Ethylene production, shelf-life and evidence of RFLP polymorphisms linked to ethylene genes in melon (Cucumis melo L.)

Sixty three cultigens from eight market types of the melon (Cucumis melo L. subsp. melo) groups Cantaloupensis and Inodorus were evaluated for ethylene production rate, shelf-life (postharvest decay), and RFLP polymorphisms. The ethylene production rates of melon fruits at maturity and (after) postharvest decay were measured on individual genotypes. The ethylene production rates of individual genotypes ranged from undetectable to 103 nl/g per h. The mean ethylene production rates of the eight market types, ranked from highest to lowest, were Eastern U.S. type, Charentais, Western U.S. type, Long Shelf-Life cantaloupes (LSL), Galia, Ananas, Honeydew, and Casaba. Ethylene production and postharvest decay rating were positively significantly correlated (r ²=0.87, P=0.05). Orange-fleshed melon fruits produced significantly (P=0.05) more ethylene than did green- or white-fleshed types. Melon fruits with a netted rind had significantly (P=0.05 for orange-flesh fruits and 0.01 for green- or white-flesh fruits) higher ethylene production than did smooth-type fruits. Using probes made from cDNAs encoding ACC oxidase (MEL1) or ACC synthase (MEACS1) genes, RFLPs were detected melon cultigens of the eight marker types showing varying ethylene production rates and different flesh colors. Low ethylene production and green- and white-flesh color were associated (r ²=0.91; P=0.05) with the presence of a putative RFLP-MEL1 allele A ₀ (15-kb), whereas high ethylene production and orange-flesh color were associated with allele B ₀ (8.5-kb) in the homozygous condition, after probing MEL1 with EcoRV-digested genomic DNA. Also, after probing MEACS1 with NdeI-digested genomic DNA, RFLP polymorphism revealed five fragments denoted as A, B, C, D and E, with molecular sizes of 5.2-, 4.2-, 3.8-, 3.0- and 1.0-kb, respectively. A two-fragment pattern, AB, and a three-fragment pattern, ACE, the two predominant RFLP patterns, were also associated with low and high ethylene production, respectively. The ACE fragment pattern was also associated with orange-flesh melons. Scoring of both probes allowed for the unique classification of most melon market types consistent with ethylene production and the postharvest decay phenotypes. Therefore, these RFLPs might have utility in marker-assisted selection for the development of melons with enhanced postharvest keeping ability. Received: 26 March 1998 / Accepted: 12 January 2000     

Comparative mapping of ZYMV resistances in cucumber (Cucumis sativus L.) and melon (Cucumis melo L.)

Zucchini yellow mosaic virus (ZYMV) routinely causes significant losses in cucumber (Cucumis sativus L.) and melon (Cucumis melo L.). ZYMV resistances from the cucumber population TMG1 and the melon plant introduction (PI) 414723 show different modes of inheritance and their genetic relationships are unknown. We used molecular markers tightly linked to ZYMV resistances from cucumber and melon for comparative mapping. A 5-kb genomic region (YCZ-5) cosegregating with the zym locus of cucumber was cloned and sequenced to reveal single nucleotide polymorphisms and indels distinguishing alleles from ZYMV-resistant (TMG1) and susceptible (Straight 8) cucumbers. A low-copy region of the YCZ-5 clone was hybridized to bacterial artificial chromosome (BAC) clones of melon and a 180-kb contig assembled. One end of this melon contig was mapped in cucumber and cosegregated with ZYMV resistance, demonstrating that physically linked regions in melon show genetic linkage in cucumber. However the YCZ-5 region segregated independently of ZYMV resistance loci in two melon families. These results establish that these sources of ZYMV resistances from cucumber TMG1 and melon PI414723 are likely non-syntenic.     

Indole-3-acetic acid, ethylene, and abscisic acid metabolism in developing muskmelon (Cucumis melo L.) fruit

Hormonal metabolism associated with fruit development in muskmelon was investigated by measuring IAA, ABA, and ACC levels in several tissues at various stages of development. In addition, levels of conjugated IAA and ABA were determined in the same tissues. Ethylene production, which is believed to signal the ripening and senescence of mature fruit, was also measured. Ethylene production was highest in the outer tissue near the rind and gradually declined during maturation, except for a dramatic increase in all fruit tissues at the climacteric. In contrast to ethylene production, ACC levels increased during maturation and remained equal throughout the fruit until the climacteric, when levels in the outer tissues increased nearly 5-fold over levels in the inner tissues. The consistent presence of ACC indicates that ACC oxidase rather than the availability of ACC regulates ethylene production in developing fruits. ABA and ABA esters generally declined during maturation, however an increase in ABA esters associated with the outer mesocarp tissue was observed in fully mature, climacteric fruit. IAA and IAA conjugates were only found in the outer tissue near the rind, and their levels remained low until the fruit was fully mature and entering the climacteric. At that time, increased levels of conjugates were detected. The late burst of hormonal metabolism in the outer mesocarp tissue appeared to signal its degeneration and the deterioration that typically occurs in ripening fruit. The tissue-specific conjugation of IAA and ABA, in addition to the production of climacteric ethylene, may represent part of the signaling mechanism initiating ripening and eventual deterioration of tissues in muskmelon fruits.Abbreviations ABA abscisic acid - ACC 1-aminocylopropane-1-carboxylic acid - DAP days after pollination - IAA indole-3-acetic acid     

Characterization of two cDNA clones for mRNAs expressed during ripening of melon (Cucumis melo L.) fruits

In vitro translation of mRNAs and polyacrylamide gel electrophoresis of proteins from melons revealed that several mRNAs increased in amount during ripening, indicating the existence of other ripening genes in addition to those cloned previously. To identify ripening-related genes we have screened a ripe melon cDNA library and isolated two novel cDNA clones (MEL2 and MEL7) encoding unidentified proteins. Southern analysis revealed that MEL2 and MEL7 are encoded by low-copy-number genes. The MEL2 cDNA clone is near full-length, corresponds to a 1600 nucleotide mRNA that accumulates during ripening and encodes a predicted protein rich in hydrophobic amino acids. The MEL7 cDNA clone is full-length, corresponds to a mRNA of 0.7 kb which accumulates during early ripening stages and is also present at low levels in other organs of the melon plant. The MEL7 predicted polypeptide is 17 kDa and shows significant homology with the major latex protein from opium-poppy. Wounding and ethylene treatment of unripe melon fruits 20 days after anthesis showed that MEL2 and MEL7 mRNAs are only induced by ethylene.     

On the genetic control of heterosis for fruit shape in melon (Cucumis melo L.)

The objective of the present work is to study the genetic basis of heterosis for fruit shape (FS) in melon observed in a cross between the Spanish cultivar "Piel de Sapo" (PS) and the Korean accession PI 161375 (Songwang Charmi [SC]) using a set of near-isogenic lines (NILs) with contrasting phenotypes for FS, each carrying a single chromosomal introgression from SC within the genetic background of PS. We investigated the FS of homozygous NILs, hybrids NIL x PS, and all 2-way crosses between NILs to test the main heterosis hypotheses (dominance, overdominance, and epistatic interactions). Gene action of alleles of quantitative trait loci inducing fruit enlargement was dominance, whereas those inducing rounder fruit were additive or recessive. Only minor epistatic interactions were found. Therefore, the most plausible explanation for FS heterosis in this cross is in agreement with the dominance complementation hypothesis. Over 70% of the hybrid heterosis could be achieved by combining just 2 loci, indicating that the genetic control of FS heterosis in this cross is relatively simple. FS is proposed as a reproductive trait in melon because of the high correlation to the number of seeds produced along the fruit longitudinal axis.     

Genetic control of fruit shape acts prior to anthesis in melon (Cucumis melo L.)

Genetic control of fruit shape in Cucumis melo was studied using QTL analysis in two Recombinant Inbred (RI) populations consisting of 163 and 63 individuals, respectively, obtained by crossing the same round-fruited parent with two different elongated-fruit lines. Fruit shape is mainly explained by fruit length in these two populations. Most QTLs for fruit shape and ovary shape detected were found to co-segregate, thus demonstrating early control of fruit shape during ovary development. A high level of correlation between fruit shape and ovary shape was also found in 14 unrelated genetic lines, a finding which suggests that control of fruit shape by gene(s) active early in the ovary is a general feature in C. melo. Two major flower genes, a ( monoecious) and p ( pentamerous), were shown to have major effects on fruit shape. Major tightly linked QTLs for fruit and ovary shape were found close to the a and p genes, probably reflecting their pleiotropic effect on fruit shape. Moreover, one of the two QTLs detected in the Védrantais x PI 414723 population was also found in the Védrantais x PI 161375 population. Variation of fruit shape in melon could be due to variations having quantitative effects on a large set of genes that are probably involved in ovary development.     

Detection of ethylene receptor protein Cm-ERS1 during fruit development in melon (Cucumis melo L.)

Antibodies against melon ethylene receptor, Cm- ERS1 was prepared. Cm-ERS1 protein formed a disulphide-linked homodimer and it was present in microsomal membranes but not in soluble fractions. Cm-ERS1 protein was present at high levels in melon fruit during early developmental stages. This transition pattern was also observed in another melon cultivar.     

Genetic difference in somatic embryogenesis from seeds in melon (Cucumis melo L.)

Significant differences in somatic embryogenesis from melon seeds were observed among 18 cultivars; especially, cultivars Earl's Favorite and Barnett which produced a large number of somatic embryos. F₁ seeds were obtained by reciprocal crosses between cultivars. Some lines produced a large number of somatic embryos whereas others showed no or poor embryogenic response. Most of the F₁ seeds formed somatic embryos. The frequency of somatic embryogenesis decreased as compared to the parents with the highest potential. Transfer of the frequency of somatic embryogenesis from superior responding cultivars to inferior cultivars was proved. It was difficult to determine the mode of inheritance of somatic embryogenesis because there was a large variation in the range of somatic embryogenesis from F₂ seeds, and cytoplasmic effect was recognized in certain combinations.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BAP 6-benzylaminopurine     

Analysis of physiological and molecular changes in melon (Cucumis melo L.) varieties with different rates of ripening

Seven melon varieties (Alpha, Delada, Marygold, Sirio, Topper,Tornado, and Viva) known to exhibit differences in their ripeningbehaviour were used in this study. The expression of mRNAs forACC oxidase (MEL1) and phytoene synthase (MEL5), required forsynthesis of ethylene and carotenoids, respectively, and tworipening-related cDNAs (MEL2 and MEL7), of unknown function,was examined and correlated with the development of colour andsoftening of fruits. The MEL2 and MEL7 mRNAs were present andaccumulated in all varieties, indicating their importance inmelon fruit ripening. The fruits of Delada and Marygold didnot show any change in the colour of the flesh even at 50 daa(days after anthesis). All other varieties changed colour fromgreen to orange between 25–30 daa. The phytoene synthasemRNA levels in most varieties seemed to be unrelated to changein fruit flesh colour. The firmness of all the fruits was reducedsignificantly between 25 and 40 daa. The expression of ACC oxidasemRNA showed the most variation among the different varitiesand was delayed in Sirio and undetectable in Marygold fruitseven at 40 daa. Varieties with delayed expression of ACC oxidasemRNAs after anthesis also showed delayed softening during ripening.The prospects of genetic engineering and breeding for melonfruits with improved quality characteristics and extended storagelife are discussed. Key words: Cucumis melo, colour development, melon varieties, ripening genes, softening     

Bin mapping of genomic and EST-derived SSRs in melon (Cucumis melo L.)

We report the development of 158 primer pairs flanking SSR motifs in genomic (gSSR) and EST (EST-SSR) melon sequences, all yielding polymorphic bands in melon germplasm, except one that was polymorphic only in Cucurbita species. A similar polymorphism level was found among EST-SSRs and gSSRs, between dimeric and trimeric EST-SSRs, and between EST-SSRs placed in the open reading frame or any of the 5′- or 3′-untranslated regions. Correlation between SSR length and polymorphism was only found for dinucleotide EST-SSRs located within the untranslated regions, but not for trinucleotide EST-SSRs. Transferability of EST-SSRs to Cucurbita species was assayed and 12.7% of the primer pairs amplified at least in one species, although only 5.4% were polymorphic. A set of 14 double haploid lines from the cross between the cultivar “Piel de Sapo” and the accession PI161375 were selected for the bin mapping approach in melon. One hundred and twenty-one SSR markers were newly mapped. The position of 46 SSR loci was also verified by genotyping the complete population. A final bin-map was constructed including 80 RFLPs, 212 SSRs, 3 SNPs and the Nsv locus, distributed in 122 bins with an average bin length of 10.2 cM and a maximum bin length of 33 cM. Map density was 4.2 cM/marker or 5.9 cM/SSR. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of modified endogenous ethylene production on sex expression, bisexual flower development and fruit production in melon (Cucumis melo L.)

Members of the Cucurbitaceae family display a range of sexual phenotypes including various combinations of male, female, or bisexual flowers. Ethylene appears to be a key hormone regulating the sex determination process. Application of ethylene, or inhibition of ethylene action, increases or decreases the number of pistil-bearing buds, respectively. Elevated levels of ethylene production and expression of genes for ethylene biosynthesis, have been correlated with pistillate flower production. In this study, we sought to determine the effect of modified endogenous ethylene production on sex expression by constitutively expressing ACS (1-aminocyclopropane-1-carboxylate synthase), the first committed enzyme for ethylene biosynthesis, in transgenic melons (Cucumis melo L.). Most melon genotypes are andromonoecious, where an initial phase of male flowers is followed by a mixture of bisexual and male flowers. ACS melon plants showed increased ethylene production by leaves and flower buds, and increased femaleness as measured by earlier and increased number of bisexual buds. ACS melons also had earlier and increased number of bisexual buds that matured to anthesis, suggesting that ethylene is important not only for sex determination, but also for development of the bisexual bud to maturity. Field studies showed that ACS melons had earlier mature bisexual flowers, earlier fruit set, and increased number of fruit set on closely spaced nodes on the main stem. These results provide a direct demonstration of the importance of endogenous ethylene production for female reproductive processes in melon.     

Selection of somaclonal variants with low-temperature germinability in melon (Cucumis melo L.)

Summary Plants were regenerated from adventitious buds and somatic embryos (R₀) of melon (Cucumis melo L.), the cultivar Andes. Somaclonal variants of melon with low temperature germinability were selected from the progenies (R₁) of R₀ plants. Among 5,618 R₁ seeds harvested from 23 R₀ plants that were regenerated from adventitious buds 4 seeds germinated after 5 days of culture at 15 °C (selection rate; 0.07%). However, among 374 R₂ seeds harvested from 2 R₁ plants no seed germinated after 7 days of culture at 14 °C. Among 9,181 R₁ seeds harvested from 50 R₀ plants regenerated from somatic embryos 110 seeds germinated after 5 days of culture at 15 °C (selection rate; 1.20%). Among 3,717 R₂ seeds harvested from 17 R₁ plants 113 seeds germinated after 7 days of culture at 14 °C (selection rate; 3.04%). R₃ seeds were collected from these R₂ plants following self-pollination. Forty-five of the 47 lines (R₃) originated from 10 R₀ plants showed higher germination rates than that of the original cultivar. Selected lines with low-temperature germinability showed greater fruit growth rate than the original cultivar during the middle stage when they were cultivated in a greenhouse under low-temperature conditions. Of fruits harvested from 31 lines, 15 lines showed greater fruit volume than the original cultivar.     

Genome-wide characterization and expression analysis of the auxin response factor (ARF) gene family during melon (Cucumis melo L.) fruit development

Protoplasma - ARFs in plants mediate auxin signaling transduction and regulate growth process. To determine genome-wide characterization of ARFs family in melon (Cucumis melo L.), ARFs were...     

新疆甜瓜地方种质资源遗传多样性的SRAP分析

为研究我国新疆甜瓜地方种质资源亲缘关系及其分类,充分高效的利用种质资源,利用SRAP(sequence-related amplified polymorphism technique)标记对117份中国新疆甜瓜地方品种和28份国内外对照材料进行亲缘关系和遗传多样性分析。结果表明,20对SRAP引物共扩增出224个带,其中多态性谱带216个,多态性比率达96%,平均每对引物扩增的带数和多态性带数分别为11.2个和10.8个,每对引物的多态性信息含量PIC值为0.73~0.94,平均为0.85;不同生态区域供试材料的Nei's基因多样性指数(H)和Shannon's信息指数(I)分别为0.1075~0.2560和0.1569~0.4061,中国新疆的南疆、东疆和北疆均高于其他生态区域供试材料,且以南疆最高,具有非常丰富的遗传多样性;不同生态区域甜瓜种质资源的遗传一致度和遗传距离分别为0.6384~0.9919和0.0081~0.4488,其中南疆、东疆和北疆两两之间的遗传一致度均在0.95以上,遗传距离均在0.04以下,三者之间遗传分化较小;中国新疆甜瓜与印度、西亚、西班牙的甜瓜种质资源亲缘关系较近,与韩国、日本、美国和前苏联的甜瓜种质资源亲缘关系较远。聚类分析结果表明,以遗传相似系数0.548为阈值,145份种质材料可分为3大类群;厚皮甜瓜与薄皮甜瓜间在分子水平上没有严格的界限,两者之间亲缘关系的远近在不同的种质材料间差异很大;117份中国新疆甜瓜地方种质资源可分为A(Ⅰ-1)、B(Ⅰ-2、Ⅰ-3、Ⅰ-5)、C(Ⅰ-6)、D(Ⅱ)等4大类6个亚类群,与传统4个变种10个品种群分类结果不同,但在每个大类或亚类群中属于同一变种或品种群的材料倾向于聚在一起。     

Detection of 3-hydroxy-3-methylglutaryl-coenzyme A reductase protein Cm-HMGR during fruit development in melon ( Cucumis melo L.)

The fruit size of melon (Cucumis melo L. reticulatus) is determined by the amount of cell proliferation in the pericarp during early fruit development. During this stage, expression and activity of the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) gene is required for fruit growth. In this study, we performed a detailed analysis of the correlation between the expression of melon HMGR (Cm-HMGR) protein and cell division in the pericarp. Flow cytometric analysis revealed that the length of the cell division stage was correlated with the fruit size. Western gel blotting and tissue printing illustrated the temporal and spatial accumulation pattern of Cm-HMGR protein during fruit development. The accumulation of Cm-HMGR transiently increased at the beginning of the cell division stage in the pericarp, where active cell division occurred. The amount of Cm-HMGR was correlated with the length of the cell division period. These results strongly suggest that the expression of Cm-HMGR is involved in the determination of melon fruit size by regulating cell division during early fruit development.     

Simple-sequence repeat markers used in merging linkage maps of melon (Cucumis melo L.)

A set of 118 simple sequence repeat (SSR) markers has been developed in melon from two different sources: genomic libraries (gSSR) and expressed sequence-tag (EST) databases (EST-SSR). Forty-nine percent of the markers showed polymorphism between the Piel de Sapo (PS) and PI161375 melon genotypes used as parents for the mapping populations. Similar polymorphism levels were found in gSSR (51.2%) and EST-SSR (45.5%). Two populations, F₂ and a set of double haploid lines (DHLs), developed from the same parent genotypes were used for map construction. Twenty-three SSRs and 79 restriction fragment length polymorphisms (RFLPs), evenly distributed through the melon genome, were used to anchor the maps of both populations. Ten cucumber SSRs, 41 gSSRs, 16 EST-SSR, three single nucleotide polymorphism (SNP) markers, and the Nsv locus were added in the DHL population. The maps developed in the F₂ and DHL populations were co-linear, with similar lengths, except in linkage groups G1, G9, and G10. There was segregation distortion in a higher proportion of markers in the DHL population compared with the F₂, probably caused by selection during the construction of DHLs through in vitro culture. After map merging, a composite genetic map was obtained including 327 transferable markers: 226 RFLPs, 97 SSRs, three SNPs, and the Nsv locus. The map length is 1,021 cM, distributed in 12 linkage groups, and map density is 3.11 cM/marker. SSR markers alone cover nearly 80% of the map length. This map is proposed as a basis for a framework melon map to be merged with other maps and as an anchor point for map comparison between species of the Cucurbitaceae family.Electronic Supplementary Material Supplementary material is available for this article at     

Effects of cyanide on the respiration of musk melon (Cucumis melo L.) roots

The characteristics of root respiration of melon were examinedwith an oxygen electrode. The Hofstee plot of root respirationbreaks into two straight lines. The results of cyanide inhibitionexperiments and curve-fitting analysis suggest that one cyanide-insensitiveand two cyanide-sensitive oxidases operate in melon roots. (Received December 24, 1976; )     

Induction of somatic embryogenesis and caulogenesis from cotyledon and leaf protoplast-derived colonies of melon (Cucumis melo L.)

Summary A procedure leading to the regeneration of whole plants from protoplasts of melon is described. Protoplasts were isolated from cotyledons and leaves of plants grown in vitro. After 14 days of culture, average viability and division rates were respectively 60% and 30% for the two organs, considering total initial protoplasts plated. The manipulation of the exogenous auxin / cytokinin balance in regeneration media enabled to direct morphogenesis towards somatic embryogenesis (1 mg·l^–1 2,4-dichlorophenoxyacetic acid and 0.1 mg·l^–1 6-benzylaminopurine) or caulogenesis (0.5 mg·l^–1 6-benzylaminopurine and 0.5 mg·l^–1 kinetin). Contrary to division ability, regeneration capacity was genotype-dependent under our conditions, but the two organs expressed similar division and regeneration capacities. Maltose was superior to sucrose for the development of caulogenic nodules into buds. Some plants were transplanted to soil, where they appeared to be fertile and produced seeds.Abbreviations BAP 6-benzylaminopurine - CPW Cell and Protoplast Washing medium - KIN kinetin - MES 2-(N-morpholino) ethanesulfonic acid - MS Murashige and Skoog (1962) - NAA 1 — naphthaleneacetic acid - PAS H (staining), Periodic Acid-Schiff / Hematoxylin - 2,4-D 2,4-dichlorophenoxyacetic acid     

Genome-wide identification,characterization and expression analysis of the TLP gene family in melon (Cucumis melo L.)

Thaumatin-like proteins (TLPs), which belong to pathogenesis-related (PR) protein family 5 (PR5), are involved in plant host defense and various developmental processes. The functions of the TLP family have been extensively discussed in multiple organisms, whereas the detailed information of this family in melon has not been reported yet. In this study, we identified 28 TLP genes in the melon genome and a N-terminal signal peptide was found highly conserved within each member of this family. Phylogeny analysis indicated that TLPs from melon and other plant species were clustered into ten groups. Twelve segmental and seven tandem duplication gene pairs that underwent purifying selection were identified. TLP genes expressed differentially in different tissues/organs, and were significantly induced after Podosphaera xanthii infection. TLPs in breeding line MR-1 tend to express early after pathogen infection compared with cultivar Top Mark. Our study provides a comprehensive understanding of the melon TLP family and demonstrates their potential roles in disease resistance, therefore provides more reference for further research.