Zn stress after EBR treatment, including 175 up-regulated DEGs and 175 down-regulated DEGs. The up-regulated DEGs were significantly enriched in ‘phenylpropanoid biosynthesis’ pathway (map00940) using KEGG enrichment analysis. The gene expression levels of PAL, 4CL, CCR, and CCoAOMT, key genes involved in phenylpropanoid pathway, were significantly induced after EBR treatment. In addition, compared with Zn stress alone, EBR treatment significantly promoted the activities of PAL, 4CL, and POD by 30.90%, 20.69%, and 47.28%, respectively, and increased the content of total phenolic compounds, total flavonoids, and lignin by 23.02%, 40.37%, and 29.26%, respectively. The present research indicates that EBR plays an active role in strengthening Zn tolerance, thus providing new insights into the mechanism of BRs enhancing heavy metal tolerance.

FonTup1 functions in growth, conidiogenesis and pathogenicity of Fusarium oxysporum f. sp. niveum through modulating the expression of the tricarboxylic acid cycle genes

The Tup1-Cyc8 complex is a highly conserved transcriptional corepressor that regulates intricate genetic network associated with various biological processes in fungi. Here, we report the role and mechanism of FonTup1 in regulating physiological processes and pathogenicity in watermelon Fusarium wilt fungus, Fusarium oxysporum f. sp. niveum (Fon). FonTup1 deletion impairs mycelial growth, asexual reproduction, and macroconidia morphology, but not macroconidial germination in Fon. The ΔFontup1 mutant exhibits altered tolerance to cell wall perturbing agent (congo red) and osmotic stressors (sorbitol or NaCl), but unchanged sensitivity to paraquat. The deletion of FonTup1 significantly decreases the pathogenicity of Fon toward watermelon plants through attenuating the ability to colonize and grow within the host. Transcriptome analysis revealed that FonTup1 regulates primary metabolic pathways, including the tricarboxylic acid (TCA) cycle, via altering the expression of corresponding genes. Downregulation of three malate dehydrogenase genes, FonMDH1–3, occurs in ΔFontup1, and disruption of FonMDH2 causes significant abnormalities in mycelial growth, conidiation, and virulence of Fon. These findings demonstrate that FonTup1, as a global transcriptional corepressor, plays crucial roles in different biological processes and pathogenicity of Fon through regulating various primary metabolic processes, including the TCA cycle. This study highlights the importance and molecular mechanism of the Tup1-Cyc8 complex in multiple basic biological processes and pathogenicity of phytopathogenic fungi.

Economic assessment of the use of growth regulators and water-soluble fertilizers in the Volgograd Volga region

Relevance. This article shows the research conducted by researchers from the agrotechnical department of the Bykovskaya melon breeding station from 2018 to 2020.Results. The data obtained make it possible to scientifically substantiate the most cost-effective methods and techniques for treating table watermelon plants to increase productivity in the Volgograd Trans-Volga region. Indicators of economic efficiency of production make it possible to compare the results of economic activity and reveal the productivity of the enterprise for this period in connection with an increase in the use of means of production and labor. In modern conditions of development of agricultural production, there is a need to develop new technologies adapted to the new conditions of land use. In connection with the sharp decline in recent years in the use of fertilizers, the problem arose of finding ways to maximize the use of the biological factor. To obtain stable yields, it is necessary to increase the adaptive capabilities of plants to extreme conditions in which gourds are grown in the zone of industrial melon growing in the Volgograd Trans-Volga region. One of them is the use of plant growth regulators and water-soluble fertilizers. One of the advantages of these drugs is their simplicity, variety of methods of their application and low cost. According to the cost-effectiveness data, it can be seen that the foliar treatment of table watermelon plants was the best option. In the first experiment, the Fitozont regulator, in the second, the water-soluble fertilizer Khakafos with one and a half norm (0.9), in the third experiment, the best results were shown by the variant with foliar treatment with a growth regulator in combination with the water-soluble fertilizer Vigor Forte + Agrovin Profi at a dosage of (0.05+0.5).

Paramyrothecium nigrum, causing leaf blight disease on watermelon in Iran

<i>Paramyrothecium nigrum</i>, causing leaf blight disease on watermelon in Iran

First Report of Watermelon Mosaic Virus Naturally Infecting Coriander (Coriandrum sativum) and causing a leaf mottling disease in California.

Watermelon mosaic virus (WMV, genus Potyvirus, family Potyviridae) is a species of considerable economic importance to cucurbit crops worldwide (Keinath et al. 2017). This virus has a wide host range that includes more than 170 plant species from 27 families (Dong et al. 2017; Lecoq et al. 2011). In 2018, leaves of coriander (Coriandrum sativum) plants in a student garden (C-SG) at UC Davis, and in a home garden in Davis, CA (C-Pet) (~1.1 miles apart) showed symptoms of light green mottling and crumpling. Symptomatic leaves from each location were weakly positive with the general potyvirus immunostrip test (Agdia, Elkhart, IN). In RT-PCR tests with total RNA extracts (RNeasy Plant Mini Kit Qiagen, Germantown, MD) of these leaves and the potyvirus degenerate primer pair CIFor/CIRev (Ha et al. 2008), the expected-size ~0.7 kb fragment was amplified. These fragments were gel-purified and sequenced, and a BLASTn search revealed highest identities of 91.6% (C-SG) and 97.9% (C-Pet) with the sequence of an isolate of WMV from watermelon in the U.S. (TX29, KU246036). Thus, these isolates are designated WMV-C-SG-18 and WMV-C-Pet-18. Mechanical inoculation experiments were next performed with sap prepared with symptomatic coriander leaf tissue in ice-cold 0.01 M phosphate buffer (pH 7.0) in a 1:4 wt/vol ratio. First, to obtain pure isolates, sap was inoculated onto celite-dusted leaves of Chenopodium quinoa plants (3-4 leaf stage). As expected for WMV, leaves inoculated with sap of each isolate developed chlorotic local lesions ~9 d post-inoculation (dpi) (Moreno et al. 2004). One lesion for each isolate was excised, ground in phosphate buffer, and the sap was mechanically inoculated onto leaves of Nicotiana benthamiana plants. By ~14 dpi, newly emerged leaves showed mild mottling and crumpling, and were weakly positive with the potyvirus immunostrip test. To confirm that these plants were only infected with WMV, total RNA was extracted from symptomatic leaves and used for high throughput sequencing (HTS) (Soltani et al. 2021) at the Foundation Plant Services at UC Davis. The HTS analyses revealed infection with only WMV, i.e., no other viral contigs were identified, and allowed for determination of the complete sequences (~10,000 nt) of WMV [US-CA-C-SG-18] and WMV [US-CA-C-Pet-18] with GenBank accession numbers: OM746964 and OM746965, respectively. Whole genome sequence comparisons revealed that the sequences are 99.0% identical, and 97.3% identical to the sequence of WMV TX29. Sap from symptomatic N. benthamiana leaves infected with each isolate was mechanical inoculated onto leaves of coriander plants (30-35 d old). Newly emerged leaves developed epinasty, crumpling and light green mottling by 14 dpi, and WMV infection was confirmed by RT-PCR with the WMV-specific primer pair WMV-UNI-1F and WMV-UNI-1R (Kim et al. 2019). Thus, Koch's postulates were fulfilled for this leaf mottling disease of coriander. Furthermore, the isolates from coriander induced stunting and distortion and mosaic in leaves of melon, pumpkin and squash plants by 7 dpi, whereas watermelon plants developed stunting and small leaves with mild mottling by 20 dpi. Similar results were obtained with sap prepared from infected coriander leaves. Thus, infected coriander plants are a potential inoculum source for cucurbits via several aphid vectors (Keinath et al. 2017). This is the first report of a mottle disease of coriander caused by WMV, and adds to the wide host range of the virus.

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.

Production of double haploid watermelon via maternal haploid induction.

Production of double haploid watermelon via maternal haploid induction.

Suppression of Fusarium Wilt in Watermelon by Bacillus amyloliquefaciens DHA55 through Extracellular Production of Antifungal Lipopeptides

Fusarium wilt caused by Fusarium oxysporum f. sp. niveum is one of the most devastating fungal diseases affecting watermelon (Citrullus lanatus L.). The present study aimed to identify potent antagonistic bacterial strains with substantial antifungal activity against F. oxysporum f. sp. niveum and to explore their potential for biocontrol of Fusarium wilt in watermelon. Out of 77 isolates from watermelon rhizosphere, six bacterial strains-namely, DHA4, DHA6, DHA10, DHA12, DHA41, and DHA55-exhibited significant antifungal activity against F. oxysporum f. sp. niveum, as well as other phytopathogenic fungi, including Didymella bryoniae, Sclerotinia sclerotiorum, Fusarium graminearum, and Rhizoctonia solani. These Gram-positive, rod-shaped, antagonistic bacterial strains were able to produce exo-enzymes (e.g., catalase, protease, and cellulase), siderophore, and indole-3-acetic acid and had the ability to solubilize phosphate. In greenhouse experiments, these antagonistic bacterial strains not only promoted plant growth but also suppressed Fusarium wilt in watermelon. Among these strains, DHA55 was the most effective, achieving the highest disease suppression of 74.9%. Strain DHA55 was identified as Bacillus amyloliquefaciens based on physiological, biochemical, and molecular characterization. B. amyloliquefaciens DHA55 produced various antifungal lipopeptides, including iturin, surfactin, and fengycin, that showed significant antifungal activities against F. oxysporum f. sp. niveum. Microscopic observations revealed that B. amyloliquefaciens DHA55 exhibited an inhibitory effect against F. oxysporum f. sp. niveum on the root surface of watermelon plants. These results demonstrate that B. amyloliquefaciens DHA55 can effectively promote plant growth and suppress the development of watermelon Fusarium wilt, providing a promising agent for the biocontrol of Fusarium wilt in watermelon.

Fusarium oxysporum f. sp. niveum Pumilio 1 Regulates Virulence on Watermelon through Interacting with the ARP2/3 Complex and Binding to an A-Rich Motif in the 3' UTR of Diverse Transcripts.

Fusarium oxysporum f. sp. niveum (Fon), a soilborne phytopathogenic fungus, causes watermelon Fusarium wilt, resulting in serious yield losses worldwide. However, the underlying molecular mechanism of Fon virulence is largely unknown. The present study investigated the biological functions of six FonPUFs, encoding RNA binding Pumilio proteins, and especially explored the molecular mechanism of FonPUF1 in Fon virulence. A series of phenotypic analyses indicated that FonPUFs have distinct but diverse functions in vegetative growth, asexual reproduction, macroconidia morphology, spore germination, cell wall, or abiotic stress response of Fon. Notably, the deletion of FonPUF1 attenuates Fon virulence by impairing the invasive growth and colonization ability inside the watermelon plants. FonPUF1 possesses RNA binding activity, and its biochemical activity and virulence function depend on the RNA recognition motif or Pumilio domains. FonPUF1 associates with the actin-related protein 2/3 (ARP2/3) complex by interacting with FonARC18, which is also required for Fon virulence and plays an important role in regulating mitochondrial functions, such as ATP generation and reactive oxygen species production. Transcriptomic profiling of ΔFonPUF1 identified a set of putative FonPUF1-dependent virulence-related genes in Fon, possessing a novel A-rich binding motif in the 3' untranslated region (UTR), indicating that FonPUF1 participates in additional mechanisms critical for Fon virulence. These findings highlight the functions and molecular mechanism of FonPUFs in Fon virulence. IMPORTANCE Fusarium oxysporum is a devastating plant-pathogenic fungus that causes vascular wilt disease in many economically important crops, including watermelon, worldwide. F. oxysporum f. sp. nievum (Fon) causes serious yield loss in watermelon production. However, the molecular mechanism of Fusarium wilt development by Fon remains largely unknown. Here, we demonstrate that six putative Pumilio proteins-encoding genes (FonPUFs) differentially operate diverse basic biological processes, including stress response, and that FonPUF1 is required for Fon virulence. Notably, FonPUF1 possesses RNA binding activity and associates with the actin-related protein 2/3 complex to control mitochondrial functions. Furthermore, FonPUF1 coordinates the expression of a set of putative virulence-related genes in Fon by binding to a novel A-rich motif present in the 3' UTR of a diverse set of target mRNAs. Our study disentangles the previously unexplored molecular mechanism involved in regulating Fon virulence, providing a possibility for the development of novel strategies for disease management.

First report of Watermelon crinkle leaf-associated virus 2 infecting watermelon (Citrullus lanatus) in Oklahoma.

Watermelon (Citrullus lanatus) is one of the major cucurbit crops in Oklahoma, which is grown on >1,200 acres. It contributes $16 million to the state's economy (Shrefler et al., 2017; NASS, 2022). During the 2021 growing season, virus-like symptoms on watermelon plants were observed in a grower's field in Blaine County, Oklahoma. These symptoms included mottling, crinkled leaf edges, and a unique yellow mosaic pattern (Fig. 1). Leaf tissue samples were randomly collected from nine plants and total RNA was extracted using Spectrum Plant Total RNA Kit (Sigma-Aldrich). Total RNA from one sample (named BL13) was subjected to high-throughput sequencing (HTS) on the NextSeq 500/550 High-Output kit v2.5 (Illumina, USA) at the genomic facility of Oklahoma State University. A total of 21,52,786 trimmed pair-end reads were assembled using CLC Genomics Workbench (v12.0.3) (Qiagen, Inc.) and subjected to BLASTn analysis. Of these, three contigs of 6,626 bp, 1,383 bp and 1,233 bp (average coverage 20,658X) showed 99% nucleotide (nt) sequence identity with RNA1 of a watermelon crinkle leaf-associated virus (WCLaV-2) isolate from Brazil (LC636073). The HTS data for BL13 samples also revealed three contigs of 263 pb, 567 bp and 1,066 bp that matched with cucumis melo crytpic virus isolate CmCV-HLI but was not confirmed by RT-PCR. The presence of WCLaV-2 in the BL13 sample was confirmed by RT-PCR using primers (RNA1-F: 5'-CAAAACGCCCATAAG AATAG-3'and RNA1-R: 5'- CTCCATTAATGAGAACTAGGAG-3') which amplified a 1.2 kb segment of the RNA1. The PCR product was confirmed on 1% agarose gel, cloned and three independent recombinant clones Sanger sequenced (Eurofins Genomics LLC, Louisville, KY, USA). The resulting consensus sequence (1.2 Kb) (ON453838) was subjected to a BLASTn search against the Genbank databases, resulting in 99.76% nt identity with WCLaV-2 RNA1 (Accession no. LC636073). Screening of the remaining eight symptomatic samples by RT-PCR revealed another positive sample (named BL7) for WCLaV-2. Consensus nt sequence (1.2 Kb) analysis for the virus isolate from the BL7 sample (Accession no. ON453839) shared 99.84% nt identities with WCLaV-2 RNA1 (LC636073). Total RNA from BL13 and BL7 samples, as well as the remaining seven samples, were tested against three major potyviruses (PRSV-W, WMV, and ZYMV) by multiplex RT-PCR (Rajbanshi & Ali, 2019). Both BL13 and BL7 samples were negative to all three potyviruses but the other eight samples were positive to one or two of the potyviruses. WCLaV-2 is a negative-sense ssRNA virus (family Phenuiviridae) and has been recently reported from watermelon in China (Xin et al., 2017) and Brazil (Maeda et al. 2022). In the United States, it has been reported from Florida (Hendrick et al., 2021), Georgia (Adeleke et al., 2022), and Texas (Hernandez et al., 2021). The mode of transmission of WCLaV-2 and its direct effect on watermelon fruit is not known (Xin et al., 2017; Maeda et al., 2022). Our results report for the first time the occurrence of WCLaV-2 infecting watermelon naturally in Oklahoma and show a further potential threat to watermelon production in the State. Further studies are needed to determine the incidence of WCLaV-2 in other counties of Oklahoma.

Predatory mites (Acari: Phytoseiidae) on Vegetable Fields in Diyarbakır, Elazığ and Muş Provinces, Turkey

This study was conducted to identify predatory mite species on pepper, tomato, bean, cucumber, pumpkin, watermelon, melon, and eggplant plant leaves between 2018 and 2019 Diyarbakır, Elazığ, and Muş provinces. 1063 plant samples were collected and 676 of these samples which were observed with mite species. Predatory mite species were identified belonging to the Phytoseiidae family, which constitues 10.65% of 676 plant samples. The identified predatory mites were listed as Neoseiulus barkeri Hughes, Neoseiulus bicaudus Wainstein, Neoseiulus marginatus (Wainstein), Neoseiulus zwoelferi (Dosse), Neoseiulus sp., Phytoseius finitimus Ribaga, Proprioseiopsis messor (Wainstein), Typhlodromus (Anthoseius) bagdasarjani Wainstein and Arutunjan, Typhlodromus (Anthoseius) rhenanus (Oudemans) and Typhlodromus (Anthoseius) recki (Wainstein) in this study. Neoseiulus barkeri wasdetected as the most common species with 57.44% total number of individuals in the three provinces. The most detected host plants were Cucumis sativus L. at 60.59%; Solanum melongena L. (Family name) at 15.94% while the least detected vegetable was Capsicum annuum L. at 1.06% percentages.

Watermelon Root Exudates Enhance Root Colonization of Bacillus amyloliquefaciens TR2.

Bacillus amyloliquefaciens TR2, one of plant growth-promoting rhizobacteria (PGPR), is capable of colonizing plant roots in a large population size. However, the interaction of watermelon root exudates and colonization of the strain TR2 has not yet been clearly elucidated. In this investigation, we demonstrated that B. amyloliquefaciens TR2 promoted watermelon plants growth and exhibited biocontrol efficacy against watermelon Fusarium wilt under greenhouse conditions. Collected watermelon root exudates significantly induced chemotaxis, swarming motility, and biofilm formation of the strain TR2. We also tested the components of root exudates (organic acids: malic acid, citric acid, succinic acid, and fumaric acid; amino acids: methionine, glutamic acid, alanine, and aspartic acid; phenolic acid: benzoic acid) and the results showed that a majority of these compounds could promote chemotactic response, swarming motility, and biofilm formation in a different degree. Benzoic acid induced the strongest chemotactic response; however, the swarming motility and biofilm formation of the strain TR2 were maximumly enhanced by supplement of fumaric acid and glutamic acid, respectively. In addition, the root colonization examination indicated that the population of B. amyloliquefaciens TR2 colonized on watermelon root surfaces was dramatically increased by adding concentrated watermelon root exudates. In summary, our studies provide evidence suggesting that root exudates are important for colonization of B. amyloliquefaciens TR2 on plant roots and help us to understand the interaction between plants and beneficial bacteria.

First Report of Lasiodiplodia brasiliensis Causing Root Rot on Watermelon in Brazil.

Watermelon (Citrullus lanatus (Thumb.) Matsum. & Nakai) is an important crop in Brazil both for export and domestic consumption. In October 2019, watermelon plants showing decline and root rot symptoms were surveyed in 16 commercial fields in Baraúna's municipality (Rio Grande do Norte, Brazil). The disease prevalence was 12.5%, and the average incidence was 5%. Affected root segments were cut into small pieces and surface-disinfected with 70% ethyl alcohol and 1.5 % NaOCl for 1 and 2 min, respectively. Tissues were plated onto potato dextrose agar (PDA) and incubated at 25°C for 7 days. Fungal colonies developed from the infected tissues were dark or greyish, and pure cultures were obtained by hyphal tip isolation technique. Six fungal isolates with the same morphology were obtained. Two of them were selected for morphological and molecular characterization (CFC-1123 and CFC-1124). Isolates grew rapidly in PDA, covering the entire surface of the Petri dishes within 3 days. The aerial mycelium was initially white, turning dark greenish-gray after 4 to 5 days of incubation at 25°C in the dark. Isolates produced pycnidia and conidia in water-agar medium with sterilized pine needles after 30 days of incubation at 25°C under near-UV light. The conidia were initially hyaline and brown with central transverse septum and longitudinal streaks when mature. Conidia were ellipsoid to oval (22.83 ± 3.1 µm long and 11.58 ± 1.5 µm wide). Based on morphological features, the isolates were initially identified as Lasiodiplodia sp. (Phillips et al. 2013). To confirm the identification, genomic DNA was extracted and the internal transcribed spacer (ITS) region as well as fragments of the translation elongation factor 1-α (TEF) and β-tubulin 2 (TUB) genes were amplified using the primer pairs ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Carbone and Kohn 1999) and Bt2a/Bt2b (Glass and Donaldson 1995), respectively. The sequences were deposited in GenBank under accession numbers OL841380, OL865376 and OL890691 for CFC-1123, and OL841381, OL865377 and OL890692 for CFC-1124. Maximum likelihood phylogenetic analysis of the concatenated sequences of ITS, TEF and TUB gene regions of some reference sequences and ex-types of Lasiodiplodia spp. was performed. Phylogenetic analysis revealed that the isolates grouped in the L. brasiliensis clade (Netto et al. 2014) with 80/79% of bootstrap. The isolates were deposited in the Culture Collection of Phytopathogenic Fungi from Cariri (CFC) at the Universidade Federal do Cariri (Crato, Brazil). Pathogenicity of the two isolates was determined using colonized wheat grains as inoculum source. One watermelon seed (cv. Crimson Sweet) was placed in a sterile plastic pot (500-mL) filled with 6 cm layer of a substrate composed of soil and Tropstrato® (5:1 w/w). Three wheat grains (50 mg) colonized with each isolate were placed 10 mm above the seed and covered with the substrate. Control pots were inoculated only with sterile wheat grains. There were five replicates for each isolate. The pots with seedlings were maintained in a greenhouse at 28 ± 2°C under natural light conditions. The inoculated seedlings showed poor growth, withering and drying leaves 45 days after inoculation (DAI), and subsequently root rot symptoms and death at 60 DAI. Control seedlings remained asymptomatic. The pathogen was re-isolated from all inoculated seedlings and identified by conidia morphology to fulfill Koch's postulates. Lasiodiplodia brasiliensis has been reported to cause postharvest rot and gummosis of watermelon (Farr and Rossman 2022). However, to our knowledge, this is the first report of watermelon decline caused by this fungus in Brazil and worldwide. This finding must be considered for developing efficient control strategies for the disease.

Evaluating the hologenome concept by analyzing the root-endosphere microbiota of chimeric plants

The hologenome concept considers the entity formed by a host and its microbiota, the holobiont, as new level of hierarchical organization subject to neutral and selective forces. We used grafted plants to formally evaluate the hologenome concept. We analyzed the root-endosphere microbiota of two independent watermelon and grapevine plant systems, including ungrafted and reciprocal-grafting combinations. Grafted and ungrafted hosts harbor markedly different microbiota compositions. Furthermore, the results indicate a non-random assembly of bacterial communities inhabiting the root endosphere of chimeric plants with interactive effect of both the rootstock and scion on the recruitment of microorganisms. Because chimeric plants did not have a random microbiota, the null hypothesis that holobionts assemble randomly and hologenome concept is an intellectual construction only can be rejected. The study supports the relevance of hologenome as biological level of organization and opens new avenues for a better fundamental understanding of plants as holobionts.

Giving Some Concentrations of Ethephon on The Growth and Yield of Watermelon (Citrullus Lanatus (Thunb.) Matsum. &amp; Nakai.)

Watermelon (Citrullus lanatus (Thunb.) Matsum. &amp; Nakai.) is one of the horticultural commodities that have a fairly high economic value. Watermelon plants are more dominant in producing male flowers than female flowers. Therefore it is necessary to be able to change the sexual expression of watermelon flowers. One of the efforts that can be made to increase production watermelon is by administering the growth regulating agent ethepon. This study aims to find the best concentration of ethepon on watermelon growth and yield. This study used a randomized block design (RBD) consisting of 5 treatments and repeated 4 times. The treatment given was giving the concentration of ethepon which consisted of 5 levels, namely control (0 ppm), 100 ppm, 200 ppm, 300 ppm and 400 ppm. The parameters observed were plant length, number of leaves, when the first male flower appeared, when the first female flower appeared, the number of male flowers, the number of female flowers, the number of fruit planted, the weight of fruit planted and the length of the fruit. The results of research that have been carried out show that the application of ethepon with a concentration of 100 ppm is the best concentration in increasing when the first male flowers appear, the number of male flowers, the number of female flowers, the number of fruits per plant and the weight of fruit per plant.

Bacillus altitudinis-Stabilized Multifarious Copper Nanoparticles Prevent Bacterial Fruit Blotch in Watermelon (Citrullus lanatus L.): Direct Pathogen Inhibition, In Planta Particles Accumulation, and Host Stomatal Immunity Modulation.

The nano-enabled crop protecting agents have been emerging as a cost-effective, eco-friendly, and sustainable alternative to conventional chemical pesticides. Here, the antibacterial activity and disease-suppressive potential of biogenic copper nanoparticles (bio-CuNPs) against bacterial fruit blotch (BFB), caused by Acidovorax citrulli (Ac), in watermelon (Citrullus lanatus L.) is discussed. CuNPs are extracellularly biosynthesized using a locally isolated bacterial strainBacillus altitudinis WM-2/2, and have spherical shapes of 29.11-78.56nm. Various metabolites, such as alcoholic compounds, carboxylic acids, alkenes, aromatic amines, and halo compounds, stabilize bio-CuNPs. Foliar application of bio-CuNPs increases the Cu accumulation in shoots/roots (66%/27%), and promotes the growth performance of watermelon plants by improving fresh/dry weight (36%/39%), through triggering various imperative physiological and biochemical processes. Importantly, bio-CuNPs at 100 µg mL-1 significantly suppress watermelon BFB through balancing reactive oxygen species system, improving photosynthesis capacity, and modulating stomatal immunity. Bio-CuNPs show obvious antibacterial activity against Ac by inducing oxidative stress, biofilm inhibition, and cellular integrity disruption. These findings demonstrate that bio-CuNPs can suppress watermelon BFB through direct antibacterial activity and induction of active immune response in watermelon plants, and highlight the value of this approach as a powerful tool to increase agricultural production and alleviate food insecurity.

Irrigation with saline water in the cultivation of mini watermelon under phosphate fertilization.

The objective of this study was to evaluate the water status, photosynthetic pigments, and photochemical efficiency of mini watermelon plants under salt stress and phosphate fertilization. The experiment was conducted in pots under greenhouse conditions in Pombal, PB, Brazil. The experimental design used was randomized blocks in a 5 × 4 factorial scheme, with five levels of electrical conductivity of irrigation water - ECw (0.3, 1.3, 2.3, 3.3, and 4.3 dS m-1) and four doses of phosphorus (60, 80, 100, and 120% of the recommendation), with three replicates. The relative water content in the tissues decreased with the increase in ECw levels in all phosphorus doses, with decreases of 7.05, 7.81 and 8.83% per unit increase in ECw, in plants fertilized with 80, 100 and 120% P2O5. On the other hand, ECw levels increased electrolyte leakage, regardless of phosphorus doses of the recommendation. The synthesis of photosynthetic pigments and the quantum efficiency of photosystem II were inhibited by increasing water salinity from 0.3 dS m-1 in plants grown under phosphorus doses above 60% of the recommendation. Water salinity from 0.3 dS m-1 reduced chlorophyll b contents, initial, maximum, and variable fluorescence of mini watermelon plants, with a decrease of 11.86, 4.51, 4.53, and 4.54% per unit increment of ECw, respectively.