Watermelon Plants Research Articles

COMMUNICATION FACTORS AFFECTING THE ADOPTION OF MODERN AGRICULTURAL PRODUCTION TECHNOLOGY

This study was entitled Communication Factors Affecting the Adoption of Modern Agricultural Production Technology. This paper evaluates the communication factors affecting the adoption of modern practices on watermelon production in Quezon, Nueva Ecija Province, Philippines. Data were obtained from randomly selected 77 watermelon producers with the aid of a structured questionnaire. Data were analyzed using various descriptive statistical techniques and correlation analysis for getting meaningful results. The findings portray that 31.2% of the respondents are in the range of 48-53 years which is the active age range. The mean age of the respondents was 50 years. It showed that 100% of the respondents are male and married, and 54.5% of them reached and completed high school. It was also revealed that 42.9% of the producers have an annual income that ranges from 50,000-100,000 pesos, and 51.9% of them has 1 hectare of their land. Finding also revealed that 36% of the respondents have the farming experience that ranges from 10-20 years. The average years spent in farming is around 18 years. Major findings revealed that the respondents’ communication media sources are leaflets and flyers, in print; television, in broadcast; and their colleagues, in interpersonal. The production practices adopted mainly by the producers are modern watermelon variety selection, land preparation and planting, fertilization, water management, weed management, pests and diseases management, and harvesting. Among all practices, ‘fertilization’, ‘weed management’, ‘pests and diseases management’, and ‘harvesting’ are the highest, and ‘modern watermelon variety selection’ is the lowest. The overall mean adoption score is 3.90. Finally, it can say that the communication factor that affects the adoption of modern practices on watermelon production is the message being received.

Microbial assembly and association network in watermelon rhizosphere after soil fumigation for Fusarium wilt control

Soil fumigation is an effective method to control soil-borne diseases like Fusarium wilt, however the processes and mechanisms driving microbial community reestablishment and pathogen suppression in the rhizosphere after fumigation remain poorly understood. In this study, we examined the dynamics of the rhizosphere microbiome and microbial network associations across different watermelon development stages and plant statuses (i.e. healthy and dead) after soil fumigation and organic fertilizer (OF) application in plastic shelters with Fusarium oxysporum f. sp. niveum (FON) heavily infected. Our results showed that fumigation treatments significantly reduced Fusarium wilt disease incidence and pathogen abundance, meanwhile, decreased soil microbial metabolic activity, fungal biomass and diversity. Bacterial community recovered from fumigation suppression in a short period, while fungal suppression was longer lasting, resulting in decreased fungi to actinomycetes (F/A) and fungi to bacteria (F/B) ratios in PLFA profiles. We further found some bacterial families, such as Actinospicaceae within Actinobacteria, Haliangiaceae, Rhizobiaceae and uncultured Rhodospirillales within Proteobacteria, Sporolactobacillaceae and Limnochordaceae within Firmicutes were greatly enriched after fumigation and might potentially contribute to pathogen suppression. The fumigation treatments significantly reduced microbial network complexity and the percentage of fungal nodes in comparison to un-fumigated control treatment. In contrast, a more complex microbial network was observed in the rhizosphere soil of healthy plants than that in the soil surrounding dead plant roots within fumigation treatments. Furthermore, healthy plant rhizosphere significantly enriched potential beneficial and nitrogen cycle-related bacterial phyla like Gemmatimonadetes, Verrucomicrobia, and Nitrospirae. More interestingly, Fusarium were markedly enriched in the rhizosphere soil of healthy plants and mainly represented by non-FON Fusarium like F. verticillioides and F. solani, implying a potential niche competition between FON and nonpathogenic Fusarium species in the rhizosphere of healthy watermelon. Taken together, our results provide vital information on the reconstruction of microbial communities and potential interactions between plant and its beneficial consortium after fumigation, which is instructive to develop more systematic strategies through targeting both beneficial and pathogen-similar taxa to improve disease control and soil suppression.

Productive potential of watermelon under different plant spacings in the semi-arid region of Brazil

This study aimed to evaluate the growth and development of watermelon plants under different plant spacings in the Semi-arid region of Brazil. A randomized block experimental design was used with four treatments and eight replications. Data were submitted to analysis of variance and the Tukey test. The treatments were composed by the following spacings: T1: 3.0 x 0.8 m; T2: 3.0 x 0.6 m; T3: 2.0 x 0.8 m and T4: 2.0 x 0.6 m (spacings between rows and between plants, respectively). The plant length, number of leaves, stem diameter, leaf area, number of flowers, number of fruits per plant, average fruit weight, total fruit production, number of commercial fruits, average weight of commercial fruits, total weight of commercial fruits and percentage of commercial fruits were evaluated in this study. There was a significant difference in the growth traits: stem diameter and leaf area at 30 days after sowing (DAS), and plant length, stem diameter and number of leaves at 60 DAS, with no significant statistical difference in the remaining days and nor for the number of flowers. The watermelon plants showed adequate vegetative and productive development at the 2.0 x 0.8 m plant spacing in the edaphoclimatic conditions of the semi-arid region under study. This spacing is well suited to small producers in the semi-arid region, which are dependent on agriculture with small areas and can obtain good productivity with no need to use larger areas due to spacing

Assessment of the Current Status of Potyviruses in Watermelon and Pumpkin Crops in Spain: Epidemiological Impact of Cultivated Plants and Mixed Infections.

Viral infections on cucurbit plants cause substantial quality and yield losses on their crops. The diseased plants can often be infected by multiple viruses, and their epidemiology may depend, in addition to the agro-ecological management practices, on the combination of these viral infections. Watermelon mosaic virus (WMV) is one of the most prevalent viruses in cucurbit crops, and Moroccan watermelon mosaic virus (MWMV) emerged as a related species that threatens these crops. The occurrence of WMV and MWMV was monitored in a total of 196 apical-leaf samples of watermelon and pumpkin plants that displayed mosaic symptoms. The samples were collected from 49 fields in three major cucurbit-producing areas in Spain (Castilla La-Mancha, Alicante, and Murcia) for three consecutive (2018–2020) seasons. A molecular hybridization dot-blot method revealed that WMV was mainly (53%) found in both cultivated plants, with an unadvertised occurrence of MWMV. To determine the extent of cultivated plant species and mixed infections on viral dynamics, two infectious cDNA clones were constructed from a WMV isolate (MeWM7), and an MWMV isolate (ZuM10). Based on the full-length genomes, both isolates were grouped phylogenetically with the Emergent and European clades, respectively. Five-cucurbit plant species were infected steadily with either WMV or MWMV cDNA clones, showing variations on symptom expressions. Furthermore, the viral load varied depending on the plant species and infection type. In single infections, the WMV isolate showed a higher viral load than the MWMV isolate in melon and pumpkin, and MWMV only showed higher viral load than the WMV isolate in zucchini plants. However, in mixed infections, the viral load of the WMV isolate was greater than MWMV isolate in melon, watermelon and zucchini, whereas MWMV isolate was markedly reduced in zucchini. These results suggest that the impaired distribution of MWMV in cucurbit crops may be due to the cultivated plant species, in addition to the high prevalence of WMV.

The OPRgene family in watermelon: Genome-wide identification and expression profiling under hormone treatments and root-knot nematode infection.

The enzyme 12-oxo-phytodienoic acid reductase (OPR) is important in the jasmonic acid (JA) biosynthesis pathway and thus plays a vital role in plant defence. However, systematic and comprehensive analyses of OPR genes in watermelon and their roles in defence responses are extremely limited. The physicochemical properties, phylogenetic tree, gene structure and cis-acting elements of watermelon OPR genes were analysed using bioinformatics, and qRT-PCR and RNA-Seq were applied to assay expression of OPR genes in watermelon. A total of five OPR family genes were identified in watermelon, which were unevenly distributed across the four chromosomes. Phylogenetic analysis assigned OPR members from different plant species to five subfamilies (OPRI-OPRV). The motif compositions of OPR members were relatively conserved. Expression analysis using qRT-PCR revealed that ClOPR genes, except for ClOPR5, were highly expressed in the flower and fruit. RNA-seq analysis showed that the ClOPR genes had different expression patterns during flesh and rind development. Furthermore, the ClOPR genes, particularly ClOPR2 and ClOPR4, were significantly upregulated by exogenous JA, salicylic acid (SA) and ethylene (ET) treatments. In addition, red light induced expression of ClOPR2 and ClOPR4 in leaves and roots of root-knot nematode (RKN)-infected watermelon plants, suggesting their involvement in red light-induced defence against RKN. These results provide a theoretical basis for elucidating the diverse functions of OPR family genes in watermelon.

First Report of Macrophomina phaseolina, Fusarium brachygibbosum, and Lasiodiplodia theobromae Causing Fungal Watermelon Vine Decline in Southwest and West-Central Florida

Wilt and vine decline symptoms were observed on watermelon plants in Glades and Hardee Counties in Florida in spring 2017 that resembled viral watermelon vine decline caused by squash vein yellowing virus (SqVYV). When no SqVYV was detected, greenhouse studies and morphological and molecular analyses revealed three fungal pathogens, Macrophomina phaseolina, Fusarium brachygibbosum, and Lasiodiplodia theobromae, that were not previously reported on watermelon in Florida. A previously reported oomycete, Pythium spinosum, was also detected in some, but not all, isolations and when applied independently resulted in disease incidence that was comparable to the untreated check, ruling it out as a primary causal agent of the symptoms observed in the field. In one of three experiments, seedlings inoculated with a combination of M. phaseolina, F. brachygibbosum, and P. spinosum suffered the highest disease severity based on AUDPC values. In another experiment, seedlings inoculated with F. brachygibbosum exhibited the most severe symptoms and rapid disease development following inoculation. When seeds were inoculated with either a single or a combination of the isolated fungi, those inoculated with L. theobromae resulted in seedlings with the greatest disease severity. This is the first report of these three fungal pathogens on watermelon in Florida.

SUPEROXIDE DISMUTASE FAMILY GENES IN WATERMELON AND THEIR RESPONSES TO DIFFERENT ABIOTIC STRESSES

<List> <ListItem><ItemContent> • A total of 8 <i>SOD</i> genes from watermelon were identified and bioinformatically analyzed. </ItemContent></ListItem> <ListItem><ItemContent> • The SOD proteins from watermelon and other different plant species can be classified into five groups consistent with their metal cofactors. </ItemContent></ListItem> <ListItem><ItemContent> • <i>ClSOD</i> genes exhibited distinctive tissue-specific and abiotic stress responsive expression patterns. </ItemContent></ListItem></List> Superoxide dismutase (SOD) is an important enzyme in the antioxidant system of plants and plays a vital role in stress responses by maintaining the dynamic balance of reactive oxygen species (ROS) concentrations. Genome-wide analysis of the <i>SOD</i> gene family in various plant species has been conducted but little is known about this gene family in watermelon (<i>Citrullus lanatus</i>). Here, eight <i>SOD</i> genes were identified in the watermelon genome and are designated <i>ClCSD1-5</i>, <i>ClFSD1-2</i> and <i>ClMSD</i> according to their metal cofactors. Phylogenetic analysis shows that SOD proteins from various plant species can be classified into five groups and members in the same group possess the same metal cofactor and similar subcellular localizations. Expression analysis of the <i>ClSOD</i> genes indicates that they had tissue-specific expression patterns with high expression in different tissues including the leaves, flowers and fruit. In addition, the expression of <i>ClSOD</i> genes differed appreciably under salinity, drought and abscisic acid (ABA) treatments, indicating that they may be involved in ROS scavenging under different abiotic stresses via an ABA-dependent signaling pathway. These results lay the foundation for elucidating the function of <i>ClSOD</i> genes in stress tolerance and fruit development in watermelon.

Sistem Pakar Dengan Metode Forward Chaining untuk Diagnosis Penyakit dan Hama Tanaman Semangka

Watermelon crops are in demand by farmers to cultivate. Diseases and Pests are not separated from watermelon crops experienced by farmers. To overcome this, farmers rely solely on rough living and getting information from others, this is ineffective because watermelon plant experts are very limited. An expert system is the solution to the limitations of an expert in their field. In this expert system use advanced chain methods and website-based applications. This expert system can be accessed online for users who need information, consultation of diseases and pests on watermelon plants. The expert system will diagnose the symptoms that will be answered by the user of the application and will produce conclusions along with solutions from diseases and pests of watermelon plants. With expert limitations online system is no longer an obstacle for watermelon plant farmers. Information and consultation of diseases and pests of watermelon plants biased online without having to meet with experts.

Sistem Pakar dengan Metode Forward Chaining untuk Diagnosis Penyakit dan Hama Tanaman Semangka

Watermelon crops are in demand by farmers to cultivate. Diseases and Pests are not separated from watermelon crops experienced by farmers. To overcome this, farmers rely solely on rough living and getting information from others, this is ineffective because watermelon plant experts are very limited. An expert system is the solution to the limitations of an expert in their field. In this expert system use advanced chain methods and website-based applications. This expert system can be accessed online for users who need information, consultation of diseases and pests on watermelon plants. The expert system will diagnose the symptoms that will be answered by the user of the application and will produce conclusions along with solutions from diseases and pests of watermelon plants. With expert limitations online system is no longer an obstacle for watermelon plant farmers. Information and consultation of diseases and pests of watermelon plants biased online without having to meet with experts.

EVALUATION OF UTILIZING INTEGRATED MANAGEMENT AS A SUBSTITUTED FOR THE BIOLOGICAL CONTROL TO CONTROL THE TWO SPOTTED SPIDER MITE, TETRANYCHUS URTICAE IN THE OPEN FIELDS IN EGYPT

Neoseiulus californicus is considered a promising agent for successful controlling the two spotted spider mite, Tetranychus urticae Koch. Vertimec, in selective doses, used to reduce the number of the two-spotted spider mite population withoutaffecting the survival of the predator. An open area was selected in El-Mahala district, El-Gharbia governorate to evaluate the utilizing of Vertimec followed by releasing N. californicus to control the population number of the two-spotted spider mite during unsuitable weather conditions for N. californicus, and activating the role of N. californicus to suppress the population number of T. urticae. An open area divided into two equal areas. The first area was allocated without Vertimec treatment and the second area was left for Vertimec treatment. The two areas are cultivated watermelon variety Sikata. The results obtained from releasing the predatory mite, N. californicus did not provide an advantage to prevent the two-spotted spider mite, T. urticae from exceeding the economic threshold level and subsequently deteriorated watermelon plant. In addition, the results obtained from spraying Vertimic pesticide before releasing the predatory mite N. californicus and duplicate the release of N. californicus was better of that obtained by releasing the predatory mite without using Vertimic in terms of suppressing the two-spotted spider mite, T. urticae.

Cucurbit leaf crumple virus (CuLCrV) associated to watermelon disease in Campeche state, Mexico.

An annual recurrent disease causing yield reduction in cultivated watermelon (Citrullus lanatus) was documented by the growers in different farms of Campeche state, Mexico. In April 2019 and March 2020 open field grown watermelon plants showed symptoms such as leaf curling, crumpling, and leaf basal or apical necrosis (Figure S1), with an incidence ranging from 30 up to 80%. These plants also presented high populations of whitefly, especially in the most affected fields. In order to identify the causal agent of the disease, a total of 22 symptomatic watermelon plants were collected in four locations from Campeche state. Total nucleic acids (DNA and RNA) were extracted from these leaf samples. Initially, RT-PCR analysis was performed with specific primers (Table S1) for cucurbit-infecting Crinivirus transmitted by whitefly but the expected size PCR product for those viruses was not amplified in any of these samples. To investigate the presence of cucurbit-infecting begomoviruses, PCR was performed by using specific primers for those begomoviruses reported in Mexico and north/central America including Squash leaf curl virus (SLCV), Watermelon chlorotic stunt virus (WmCSV), Melon chlorotic leaf curl virus (MCLCuV), and Cucurbit leaf crumple virus (CuLCrV) (Table S1). Only the expected amplicon size of ~1089 bp for CuLCrV was amplified from DNA extracts from all 22 watermelon samples, suggesting a single cucurbit-associated virus. The putative complete genome of the CuLCrV Campeche isolate was amplified by circular DNA enrichment using a Rolling Circle Amplification (RCA) procedure from two representative samples, followed by enzymatic digestion using BamHI, EcoRI, KpnI, and SacI enzymes (Inoue-Nagata et al., 2004). Expected linearized full-length viral components (~2.7 kb) were obtained with EcoRI and SacI, and both products, from one selected sample, were cloned in to pGreen0029 vector and were fully sequenced. Sequence analysis of the EcoRI clone, designated as LV2019Camp_A (deposited in GenBank accession no. MW273384) revealed the highest identity of 97.52% to CuLCrV DNA-A isolate Baja California Sur isolate (GeneBank accession no. MN625831.1), whereas the KpnI clone, designated as LV2019Camp_B (deposited in GenBank accession no. MW273385), shared 94.87% identity with DNA B of CuLCrV isolate Arizona (GeneBank accession no. AF327559.1). Subsequently, CuLCrV isolate Campeche-derived agroinfectious clone, was obtained by constructing a partial dimeric tandem repeat of both DNA-A and DNA-B components (Bang et al., 2014). Twelve watermelon plants were agroinfiltrated with the infectious clone at the fourth true leaf stage, resulting in symptomatic plants (11/12) exhibiting leaf yellowing, curling, and crumpling 15 days after agroinfiltrated (Figure S1), and CuLCrV infection was confirmed by PCR specific detection using DNA extract from non-inoculated leaves. Previously CuLCrV has been detected in the USA (Arizona, Texas, California, Florida, South Carolina, and Georgia), and north Mexico (Coahuila) infecting cucurbits including squash, cucumber, cantaloupe, pumpkin, and watermelon (Brown et al., 2000., Keinath et al., 2018), in both single and mixed infection with other whitefly transmitted RNA viruses (CYSDV, genera Crinivirus), and DNA viruses (SLCV, genera Begomovirus) (Kuo et al., 2007). To our knowledge, this is the first report of CuLCrV infecting a cucurbit crop in the Campeche state from the Yucatán peninsula, in Mexico.

Pathogen Infection and Host-Resistance Interactively Affect Root-Associated Fungal Communities in Watermelon.

Interactions of pathogen infection, host plant resistance, and fungal communities are poorly understood. Although the use of resistant watermelon cultivars is an effective control measure of watermelon wilt disease, fungal communities may also have significant effects on the development of the soil-borne pathogen complexes. We characterized the root and rhizosphere fungal communities associated with healthy and diseased watermelons of three different cultivars with different susceptibilities toward wilt disease by paired-end Illumina MiSeq sequencing. Thirty watermelon plants including highly wilt-resistant, moderately resistant, and susceptible cultivars were collected from a greenhouse, half of which showing clear wilt symptoms and the other half with no symptoms. Patterns of watermelon wilt disease and the response of the fungal communities varied among the three cultivars. The amount of the pathogen Fusarium oxysporum f. sp. niveum was higher in diseased root and rhizosphere samples, particularly in the susceptible cultivar, and was significantly positively correlated with the disease index of Fusarium wilt. Plant health had significant effects on root-associated fungal communities, whereas only the highly resistant cultivar had significant effects only on the rhizosphere fungal communities. Co-occurrence networks revealed a higher complexity of fungal communities in the symptom-free roots compared to diseased roots. In addition, networks from roots of the highly resistant plants showing symptoms had a higher complexity compared to the susceptible cultivars. Keystone species were identified for the plants with different symptom severity and the different cultivars in the root and rhizosphere, such as Fusarium oxysporum, Monosporascus cannonballus, and Mortierella alpina. Overall, the most important factor determining fungal communities in the roots was plant symptom severity, whereas in the rhizosphere, plant genotype was the most important factor determining fungal communities.

Research Progress of Regulated Deficit Irrigation Technology in Watermelon (Citrullus lanatus) Cultivation

Regulated deficit irrigation (RDI) technology provides a new way to solve the contradiction between agricultural water supply-demand and the shortage of water resources. The paper briefly introduces the concept of RDI technology and its water-saving mechanism, and then describes the specific application of RDI technology in watermelon planting and the impact of RDI on watermelon growth dynamics, photosynthetic physiological characteristics, water productivity, and quality. It is concluded that timely and appropriate RDI of watermelon can not only improve the quality of the watermelon and maintain or even increase the yield, but also increase the water use efficiency (WUE). Finally, the main problems existing in the watermelon RDI technology are summarized, and its application is prospected, in order to obtain new results in the follow-up research of watermelon RDI.

Response of watermelon (Citrullus lanatus) to plant compost, kitchen wastes and chicken manure composted with PGPR microbes as Bio-Organic fertilizers

Field experiments in two different locations were conducted at the Faculty of Agriculture, (Saba-Basha) - Alexandria University, during summer season of 2018/2019. The main objective was to investigate the effectiveness of different combinations of compost types on yield and quality of watermelon (cv.Skata F1 hyprid). The study was conducted with randomized complete block design with three replicates. Seven treatments were carried out in this investigation i.e. (T1-Jojoba leaves compost, T2-Compost A,T3-Compost B, T4-Compost C, T5-Compost D, T6-Compost E and T7- Control treatment (R100% NPK). The effects of the treatments on the growth and yield of watermelon were determined. Application of different types of compost increased the vine length, number of leaves, number of branches, number of fruits/plant, average fruit weight, fruit length, fruit diameter, mineral contents of leaves and fruits and improved total fruit yield. The obtained results indicated generally that application of chicken manure (T6) produced the highest values of all yield and its components and chemical composition of watermelon plants during both locations compared with the inorganic treatment. Also,Jojoba leaves compost (T1) and compost B ( 100% Compost A + PGPR) gave the highest mean values of the chlorophyll content in leaves character. In addition to Compost C ( 50% Compost A + 50% Chicken manure) gave the best results in mineral content of leaves characters. The findings in this study strongly recommended that chicken manure, beneficial microbes (PGPR), plant composted residues and kitchen wastes would be advantage if the farmer's target is to maximize watermelon yield.

Production and quality of watermelon grown under seaweed extract

The use of biofertilizers with macroalgae base has become a viable alternative to conventionally used synthetic fertilizers. Among the advantages of using these extracts is the increase in productivity and improvements in the agronomic performance of the crop. Its use is allowed in organic agriculture as it is a natural product. The objective of this research was to evaluate the influence of the seaweed extract, Ascophyllum nodosum (L.) to the productive development and quality of watermelon plants. A randomized block design with 6 treatments and 4 replications was applied. The treatments comprised of full or divided doses (total of 3.0 ml L-1) of seaweed extract (T1: producer standard; T2: (1.0 – 1.0 – 1.0 mL L-1) applied 2 - 16 - 30 days after transplanting (d.a.t.); T3: (1.5 - 1.5 ml L-1) 2 - 30 (d.a.t.); T4: (1.0 – 1.0 – 1.0 mL L-1) 16 - 30 - 44 (d.a.t.); T5: (1.5 - 1.5 mL L-1) 16 - 30 (d.a.t.) T6: (3.0 mL L-1) 2 (d.a.t.). 100 mL of the prepared solution was used for each experiment. The application of Acadian® improved the yield of water melon in the order of 12.69 to 27.76% and at different periods of the crop cycle.

Gas exchange, growth, and production of mini-watermelon under saline water irrigation and phosphate fertilization

In the semi-arid region of Northeastern Brazil, due to the occurrence of excess salts, both in the water and soil, plants are constantly exposed to various conditions of abiotic stress. Thus, it is extremely important to identify methods capable of minimizing the effects of salt stress on plants as a way to ensure the expansion of irrigated areas. In this context, the objective of this study was to evaluate the gas exchange, growth, and production of mini-watermelon irrigated with saline waters and fertilized with phosphorus. The experiment was conducted in pots under greenhouse conditions in Pombal, PB, Brazil, using a randomized block design in a 5 x 4 factorial scheme, corresponding to five levels of electrical conductivity of irrigation water—ECw (0.3, 1.3, 2.3, 3.3, and 4.3 dS m-1), four phosphorus doses— PD (60, 80, 100, and 120% of the recommendation), and with three replicates. Watermelon plants cv. Sugar Baby were sensitive to water salinity greater than 0.3 dS m-1, with more pronounced inhibition of gas exchange, growth, and production. Reduction in the CO2 assimilation rate of watermelon plants cv. Sugar Baby was associated with factors of stomatal and non-stomatal origin. Phosphorous doses corresponding to 73 and 88% of the recommended values promoted an increase in the intercellular CO2 concentration and stem diameter of mini-watermelon plants. P2O5 doses ranging from 60 to 120% of the recommendation did not mitigate the effects of salt stress on the cultivation of watermelon cv. Sugar Baby.

Effect of Different Sources of Organic Manures and Different Levels of Humic and Fulvic Acid on Growth, Flowering, Yield and its Components of Watermelon Plants

Effect of Different Sources of Organic Manures and Different Levels of Humic and Fulvic Acid on Growth, Flowering, Yield and its Components of Watermelon Plants

Nitric oxide regulates watermelon (Citrullus lanatus) responses to drought stress.

The role of exogenous nitric oxide (NO) application in alleviating drought stress responses by enhancing the antioxidant activities in plants is well established for several species. However, none of the studies reported its role in protecting the watermelon genotypes from drought stress. In this study, we aimed to observe the effect of NO application on the physiological and biochemical responses of the two watermelon (Citrullus lanatus var. lanatus) genotypes grown under drought stress conditions by treating the plants with 15% polyethylene glycol 6000 (PEG 6000) and 100µM sodium nitroprusside (SNP), which is a NO donor in Hoagland solution. Among the two genotypes, one genotype, KAR 98 was drought tolerant; while another, KAR 147 was drought sensitive. Drought stress showed a decrease in the growth parameters of both the genotypes; however, as expected it was higher in the susceptible genotype, KAR 147. NO application could not prevent the reductions in the growth parameters; however, it reduced the increment in malondialdehyde (MDA) content caused by the drought stress in both watermelon genotypes. Moreover, while drought stress condition reduced the ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), and peroxidase (POX) activities in both genotypes, NO + PEG application increased the APX activity in the tolerant genotype, KAR 98. Though the obtained results does not show the direct involvement of NO in increasing drought tolerance of watermelon plants, the increase in the APX antioxidant enzyme activity on NO application under drought stress confirmed its role in protecting the watermelon genotypes from the oxidative damage caused by the drought stress. Moreover, it can be concluded that the effect of NO application on watermelons' responses towards drought stress condition may vary according to the specific genotypes. As to date none of the studies reported the effect of NO application on the antioxidant activity of watermelon genotypes under drought stress, the present study may provide information about the mechanisms that can be focused to improve drought stress tolerance of watermelon genotypes.

Hormonal and metabolites responses in Fusarium wilt-susceptible and -resistant watermelon plants during plant-pathogen interactions

BackgroundFusarium oxysporum f. sp. niveum (FON) causes Fusarium wilt in watermelon. Several disease-resistant watermelon varieties have been developed to combat Fusarium wilt. However, the key metabolites that mount defense responses in these watermelon varieties are unknown. Herein, we analyzed hormones, melatonin, phenolic acids, and amino acid profiles in the leaf tissue of FON zero (0)-resistant (PI-296341, Calhoun Grey, and Charleston Grey) and -susceptible (Sugar Baby) watermelon varieties before and after infection.ResultsWe found that jasmonic acid-isoleucine (JA-Ile) and methyl jasmonate (MeJA) were selectively accumulated in one or more studied resistant varieties upon infection. However, indole-3-acetic acid (IAA) was only observed in the FON 0 inoculated plants of all varieties on the 16th day of post-inoculation. The melatonin content of PI-296341 decreased upon infection. Conversely, melatonin was only detected in the FON 0 inoculated plants of Sugar Baby and Charleston Grey varieties. On the 16th day of post-inoculation, the lysine content in resistant varieties was significantly reduced, whereas it was found to be elevated in the susceptible variety.ConclusionsTaken together, Me-JA, JA-Ile, melatonin, and lysine may have crucial roles in developing defense responses against the FON 0 pathogen, and IAA can be a biomarker of FON 0 infection in watermelon plants.

First Report of Nigrospora sphaerica causing leaf spot on watermelon (Citrullus lanatus L.) in Malaysia.

Watermelon (Citrullus lanatus L.) is widely cultivated and consumed in Malaysia for its nutritional value. In June 2018, nearly 40% of the 'Red Rocky' watermelon plants in experimental plots of the research farm at Faculty of Agriculture, UPM Serdang, Selangor, Malaysia had leaf spot symptoms. Leaf spots were small, ranging 5 to 30 mm, yellow to brown, and circular to irregular in shape. With ages, the leafspots gradually enlarged and coalesced. To investigate the disease, ten symptomatic leaves were collected from the experimental plots. Diseased tissues (5 x 5 mm) were excied and surface sterilized with 0.5% sodium hypochlorite (NaOCl) for 2 min, rinsed twice with sterile distilled water, plated on potato dextrose agar (PDA), and incubated at 25 °C for 5 days. A total of ten isolates with similar colony morphologies were obtained from tissue samples. A single representative isolate "F" was further characterized by molecular analysis. All colonies were initially white in color, but later turned gray to black upon sporulation after 7 days. Conidia were produced in culture and were single-celled, black, smooth-walled, spherical in shape measuring 11.4 to 14 μm x 13.8 to 19 μm in diameter (n=40). These were borne on hyaline vesicles at the tip of a conidiophore. For molecular identification, genomic DNA was extracted from fresh mycelium of isolate F using DNeasy Plant Mini kit (Qiagen, Germantown, MD, USA). The internal transcribed spacer (ITS) region of rDNA and the translation elongation factor 1-alpha (TEF1-α) gene were amplified using the ITS5/ITS4 (White et al. 1990) and EF1-728F/EF1-986R primer sets (Carbone and Kohn 1999), respectively. BLASTn analysis of the ITS sequence revealed 100% identity (526 bp out of 526 bp) to Nigrospora sphaerica (GenBank Accession no. HQ608063). TEF1-α sequence had 100% identity (494 bp out 494 bp) with N. sphaerica (GenBank Accession no. MN995332). The resulting sequences were deposited in GenBank (ITS: Accession no. MK544066; TEF1-α Accession no. MT708197). Based on morphological and molecular characteristics, isolate "F" was identified as Nigrospora sphaerica (Sacc.) Mason (Chen et al. 2018). A pathogenicity test was conducted on five healthy leaves of five one-month-old watermelon 'Red Rocky' plants grown in a greenhouse. Leaves were wounded using a 34-mm-diameter florist pin frog and spray-inoculated until runoff with a conidial suspension (1 × 106 conidia/ml) of a 7-day-old culture. Five leaves from additional 2 plants were sprayed with sterile distilled water to serve as controls. Inoculated plants were covered with polyethylene bags for 48 h to maintain high humidity. Ten days post-inoculation, symptoms on inoculated leaves developed brown-to-black lesions similar to those observed in the field, while control leaves remained asymptomatic. N. sphaerica was re-isolated from all symptomatic tissues confirming Koch's postulates. N. sphaerica is distributed on a wide range of hosts and has been reported from 40 different host genera including monocotyledonous and dicotyledonous hosts (Wang et al. 2017). N. sphaerica has been reported to cause leaf spot of date palm in Pakistan (Alam et al. 2020) and kiwifruit in China (Chen et al. 2016). To our knowledge, this is the first report of N. sphaerica causing leaf spot of watermelon in Malaysia. This new disease could reduce fruit quality since sweetness and ripening are dependent on healthy foliage. Additionally, this disease can cause premature defoliation which would also reduce watermelon productivity.