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Melon (Cucumas melon) is widely cultivated and popular because of its quality value and unique flavor. However, the continuous cropping of melons in greenhouses has various negative effects on the soil environment, melon growth, and quality. Recently, farmers have utilized organic fertilization, especially vermicompost, for melons to resist the harmful effects of continuous cropping. A field experiment was conducted to explore the effects of vermicompost on soil microbes and melon fruit quality via high throughput sequencing and chemical sequencing methods. The results showed that the application of vermicompost decreased (p < 0.05) soil pH and increased organic matter, available phosphorus, biomass, urease, catalase, peroxidase, and alkaline phosphatase. A total of 3447 bacterial and 718 fungal operational taxonomic units were identified in all soil samples. Application of vermicompost decreased (p < 0.05) the relative abundances of Acidobacteriota, Gemmatimonadota, Actinobacteriota, and unclassified and increased the relative abundance of Planctomycetota. Compared with the control soil, vermicompost application resulted in significantly higher bacterial Chao indices and a significantly lower Chao index under vermicompost of 60 t ha−1 based on farmers' normal fertilizer and significantly lower diversity under vermicompost of 90 t ha−1. Otherwise, vermicompost application increased the photosynthetic rate and chlorophyll content of melon leaves and increased the total sugar, soluble solids, vitamin C, soluble protein, and organic acid contents of melon. The results of redundancy analysis indicated that Proteobacteria exhibited a positive correlation with soil ammonium nitrogen (AN) and pH, while showing a negative association with soil available phosphorus and organic matter. Spearman's correlation analysis revealed that both total sugar content and central soluble solid content in melon had a significant positive correlation (p < 0.05) with Patescibacteria. This study demonstrates that the application of vermicompost alters the microbial community structure in melon cultivation, enhancing fruit quality; this not only promotes a healthier soil ecosystem but also contributes to sustainable and productive practices in melon farming. [ABSTRACT FROM AUTHOR]

Melon damping off, which has a negative impact on melon quality and yield, can be safely and effectively managed with Trichoderma. Melon cultivar 'Longtian No. 1' was evaluated at both the adult and seedling stages in a pot experiment. The Rs and PD liquids were utilized as CK1 and CK2, respectively. Trichoderma viride Tv286 treatments T1B, T2B, T3B, and T4B were used based on Rs at concentrations of 104, 105, 106, and 107 CFU·g−1, respectively. The impact of several treatments on the antioxidant system and seedling quality of melon were assessed at 15, 25, and 35 days after sowing. We examined the effects of several treatments on melon quality, yield attributes, and physiological and biochemical markers during the adult stage at 10, 20, and 30 days after pollination. The effects of several treatments on melon damping off were also studied. Applying T. viride Tv286 at different rates effectively increased the activities of enzymes, including catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and polyphenol oxidase (PPO), in the leaves of melon seedlings, significantly reduced the malondialdehyde (MDA) content, and improved the root–shoot ratio and seedling strength index. In terms of its influence on promoting the effect of antioxidant system indicators, T3B performed well. Melon seedlings treated with T3B showed higher CAT, POD, SOD, APX, and PPO activities in their leaves 35 days after sowing compared to CK1 (189.74, 169.61, 175.36, 224.20, and 477.39%, respectively). The strong seedling index and root–shoot ratio showed improvements of 130.43 and 79.71%, respectively, and the MDA content dropped by 35.66% at 35 days after sowing compared to CK1. Varying the rates at which T. viride Tv286 was applied increased the nitrate reductase (NR) activity and nitrate nitrogen, proline (Pro), chlorophyll, soluble sugar, and soluble protein contents in mature melon leaves, increasing melon quality and yield. T3B is the most effective marketing campaign. Compared to CK1, mature T3B leaves had higher NR activity, nitrate nitrogen content, chlorophyll content, soluble sugar content, soluble protein content, and Pro content 30 days after melon pollination (100.40, 135.17, 68.59, 93.65, 158.13, and 238.67%, respectively). The soluble solids, soluble protein, soluble sugar, vitamin C contents, and yield of melon fruit increased by 50.07, 126.82, 60.62, 70.79, and 61.45%, respectively, at 30 days after melon pollination compared to CK1. Optimal management of melon damping off can be accomplished with the application of T. viride Tv286 at different concentrations, with T3B exhibiting the best effect. The control effects reached 90.48 and 72.99% at the seedling and adult stages, respectively. Overall, T. viride Tv286 improved seedling quality, damping off control efficacy, melon yield and quality, and the antioxidant system during the seedling stage and enhanced physiological and biochemical characteristics during the adult stage. This study indicates the potential of T. viride Tv286 conidia as a biological control agent because it can prevent plant disease, increase yield, and improve quality. [ABSTRACT FROM AUTHOR]

Fruit rind patterns are vital commercial quality traits in melon, in which the spotted or striped fruit rinds contribute to the commercial value of melon and can directly affect the choice of consumers. Although the spotted or non-spotted fruit rind pattern was studied in several cultivated melon accessions, the inheritance and regulating locus of this trait in wild melons are still unknown. Therefore, in this study, the inheritance and regulating loci of the green spotted fruit rind in a wild melon accession XNM020 were explored with F2 segregating populations derived from crossing between XNM020 and a cultivated melon XNM125. Segregating ratios of phenotypic data indicated that the green spotted fruit rind in XNM020 has a monogenic dominant inheritance. BSA-Seq showed that two potential genomic regions on chromosomes 4 (from 0.00 to 2.97 Mb) and 5 (from 0.00 to 2.34 Mb) regulate the formation of the green spotted fruit rind in wild melon XNM020. According to the annotations of polymorphic SNPs (single-nucleotide polymorphisms) and small InDels (insertions and deletions) in target genomic regions and the predicted gene functions, four genes MELO3C003316, MELO3C003375, MELO3C003388, and MELO3C014660 regulating chloroplast development or chlorophyll biosynthesis may be the best candidate genes. The results of this study enriched the inheritances of spotted fruit rinds in melon and also provided target genomic regions for marker-assisted selection breeding of melon focusing on fruit rinds. [ABSTRACT FROM AUTHOR]

Melon (Cucumas melon) is widely cultivated and popular because of its quality value and unique flavor. However, the continuous cropping of melons in greenhouses has various negative effects on the soil environment, melon growth, and quality. Recently, farmers have utilized organic fertilization, especially vermicompost, for melons to resist the harmful effects of continuous cropping. A field experiment was conducted to explore the effects of vermicompost on soil microbes and melon fruit quality via high throughput sequencing and chemical sequencing methods. The results showed that the application of vermicompost decreased (p < 0.05) soil pH and increased organic matter, available phosphorus, biomass, urease, catalase, peroxidase, and alkaline phosphatase. A total of 3447 bacterial and 718 fungal operational taxonomic units were identified in all soil samples. Application of vermicompost decreased (p < 0.05) the relative abundances of Acidobacteriota, Gemmatimonadota, Actinobacteriota, and unclassified and increased the relative abundance of Planctomycetota. Compared with the control soil, vermicompost application resulted in significantly higher bacterial Chao indices and a significantly lower Chao index under vermicompost of 60 t ha−1 based on farmers’ normal fertilizer and significantly lower diversity under vermicompost of 90 t ha−1. Otherwise, vermicompost application increased the photosynthetic rate and chlorophyll content of melon leaves and increased the total sugar, soluble solids, vitamin C, soluble protein, and organic acid contents of melon. The results of redundancy analysis indicated that Proteobacteria exhibited a positive correlation with soil ammonium nitrogen (AN) and pH, while showing a negative association with soil available phosphorus and organic matter. Spearman’s correlation analysis revealed that both total sugar content and central soluble solid content in melon had a significant positive correlation (p < 0.05) with Patescibacteria. This study demonstrates that the application of vermicompost alters the microbial community structure in melon cultivation, enhancing fruit quality; this not only promotes a healthier soil ecosystem but also contributes to sustainable and productive practices in melon farming.

Melon damping off, which has a negative impact on melon quality and yield, can be safely and effectively managed with Trichoderma. Melon cultivar ‘Longtian No. 1’ was evaluated at both the adult and seedling stages in a pot experiment. The Rs and PD liquids were utilized as CK1 and CK2, respectively. Trichoderma viride Tv286 treatments T1B, T2B, T3B, and T4B were used based on Rs at concentrations of 104, 105, 106, and 107 CFU·g−1, respectively. The impact of several treatments on the antioxidant system and seedling quality of melon were assessed at 15, 25, and 35 days after sowing. We examined the effects of several treatments on melon quality, yield attributes, and physiological and biochemical markers during the adult stage at 10, 20, and 30 days after pollination. The effects of several treatments on melon damping off were also studied. Applying T. viride Tv286 at different rates effectively increased the activities of enzymes, including catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and polyphenol oxidase (PPO), in the leaves of melon seedlings, significantly reduced the malondialdehyde (MDA) content, and improved the root–shoot ratio and seedling strength index. In terms of its influence on promoting the effect of antioxidant system indicators, T3B performed well. Melon seedlings treated with T3B showed higher CAT, POD, SOD, APX, and PPO activities in their leaves 35 days after sowing compared to CK1 (189.74, 169.61, 175.36, 224.20, and 477.39%, respectively). The strong seedling index and root–shoot ratio showed improvements of 130.43 and 79.71%, respectively, and the MDA content dropped by 35.66% at 35 days after sowing compared to CK1. Varying the rates at which T. viride Tv286 was applied increased the nitrate reductase (NR) activity and nitrate nitrogen, proline (Pro), chlorophyll, soluble sugar, and soluble protein contents in mature melon leaves, increasing melon quality and yield. T3B is the most effective marketing campaign. Compared to CK1, mature T3B leaves had higher NR activity, nitrate nitrogen content, chlorophyll content, soluble sugar content, soluble protein content, and Pro content 30 days after melon pollination (100.40, 135.17, 68.59, 93.65, 158.13, and 238.67%, respectively). The soluble solids, soluble protein, soluble sugar, vitamin C contents, and yield of melon fruit increased by 50.07, 126.82, 60.62, 70.79, and 61.45%, respectively, at 30 days after melon pollination compared to CK1. Optimal management of melon damping off can be accomplished with the application of T. viride Tv286 at different concentrations, with T3B exhibiting the best effect. The control effects reached 90.48 and 72.99% at the seedling and adult stages, respectively. Overall, T. viride Tv286 improved seedling quality, damping off control efficacy, melon yield and quality, and the antioxidant system during the seedling stage and enhanced physiological and biochemical characteristics during the adult stage. This study indicates the potential of T. viride Tv286 conidia as a biological control agent because it can prevent plant disease, increase yield, and improve quality.

Fruit rind patterns are vital commercial quality traits in melon, in which the spotted or striped fruit rinds contribute to the commercial value of melon and can directly affect the choice of consumers. Although the spotted or non-spotted fruit rind pattern was studied in several cultivated melon accessions, the inheritance and regulating locus of this trait in wild melons are still unknown. Therefore, in this study, the inheritance and regulating loci of the green spotted fruit rind in a wild melon accession XNM020 were explored with F2 segregating populations derived from crossing between XNM020 and a cultivated melon XNM125. Segregating ratios of phenotypic data indicated that the green spotted fruit rind in XNM020 has a monogenic dominant inheritance. BSA-Seq showed that two potential genomic regions on chromosomes 4 (from 0.00 to 2.97 Mb) and 5 (from 0.00 to 2.34 Mb) regulate the formation of the green spotted fruit rind in wild melon XNM020. According to the annotations of polymorphic SNPs (single-nucleotide polymorphisms) and small InDels (insertions and deletions) in target genomic regions and the predicted gene functions, four genes MELO3C003316, MELO3C003375, MELO3C003388, and MELO3C014660 regulating chloroplast development or chlorophyll biosynthesis may be the best candidate genes. The results of this study enriched the inheritances of spotted fruit rinds in melon and also provided target genomic regions for marker-assisted selection breeding of melon focusing on fruit rinds.

Phelipanche aegyptiaca is an obligate holoparasite that causes serious negative effects on crop growth and productivity, effective control of which is difficult due to its unique biological characteristics. In this study, we performed a comparative transcriptome analysis of resistant and susceptible Cucumis melo cultivars (KR1326 and K1237) inoculated with P. aegyptiaca. CmNLR (encodes a TIR-type NLR protein, consistently highly expressed in KR1326 roots) and CmNLRh (homologous gene of CmNLR) were cloned and overexpressed in K1237 roots to verify whether the TIR-type NLR protein can enhance C. melo resistance to P. aegyptiaca. The variations in enzymes related to active oxygen metabolism were further detected in transformed roots. The results showed that (1) some differentially expressed genes (DEGs) were enriched in pathways associated with active oxygen scavenging; (2) several DEGs encoded transcription factors, calcium channel proteins, and receptor-like proteins were upregulated and expressed in KR1326 roots; (3) the complete CmNLR and CmNLRh proteins prevented P. aegyptiaca from connecting to the vascular system of C. melo roots; and (4) stronger active oxygen burst and scavenging capacity were detected in transformed roots. We herein demonstrated that the TIR-type NLR protein confers C. melo resistance to P. aegyptiaca. The results provided clues for finding a new direction for host resistance against parasitic plants and shed new light on the cultivation of resistant varieties to control P. aegyptiaca. [ABSTRACT FROM AUTHOR]

Mature fruit abscission (MFA) is an important trait in terms of both harvest and yield. MFA can affect the production and economic value of melon fruit. An F3 population segregating for a single gene and derived from a cross between line M2-10, which shows no mature fruit abscission (None MFA), and the MFA line ZT00091 was used to map candidate genes. Specific length amplified fragment (SLAF) sequencing, in conjunction with bulked-segregant analysis (BSA), was used to map loci governing the natural fruit abscission of plants composing the F3-57 family. A candidate locus, mfa10.1, located on chromosome 10 between genomic positions 73,229 and 818,251, was obtained. An insertion-deletion (InDel) marker and 46 recombinant individuals were used to narrow the candidate region to within 35 kb at the genomic position of 650,203 to 685,250; this region included six candidate genes. qRT–PCR gene expression and gene sequence data showed that the CmARM14 gene, which encodes a RING-type E3 ubiquitin transferase (MELO3C012406), was a candidate for melon MFA. Subcellular localization observations revealed that the CmARM14 fusion protein was localized to the golgi apparatus. Taken together, these results provide a molecular basis for melon breeding. [ABSTRACT FROM AUTHOR]

Proximal remote sensing devices are novel tools that enable the study of plant health status through the measurement of specific characteristics, including the color or spectrum of light reflected or transmitted by the leaves or the canopy. The aim of this study is to compare the RGB and multispectral data collected during five years (2016–2020) of four fruiting vegetables (melon, tomato, eggplant, and peppers) with trial treatments of non-grafted and grafted onto resistant rootstocks cultivated in a Meloidogyne incognita (a root-knot nematode) infested soil in a greenhouse. The proximal remote sensing of plant health status data collected was divided into three levels. Firstly, leaf level pigments were measured using two different handheld sensors (SPAD and Dualex). Secondly, canopy vigor and biomass were assessed using vegetation indices derived from RGB images and the Normalized Difference Vegetation Index (NDVI) measured with a portable spectroradiometer (Greenseeker). Third, we assessed plant level water stress, as a consequence of the root damage by nematodes, using stomatal conductance measured with a porometer and indirectly using plant temperature with an infrared thermometer, and also the stable carbon isotope composition of leaf dry matter.. It was found that the interaction between treatments and crops (ANOVA) was statistically different for only four of seventeen parameters: flavonoid (p < 0.05), NBI (p < 0.05), NDVI (p < 0.05) and the RGB CSI (Crop Senescence Index) (p < 0.05). Concerning the effect of treatments across all crops, differences existed only in two parameters, which were flavonoid (p < 0.05) and CSI (p < 0.001). Grafted plants contained fewer flavonoids ( x ¯ = 1.37) and showed lower CSI ( x ¯ = 11.65) than non-grafted plants ( x ¯ = 1.98 and x ¯ = 17.28, respectively, p < 0.05 and p < 0.05) when combining all five years and four crops. We conclude that the grafted plants were less stressed and more protected against nematode attack. Leaf flavonoids content and the CSI index were robust indicators of root-knot nematode impacts across multiple crop types. [ABSTRACT FROM AUTHOR]

Phelipanche aegyptiaca is an obligate holoparasite that causes serious negative effects on crop growth and productivity, effective control of which is difficult due to its unique biological characteristics. In this study, we performed a comparative transcriptome analysis of resistant and susceptible Cucumis melo cultivars (KR1326 and K1237) inoculated with P. aegyptiaca. CmNLR (encodes a TIR-type NLR protein, consistently highly expressed in KR1326 roots) and CmNLRh (homologous gene of CmNLR) were cloned and overexpressed in K1237 roots to verify whether the TIR-type NLR protein can enhance C. melo resistance to P. aegyptiaca. The variations in enzymes related to active oxygen metabolism were further detected in transformed roots. The results showed that (1) some differentially expressed genes (DEGs) were enriched in pathways associated with active oxygen scavenging; (2) several DEGs encoded transcription factors, calcium channel proteins, and receptor-like proteins were upregulated and expressed in KR1326 roots; (3) the complete CmNLR and CmNLRh proteins prevented P. aegyptiaca from connecting to the vascular system of C. melo roots; and (4) stronger active oxygen burst and scavenging capacity were detected in transformed roots. We herein demonstrated that the TIR-type NLR protein confers C. melo resistance to P. aegyptiaca. The results provided clues for finding a new direction for host resistance against parasitic plants and shed new light on the cultivation of resistant varieties to control P. aegyptiaca.

Mature fruit abscission (MFA) is an important trait in terms of both harvest and yield. MFA can affect the production and economic value of melon fruit. An F3 population segregating for a single gene and derived from a cross between line M2-10, which shows no mature fruit abscission (None MFA), and the MFA line ZT00091 was used to map candidate genes. Specific length amplified fragment (SLAF) sequencing, in conjunction with bulked-segregant analysis (BSA), was used to map loci governing the natural fruit abscission of plants composing the F3-57 family. A candidate locus, mfa10.1, located on chromosome 10 between genomic positions 73,229 and 818,251, was obtained. An insertion-deletion (InDel) marker and 46 recombinant individuals were used to narrow the candidate region to within 35 kb at the genomic position of 650,203 to 685,250; this region included six candidate genes. qRT–PCR gene expression and gene sequence data showed that the CmARM14 gene, which encodes a RING-type E3 ubiquitin transferase (MELO3C012406), was a candidate for melon MFA. Subcellular localization observations revealed that the CmARM14 fusion protein was localized to the golgi apparatus. Taken together, these results provide a molecular basis for melon breeding.

Melon is an important horticultural crop worldwide. The high diversity of melon makes it a model plant for various different properties. Some quantitative trait loci or candidates have been discovered, but few were verified as limiting genetic transformation and genome editing systems. Identifying new genetic resources with resistance and special fruit quality traits is imperative to develop effective and useful breeding technologies in melon. This review describes the advances in genetics, genomics, and the breeding of melon and puts forward some recommendations in these areas.

Proximal remote sensing devices are novel tools that enable the study of plant health status through the measurement of specific characteristics, including the color or spectrum of light reflected or transmitted by the leaves or the canopy. The aim of this study is to compare the RGB and multispectral data collected during five years (2016–2020) of four fruiting vegetables (melon, tomato, eggplant, and peppers) with trial treatments of non-grafted and grafted onto resistant rootstocks cultivated in a Meloidogyne incognita (a root-knot nematode) infested soil in a greenhouse. The proximal remote sensing of plant health status data collected was divided into three levels. Firstly, leaf level pigments were measured using two different handheld sensors (SPAD and Dualex). Secondly, canopy vigor and biomass were assessed using vegetation indices derived from RGB images and the Normalized Difference Vegetation Index (NDVI) measured with a portable spectroradiometer (Greenseeker). Third, we assessed plant level water stress, as a consequence of the root damage by nematodes, using stomatal conductance measured with a porometer and indirectly using plant temperature with an infrared thermometer, and also the stable carbon isotope composition of leaf dry matter.. It was found that the interaction between treatments and crops (ANOVA) was statistically different for only four of seventeen parameters: flavonoid (p < 0.05), NBI (p < 0.05), NDVI (p < 0.05) and the RGB CSI (Crop Senescence Index) (p < 0.05). Concerning the effect of treatments across all crops, differences existed only in two parameters, which were flavonoid (p < 0.05) and CSI (p < 0.001). Grafted plants contained fewer flavonoids (x¯ = 1.37) and showed lower CSI (x¯ = 11.65) than non-grafted plants (x¯ = 1.98 and x¯ = 17.28, respectively, p < 0.05 and p < 0.05) when combining all five years and four crops. We conclude that the grafted plants were less stressed and more protected against nematode attack. Leaf flavonoids content and the CSI index were robust indicators of root-knot nematode impacts across multiple crop types.

Soil salinization is a major and increasing problem adversely impacting plant growth and crop production. Accordingly, coping with this problem has become a central topic in agriculture. In this study, we address this issue by evaluating the potential effectiveness of two bacterial species, Azospirillum brasilense and Paenibacillus dendritiformis, in enhancing growth and yield of melon and tomato plants under salinity stress. In vitro laboratory experiments indicated that these bacteria can efficiently colonize plant roots, and increase root length (25–33%) and root biomass (46–210%) of three melon plant varieties under saline stress. Similarly, greenhouse experiments showed that these bacteria significantly induced root (78–102%) and shoot weights (37–57%) of the three melon varieties irrigated with saline water. Tomato plants grown under the same conditions did not exhibit growth deficiency upon exposure to the saline stress and their growth was not enhanced in response to bacterial inoculation. Interestingly, saline-stressed melon plants inoculated with P. dendritiformis and A. brasilense exhibited lower total antioxidant activity compared to un-inoculated plants (80% vs. 60% of DPPH radical scavenging activity, respectively), suggesting that the inoculated plants experienced lower stress levels. These positive effects were further manifested by an increase of 16% in the crop yield of melon plants grown in the field under standard agricultural fertilization practices, but irrigated with saline water. Overall, these results demonstrate the beneficial effects of two plant-growth-promoting rhizobacteria, which can significantly alleviate the negative outcome of salt stress.

Imbalanced and excessive fertilizer application has resulted in low yields and reduced nutrient use efficiency for melon production in China. Estimating nutrient requirements is crucial for effectively developing site-specific fertilizer recommendations for increasing yield and profit while reducing negative environmental impacts. Relationships between the yield and nutrient uptake requirements of above-ground dry matter were assessed using 1127 on-farm observations (2000–2020) from melon production regions of China. The quantitative evaluation of fertility of tropical soils (QUEFTS) model was used to estimate nutrient requirements. It predicted a linear increase in yield at balanced nutrient uptake levels until the yield reached approximately 60–80% of the potential yield. In order to produce 1000 kg of fruit, 2.9, 0.4 and 3.2 kg/ha of N, P and K (7.2:1.0:7.8), respectively, were required for above-ground parts, while the corresponding nutrient internal efficiencies were 345.3, 2612.6 and 310.0 kg per kg N, P and K, respectively, whereas 1.4, 0.2 and 1.9 kg of N, P and K were required to replace nutrients removed after harvest. The corresponding fruit absorption rates were 47.0%, 59.5% and 58.2%, respectively. Field validation experiments confirmed the consistency between observed and simulated uptake rates, indicating that this model could estimate nutrient requirements. These findings will help develop fertilizer recommendations for improving melon yield and nutrient use efficiency.

Zucchini yellow mosaic virus (ZYMV; potyviridae) represents a major pathogen of Cucurbitaceae crops. ZYMV resistance in melon PI 414723 is conditioned by a dominant allele at the Zym locus. This resistant accession restricts viral spread and does not develop mosaic symptoms, but necrosis sometimes develops in response to inoculation. In previous studies, Zym has been mapped to linkage group II of the melon genetic map. In the present study, positional cloning of the locus was undertaken, starting from the CM-AG36 SSR marker at approximately 2 cm distance. We utilized five mapping populations that share the same resistant parent, PI 414723, and analyzed a total of 1630 offspring, to construct a high-resolution genetic map of the Zym locus. Two melon BAC libraries were used for chromosome walking and for developing new markers closer to the resistance gene by BAC-end sequencing. A BAC contig was constructed, and we identified a single BAC clone, from the ZYMV susceptible genotype MR-1, that physically encompasses the resistance gene. A second clone was isolated from another susceptible genotype, WMR 29, and the two clones were fully sequenced and annotated. Additional markers derived from the sequenced region delimited the region to 17.6 kb of a sequence that harbors a NAC-like transcription factor and, depending on the genotype, either two or three R-gene homologs with a CC-NBS-LRR structure. Mapping was confirmed by saturating the map with SNP markers using a single mapping population. The same region was amplified and sequenced also in the ZYMV resistant genotype PI 414723. Because numerous polymorphic sites were noted between genotypes, we could not associate resistance with a specific DNA polymorphism; however, this study enables molecular identification of Zym and paves the way to functional studies of this important locus.

N1-(2-chloro-4-pyridyl)-N3-phenylurea (CPPU), a synthetic cytokinin-active compound, is widely applied to induce parthenocarpic fruit set and enhance melon fruit enlargement (Cucumis melo L.). CPPU may also influence fruit quality; however, the mechanisms through which this occurs remain unknown. We investigated the differences in volatile emissions between parthenocarpic fruit set by CPPU (C) and seeded fruit set by artificial pollination (P). Gas chromatography–mass spectrometry (GC–MS) analysis revealed that six volatile organic compounds (VOCs) emitted by the P-group fruits were not detected in C-group fruits. The relative abundances of another 14 VOCs emitted by the CPPU-treated fruits were less than those in the P-group fruits. RNA sequencing analysis indicated that a total of 1027, 994, and 743 differentially expressed genes (DEGs) were detected in the C20 (treatment with 20 mg·L–1 CPPU) vs. P, P-C20 (pollination followed by 20 mg·L−1 CPPU treatment) vs. P, and P-C20 vs. C20 treatments, respectively. Compared with the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, the DEGs related to fatty acid degradation and metabolism, which contribute to volatile production, were enriched. In particular, DEGs such as carotenoid cleavage dioxygenase (CCD)-, lipoxygenase (LOX)-, alcohol dehydrogenase (ADH)-, and alcohol acyltransferase (ATT)-related genes were closely related to the formation of volatiles. In summary, our study provides a metabolic and transcriptomic atlas, reveals the impact of CPPU on VOCs, and enhances our understanding of the mechanisms of CPPU that contribute towards generally reducing the quality of melon fruit.

Microbes can establish a pathogenetic or symbiotic relationship with plants in soil and aquatic ecosystems. Although change in bacterial and fungal community in soil and their interaction with plants have been widely studied, little is known about their community structure in hydroponic systems across plant growth stages under different nutrient treatments. This study used next-generation sequencing analysis to assess the temporal changes in melon rhizosphere bacterial and fungal community structure across six different nutrient treatments. We found significant changes in the microbial community composition (especially for bacteria) between growth stages (R = 0.25–0.63, p < 0.01) than nutrient treatments. Proteobacteria dominated the bacterial community at the phylum level across melon growth stages (59.8% ± 16.1%). The genera Chryseobacterium, Pseudomonas, and Massilia dominated the rhizosphere in the flowering and pollination stage, while Brevibacillius showed the highest relative abundance in the harvesting stage. However, the rhizosphere was dominated by uncultured fungal taxa, likely due to the application of fungicides (Ridomil MZ). Further, linear regression analysis revealed a weak influence of bacterial community structure on melon yield and quality, while fruit weight and quality moderately responded to Mg and K deficiency. Nevertheless, the relative abundance of bacterial genus Chryseobacterium in the vegetative stage showed a strong correlation with fruit weight (R2 = 0.75, p < 0.05), while genera Brevibacillus, Lysobacter, and Bosea in late growth stages strongly correlated with fruit sweetness. Overall, temporal variability in the microbial (especially bacterial) community structure exceeds the variability between nutrient treatments for the given range of nutrient gradient while having little influence on melon yield.

Soil-borne pathogenic fungi (SBPF) and root-knot nematodes (RKN) co-exist in the rhizosphere and are major pathogens causing root diseases in cucurbits. Current knowledge on soil-borne pathogens of cucurbit crops grown under protected cultivation, their host-pathogen interactions, and mechanisms of resistance has been reviewed. Plant resistance is an effective and sustainable method to control soil-borne diseases and the available resistant cultivars and rootstocks to key soil-borne pathogens are reported. The importance of proper pathogen diagnosis in the right choice of cultivar or rootstock is highlighted because of the specificity in the response of the cucurbit crops to fungal and nematode species and races. Plants protect themselves through common mechanisms of resistance against SBPF and RKN including hardening of their cell walls, pathogenesis-related (PR) proteins, and production of antimicrobial molecules. The activity of some enzymes, such as peroxidases and phenylalanine lyase, is increased after pathogen infection and is higher on SBPF and RKN resistant than susceptible cucurbits. Plant hormones such as salicylic acid, jasmonic acid, and ethylene are involved in the response of cucurbits to SBPF. Most mechanisms of resistance to RKN affect post-infection development of the nematode, which results in a delay or disruption of the life cycle. Traditional and biotechnological tools used for breeding for resistance in cucurbits are described. Grafting is an effective non-host resistance method to control primarily Fusarium wilt but not to control RKN. However, new rootstocks with resistance to both pathogens have been developed recently and their effects on fruit quality and yield stability need additional studies. The impact of grafting on yield in pathogen-infested soils is discussed.

Powdery mildew (PM) is a fungal disease occurring in both field and greenhouse conditions worldwide. It infects many plant species and reduces both the productivity and quality of crops. Melon (Cucumis melo L.) is an economically important crop. In order to develop a molecular marker that can be used more conveniently in the development of PM-resistant melon using MR-1 melon resources, the previously reported cleaved amplified polymorphic sequence (CAPS) marker was improved with a length polymorphism PCR marker. Two cleaved CAPS markers—BSA12-LI3ECORI and BSA12-LI4HINFI—associated with BPm12.1, a major quantitative trait locus (QTL) corresponding to the PM resistance of MR-1, have been reported. In this study, we found that in the BSA12-LI3ECORI CAPS marker specifically, a 41 bp deletion was present in the PCR DNA region of the MR-1 melon genome. A new marker capable of distinguishing polymerase chain reaction (PCR) length polymorphism was produced using insertion-deletion (InDel) information in this region. This PCR-based InDel marker distinguished the genotypes of PM-resistant MR-1, PM-susceptible Top Mark, and their F1 progeny. These results suggest that this InDel marker could be used to develop PM-resistant melon varieties based on MR-1.

The stable isotope 15N was used to assess the recovery of mineral N fertilizer applied to fertigated and drip-irrigated spring muskmelon and autumn-winter sweet pepper crops grown in greenhouse soil plots. They received 92–96% of mineral N fertilizer as NO3−. 15N-labeled Ca (NO3)2 fertilizer was applied to crops during vegetative growth and fruit production phases. Crops were grown with either conventional management or combined improved N and irrigation management. Improved management for both irrigation and N was based on the combined use of models, to estimate crop requirements, and of monitoring of soil parameters. In sweet pepper, from conventional management, 15N recoveries from the 15N applications made during vegetative growth and fruit production were 66% and 58%, respectively. With improved management in sweet pepper, the corresponding 15N recoveries were 82% and 77%. In muskmelon, 15N recoveries from conventional management from the 15N applications made during vegetative growth and fruit production were 71% and 42%, respectively. With improved management, the corresponding 15N recoveries were 68% and 44%, respectively. The results demonstrated that combined drip irrigation and fertigation systems with frequent irrigation and N fertilizer application can have very high recovery of applied N fertilizer, of 77–82%.

Research into the symbiotic relationship between plants and arbuscular mycorrhizal fungi (AMF) is key for sustainable agricultural intensification. The objective of the present study is to evaluate native AMF at the monosporic level in greenhouse-grown, economically important crops. Agricultural soil samples from three locations (Saltillo, Zaragoza, and Parras) were obtained by combining portions resulting from a zigzag sampling pattern. From these samples, 15 morphotypes were extracted according to a modified Gerdemann’s technique and monosporically inoculated on melon, cucumber, tomato, and onion, 30 days after their sowing. Under a completely random experimental design, 16 treatments with three repetitions were defined. Plant height, root length, stem diameter, total fresh weight, fresh root weight, dry root weight, bulb weight, fresh leaf weight, total dry weight, flower number, leaf number, fruit number, spore number, and percentage of colonization were all evaluated. The results were subjected to the analysis of variance (ANOVA) and the Tukey comparison test (p ≤ 0.05), which showed that the monosporic inoculation favors significantly the AMF and the host, while the T6 (Saltillo spore + Steiner modified with 20% of the normal phosphorus concentration) showed a greater response uniformity on onion and melon, which indicates its great potential as an inoculum.

Soil salinization is a major and increasing problem adversely impacting plant growth and crop production. Accordingly, coping with this problem has become a central topic in agriculture. In this study, we address this issue by evaluating the potential effectiveness of two bacterial species, Azospirillum brasilense and Paenibacillus dendritiformis, in enhancing growth and yield of melon and tomato plants under salinity stress. In vitro laboratory experiments indicated that these bacteria can efficiently colonize plant roots, and increase root length (25–33%) and root biomass (46–210%) of three melon plant varieties under saline stress. Similarly, greenhouse experiments showed that these bacteria significantly induced root (78–102%) and shoot weights (37–57%) of the three melon varieties irrigated with saline water. Tomato plants grown under the same conditions did not exhibit growth deficiency upon exposure to the saline stress and their growth was not enhanced in response to bacterial inoculation. Interestingly, saline-stressed melon plants inoculated with P. dendritiformis and A. brasilense exhibited lower total antioxidant activity compared to un-inoculated plants (80% vs. 60% of DPPH radical scavenging activity, respectively), suggesting that the inoculated plants experienced lower stress levels. These positive effects were further manifested by an increase of 16% in the crop yield of melon plants grown in the field under standard agricultural fertilization practices, but irrigated with saline water. Overall, these results demonstrate the beneficial effects of two plant-growth-promoting rhizobacteria, which can significantly alleviate the negative outcome of salt stress. [ABSTRACT FROM AUTHOR]

Imbalanced and excessive fertilizer application has resulted in low yields and reduced nutrient use efficiency for melon production in China. Estimating nutrient requirements is crucial for effectively developing site-specific fertilizer recommendations for increasing yield and profit while reducing negative environmental impacts. Relationships between the yield and nutrient uptake requirements of above-ground dry matter were assessed using 1127 on-farm observations (2000–2020) from melon production regions of China. The quantitative evaluation of fertility of tropical soils (QUEFTS) model was used to estimate nutrient requirements. It predicted a linear increase in yield at balanced nutrient uptake levels until the yield reached approximately 60–80% of the potential yield. In order to produce 1000 kg of fruit, 2.9, 0.4 and 3.2 kg/ha of N, P and K (7.2:1.0:7.8), respectively, were required for above-ground parts, while the corresponding nutrient internal efficiencies were 345.3, 2612.6 and 310.0 kg per kg N, P and K, respectively, whereas 1.4, 0.2 and 1.9 kg of N, P and K were required to replace nutrients removed after harvest. The corresponding fruit absorption rates were 47.0%, 59.5% and 58.2%, respectively. Field validation experiments confirmed the consistency between observed and simulated uptake rates, indicating that this model could estimate nutrient requirements. These findings will help develop fertilizer recommendations for improving melon yield and nutrient use efficiency. [ABSTRACT FROM AUTHOR]

Zucchini yellow mosaic virus (ZYMV; potyviridae) represents a major pathogen of Cucurbitaceae crops. ZYMV resistance in melon PI 414723 is conditioned by a dominant allele at the Zym locus. This resistant accession restricts viral spread and does not develop mosaic symptoms, but necrosis sometimes develops in response to inoculation. In previous studies, Zym has been mapped to linkage group II of the melon genetic map. In the present study, positional cloning of the locus was undertaken, starting from the CM-AG36 SSR marker at approximately 2 cm distance. We utilized five mapping populations that share the same resistant parent, PI 414723, and analyzed a total of 1630 offspring, to construct a high-resolution genetic map of the Zym locus. Two melon BAC libraries were used for chromosome walking and for developing new markers closer to the resistance gene by BAC-end sequencing. A BAC contig was constructed, and we identified a single BAC clone, from the ZYMV susceptible genotype MR-1, that physically encompasses the resistance gene. A second clone was isolated from another susceptible genotype, WMR 29, and the two clones were fully sequenced and annotated. Additional markers derived from the sequenced region delimited the region to 17.6 kb of a sequence that harbors a NAC-like transcription factor and, depending on the genotype, either two or three R-gene homologs with a CC-NBS-LRR structure. Mapping was confirmed by saturating the map with SNP markers using a single mapping population. The same region was amplified and sequenced also in the ZYMV resistant genotype PI 414723. Because numerous polymorphic sites were noted between genotypes, we could not associate resistance with a specific DNA polymorphism; however, this study enables molecular identification of Zym and paves the way to functional studies of this important locus. [ABSTRACT FROM AUTHOR]

N1-(2-chloro-4-pyridyl)-N3-phenylurea (CPPU), a synthetic cytokinin-active compound, is widely applied to induce parthenocarpic fruit set and enhance melon fruit enlargement (Cucumis melo L.). CPPU may also influence fruit quality; however, the mechanisms through which this occurs remain unknown. We investigated the differences in volatile emissions between parthenocarpic fruit set by CPPU (C) and seeded fruit set by artificial pollination (P). Gas chromatography–mass spectrometry (GC–MS) analysis revealed that six volatile organic compounds (VOCs) emitted by the P-group fruits were not detected in C-group fruits. The relative abundances of another 14 VOCs emitted by the CPPU-treated fruits were less than those in the P-group fruits. RNA sequencing analysis indicated that a total of 1027, 994, and 743 differentially expressed genes (DEGs) were detected in the C20 (treatment with 20 mg·L–1 CPPU) vs. P, P-C20 (pollination followed by 20 mg·L−1 CPPU treatment) vs. P, and P-C20 vs. C20 treatments, respectively. Compared with the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, the DEGs related to fatty acid degradation and metabolism, which contribute to volatile production, were enriched. In particular, DEGs such as carotenoid cleavage dioxygenase (CCD)-, lipoxygenase (LOX)-, alcohol dehydrogenase (ADH)-, and alcohol acyltransferase (ATT)-related genes were closely related to the formation of volatiles. In summary, our study provides a metabolic and transcriptomic atlas, reveals the impact of CPPU on VOCs, and enhances our understanding of the mechanisms of CPPU that contribute towards generally reducing the quality of melon fruit. [ABSTRACT FROM AUTHOR]

Microbes can establish a pathogenetic or symbiotic relationship with plants in soil and aquatic ecosystems. Although change in bacterial and fungal community in soil and their interaction with plants have been widely studied, little is known about their community structure in hydroponic systems across plant growth stages under different nutrient treatments. This study used next-generation sequencing analysis to assess the temporal changes in melon rhizosphere bacterial and fungal community structure across six different nutrient treatments. We found significant changes in the microbial community composition (especially for bacteria) between growth stages (R = 0.25–0.63, p < 0.01) than nutrient treatments. Proteobacteria dominated the bacterial community at the phylum level across melon growth stages (59.8% ± 16.1%). The genera Chryseobacterium, Pseudomonas, and Massilia dominated the rhizosphere in the flowering and pollination stage, while Brevibacillius showed the highest relative abundance in the harvesting stage. However, the rhizosphere was dominated by uncultured fungal taxa, likely due to the application of fungicides (Ridomil MZ). Further, linear regression analysis revealed a weak influence of bacterial community structure on melon yield and quality, while fruit weight and quality moderately responded to Mg and K deficiency. Nevertheless, the relative abundance of bacterial genus Chryseobacterium in the vegetative stage showed a strong correlation with fruit weight (R2 = 0.75, p < 0.05), while genera Brevibacillus, Lysobacter, and Bosea in late growth stages strongly correlated with fruit sweetness. Overall, temporal variability in the microbial (especially bacterial) community structure exceeds the variability between nutrient treatments for the given range of nutrient gradient while having little influence on melon yield. [ABSTRACT FROM AUTHOR]

Soil-borne pathogenic fungi (SBPF) and root-knot nematodes (RKN) co-exist in the rhizosphere and are major pathogens causing root diseases in cucurbits. Current knowledge on soil-borne pathogens of cucurbit crops grown under protected cultivation, their host-pathogen interactions, and mechanisms of resistance has been reviewed. Plant resistance is an effective and sustainable method to control soil-borne diseases and the available resistant cultivars and rootstocks to key soil-borne pathogens are reported. The importance of proper pathogen diagnosis in the right choice of cultivar or rootstock is highlighted because of the specificity in the response of the cucurbit crops to fungal and nematode species and races. Plants protect themselves through common mechanisms of resistance against SBPF and RKN including hardening of their cell walls, pathogenesis-related (PR) proteins, and production of antimicrobial molecules. The activity of some enzymes, such as peroxidases and phenylalanine lyase, is increased after pathogen infection and is higher on SBPF and RKN resistant than susceptible cucurbits. Plant hormones such as salicylic acid, jasmonic acid, and ethylene are involved in the response of cucurbits to SBPF. Most mechanisms of resistance to RKN affect post-infection development of the nematode, which results in a delay or disruption of the life cycle. Traditional and biotechnological tools used for breeding for resistance in cucurbits are described. Grafting is an effective non-host resistance method to control primarily Fusarium wilt but not to control RKN. However, new rootstocks with resistance to both pathogens have been developed recently and their effects on fruit quality and yield stability need additional studies. The impact of grafting on yield in pathogen-infested soils is discussed. [ABSTRACT FROM AUTHOR]

Powdery mildew (PM) is a fungal disease occurring in both field and greenhouse conditions worldwide. It infects many plant species and reduces both the productivity and quality of crops. Melon (Cucumis melo L.) is an economically important crop. In order to develop a molecular marker that can be used more conveniently in the development of PM-resistant melon using MR-1 melon resources, the previously reported cleaved amplified polymorphic sequence (CAPS) marker was improved with a length polymorphism PCR marker. Two cleaved CAPS markers—BSA12-LI3ECORI and BSA12-LI4HINFI—associated with BPm12.1, a major quantitative trait locus (QTL) corresponding to the PM resistance of MR-1, have been reported. In this study, we found that in the BSA12-LI3ECORI CAPS marker specifically, a 41 bp deletion was present in the PCR DNA region of the MR-1 melon genome. A new marker capable of distinguishing polymerase chain reaction (PCR) length polymorphism was produced using insertion-deletion (InDel) information in this region. This PCR-based InDel marker distinguished the genotypes of PM-resistant MR-1, PM-susceptible Top Mark, and their F1 progeny. These results suggest that this InDel marker could be used to develop PM-resistant melon varieties based on MR-1. [ABSTRACT FROM AUTHOR]

The stable isotope 15N was used to assess the recovery of mineral N fertilizer applied to fertigated and drip-irrigated spring muskmelon and autumn-winter sweet pepper crops grown in greenhouse soil plots. They received 92–96% of mineral N fertilizer as NO3−. 15N-labeled Ca (NO3)2 fertilizer was applied to crops during vegetative growth and fruit production phases. Crops were grown with either conventional management or combined improved N and irrigation management. Improved management for both irrigation and N was based on the combined use of models, to estimate crop requirements, and of monitoring of soil parameters. In sweet pepper, from conventional management, 15N recoveries from the 15N applications made during vegetative growth and fruit production were 66% and 58%, respectively. With improved management in sweet pepper, the corresponding 15N recoveries were 82% and 77%. In muskmelon, 15N recoveries from conventional management from the 15N applications made during vegetative growth and fruit production were 71% and 42%, respectively. With improved management, the corresponding 15N recoveries were 68% and 44%, respectively. The results demonstrated that combined drip irrigation and fertigation systems with frequent irrigation and N fertilizer application can have very high recovery of applied N fertilizer, of 77–82%. [ABSTRACT FROM AUTHOR]

Research into the symbiotic relationship between plants and arbuscular mycorrhizal fungi (AMF) is key for sustainable agricultural intensification. The objective of the present study is to evaluate native AMF at the monosporic level in greenhouse-grown, economically important crops. Agricultural soil samples from three locations (Saltillo, Zaragoza, and Parras) were obtained by combining portions resulting from a zigzag sampling pattern. From these samples, 15 morphotypes were extracted according to a modified Gerdemann's technique and monosporically inoculated on melon, cucumber, tomato, and onion, 30 days after their sowing. Under a completely random experimental design, 16 treatments with three repetitions were defined. Plant height, root length, stem diameter, total fresh weight, fresh root weight, dry root weight, bulb weight, fresh leaf weight, total dry weight, flower number, leaf number, fruit number, spore number, and percentage of colonization were all evaluated. The results were subjected to the analysis of variance (ANOVA) and the Tukey comparison test (p ≤ 0.05), which showed that the monosporic inoculation favors significantly the AMF and the host, while the T6 (Saltillo spore + Steiner modified with 20% of the normal phosphorus concentration) showed a greater response uniformity on onion and melon, which indicates its great potential as an inoculum. [ABSTRACT FROM AUTHOR]