Melon Groups Research Articles

Cytogenetical treatise of Indian representative species of Cucumis. A karyotypic approach

Karyomorphological studies have been carried out in nine species and five varieties of the genus Cucumis representing Indian gene pool. The present investigations reveal the occurrence of two somatic chromosome numbers 2n = 14, 24 in the genus. C. ritchiei and C. indicus the two new species, were found to be having somatic chromosome numbers of 2n = 24 and 2n = 20 respectively. The wild species viz. C. hystrix, C. setosus, C. prophetarum, C. dipsaceus, C. indicus have very less number of median-centromeric chromosomes, high asymmetry indices, while melon groups have intermediate number of median -centromeric chromosomes. C. sativus, C. callosus, C. ritchiei show lesser number median-cen-tromeric chromosomes and very less asymmetry indices. The importance of karyotypic variation with respect to speciation within the genus Cucumis have been discussed.

Diversity of Melon Accessions from Northeastern Brazil and Their Relationships with Germplasms of Diverse Origins

Melon (Cucumis melo) is one of the most important horticultural crops in Brazil. A set of 40 melon landraces representing a northeastern Brazilian variation was agronomically evaluated with 13 morphological traits and molecularly with 13 simple sequence repeat markers and compared with a set of 21 reference accessions of diverse taxonomic and geographic origins. Brazilian accessions were highly variable for seed, flowering time, fruit, and yield-related traits. However, most of them shared a monoecious sex type, a climacteric ripening behavior, and fruit that were low to medium in sugar with a high acid content, characteristics in accordance with those of Asian melons belonging to Momordica, Flexuosus, and Chate, and Far-Eastern Makuwa and Chinensis melon groups. Molecular analysis confirmed the genetic similarity of the Brazilian landraces to reference accessions from India, the Far East, and the Middle East belonging to those botanical groups. Momordica, Makuwa, and Chinensis melons are rarely found as landraces outside of this area thus suggesting that these landraces were introduced into Brazil from these regions. Our molecular results also support a high genetic diversity in the Brazilian collection [polymorphism information content (PIC) = 0.43], which is only slightly lower than that of the references (PIC = 0.59) that include most of the main horticultural groups of the two C. melo subspecies. This study shows that in Brazil, there is currently a large variability of this species maintained in the form of landraces, which are a potentially useful resource for breeding melons.

Bitter Melon Improves Glycemic Control and Inflammation in Adipose Tissue of Obese and Diabetic Rats

Momordica charantia, known as bitter melon has been used for the prevention and treatment of obesity and diabetes, but the mechanisms have not been fully determined. In the present study, we investigated the effects of bitter melon on glycemic control using a rat model representing late onset of hyperglycemia, a chronic course of disease, mild obesity and clinical onset of diabetes mellitus. Male OLETF rats were fed 45% high fat (HF) diet supplemented with either 1% bitter melon or 3% BM for 6 weeks. Without significant changes of body weight and food intake, bitter melon supplementation significantly improved glycemic control during oral glucose tolerance test. Moreover, 3% bitter melon supplementation in high fat diet significantly decreased serum concentrations of insulin and triglycerides, compared to high fat diet. mRNA expression of genes involved in inflammation such as TNFα and 11β‐Hydroxysteroid dehydrogenase1 were significantly reduced in 3% bitter melon group. In addition, bitter melon‐contained diet significantly decreased GRP78, IRE1, XBP1, and ATF4 mRNA levels related to ER stress in adipose tissue. In conclusion, bitter melon may be useful in the prevention/treatment of hyperglycemia by decreasing adipose tissue inflammation.

Morphological and Molecular Characterization of Turkish Landraces of <i>Cucumis melo</i> L.</span>

Cucumis melo L. from Eastern and South-eastern Anatolian regions of Turkey were characterized by using 43 morphological traits and 207 markers obtained from 31 ISSR and 16 SSR primers. The genetic relatedness was studied by examining the Euclidian/UPGMA dendrogram obtained from the combined phenotypic-molecular data. In the combined morphological-molecular dendrogram, there were two main clusters. Sweet and non-sweet melon groups were separated and the flexuosus group accessions were discriminated from the sweet ones, but the momordica group accession was clustered with the sweet ones. Unclear South-eastern Anatolian accessions were sub-clustered separately among the sweet ones. Principle component analysis (PCA) of morphological characters was used in detail to discriminate melon accessions. The cumulative proportion of variation reached 44% by first three PCA axes. The first component was mainly based on sex expression, ovary index, ovary shape, flesh thickness, seed cavity length, seed cavity width, soluble solids content, fruit shape, aroma, netting, and taste. The PCA plot based on all measured traits allowed distinction between flexuosus group, subsp.agrestis and reticulatus group. A high variation among groups was observed for the fruits characters. Netting, aroma and abscission of peduncle represent reticulatus group; a small fruit size, strong typical aroma and secondary colour distribution characterize dudaim group. Monoecy, very long fruit shape and mature fruit rind colour discriminate flexuous group; Ovary index, fruit size and flesh width distinguish subsp. agrestis group. These findings indicated wide range of variations for investigated characteristics in Turkish gene pool that provides a good source of diversity to use in melon improvement program for better yield and other traits of interest.

Diversity among melon (Cucumis melo L.) landraces from the Indo-Gangetic plains of India and their genetic relationship with USA melon cultivars

We report here the first broad genetic characterization of farmer-developed landraces of melon (Cucumis melo L.) from the Indo-Gangetic plains of India, an area overlooked in previous melon genetic diversity analyses of Indian melon germplasm. Eighty-eight landraces from three melon Groups in two subspecies (C. melo subsp. agrestis Momordica Group, and C. melo subsp. melo Cantalupensis Group and Reticulatus Group) were collected from the four agro-ecological regions (six sub-regions) of two northern states of the Indo-Gangetic plains of India, Uttar Pradesh and Uttarakhand. Significant differences were found among the landraces and eight USA Reticulatus Group reference cultivars for 18 plant and fruit traits: no. of primary branches per plant, days to marketable maturity, sex expression, fruit shape, flesh colour, netting, no. of fruit per plant, fruit weight, shelf life, total soluble solids (°Bx), ascorbic acid (mg/100 g), titratable acidity (%), fruit length and diameter, seed cavity length and diameter, flesh thickness, and resistance to Cucumber mosaic virus. The three melon groups differed significantly for 10 of the plant and fruit traits. Cantalupensis Group and Reticulatus Group accessions were andromonoecious, and the Momordica Group was monoecious. Neighbour-joining (NJ) tree and factorial correspondence analysis (FCA) of simple sequence repeat loci also revealed a high level of genetic variability in this germplasm. The 96 melon genotypes clustered into five groups in the NJ tree analysis: the 16 Indian Reticulatus Group accessions and eight USA reference cultivars formed a distinct group; and the 60 Cantalupensis Group accessions clustered in four other groups with the 12 Momordica Group accessions in a distinct subgroup of one of the Cantalupensis groups. The FCA plot largely confirmed the NJ tree with three distinct groups, one for each melon group. The close affinity of the Indian and USA Reticulatus melons was not unexpected, but it is not clear whether it was inherent in the group and maintained as Reticulatus melons moved from India through Central Asia and Europe to North America, or the result of recent intercrossing of Indian landraces with the USA-derived cultivars and selection for a broad range of Reticulatus type melons.

Map-based molecular diversity, linkage disequilibrium and association mapping of fruit traits in melon

Melon has tremendous fruit diversity, the product of complex interactions of consumer preferences in different countries and a wide range of agro-climatic zones. Understanding footprints of divergence underlying formation of various morphotypes is important for developing sustainable and high-quality melons. Basic understanding of population structure and linkage disequilibrium (LD) is limited in melon and has lagged behind other crops. Characterization of population structure and LD are essential for carrying out association mapping of quantitative trait loci (QTL) underlying various complex traits. Mapped single-locus microsatellite markers are known to be very valuable for resolving the population structure and 268 such markers were used in the current study to resolve population structure and LD pattern using 87 accessions of melons belonging to Eastern European, Euro-North American and Asian types. A mixed linear model was implemented to detect QTL for various fruit traits. Various levels of QTL with high to moderate stringency were detected for fruit shape, fruit weight, soluble solids, and rind pressure and a majority of them was found to be in agreement with the previously published data, indicating that association mapping can be very useful for melon molecular breeding. Minor discrepancies in the position, strength and the variation explained by the QTL present between the methods of association and recombinant mapping approaches can be bridged if more melon groups and larger sets of accessions are involved in future studies, combined with high-throughput marker panels.

Diversification and genetic differentiation of cultivated melon inferred from sequence polymorphism in the chloroplast genome

Molecular analysis encouraged discovery of genetic diversity and relationships of cultivated melon (Cucumis melo L.). We sequenced nine inter- and intra-genic regions of the chloroplast genome, about 5500 bp, using 60 melon accessions and six reference accessions of wild species of Cucumis to show intra-specific variation of the chloroplast genome. Sequence polymorphisms were detected among melon accessions and other Cucumis species, indicating intra-specific diversification of the chloroplast genome. Melon accessions were classified into three subclusters by cytoplasm type and then into 12 subgroups. Geographical origin and seed size also differed between the three subclusters. Subcluster Ia contained small-seed melon from Southern Africa and South and East Asia and subcluster Ib mainly consisted of large-seed melon from northern Africa, Europe and USA. Melon accessions of subcluster Ic were only found in West, Central and Southern Africa. Our results indicated that European melon groups and Asian melon groups diversified independently and shared the same maternal lineage with northern African large-seed melon and Southern African small-seed melon, respectively. Cultivated melon of subcluster Ic may have been domesticated independently in Africa. The presence of 11 cytoplasm types in Africa strongly supported African origin of cultivated melon and indicated the importance of germplasm from Africa.

A Severe Outbreak of Charcoal Rot in Cantaloupe Melon Caused by Macrophomina phaseolina in Chile

A severe outbreak of charcoal rot was observed in cantaloupe melon (Cucumis melo L.) in the summer of 2011 to 2012 in Curacaví Valley, Chile. Prior to harvest, of 72 plants per cultivar, charcoal rot prevalence varied from 32% to 82% in cvs. Colima, Charantias, Navigator, Origami, Otero, and Samoa. Symptoms were wilting and leaf browning associated with water-soaked lesions at the base of the crown with amber to dark brown exudates. Lesions dried out progressively, turned tan, and cracked. Affected plants declined and died before harvest. Reddish fruit decay was observed. Symptomatic stem and root samples (n = 97) were collected, surface disinfected (96% ethanol, 30 s), plated on PDA acidified with 0.5 ml/liter of 92% lactic acid (APDA), and incubated at 20 ± 1°C. A white, fast-growing mycelium was obtained that turned gray to black after 7 days due to the presence of spherical to oblong black microsclerotia 136 ± 52 μm (n = 80) in diameter. On the basis of colony morphology and microsclerotia, 57 isolates (59%), obtained from 97 melon samples, were tentatively identified as Macrophomina phaseolina (Tassi) Goid. (2,3). The morphological identification of four isolates M1HB-B, M2CO-B, M3CH-R, and M4OT-B (GenBank Accession Nos. JX203630, JX203631, JX203632, and JX203633) was confirmed by sequencing of the internal transcribed spacer region (ITS1-5.8S-ITS2) of rDNA, using primers ITS4 and ITS5, with >99% similarity with the sequences of M. phaseolina (GenBank Accession No. HQ660592) (4). Pathogenicity tests were conducted with isolates M1HB-B, M2CO-B, M3CH-R, and M4OT-B on melon fruits cvs. Colima, Origami, Charantias, and Diva. Four mature melon fruits per cultivar per isolate were surface disinfected with 0.5% sodium hypochlorite for 2 min before inserting a mycelium plug (19 mm2) in a 6 mm diameter hole made with a sterile cork borer. An equal number of perforated fruits in which a sterile agar plug was inserted were left as non-inoculated controls. After 8 days of incubation at 20°C, inoculated fruits developed a spherical, reddish, soft necrotic lesion of 15 to 20 mm in diameter in the pulp. Non-inoculated fruits remained symptomless. The pathogenicity of the four isolates was also studied in 3-month-old melon plants (n = 4) cvs. Colima and Navigator. Plants were inoculated by inserting a mycelial plug (9 mm2) underneath the epidermis of the crown, 5 cm above the soil level. The inoculation site was immediately wrapped with Parafilm to avoid dehydration. An equal number of non-inoculated, but injured plants, treated with a sterile agar plug, were left as controls. After 21 days of incubation under greenhouse conditions (17 ± 5.5°C), all inoculated plants developed water-soaked to dry necrotic lesions, 20 to 70 mm long, yellow to tan in color. No symptoms were obtained in non-inoculated controls. M. phaseolina was reisolated in 84% and 100% of the inoculated plants and fruits, respectively. To our knowledge, this study is the first report of charcoal rot in cantaloupe melon in Chile, previously found on watermelon and melon group inodorus (1). Charcoal rot appears as an emerging disease that aggressively affects current cantaloupe melon cultivars in central Chile.

Comparison of in vivo and in vitro Colchicine Application for Production of Dihaploid Kirkagac and Yuva Hasanbey Melons

This study was performed to compare the efficiency of different colchicine application methods for doubling of haploid melon plants in melon breeding programs. Doubled haploids assist breeding by reducing time for the recovery of homozygous breeding lines. Irradiated pollen technique provides successful results in melons and pure breeding lines can be produced in relatively shorter time. Despite the advantages, low frequency of haploid embryos, difficulties for detecting and excising the embryos and low percentage of duplication rate are the limiting factors of this technique. The objective of this study was to determine the effect of different colchicine treatments to double haploid melon plants. The same dose of colchicine (0.5 %) was applied either in vitro or in vivo and the resulting doubled haploids were compared. The results indicated that the most convenient method was found in vivo application of colhicine (0.5 %) by shoot tip immersing method for 2 hours. The mean duplication rate was 10.13 % after in vitro colchicine application and 46.03 % after in vivo colchicine application among the genotypes of ‘Kirkagac’ and ‘Yuva Hasanbey melon groups. Key words: Irradiation, Co60, haploid, duplication, embryo rescue.

Comparison of in vivo and in vitro Colchicine Application for Production of Dihaploid ‘Kirkagac’ and ‘Yuva Hasanbey’ Melons

This study was performed to compare the efficiency of different colchicine application methods for doubling of haploid melon plants in melon breeding programs. Doubled haploids assist breeding by reducing time for the recovery of homozygous breeding lines. Irradiated pollen technique provides successful results in melons and pure breeding lines can be produced in relatively shorter time. Despite the advantages, low frequency of haploid embryos, difficulties for detecting and excising the embryos and low percentage of duplication rate are the limiting factors of this technique. The objective of this study was to determine the effect of different colchicine treatments to double haploid melon plants. The same dose of colchicine (0.5 %) was applied either in vitro or in vivo and the resulting doubled haploids were compared. The results indicated that the most convenient method was found in vivo application of colhicine (0.5 %) by shoot tip immersing method for 2 hours. The mean duplication rate was 10.13 % after in vitro colchicine application and 46.03 % after in vivo colchicine application among the genotypes of ‘Kirkagac’ and ‘Yuva Hasanbey melon groups.

Distribution of degradative enzymatic activities in the mesocarp of two melon groups

SummaryThe differences in polyphenol oxidase, peroxidase, pectin methylesterase and polygalacturonase activities as well as the main physical and chemical attributes of nine different slice portions (from the inner to the outer end and from the blossom to the stem end) of two groups of melon (Cucumis melo var. cantalupensis‘Galia’ cv. and inodorus‘Piel de sapo’ cv.) at commercial maturity were studied. Moving from the inner to the outer end of the pulp, physico‐chemical properties, such as pH, total soluble solids and phenolics increased whereas titratable acidity, firmness and Chroma decreased in both types, reflecting different degrees of maturity within the same fruit. As for physico‐chemical attributes, the enzymatic activities responsible for browning and softening phenomena showed an increasing trend moving from the inner to the outer end of mesocarp in both cv., except for polygalacturonase in cantalupensis type.

Molecular analysis of genetic diversity in melon landraces (Cucumis melo L.) from Myanmar and their relationship with melon germplasm from East and South Asia

Genetic diversity of Myanmar melon was evaluated by analysis of 27 RAPD markers and morphological characters using 41 accessions of melon landraces of which 36 accessions were small-seed type. The gene diversity was 0.239, higher than for group Conomon from East Asia and equivalent to Indian melon populations. Melon accessions were classified into six major clusters. The largest cluster IV comprised mainly group Conomon which was closely related to cluster V consisting of mainly group Agrestis. Most of the accessions of group Cantalupensis were grouped into clusters II or VII and were distantly related to groups Conomon and Agrestis. The genetic relationship to melon accessions from neighboring countries was analyzed. The 24 accessions of clusters IV and V were mostly clustered together with small-seed type melon of India, but the 14 accessions of clusters VI and VII were mostly clustered together with large-seed type melon of India. These results indicated that the genetic diversity of Indian melon is conserved in Myanmar. Genetic introgression among melon groups through spontaneous hybridization was also indicated and was considered important to maintain or increase the genetic diversity in Myanmar.

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 (r2=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 (r2=0.91; P=0.05) with the presence of a putative RFLP-MEL1 allele A0 (15-kb), whereas high ethylene production and orange-flesh color were associated with allele B0 (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.

Comparative analysis of cultivated melon groups (Cucumis melo L.) using random amplified polymorphic DNA and simple sequence repeat markers.

Random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers were used to characterize genetic relationships among 46 accessions in two C. melo L. subsp. melo (Cantalupensis, Inodorus) and subsp.agrestis (Conomon, and Flexuosus) groups. Genetic distance (GD) estimates were made among and between accessions in four melon market classes [Galia, Ogen, Charentais, and Shipper (European and U.S. types)] of Cantalupensis, one market class of Inodorus (Cassaba and Honey Dew), one accession of Conomon, and one accession of Flexuosus by employing three GD estimators; simple matching coefficient, Jaccard's coefficient, and Nei's distance-D. Differences detected among 135 RAPD bands and 54 SSR bands (products of 17 SSR primers) were used to calculate GD. Band polymorphisms observed with 21 RAPD primers and 7 SSR primers were important (p =0.01) in the detection of genetic differences. Estimators of GD were highly correlated (p 0.0001; rs = 0.64 to0.99) when comparisons were made between estimation methods within a particular marker system. Lower correlations (rs = 0.17 to 0.40) were detected (P > 0.001) between marker systems using any one estimator. The GD of the Conomon and Flexuosus accessions was significantly different (p> 0.001)from the mean GD of all the market classes examined. The mean GD (Jaccard's coefficient) among accessions of Ogen, Galia, Cassaba, Charentais, European shipper, and U.S. shipper groups was 0.11 ± 0.04, 0.33± 0.09, 0.21 ± 0.04, 0.26 ± 0.10, 0.17± 0.05 and 0.22 ± 0.08, respectively. Market classes were distinct (p > 0.001), such that GDs between Galia and other accessions were the largest(mean GD 0.34 to 0.35), and GDs between Ogen and other accessions were the smallest (mean GD 0.29 to 0.30). Contrasts between the U.S. shipper cultivar Top Mark and accessions within any market class was relatively large (mean GD = 0.42 ± 0.06). Empirical estimations of variances associated with each marker type in the accessions examined indicated that, per band, lower coefficients of variation can be attained in the estimation of GD when using RAPDs compared to SSRs. Nevertheless, the genetic relationships identified using these markers were generally similar. The disparity between the analyses of the two markers made may be related to the amount of genome coverage which is characteristic of a particular marker system and/or its efficiency in sampling variation in a population. Results of RAPD marker analysis suggest that 80 marker bands were adequate for assessing the genetic variation present in the accessions examined.