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.     

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.     

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.     

An improved method of Agrobacterium tumefaciens-mediated genetic transformation system of melon (Cucumis melo L.)

A reliable Agrobacterium-mediated transformation and shoot regeneration protocol was developed for breeding lines of commercially important melon. Genetic manipulation has been considered a feasible approach for melon improvement; however, melon is considered a crop species difficult to manipulate. Here we proposed meristematic cells from mature embryos as target for gene transfer by Agrobacterium. In vitro meristems proliferation and multiple shoots regeneration were evaluated by sowing melon mature seeds on MS with 1.0 mg/L benzyladenine (BA), and 0.05 mg/L indole acetic acid (IAA) were used for shoot regeneration. The highest number of regenerated shoots was obtained from half mature seeds. A DNA fragment corresponding to selection marker nptII was amplified from genomic DNA extracted from leaves of regenerated plant on hormone free MS medium with 75 mg/L kanamycin, suggesting their transgenic nature. Southern hybridization of transgenic lines revealed random insertion of the transgene in host genome, with insert numbers differing among transformants anthesis, suggesting that ethylene is important for sex determination. Field studies showed that CmACS-7 melons had earlier mature bisexual flowers, increased femaleness as measured by earlier and bisexual buds, and increased number of fruit set on closely spaced nodes on the main stem. Transformation efficiencies of cultivar CM-23 with EHA105 (pBI121-cm) were 4 %, demonstrating that melon meristematic cells are an useful target for genetic manipulation by agroinfection.     

Fine genetic mapping of a locus controlling short internode length in melon (Cucumis melo L.)

Compact and dwarfing vining habits in melon (Cucumis melo L.; 2n = 2x = 24) may have commercial importance since they can contribute to the promotion of concentrated fruit set and can be planted in higher plant densities than standard vining types. A study was designed to determine the genetics of dwarfism associated with a diminutive (short internodes) melon mutant line PNU-D1 (C. melo ssp. cantalupensis). PNU-D1 was crossed with inbred wild-type melon line PNU-WT1 (C. melo ssp. agrestis), and resultant F₁ progeny were then self-pollinated to produce an F₂ population that segregated as dwarf and vining plant types. Primary stem length of F₂ progeny assessed under greenhouse conditions indicated that a single recessive gene, designated mdw1, controlled dwarfism in this population. To identify the chromosomal location associated with mdw1, an simple sequence repeat (SSR)-based genetic linkage map was constructed using 94 F₂ progeny. Using 76 SSR markers positioned on 15 linkage groups spanning 462.84 cM, the location of mdw1 was localized to Chromosome 7. Using the putative dwarfing-associated genes, fine genetic mapping of the mdw1 genomic region was facilitated with 1,194 F₂ progeny that defined the genetic distance between mdw1 and cytokinin oxidase gene, a candidate gene for compact growth habit (cp) in cucumber, to be 1.7 cM. The candidate gene ERECTA (serin/threonine kinase) and UBI (ubiquitin) were also mapped to genomic regions flanking mdw1 at distances of 0.6 and 1.2 cM, respectively.     

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.     

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.     

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     

Food-grade sugar can promote differentiation in melon (Cucumis melo L.) tissue culture

The objective of the present study was to investigate the origin of discrepancy between experimental results in in vitro culture of Turkish melon (Cucumis melo L.) cultivars, conducted by the same individual using the same protocol and same seed batches in two different laboratories. The difference in the sucrose source was found to be the major reason for the deviation in results between the two laboratories. The percentage of regenerating explants and the number of bud-like protuberances and/or shoots were significantly greater when a food-grade Turkish sucrose was used in the medium compared with analytical-grade sucrose. Media formulated with the food-grade sucrose regenerated 37 and 67 % more explants and bud-like protuberances and/or shoots per explant, respectively, than media containing analytical-grade sucrose. No meaningful differences were found in added elements or anions between the sucrose sources or by liquid chromatography/mass spectroscopy. The only significant chemical difference observed between the sucrose samples was the presence of melanoidins (Maillard reaction products) in the food-grade sucrose. The melanoidins were of high molecular weight (>3,000 Da determined by ultrafiltration), with characteristic ultraviolet?Cvisible spectra and in vitro antioxidant activity. Melanoidin-containing sucrose can be differentiated by color and spectroscopy.     

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; )     

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     

Catabolism of l–methionine in the formation of sulfur and other volatiles in melon (Cucumis melo L.) fruit

Sulfur‐containing aroma volatiles are important contributors to the distinctive aroma of melon and other fruits. Melon cultivars and accessions differ in the content of sulfur‐containing and other volatiles. l –methionine has been postulated to serve as a precursor of these volatiles. Incubation of melon fruit cubes with ¹³C‐ and ²H‐labeled l –methionine revealed two distinct catabolic routes into volatiles. One route apparently involves the action of an l ‐methionine aminotransferase and preserves the main carbon skeleton of l ‐methionine. The second route apparently involves the action of an l ‐methionine‐γ–lyase activity, releasing methanethiol, a backbone for formation of thiol‐derived aroma volatiles. Exogenous l ‐methionine also generated non‐sulfur volatiles by further metabolism of α–ketobutyrate, a product of l ‐methionine‐γ–lyase activity. α–Ketobutyrate was further metabolized into l –isoleucine and other important melon volatiles, including non‐sulfur branched and straight‐chain esters. Cell‐free extracts derived from ripe melon fruit exhibited l ‐methionine‐γ–lyase enzymatic activity. A melon gene (CmMGL) ectopically expressed in Escherichia coli, was shown to encode a protein possessing l ‐methionine‐γ–lyase enzymatic activity. Expression of CmMGL was relatively low in early stages of melon fruit development, but increased in the flesh of ripe fruits, depending on the cultivar tested. Moreover, the levels of expression of CmMGL in recombinant inbred lines co‐segregated with the levels of sulfur‐containing aroma volatiles enriched with +1 m/z unit and postulated to be produced via this route. Our results indicate that l ‐methionine is a precursor of both sulfur and non‐sulfur aroma volatiles in melon fruit.     

Population structure,morphological and genetic diversity within and among melon (Cucumis melo L.) landraces in Iran

ISSR markers were applied to evaluate the genetic diversity and differentiation of 270 individuals of 27 Iranian C. melo landraces of various varietal groups include vars. inodorous, cantalupensis, reticulatus, ameri, dudaim. Genetic diversity among the studied genotypes obtained by GeneAlex analysis (H?=?0.08, I?=?0.12, Na?=?0.77, PPL?=?22.6%). Cluster analysis divided Iranian melon landraces into two main cluster. Non-sweet genotype (dudaim group) was well separated from sweet genotypes (inodorous, ameri, reticulatus, cantalupensis). The most similar genotypes were BANI and TONI (0.95) and the most dissimilar ones were GER and TS (0.58). AMOVA result showed that the percentage of genetic variation among and within Iranian melon is 69% and 31%, respectively. All landraces evaluated based on 10 morphological traits which revealed the diversity of melon varietal groups. Bayesian analysis assigned ten landraces to Pop 1, eight landraces to Pop 2 and nine melon landraces to Pop 3. Bayesian and UPGMA cluster analyses demonstrated the almost related results. Our results indicated that ISSR markers technique alongside polyacrylamide gel analysis could be helpful to discriminate varieties of melon.     

A genetic map of melon (Cucumis melo L.) based on amplified fragment length polymorphism (AFLP) markers

 Genetic maps facilitate the study of genome structure and evolution, and the identification of monogenic traits or Mendelian components of quantitative traits. We evaluated 228 RAPD, microsatellite and AFLP markers for linkage analysis in melon (Cucumis melo L.) varieties MR-1 (resistant to Fusarium wilt, powdery and downy mildews) and Ananas Yokneum (AY; susceptible to these diseases) and constructed a detailed genetic map. The mapping population consisted of 66 backcross progenies derived from AY×(MR-1×AY). Despite a relatively low level of polymorphism in the species, AFLP markers were found to be more efficient in mapping the melon genome than RAPD or microsatellite markers. The map contains 197 AFLPs, six RAPDs and one microsatellite marker assigned to 14 major and six minor linkage groups, and covers 1942 cM with the average distance between adjacent markers of approximately 10 cM. The maximum distance allowed between markers is 27.5 cM. About 11% of the intervals (20 out of 173) are over 20 cM (but less than 27.5 cM). The map has immediate utility for identifying markers linked to disease resistance genes that are suitable for marker-assisted breeding. The use of microsatellite markers for integration with other maps is also discussed. Received: 12 March 1997 / Accepted: 20 May 1997     

Ploidy of somatic embryos and the ability to regenerate plantlets in melon (Cucumis melo L.)

Summary The number of chromosomes in cells of callus, somatic embryos and regenerated plantlets during somatic embryogenesis were examined in two cultivars of melon (Cucumis melo L.). Somatic embryos were diploid (50.0%/32.1%), tetraploid (38.5%/57.5%) and octoploid (11.5%/10.4%) whereas in callus cells diploidy (41.9%/43.3%), tetraploidy (27.9%/25.8%), octoploidy (11.6%/15.5%) and a low frequency of other types of ploidy and aneuploidy were observed. Mixoploid somatic embryos were not observed. These results suggest that the somatic embryos were selectively differentiated from diploid, tetraploid and octoploid cells, and that endopolyploidization of cultured cells occurred before the start of cell division leading to somatic embryogenesis. The ratio of diploid to tetraploid (1.30/0.55) in somatic embryos was less than that in callus cells (1.50/1.68) while ratios of diploid to octoploid (4.35/3.09) and tetraploid to octoploid (3.35/5.52) in somatic embryos were greater than those in callus cells (3.61/2.80 and 2.40/1.67). Therefore, it appears that the ability of callus cell to differentiate into somatic embryos increases in the following order: octoploid < diploid < tetraploid. Regenerated plantlets were diploid (65.5%/55.1%) and tetraploid (34.5%/44.9%). No octoploid plantlets were observed. The ratio of diploid to tetraploid in regenerated plantlets (1.72/1.23) was greater than that in somatic embryos. Therefore, it appears that the ability of somatic embryos to develop into plantlets increases in the following order: octoploid < tetraploid < diploid.     

Carbohydrate metabolism during early fruit development of sweet melon (Cucumis melo)

In sink tissues of cucurbits, including sweet melon fruits, the galactosyl-sucrose oligosaccharides, stachyose and raffinose, together with sucrose, are the major translocated carbohydrates. In the present study we investigated the carbohydrate metabolism of young melon ( Cucumis melo L. cv. C-8) fruit during the period of initial fruit set and development, from 3 days prior to anthesis until 20 days after anthesis (DAA), prior to the onset of sucrose accumulation. The enzymes assayed could be classified into two categories according to developmental patterns. Two of the enzymes, alkaline α -galactosidase I [EC 3.2.1.22], which hydrolyzes both raffinose and stachyose, and acid invertase [EC 3.2.1.26] either increased or remained stable during the first 10 DAA. The remaining measured enzymes (the stachyose-specific alkaline α -galactosidase form II, acid α -galactosidase, alkaline invertase, sucrose synthase [EC 2.4.1.13], galactokinase [EC 2.7.1.6], UDP-Gal PPase [EC 2.7.7.10], UDP-Glc-4 epimerase [EC 5.1.3.2], UDP-Glc PPase [EC 2.7.7.9], phosphoglucomutase [EC 5.4.2.2] and phosphoglucoisomerase [EC 5.3.1.9]) all showed a similar developmental pattern of steady decrease in activity following anthesis. We also compared the saccharide metabolism of pollinated and non-pollinated ovaries during the initial days following anthesis. In the absence of pollination, ovary growth dramatically decreased by the first DAA and was accompanied by a sharp decrease in the activity of UDP-Glc PPase. Other enzymes in the pathway, including the enzymes of stachyose and raffinose hydrolysis, did not decrease in activity until 2 or 4 DAA, after ovary growth was affected. These results provide information to assess the possible regulating enzymes in cucurbit ovary development and fruit set.