Resistant Melon Research Articles

QTL mapping of resistance to Pseudoperonospora cubensis clade 1, mating type A2, in Cucumis melo.

This is the first identification of QTLs underlying resistance to Pseudoperonospora cubensis in Cucumis melo using a genetically characterized isolate. Pseudoperonospora cubensis, causal organism of cucurbit downy mildew (CDM), is one of the largest threats to cucurbit production in the eastern USA. Currently, no Cucumis melo (melon) cultivars have significant levels of resistance. Additionally, little is understood about the genetic basis of resistance in C. melo. Recombinant inbred lines (RILs; N = 169) generated from a cross between the resistant melon breeding line MR-1 and susceptible cultivar Ananas Yok'neam were phenotyped for CDM resistance in both greenhouse and growth chamber studies. A high-density genetic linkage map with 5,663 binned SNPs created from the RIL population was utilized for QTL mapping. Nine QTLs, including two major QTLs, were associated with CDM resistance. Of the major QTLs, qPcub-10.1 was stable across growth chamber and greenhouse tests, whereas qPcub-8.2 was detected only in growth chamber tests. qPcub-10.1 co-located with an MLO-like protein coding gene, which has been shown to confer resistance to powdery mildew and Phytophthora in other plants. This is the first screening of C. melo germplasm with a genetically characterized P. cubensis isolate.

Effect of phosphate-solubilizing bacteria on the gene expression and inhibition of bacterial fruit blotch in melon

Pathogenic bacteria Acidovorax avenae subsp. citrulli can cause bacterial fruit blotch (BFB) in melon (Cucumis melo L.). However, the process in which melon plant inoculated with biocontrol bacteria cope with A. citrulli invasion remains unclear. This study aimed to analyze the expression of genes involved in the BFB with a biocontrol strain through RNA sequencing. Results showed that the disease incidence of BFB was reduced by 57.1 % when melon was inoculated with antagonistic phosphate-solubilizing bacteria (PSB) Burkholderia sp. ‘N3’ strain. The plant height, dry weight, leaf area, and uptake of nutrients of melon seedlings increased after it was inoculated with two strains (‘N3’ and ‘M01’). The P content in TN (inoculated with ‘N3’) significantly increased by 17.48 % compared with the control (TR1). Fe3+ significantly increased in melon plant inoculated with ‘N3’ and ‘Pslb24’ and might play an important role in the suppression of BFB in melon. A total of 129 upregulated genes and 33 downregulated genes were involved in the resistance of melon to A. citrulli infection (TP2 versus TP1). Gene ontology analysis revealed that most differentially expressed genes were located in biological regulation, cell component organization, binding, and catalytic activity functions. Kyoto Encyclopedia of Genes and Genomes analysis illustrated that pathways related to cell cycle, ribosome biogenesis, plant hormone signal transduction, starch and sucrose, and signal transmission mechanisms were involved. These findings will be helpful to elaborate and uncover the expression of resistance genes involved in controlling BFB in melon inoculated with beneficial PSB.

Development of KASP Markers and Identification of a QTL Underlying Powdery Mildew Resistance in Melon (Cucumis melo L.) by Bulked Segregant Analysis and RNA-Seq.

Powdery mildew (PM), caused by Podosphaera xanthii (Px), is one of the most devastating fungal diseases of melon worldwide. The use of resistant cultivars is considered to be the best and most effective approach to control this disease. In this study, an F2 segregating population derived from a cross between a resistant (wm-6) and a susceptible cultivar (12D-1) of melon was used to map major powdery mildew resistance genes using bulked segregant analysis (BSA), in combination with next-generation sequencing (NGS). A novel quantitative trait locus (QTL) named qCmPMR-12 for resistance to PM on chromosome 12 was identified, which ranged from 22.0 Mb to 22.9 Mb. RNA-Seq analysis indicated that the MELO3C002434 gene encoding an ankyrin repeat-containing protein was considered to be the most likely candidate gene that was associated with resistance to PM. Moreover, 15 polymorphic SNPs around the target area were successfully converted to Kompetitive Allele-Specific PCR (KASP) markers (P < 0.0001). The novel QTL and candidate gene identified from this study provide insights into the genetic mechanism of PM resistance in melon, and the tightly linked KASP markers developed in this research can be used for marker-assisted selection (MAS) to improve powdery mildew resistance in melon breeding programs.

Genetic mapping and candidate gene analysis for melon resistance to Phytophthora capsici

Phytophthora blight is one of the most serious diseases affecting melon (Cucumis melo) production. Due to the lack of highly resistant germplasms, the progress on disease-resistant research is slow. To understand the genetics of melon resistance to Phytophthora capsici, an F2 population containing 498 individuals was developed by crossing susceptible line E31 to highly resistant line ZQK9. Genetic analysis indicated that the resistance in ZQK9 was controlled by a dominant gene, tentatively named MePhyto. Through bulked-segregant analysis (BSA-Seq) and chromosome walking techniques, the MePhyto gene was mapped to a 52.44 kb interval on chromosome 12. In this region, there were eight genes and their expression patterns were validated by qRT-PCR. Among them, one wall-associated receptor kinase (WAK) gene MELO3C002430 was significantly induced in ZQK9 after P. capsici inoculation, but not in E31. Based on the non-synonymous mutation site in MELO3C002430, a cleaved amplified polymorphic sequence (CAPS) marker, CAPS2430, was developed and this maker was co-segregated with MePhyto in both F2 population and a collection of 36 melon accessions. Thus MELO3C002430 was considered as the candidate gene and CAPS2430 was a promising marker for marker-assisted selection (MAS) in breeding. These results lay a foundation for revealing the resistance mechanism of melon to P. capsici.

Tomato and Melon Meloidogyne Resistant Rootstocks Improve Crop Yield but Melon Fruit Quality Is Influenced by the Cropping Season.

Four rotation sequences consisting of ungrafted tomato cv. Durinta – melon cv. Paloma or tomato grafted onto the resistant rootstock ‘Aligator’ – melon grafted onto the resistant Cucumis metuliferus accession BGV11135, and in reverse order, were conducted from 2015 to 2017 in a plastic greenhouse infested or not with Meloidogyne incognita to determine the plant tolerance (T), the minimum relative crop yield (m) and fruit quality. The relationship between M. incognita densities in soil at transplanting (Pi) of each crop and the crop yield was assessed and T and m were estimated by the Seinhorst’s damage model. In addition, the volume and the number of nuclei of single giant cells and the number of giant cells, its volume and the number of nuclei per feeding site in susceptible tomato and melon were compared to those in the resistant tomato and C. metuliferus 15 days after nematode inoculation in pot test. The relationship between the Pi and the relative crop yield fitted the Seinhorst’s damage model in both ungrafted and grafted tomato and melon, but not for all years and cropping seasons. The estimated T for ungrafted and grafted tomato did not differ but m was lower in the former (34%) than the latter (67%). Sodium concentration in fruits from ungrafted but not from grafted tomato increased with nematode densities in spring 2015 and 2016. The estimated ungrafted melon T did not differ from the grafted melon cultivated in spring, but it did when it was cultivated in summer. The relative crop yield of ungrafted melon was lower (2%) than the grafted cultivated in spring (62%) and summer (20%). Sodium concentration in melon fruits from ungrafted plants increased with nematode densities. No variations in fruit quality from grafted melon cultivated in spring were found, although less dry matter and soluble solid content at highest nematode densities were registered when it was cultivated in summer. Lower number of giant cells per feeding site was observed in both susceptible tomato germplasms compared to the resistant ones but they were more voluminous and held higher number of nuclei per giant cell and per feeding site.

Characterization, identification and expression profiling of genome-wide R-genes in melon and their putative roles in bacterial fruit blotch resistance

BackgroundBacterial fruit blotch (BFB), a disease caused by Acidovorax citrulli, results in significant economic losses in melon. The causal QTLs and genes for resistance to this disease have yet to be identified. Resistance (R)-genes play vital roles in resistance to plant diseases. Since the complete genome sequence of melon is available and genome-wide identification of R-genes has been performed for this important crop, comprehensive expression profiling may lead to the identification of putative candidate genes that function in the response to BFB.ResultsWe identified melon accessions that are resistant and susceptible to BFB through repeated bioassays and characterized all 70 R-genes in melon, including their gene structures, chromosomal locations, domain organizations, motif distributions, and syntenic relationships. Several disease resistance-related domains were identified, including NBS, TIR, LRR, CC, RLK, and DUF domains, and the genes were categorized based on the domains of their encoded proteins. In addition, we profiled the expression patterns of the genes in melon accessions with contrasting levels of BFB resistance at 12 h, 1 d, 3 d, and 6 d after inoculation with A. citrulli. Six R-genes exhibited consistent expression patterns (MELO3C023441, MELO3C016529, MELO3C022157, MELO3C022146, MELO3C025518, and MELO3C004303), with higher expression levels in the resistant vs. susceptible accession.ConclusionWe identified six putative candidate R-genes against BFB in melon. Upon functional validation, these genes could be targeted for manipulation via breeding and biotechnological approaches to improve BFB resistance in melon in the future.

Determining the main agronomic traits of snake melon (Cucumis melo var. flexuosus L.) fruits as affected by genotypic differences

The variability affecting the main agronomic traits of 10 snake melon genotypes (Cucumis melo var. flexuosus L.) (three F1 hybrids, six breeding lines and the widely grown and consumed traditional cultivar Mornagui), grown under greenhouse conditions during 2014 and 2015 seasons, was examined and compared. Their resistance to powdery mildew was also checked. The main production-driving agronomic traits varied significantly (P<0.05) depending on the genotype. The major skin colour determined visually was different among the considered genotypes. The hybrids (H5 and H12) and the breeding lines (L1, L2, L5, L6 and L9) had dark green skin. The fruits of the hybrid H7 were dark and light green and the breeding line L4 has intense and dark green fruits whereas cv. Mornagui was characterized by medium light green fruits. Regarding fruit shape, the hybrids H7 and H5 produced straight fruits whereas the hybrid H12 and the breeding lines; L2, L4, L5, and L9 and the cv Mornagui had elongate fruits. However both breeding lines L1 and L6 were characterized by straight elongate fruits. The F1 hybrid H5 was the most productive (3.6 Kg/plant and ≈ 21 fruits/plant for total yield and number of fruit/plant respectively). These findings are useful for further breeding programs aiming to develop new powdery mildew resistant snake melon cultivars with satisfying agronomic traits.

Development of Molecular Marker Linked with Bacterial Fruit Blotch Resistance in Melon (Cucumis melo L.).

Bacterial fruit blotch (BFB) causes losses in melon marketable yield. However, until now, there has been no information about the genetic loci responsible for resistance to the disease or their pattern of inheritance. We determined the inheritance pattern of BFB resistance from a segregating population of 491 F2 individuals raised by crossing BFB-resistant (PI 353814) and susceptible (PI 614596) parental accessions. All F1 plants were resistant to Acidovorax citrulli strain KACC18782, and F2 plants segregated with a 3:1 ratio for resistant and susceptible phenotypes, respectively, in a seedling bioassay experiment, indicating that BFB resistance is controlled by a monogenic dominant gene. In an investigation of 57 putative disease-resistance related genes across the melon genome, only the MELO3C022157 gene (encoding TIR-NBS-LRR domain), showing polymorphism between resistant and susceptible parents, revealed as a good candidate for further investigation. Cloning, sequencing and quantitative RT-PCR expression of the polymorphic gene MELO3C022157 located on chromosome 9 revealed multiple insertion/deletions (InDels) and single nucleotide polymorphisms (SNPs), of which the SNP A2035T in the second exon of the gene caused loss of the LRR domain and truncated protein in the susceptible accession. The InDel marker MB157-2, based on the large (504 bp) insertion in the first intron of the susceptible accession, was able to distinguish resistant and susceptible accessions among 491 F2 and 22 landraces/inbred accessions with 98.17% and 100% detection accuracy, respectively. This novel PCR-based, co-dominant InDel marker represents a practical tool for marker-assisted breeding aimed at developing BFB-resistant melon accessions.

Comparative transcriptome analysis uncovers regulatory roles of long non-coding RNAs involved in resistance to powdery mildew in melon

BackgroundLong non-coding RNAs (lncRNAs) are a class of non-coding RNAs with more than 200 nucleotides in length, which play vital roles in a wide range of biological processes. Powdery mildew disease (PM) has become a major threat to the production of melon. To investigate the potential roles of lncRNAs in resisting to PM in melon, it is necessary to identify lncRNAs and uncover their molecular functions. In this study, we compared the lncRNAs between a resistant and a susceptible melon in response to PM infection.ResultsIt is reported that 11,612 lncRNAs were discovered, which were distributed across all 12 melon chromosomes, and > 85% were from intergenic regions. The melon lncRNAs have shorter transcript lengths and fewer exon numbers than protein-coding genes. In addition, a total of 407 and 611 lncRNAs were found to be differentially expressed after PM infection in PM-susceptible and PM-resistant melons, respectively. Furthermore, 1232 putative targets of differently expressed lncRNAs (DELs) were discovered and gene ontology enrichment (GO) analysis showed that these target genes were mainly enriched in stress-related terms. Consequently, co-expression patterns between LNC_018800 and CmWRKY21, LNC_018062 and MELO3C015771 (glutathione reductase coding gene), LNC_014937 and CmMLO5 were confirmed by qRT-PCR. Moreover, we also identified 24 lncRNAs that act as microRNA (miRNA) precursors, 43 lncRNAs as potential targets of 22 miRNA families and 13 lncRNAs as endogenous target mimics (eTMs) for 11 miRNAs.ConclusionThis study shows the first characterization of lncRNAs involved in PM resistance in melon and provides a starting point for further investigation into the functions and regulatory mechanisms of lncRNAs in the resistance to PM.

Metodologia para avaliação da resistência à rizoctoniose em germoplasma de meloeiro

The intensive cultivation of melon, mainly in the Northeast of Brazil, has favored the occurrence of root diseases such as rhizoctonia, caused by the fungus Rhizoctonia solani Kuhn. The use of resistant cultivars is one of the most efficient strategic measures for integrated management of diseases in this crop. It is necessary to use an efficient inoculation method to evaluate rhizoctonia in melon germplasm with the aim of identifying sources of resistance. The objective of this study was to develop an efficient method to inoculate the pathogen to proceed in selection of R. solani resistant melon germplasm. Five experiments were conducted under greenhouse conditions to define the adequate container, growth environment, substrate for inoculum production, aggressiveness of the isolates, inoculum density, manner of inoculation, phenological stage of the plant, and time for evaluation after inoculation. The results obtained showed that for selection of R. solani resistant melon germplasm, the use of seedlings with roots cut during transplanting to pots is recommended. The pots should contain sand with organic inoculum obtained from rice grains at the concentration of 150 mg.kg-1 of soil, associated with inoculation through a puncture in the plant stem by an infested toothpick, without the need for a moist chamber. The most aggressive isolate was CMM-1068.

Molecular characterization of Acidovorax citrulli strain NIHHS15-280 causing bacterial fruit blotch disease in Korea and screening of resistance sources in melon

Bacterial fruit blotch (BFB), caused by Acidovorax citrulli, is an economically devastating disease in melon. Molecular characterization of causal strains and identification of sources of resistance are necessary to control this important disease. Many strains of BFB were identified by partial sequencing and documented in GenBank. Recently, there was an outbreak of BFB strain NIHHS15-280 in melon fields (Goksung, Jeonnam, Korea) that severely hampered melon production in Korea. For this reason, we characterized NIHHS15-280 by partially sequencing the 16S rRNA gene using PCR-based markers. The partial sequence of the 16S rRNA gene of NIHHS15-280 was much more similar to A. citrulli strains associated with melon and watermelon hosts than other cucurbit hosts. A PCR-based assay identified the strain (NIHHS15-280) as belonging to A. citrulli group I, which predominantly infects non-watermelon cucurbits (virulent to melon). Thirty-five melon genotypes were screened against NIHHS15-280 in a detached-leaf inoculation assay. The lack of visible disease symptoms 11 days after inoculation in lines PI353814 and PI140471 indicated these to be highly resistant lines, whereas moderate resistance was observed in lines PI420145 and SCNU1154 and cultivars ME6 and ME5. Also, the most resistant lines were corroborated by a fruit inoculation assay. The characterized A. citrulli strain NIHHS15-280 (group I) and identified resistant lines will serve as a valuable resource for further genetic studies and improvement of BFB resistance in melon.

New source of resistance to Aphis gossypii in Tunisian melon accessions using phenotypic and molecular marker approaches

Aphis gossypii (Glover) is one of the major pests of melon crops as well as an efficient vector of non-persistent virus such as Cucumber Mosaic Virus and Zucchini Yellow Mosaic Virus among others. Host-plant resistance is one of the best strategies that can be used to control this pest. In this study 14 Tunisian melon accessions were screened to identify new sources of resistance/tolerance to Aphis gossypii using phenotypic and molecular approaches. Antixenosis, antibiosis and tolerance tests were carried out to phenotype those accessions which were also analyzed by molecular markers linked to the Vat gene which confers resistance to both A. gossypii colonization and virus transmission. Results evidenced that only the accession TUN-7 showed antixenosis, antibiosis and tolerance (no leaf curling), at a similar level to that of the resistant control PI414723. Although plants of the accession TUN-13 did not show leaf curling either, the presence of the Vat gene was only detected in TUN-7; its fruit characteristics, of Ananas type, makes this accession as a valuable source of resistance to this aphid that can be used in breeding programs to develop new aphid resistant melon cultivars.

Diversity in Melon (Cucumis melo L.) Landraces of Karnataka State of Southern India for Downy and Powdery Mildew Disease Resistance

We present here the report on evaluation of melon landraces from the Karnataka state of India for resistance to downy mildew (Pseudoperonospora cubensis) and powdery mildew (Podosphaera xanthii), the major diseases of melon as well as other cucurbits. Thirty four melon landraces collected from different agro-climatic regions of the state were evaluated for resistance against downy mildew under natural epiphytotic conditions and powdery mildew under artificial conditions. Percent disease index (PDI) was calculated for each entry and based on that accessions were categorised as resistant, moderately resistant and susceptible. A very wide variation was observed among the accessions for resistance to both the diseases. Based on PDI, out of 34 accessions, COHB04, COHB37, COHB38, COHB41 and COHB43 were resistant to downy mildew. Ten genotypes were moderately resistant, fifteen were susceptible and four lines including susceptible check were highly susceptible to disease. Three landraces, COHB12, COHB38 and COHB40 were resistant to powdery mildew disease. Two genotypes were moderately resistant and rest of the lines were susceptible to disease. COHB38, an unexplored and uncultivated genotype was resistant to both the diseases. The highly resistant genotype COHB38 identified within the accessions tested offers an additional source for the development of downy and powdery mildew resistant melon cultivars.

Induction of postharvest resistance in melon using pulsed light as abiotic stressor

The aim of this study was use the pulsed light (PL) as tool to booster the postharvest resistance in melons. Cantaloupe melons at mature stage were submitted to the treatments as follows: control, pulsed light (PL; 9 J cm−2), 1-methylcyclopropene (1-MCP; 600 nL L-1) and 1-MCP + PL (600 nL L-1 + 9 J cm−2). Postharvest resistance measurements according survival analysis developed at 4 °C, included: ethylene production, 1-aminocyclopropane-l-carboxylic acid (ACC) oxidase activity, ACC synthase activity, firmness, pH, soluble solids, titratable acidity, SS/AT ratio, soluble sugars, vitamin C, total polyphenols, phenylalanine ammonia lyase (PAL) activity, colour epicarp, free polyamines (putrescine-Put, spermine-Spe and spermidine-Spd) and total polyamines (TPo). Combined effect of the PL+1-MCP promoted an additional of 12 days in the shelf life of melons. PL limited the ethylene biosynthesis leading to an immediate upregulation of polyamines (Put + Spe + Spd), hence, associated with high amounts of TPo (56%). PL treatment promoted an increase of PAL activity (67%) that synthesized high content of phenolic compounds (55%). The results suggest that PL with a fluence of 9 J cm−2 stimulate the postharvest defense mechanisms in melon, due to the ethylene production limitation, which was influenced by the increased polyamines, maintaining the quality attributes.

Evaluation of powdery mildew resistance in various melon (Cucumis melo L.) genotypes

Evaluation of powdery mildew resistance in various melon (Cucumis melo L.) genotypes

Changes in feeding behaviour are not related to the reduction in the transmission rate of plant viruses by Aphis gossypii (Homoptera: Aphididae) to melon plants colonized by Beauveria bassiana (Ascomycota: Hypocreales)

Aphids are considered by far the most common and efficient vectors of non-persistent (NP) and persistent (P) plant viruses, with new, more environmentally friendly aphid control strategies urgently needed. Among these strategies, entomopathogenic fungi (EF) have successfully been employed against aphids mainly by foliar spray over infested crops. Plants benefit from not only their direct insecticidal activity on aphids but also a number of side outcomes of their application, such as sub-lethal effects on the target pest or their endophytic behaviour. Beyond aphid control, this endophytic quality has also been exploited to control diverse plant pathogenic microorganisms. In the present study, possible changes in cotton aphid (Aphis gossypii) probing and feeding behaviour mediated by the endophytic colonization of melon plants with Beauveria bassiana were studied using the electrical penetration graph (EPG) technique. Similarly, the effect of this endophytic colonization on P (Cucurbit aphid-borne yellows virus, Polerovirus) and NP (Cucumber mosaic virus, Cucumovirus) virus transmission by the cotton aphid was also studied. B. bassiana colonization did not alter the aphid feeding behaviour related to the NP or P virus inoculation process, but significant changes were detected in other variables that were not related to the virus inoculation process, such as the intracellular probe (pd) duration, which could suggest a possible effect of EF on the acquisition of CMV. Notably, a remarkable effect of B. bassiana endophytic colonization was found on CMV and CABYV transmission, with significant reductions of 21.9 and 24.4%, respectively, of the inoculation rates in B. bassiana-treated plants. These results suggest a possible systemic virus resistance in melon induced by fungal colonization.

Screening of melon genotypes identifies gummy stem blight resistance associated with Gsb1 resistant loci

Md Zahid Hassan, Arif Hasan Khan Robin, Md Abdur Rahim, Sathishkumar Natarajan, Hoy-Taek Kim, Jong-In Park, and Ill-Sup Nou. J Plant Biotechnol 2018;45:217-27. https://doi.org/10.5010/JPB.2018.45.3.217

Gummy Stem Blight Resistance in Melon: Inheritance Pattern and Development of Molecular Markers.

Gummy stem blight (GSB) causes enormous losses to melon (Cucumis melo L.) production worldwide. We aimed to develop useful molecular markers linked to GSB resistance. In this study, 168 F2 plants were obtained from the F1 population of a cross between the GSB-susceptible ‘Cornell ZPPM 339’ and the GSB-resistant ‘PI482399’ lines. A 3:1 ratio of susceptible and resistant genotypes was observed in the F2 population, indicating control by a single recessive gene. Nucleotide-binding site leucine-rich repeat (NBS-LRR) genes confer resistance against insects and diseases in cucurbits including melon. We cloned and sequenced the TIR-NBS-LRR-type resistance gene MELO3C022157, located on melon chromosome 9, from resistant and susceptible lines. Sequence analysis revealed deletions in the first intron, a 2-bp frameshift deletion from the second exon and a 7-bp insertion in the 4th exon of the resistant line. We developed two insertion/deletion (InDel) markers, GSB9-kh-1 and GSB9-kh-2, which were found in the first intron of MELO3C022157 linked to GSB resistance. We validated these markers with the F2 population and inbred lines. These InDels may be used to facilitate marker-assisted selection of GSB resistance in melon. However, functional analysis of overexpressing and/or knock-down mutants is needed to confirm the frameshift mutation.

SNP Marker Assisted Selection for Identification of Fusarium Resistant Melon Plants

SNP Marker Assisted Selection for Identification of Fusarium Resistant Melon Plants

Construction of expression vectors of the melon resistance gene Fom-2 and genetic transformation

Construction of expression vectors of the melon resistance gene Fom-2 and genetic transformation