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Linking genotype with phenotype is a fundamental goal in biology and requires robust data for both. Recent advances in plant-genome sequencing have expedited comparisons among multiple-related individuals. The abundance of structural genomic within-species variation that has been discovered indicates that a single reference genome cannot represent the complete sequence diversity of a species, leading to the expansion of the pan-genome concept. For high-resolution forward genetics, this unprecedented access to genomic variation should be paralleled and integrated with phenotypic characterization of genetic diversity. We developed a multi-parental framework for trait dissection in melon (Cucumis melo), leveraging a novel pan-genome constructed for this highly variable cucurbit crop. A core subset of 25 diverse founders (MelonCore25), consisting of 24 accessions from the two widely cultivated subspecies of C. melo, encompassing 12 horticultural groups, and 1 feral accession was sequenced using a combination of short- and long-read technologies, and their genomes were assembled de novo. The construction of this melon pan-genome exposed substantial variation in genome size and structure, including detection of ~300 000 structural variants and ~9 million SNPs. A half-diallel derived set of 300 F

Linking between genotype and phenotype is a fundamental goal in biology and requires robust data for both layers. The prominent increase in plant genome sequencing and comparisons of multiple related individuals, exposed the abundance of structural genomic variation and suggest that a single reference genome cannot represent the complete sequence diversity of a crop species, leading to the expansion of the pan-genome concept. For high-resolution forward genetics, this unprecedented access to genomic variation should be paralleled by availability and phenotypic characterization of genetic diversity, and effective integration between these layers. Here, we describe a multi-parental framework for trait dissection in melon, leveraging a novel pan-genome constructed for this crop. Melon (Cucumis melo L.) is an important crop from the Cucurbitaceae family, which display extensive phenotypic variation available for breeding. A diverse core set of 25 founder lines (MelonCore25) was sequenced using a combination of short and long-read technologies and their genomes were assembled de novo. The construction of a melon pan-genome exposed substantial variation in genome size and structure, including detection of ~300,000 structural variants and ~9 million SNPs. A half-diallel derived set of 300 F2 populations representing all possible MelonCore25 parental combinations was constructed as framework for trait dissection through integration with the pan-genome. We demonstrate the potential of this unified framework for genetic analysis of various melon traits, including rind color and mottling pattern, fruit sugar content and resistance to fungal diseases. We anticipate that utilization of this integrated resource will enhance genetic dissection of important traits and accelerate melon breeding.Significance statementPan-genomes aim to address the abundance of genome structural variation within species for improved genomic analyses. New pan-genome, constructed from de novo genome assemblies of 25 diverse melon (Cucumis melo L.) accessions is integrated with a half-diallel derived set of 300 F2 populations representing all possible parental combinations. The potential of this unified multi-parental trait dissection framework for melon genetics and breeding is presented.

Commercial cucurbits are commonly grafted onto interspecific Cucurbita hybrid rootstocks. The unproven paradigm is that hybrid rootstocks are more vigorous, resulting in better yields and high-level resistance. The objective of this study was to test the above hypothesis by comparing the performance of parental lines to that of derived F1 hybrids as non-grafted Cucurbita accessions and as grafted melons, in experiments conducted in the greenhouse and in the field. The response to biotic stress was evaluated in with Rhizoctonia solani inoculated non-grafted Cucurbita parents and hybrids. In four out of the five hybrid–parent sets evaluated, susceptibility of the hybrid to R. solani was reduced or comparable to that of the parents. Grafted melon performance, expressed by plant development index, physiological wilt incidence and fruit yield, was evaluated in the field and in the greenhouse. Three hybrids out of the five tested in the field exhibited lower physiological wilt incidence than their parents. In three parent–hybrid sets, the male parent exhibited the worst rootstock performance and in one case, the male parent exhibited the lowest wilting. Fruit yield of grafted melons was highly correlated to wilt incidence. According to our results, the superiority of the hybrid over its parents and the benefit of the interspecific Cucurbita rootstock are not conclusive and varies among crosses and traits. The pathological, horticultural and economic benefits of this approach should therefore be further tested and reconsidered.

Macrophomina phaseolina is the causal agent of charcoal rot disease, which attacks many plant species, including those in the Cucurbitaceae. The fungus is frequently isolated from wilted melon and watermelon plants in Israel. Nevertheless, the role of M. phaseolina in disease progress and induction of wilting or yield reduction in watermelons and melons is not clear and not similar. Precise disease identification is important in order to suggest effective control measures. The objective of the current study was therefore to investigate disease progress and document its damage in watermelon and melon. Watermelons and melons were seeded in a field naturally infested with M. phaseolina and in the greenhouse in 10-L pots containing dune sand. Plants were inoculated at 35 days of age using two methods: drenching with macerated fungus around the crown area or stabbing the lower stem with an M. phaseolina- infested toothpick. Disease progress was documented in the field and in the greenhouse. Plant colonization and symptom development were more pronounced in melon than in watermelon. Large lesions and significant internal rotting developed in melon plants inoculated by the two methods in both field and greenhouse. In watermelon, however, no lesions or internal rotting were observed. Disease effect on melons and watermelons was observed only in the field, a short time before harvest, and was expressed as partial wilting and significant loss of shoot and fruit fresh weight similarly to disease appearance under natural infection. No wilting of melons or watermelons was observed in the greenhouse experiment.

Melon plants grafted on Cucurbita rootstock may suffer from nutritional deficiencies due to reduced absorption and translocation of minerals to the foliage. Melon (Cucumis melo L.) cv. 6023 was grafted onto two interspecific Cucurbita rootstocks (Cucurbita maxima × Cucurbita moschata) ‘TZ-148’ and ‘Gad’. Nongrafted melons were used as controls. Two fertilization field experiments were conducted in walk-in tunnels in the northern Arava valley of southern Israel. Two fertigation regimes were used: 1) standard and 2) enriched for magnesium (Mg; 150 mg·L−1), manganese (Mn; 7.5 mg·L−1), and zinc (Zn; 0.75 mg·L−1) to increase the concentrations of the lacking elements. The enriched fertigation significantly increased Mn, Zn, and Mg contents in the leaf tissue. Concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), chloride (Cl), iron (Fe), and boron (B) were unaffected by the enriched fertilizer. There were no deficiency symptoms in grafted plants supplied with the enriched fertilizer.

Fusarium oxysporum f. sp. radicis-cucumerinum (fusarium crown rot, Forc) is an emerging pathogen of melons, Cucumis melo . Forc incites rotting of the plant crown, causing the plants to die prematurely. Most melon accessions are susceptible to this pathogen but the cantaloupe ‘Hemed’ is highly resistant. ‘Hemed’ was crossed with the susceptible muskmelon ‘Dulce’ to ascertain the mode of inheritance of resistance to Forc. Parental-, filial-, and backcross-generation plants were grown under controlled conditions and inoculated with Forc by using a root-dip methodology. Plants were scored as resistant or susceptible at 18 days post inoculation (dpi), when all plants of the susceptible parent ‘Dulce’ were dead or showed severe disease symptoms. At 18 dpi, plants of ‘Hemed’, the F 1 , and the backcross to ‘Hemed’ were resistant. The F 2 population segregated in accordance with a 13:3 ratio, deviating significantly from a 3:1 ratio of resistant to susceptible. The backcross to ‘Dulce’ segregated in accordance with a 1:1 ratio of resistant to susceptible. These results indicate that ‘Hemed’ carries two genes for resistantance to Forc, one dominant and one recessive, which are herein designated, respectively, as Forc-1 and forc-2 . Resistance to Forc is not co-inherited with resistance to F. oxysporum f. sp. melonis (fusarium wilt, Fom) races 0, 1, and 2, as both ‘Hemed’ and ‘Dulce’ are resistant to Fom races 0 and 2 and susceptible to Fom race 1.

Fusarium root and stem rot caused by the fungus Fusarium oxysporum f. sp. radicis-cucumerinum is a major disease in greenhouse cucumbers. Over the past decade, the disease has been documented in melon greenhouses in Greece, and recently it has been sporadically recorded in greenhouse melons in Israel. Variations in disease response were found among 41 melon accessions artificially inoculated with the pathogen: 10 accessions were highly susceptible (90–100% mortality), 23 exhibited an intermediate response (20–86%) and eight were resistant (0–4%). Two melon accessions – HEM (highly resistant) and TAD (partially resistant) – were crossed with the susceptible accession DUL. The responses of the three accessions and F1 crosses between the resistant and susceptible parents were evaluated. HEM contributed higher resistance to the F1 hybrid than TAD. Roots of susceptible and resistant accessions were 100 and 79% colonized, respectively, following artificial inoculation. However, only susceptible plants showed colonization of the upper plant tissues. Microscopic evaluation of cross sections taken from the crown region of the susceptible DUL revealed profuse fungal growth in the intercellular spaces of the parenchyma and in xylem vessels. In the resistant cultivar HEM, very little fungal growth was detected in the intercellular spaces of the parenchyma, and none in the xylem or any other vascular tissue. Finding resistant accessions may create an opportunity to study the genetics of resistance inheritance and to develop molecular markers that will facilitate breeding resistant melon cultivars.

The authenticity of fruit flavours in foods and beverages is of great importance for the producers of jams, ice creams, soft drinks, yogurt, etc. Regulations regarding the authenticity of flavours in foods and beverages will help consumers choose the foods best suitable for them. In order to enhance this goal, we have used headspace–solid phase microextraction stereoselective gas chromatography–mass spectrometry (HS–SPME stereoselective GC–MS) to determine the enantiomeric ratios of chiral flavour and fragrance indicators present in the raw materials and in the products. γ-Decalactone in peach, nectarine, strawberry, passion fruit and apricot, as well as (E)-α-ionone in raspberry and linalool and linalyl acetate in bergamot, were used as indicators in stereoselective analysis of commercial foods and beverages. In the fresh fruit aromas only one enantiomer was predominant or enantiomerically pure. In many commercial fruit products we detected racemic mixtures of the above-mentioned chiral flavour compounds. The results suggest that HS–SPME stereoselective GC–MS could be a useful tool for differentiating natural flavour compounds from synthetic ingredients in quality control of foods and beverages. Copyright © 2009 John Wiley & Sons, Ltd.

Oxidative stress has been implicated in pathologic processes associated with neurodegenerative diseases. Astrocytes, the most abundant glial cell type in the brain, protect neurons from reactive oxygen species (ROS), and any damage to them will affect neuronal survival. This study compares the ability of essential oils prepared from different herbs and spices to protect cultured primary brain astrocytes from H2O2-induced death. The results show that the essential oil of Salvia fruticosa (Sf) among the tested essential oils demonstrated remarkable protective activity. The protective effect of Sf could be attributed to alpha-humulene and alpha-pinene. Following incubation, alpha-humulene and trans-beta-caryophyllene could be found in the cytosol of astrocytes. It is proposed that Sf, by attenuating H2O2-induced cell death, might be used as a functional food or may be offered as a means of therapy in the treatment of neurodegenerative diseases.