Triploid Genotypes Research Articles

Coexistence of diploids and triploids in a Saharan relict olive: Evidence from nuclear microsatellite and flow cytometry analyses

Polyploidy was recently reported in two endangered olive subspecies from North-West Africa. The origin of this phenomenon remains unclear. In the present study, 106 genotypes of a relict Laperrine's olive population form Hoggar (Algeria) were analysed using eight nuclear microsatellites. Diploid and triploid genetic profiles were observed. A flow cytometry analysis confirmed that trees displaying three alleles at several loci are effectively triploid. This report constitutes the first evidence for the coexistence of two ploidy types in an olive population. The triploid genotypes, probably in mean more vigorous than diploid trees, may be positively selected in the absence of sexual regeneration since a very long time, explaining their relative high frequency in the investigated population. To cite this article: G. Besnard, D. Baali-Cherif, C. R. Biologies 332 (2009).

Development of triploid daylily (Hemerocallis) germplasm by embryo rescue

Interploidy crosses between diploid daylily (Hemerocallis) cultivars (2n = 22) and tetraploid cultivars (2n = 44) were performed via in vivo hybridization aiming to produce triploid hybrid germplasm (3n = 33). Plant growth regulator-free MS based medium containing 5 levels of sucrose—1, 2, 3, 4 or 5% was used to optimize the embryo rescue medium. It was determined that the medium supplemented with 3% sucrose gave highest rate of immature hybrid embryo rescue. Thirty-seven hypothetically triploid genotypes were subjected to verification of ploidy status by root tip chromosome counting and flow cytometry. Thirty-one of them were confirmed triploids. These genotypes were in vitro propagated, acclimatized to ex vitro conditions, and planted for future field performance evaluation and environmental testing. The newly developed triploid genotypes could open new horizons for further polyploidy breeding.

Types of water frog populations (Rana esculenta complex) in Poland

Poland is inhabited by the two water frog species Rana ridibunda (genotype RR) and Rana lessonae (LL) and their hybrido-genetic hybrid Rana esculenta. Besides diploid (RL) hybrids two triploid (RRL, RLL) forms were found. In most populations the hybrid occurs syntopically with only one of the parental species. Concerning their genotypic structure water frog populations can be subdivided into three systems: the L-E (lessonae-esculenta) system, the R-E (ridibunda-esculenta) system and the E-E (esculenta-esculenta) system. The composition of water frog populations in Poland is highly differentiated. Among 27 population types described from central Europe 18 types were found in Poland. The highest diversity of population types was seen in the R-E system (8 types). In the L-E system three and in the E-E system four different types were found. Among 11170 investigated adult water frogs 690 (6%) presumptive triploid R. esculenta individuals occurred. In western Poland the proportion of triploid individuals and the diversity of population types was higher (7.7% triploid individuals, 13 population types) than in the eastern parts of the country (0.2% triploid individuals, six population types). The distribution picture of triploid individuals in western Poland is similar to that seen in eastern Germany (as a rule a high proportion of triploids occurs) while in eastern Poland the distribution pattern of triploid genotypes resembles the situation observed in the territory of the former Soviet Union (nearly no triploids appear).

A Tetraploid Amazon Molly, Poecilia formosa

Polyploidization is thought to be an important driving force in evolution as it increases the genetic material on which mutation and selection can act. In the Amazon molly, Poecilia formosa, triploid genotypes can be found in the field and frequently arise from diploid breeding stocks, a tetraploid individual, however, was so far never documented. Here, we report the first tetraploid Amazon molly. Flow cytometry clearly showed the tetraploid DNA content, whereas microsatellite analysis not only confirmed the tetraploidy but also pointed to allotetraploidy. Most likely the fourth genome was received through paternal leakage, namely, by fertilization of a triploid egg with a haploid sperm. The existence of tetraploid individuals offers new explanations for the enormous clonal diversity observed in wild populations of P. formosa.

Sink Competition and Desuckering Effects on Field Performance of Triploid and Tetraploid Plantain Genotypes

Reproductive growth in polyarchic Musa spp. varieties occurs by the simultaneous growth of several shoots, resulting in competitive inhibition of fruit development in the individual shoots, particularly under poor soil fertility conditions. Nine plantain genotypes were forced into single-culm growth by continuous sucker removal in the ratoon crop (RC). There were no significant differences among genotypes for days to flowering (DTF) and days to harvest (DTH) in the plant crop (PC), but significant differences occurred in RC for both traits. There was a negative correlation between degree of sucker growth in the PC and DTF or DTH in RC, indicating that early flowering and maturity in the RC occurred as a result of fast sucker development in the PC. Likewise, bunch weight in the RC was positively correlated with sucker growth in the previous crop. However, sucker growth appeared to compete against the development of the bunch in the PC, resulting in a significant reduction in fruit size but not fruit number. Desuckering significantly reduced DTF and DTH in the RC. Bunch weight and fruit size were significantly improved by sucker removal in the RC. Gains were highest for genotypes that normally produce multiple lateral shoots and lowest for those displaying a more hierarchical growth habit. Thus, sucker removal could be recommended as a crop management option for the polyarchic Musa genotypes.

Simultaneous formation of haploid, diploid and triploid eggs in diploid–triploid mosaic loaches

In the loach Misgurnus anguillicaudatus, very few diploid–triploid mosaic individuals, which are generated by accidental incorporation of the sperm nucleus into diploid eggs produced by clonal diploid loach, occur in nature. Ploidy examination of gynogenetic progeny induced by activation with ultraviolet‐irradiated goldfish sperm indicated that diploid–triploid mosaic females laid haploid, diploid and triploid eggs, simultaneously. In addition, triploid eggs exhibited larger egg sizes. Microsatellite genotyping of diploid–triploid mosaics revealed that triploid genotypes of mosaic mothers possessed two alleles specific to the clonal diploid and one allele from normal diploid male. Diploid eggs from a mosaic mother had genotypes absolutely identical to the diploid clone. Most genotypes of triploid eggs were identical to the mosaic mother, and one of the three alleles of the mosaic mother was transmitted to haploid eggs. These results suggested that diploid germ cells, which had a clonal genome, were differentiated into clonal diploid eggs, and triploid and haploid eggs were produced from triploid germ cells in the same ovary of mosaic individuals.

Production and characterization of new triploid seedless progenies for mandarin improvement

Eighty-six triploid Citrus plants were recovered from interploid crosses between a natural tetraploid selection of the tangerine ‘Dancy’ ( Citrus reticulata Blanco, cultigroup ‘Tangerine’), used as the pollen parent, and two seedy selections of diploid mandarins ( C. reticulata Blanco) as well as one clementine ( Citrus clementina Hort. ex Tan.): ‘Fortune’ mandarin, ‘Wilking’ mandarin and ‘Monreal’ clementine. Flow cytometric analysis was used for screening the triploid plantlets and the ISSR-PCR technique was used to characterize the obtained triploids through a double approach, confirming the hybrid nature of the offspring and allowing the analysis of the genetic pool obtained. Selection among triploid genotypes generated from elite seedy parents will give us a better chance to obtain superior mandarin cultivars characterized by true seedlessness.

INTERACTION BETWEEN FOURNDER EFFECT AND SELECTION DURING BIOLOGICAL INVASION IN AN AQUATIC PLANT

Long-distance colonization and rapid range expansion associated with biological invasion may have major evolutionary consequences via both stochastic processes and selection. Using large-scale population genetic surveys, we demonstrate a major shift in the relative frequency of sexually fertile diploid versus sexually sterile triploid populations associated with the invasion of North America by a clonal aquatic plant, Butomus umbellatus. Most populations across the native European range were triploid (84% of 108), whereas most introduced populations were diploid (71% of 136). We evaluated the roles of stochastic processes versus natural selection in causing this shift by surveying predominantly neutral genetic variation at 28 RAPD loci. In Europe (EU) we detected 47 distinct genotypes among 142 plants sampled from 71 populations, whereas in North America (NA) we detected only six genotypes among 138 plants from 69 populations. Of the six NA genotypes, a set of four closely related genotypes were found only in triploid populations and a pair of closely related genotypes were found only in diploid populations, and these were genetically divergent from the triploid genotypes. This result is consistent with severe founder effect. Because sex creates genotypic variation and produces offspring with greater dispersal potential than those produced clonally, we tested the hypothesis that sexual reproduction characteristic of diploids has given them a colonization advantage that accounts for their high frequency in NA. However, we found little or no evidence of sexual recruitment in introduced diploids. One very widespread heterozygous genotype occurred in 95% of 38 introduced diploid populations (i.e., 72 of 76 plants surveyed) suggesting predominant clonal reproduction. Moreover genotypic diversity was not higher within or among diploid than triploid populations in either the native or introduced range. Low genetic diversity in diploid populations was also supported by a comparison of within-population quantitative variation for plant size under a common greenhouse environment. Thus, diploids have not been favored during colonization owing to their sexual fertility. However, concurrent studies have shown that NA diploids exhibit a much higher capacity for clonal reproduction, via small vegetative bulbils, than NA triploids, which almost never produce bulbils. The same difference in clonal capacity is not a consistent feature of the native EU populations. Taken together, these results suggest that strong founder effect has set the stage for a major increase in diploid frequency due to the particular, and possibly idiosyncratic, features of the diploid and triploid lineages introduced to North America.

INTERACTION BETWEEN FOUNDER EFFECT AND SELECTION DURING BIOLOGICAL INVASION IN AN AQUATIC PLANT

Long-distance colonization and rapid range expansion associated with biological invasion may have major evolutionary consequences via both stochastic processes and selection. Using large-scale population genetic surveys, we demonstrate a major shift in the relative frequency of sexually fertile diploid versus sexually sterile triploid populations associated with the invasion of North America by a clonal aquatic plant, Butomus umbellatus. Most populations across the native European range were triploid (84% of 108), whereas most introduced populations were diploid (71% of 136). We evaluated the roles of stochastic processes versus natural selection in causing this shift by surveying predominantly neutral genetic variation at 28 RAPD loci. In Europe (EU) we detected 47 distinct genotypes among 142 plants sampled from 71 populations, whereas in North America (NA) we detected only six genotypes among 138 plants from 69 populations. Of the six NA genotypes, a set of four closely related genotypes were found only in triploid populations and a pair of closely related genotypes were found only in diploid populations, and these were genetically divergent from the triploid genotypes. This result is consistent with severe founder effect. Because sex creates genotypic variation and produces offspring with greater dispersal potential than those produced clonally, we tested the hypothesis that sexual reproduction characteristic of diploids has given them a colonization advantage that accounts for their high frequency in NA. However, we found little or no evidence of sexual recruitment in introduced diploids. One very widespread heterozygous genotype occurred in 95% of 38 introduced diploid populations (i.e., 72 of 76 plants surveyed) suggesting predominant clonal reproduction. Moreover genotypic diversity was not higher within or among diploid than triploid populations in either the native or introduced range. Low genetic diversity in diploid populations was also supported by a comparison of within-population quantitative variation for plant size under a common greenhouse environment. Thus, diploids have not been favored during colonization owing to their sexual fertility. However, concurrent studies have shown that NA diploids exhibit a much higher capacity for clonal reproduction, via small vegetative bulbils, than NA triploids, which almost never produce bulbils. The same difference in clonal capacity is not a consistent feature of the native EU populations. Taken together, these results suggest that strong founder effect has set the stage for a major increase in diploid frequency due to the particular, and possibly idiosyncratic, features of the diploid and triploid lineages introduced to North America.

Suscetibilidade à queda natural e caracterização dos frutos de diversos genótipos de bananeiras

A queda natural de frutos maduros da bananeira, resultado da separação individual de frutos da coroa da penca, também chamada despencamento, é uma característica indesejável, que pode limitar o lançamento de uma nova cultivar. O fruto destacado da penca tem vida de prateleira reduzida, além de não demonstrar boa aparência aos olhos do consumidor. Os objetivos do presente trabalho foram quantificar a suscetibilidade à queda natural dos frutos de bananeiras de grupos genômicos e ploidias diferentes, e identificar correlações entre a queda natural e diversas características físicas dos frutos. Foram utilizados 37 genótipos de bananeiras. De acordo com análise de variância e teste de Scott-Knott, os resultados evidenciaram a alta resistência ao despencamento dos genótipos pertencentes ao grupo genômico BB (Butuhan, Piraí e BB França), Terra (AAB), Poteau Nain (tipo figo) (ABB) e Thap Maeo (AAB), enquanto Prata-Anã (AAB), Grande Naine (AAA), Ambrósia (AAAA), Ouro (AA) e FHIA 18 (AAAB) obtiveram valores intermediários de resistência ao despencamento. Com relação às bananeiras suscetíveis, destacam-se os híbridos melhorados Pioneira (AAAB), YB42-21 (AAAB), Buccaneer (AAAA) e Calypso (AAAA) e a cultivar Ouro da Mata (AAAB). Verificou-se associação de 74% entre a firmeza do fruto e a resistência ao despencamento. Os estudos de grupos genômicos e ploidias indicaram maior resistência ao despencamento das bananeiras pertencentes ao grupo BB e dos genótipos triplóides ABB e AAB.

Genetic diversity of Musa diploid and triploid accessions from the Brazilian banana breeding program estimated by microsatellite markers

Banana (Musa spp.) is one of the most consumed fruits worldwide. Production is based mainly on triploid cultivars, and most genetic improvement programs aim to generate tetraploid hybrids obtained from the crossing of established triploid cultivars with a diploid parent genotype, improved or wild, exhibiting the trait of interest, normally resistance to biotic factors. Microsatellites were used to investigate the genetic variability and relationships between 58 Musa genotypes, including 49 diploids and nine triploid cultivars maintained at the Musa germplasm collection of the Brazilian dessert banana breeding program. Thirty-three primer pairs developed for banana were tested, and nine amplified reproducible and discrete fragments, producing a total of 115 alleles. The average number of alleles amplified per primer was 12.8, ranging from 10 to 15. The diploid genotypes presented the largest genetic variability, demonstrated by the large number of alleles detected, and the low similarity between the clones. The phenetic analysis clustered the triploid cultivars in a separated group, with the exception of the ‘Nanica’ and ‘Gros Michel’ cultivars, which showed high similarity with the diploid cultivar ‘Mambee Thu’. It was not possible to separate the wild diploid genotypes from the cultivated ones, indicating a common origin of these genotypes. A high proportion of duplicated alleles and/or loci was observed for diploid and triploid genotypes. The information gathered about the similarity between diploid and triploid accessions will help to define potential crosses to maximize the recovery of the typical fruit qualities required in Brazil (AAB, Pome and Silk dessert banana).

Natural and induced polyploidy in Acacia dealbata Link. and Acacia mangium Willd.

Seeds were obtained from seven natural populations of Acacia dealbata, three natural populations of A. mangium and a seed orchard of A. mangium, representing the natural range of the two species. Polyploids were discovered in two of the seven populations of A. dealbata. The 2C DNA amount for diploid A. dealbata (2n = 2x = 26) was 1.74 pg, and for diploid A. mangium (2n = 2x = 26) was 1.30 pg. A naturally occurring tetraploid of A. dealbata (2n = 4x = 52) had a 2C DNA amount of 3.41 pg and a naturally occurring triploid genotype had a 2C DNA amount of 2.53 pg. The use of colchicine and oryzalin was investigated as a means of producing higher frequencies of tetraploids of both A. mangium and A. dealbata for incorporation into breeding programmes. Colchicine treatment gave tetraploid frequencies up to 29% for A. dealbata seedlings, and up to 18% for A. mangium seedlings. In contrast, no tetraploid A. mangium was detected following oryzalin treatment, and the low frequencies of tetraploids observed in A. dealbata could be attributed to their natural occurrence.

Screening Miscanthus genotypes in field trials to optimise biomass yield and quality in Southern Germany

Field experiments to test the biomass production from the C 4 perennial grass Miscanthus have concentrated on one triploid genotype, namely M.× giganteus. Several limitations to production from M.× giganteus including insufficient winter rhizome cold tolerance demonstrated the need to broaden the genetic base. This paper presents results from a field trial in Southern Germany planted with 15 Miscanthus genotypes including M.× giganteus, M. sacchariflorus, wild M. sinensis and bred M. sinensis hybrids over 3 years. Under field conditions, establishment from micro-propagation was high and all genotypes survived the first winter (losses<6%). Genotype growth characteristics were determined by measurements of height, shoot density, stem diameter, flowering time and autumn senescence rate. Increasing plant age was associated with higher yields (2, 6, and 17 t dry matter ha −1 in autumn of years one to three, respectively) and better biomass qualities for combustion. Delaying harvest time from autumn until spring in the second and third years reduced harvestable yields but increased combustion quality by lowering moisture, ash, Cl and N contents for all genotypes. Yields were highest for the M.× giganteus and some newly bred M. sinensis hybrids, but biomass qualities were best in the pure M. sinensis genotypes. These trials showed that new hybrids between M. sacchariflorus and M. sinensis should be developed that have many growth characteristics similar to M.× giganteus but with improved rhizome freeze tolerance in winter. As the biomass yield and quality of a particular genotype after 1 year of growth does not always relate to that measured in subsequent years, identification of the most suitable genotypes requires at least 2 years.

The occurrence of 2 n eggs in the dihaploids derived from Rosa hybrida L.

Dihaploid derivatives of 4x Rosa hybrida L. obtained through parthenogenesis induced by irradiated pollen significantly produce 2n eggs,often accompanied by gametes with higher ploidy levels (3x and 4x). The gamete ploidy level distribution depends on the originating genotype. The ploidy level of the male parent affects the maternal /paternal ratio in the endosperm, which can be involved in the counter-selection of triploid genotypes resulting from the crosses made between dihaploid and 4x Rosa hybrida.The observed segregation ratios of flower doubleness in triploid progenies of dihaploids × R. wichuraianasuggest that the relevant locus could be positioned far from the centromere.

Yield Components of Triploid and Tetraploid Musa Genotypes in Nigeria

The additive main effects and multiplicative interaction (AMMI) model was used to evaluate the stability patterns of 36 Musa genotypes in four cropping environments for bunch weight, pulp weight, and dry matter content. Alleycropping generally induced higher means for all traits than did sole cropping. The triploid plantains produced smaller bunch weights and were less stable than dessert and cooking bananas. In this ploidy group, bunch weight was highest for the cooking bananas `Cardaba' and `Fougamou', but only `Fougamou' was stable across environments. Among the hybrids, only `FHIA23' (dessert banana) expressed high and stable bunch weights, while other high-yielding hybrids displayed specific adaptation to alleycropping. Pulp weight was lower but more stable in plantains than in other triploid genotypes. Among the hybrids, pulp weight was high and stable for one cooking banana (`FHIA3'), one dessert banana (`FHIA1'), and three plantains (`PITA1', `PITA2', and `PITA7'). Dry matter content was highest in plantains and lowest in dessert bananas at both triploid and tetraploid levels, and was also more stable than the other traits. Thus, the adaptation patterns of genotypes across environments varied according to the trait studied. When rank changes were not observed across traits for a given genotype, differences were still noted in the relative magnitude of the IPCA1 score. Hence, both farm gate traits and postharvest processing traits should be considered in selecting for broad or specific adaptation. Determination of the genetic relationships between processing traits and farm gate traits could allow Musa breeders to construct selection indices that would facilitate multiple trait selection and enhance breeding efficiency, with respect to cultivar stability and adaptation across environments.

Photoautotrophic shoot and root development for triploid melon

The aim of this investigation was to establish environmental factors which promote growth and photosynthesis of melon (Cucumis melo L.) shoot buds, in vitro, and determine if photoautotrophic shoots had superior root forming ability in photoautotrophic environments. Buds from the triploid melon clone ‘(L-14×B)×L-14’ were observed for 21 days after transfer from a multiplication MS medium with 3% sucrose and 10 μM benzyladenine (BA) to a shoot development medium with 1 μM BA at three levels of sucrose in the medium (0, 1 and 3%), and light (50, 100 and 150 PPF) and CO2 (500, 1000 and 1500 ppm) in the culture chamber. More shoot buds were observed with 3% sucrose in the medium. Increased light and CO2 had a positive interaction with shoot proliferation. Fresh and dry weights were greatest at 3% sucrose, 150 PPF light and 1500 ppm CO2. Shoot buds grew more slowly in sugar-free medium, but fresh and dry weight still doubled over 21 days of culture. Net photosynthetic rates (NPR) of buds were negative after four days in treatment conditions, but became positive after transfer to fresh, sugar-free medium. Two triploid genotypes of melon were (1) grown in vitro with sugar (photomixotrophic) and without sugar (photoautotrophic), (2) rooted in sugar-free media, both in a laboratory controlled environment chamber (in vitro) and a greenhouse acclimatization unit (ex vitro), and (3) compared for subsequent nursery growth in the greenhouse unit. The genotype ‘(L-14×B)×L-14’ produced more shoots than ‘(L-14×B)×Mainstream’ in both photomixotrophic or photoautotrophic conditions. ‘(L-14×B)×L-14’ rooted as well from either photoautotrophic and photomixotrophic shoots but ‘(L-14×B)×Mainstream’ rooted less frequently from photoautotrophic shoots. Seventy-six percent of the shoots in the laboratory controlled environment chamber were able to root photoautotrophically, whereas 47% of the shoots in the greenhouse acclimatization unit were rooted. Between 77% and 88% of plantlets from all treatment combinations survived transfer to the nursery. After growth in the nursery, the sizes of plants (fresh weight, dry weight, leaf area) were the same for either genotype, from either photoautotrophic or photomixotrophic shoots. Nursery plants that had been rooted in the laboratory controlled environment chamber were larger than those rooted in the acclimatization greenhouse chamber.

Perspectives on the application of biotechnology to assist the genetic enhancement of plantain and banana (Musa spp.)

Bananas and plantains (Musa spp.) are the most important tropical fruit crops. They form an integral component of the farming systems in the humid agroecological zones of the tropics. A broad array of applied cell and molecular techniques are increasingly being used worldwide to facilitate and enhance the handling and improvement of plantain and banana germplasm. Tissue culture is used for germplasm exchange, conservation and rapid multiplication, while in vitro seed germination (based on embryo culture or rescue) plays a critical role in generating hybrid plants. DNA marker systems have been developed in Musa to assist germplasm management, selection within the breeding pool or gene introgression from wild species, and for disease diagnosis. Likewise, genetic transformation using the particle gun method or through Agrobacterium co-cultivation shows potential for the genetic betterment of the crop. This article discusses the applications of biotechnology for the genetic enhancement of banana and plantain. It highlights current advances by research teams across the world and reviews progress in molecular breeding of Musa by the International Institute of Tropical Agriculture and its collaborators. Plantains and bananas (Musa spp.) are staple foods for rural and urban consumers in the humid tropics and an important source of rural income, particularly in some locations where smallholders produce them in compound or home gardens. World Musa production is around 85.5 million tonnes annually (FAO 1998), of which bananas cultivated for the export trade account for only 10%. Hence, fruit harvested from bananas and plantains are important components of food security in the tropical world, and provide income to the farming community through local and international trade. Most banana cultivars and all plantain landraces have 33 chromosomes (2n = 3x). These triploid genotypes are virtually or completely sterile and develop their fruit by vegetative parthenocarpy. Diploid landraces and tetraploid cultivars (mostly artificial hybrids) are also cultivated. The

Isolation of triploid and tetraploid olive (Olea europaea L.) plants from mixoploid cv. ‘Frantoio’ and ‘Leccino’ mutants by in vivo and in vitro selection

AbstractThis paper reports a procedure for isolating triploid and tetraploid olive plants, which have not been produced before either artificially or in nature. These polyploids were isolated from two mixoploid somatic mutants obtained earlier by treating Trantoio' and ‘Leccino’ plantlets with gamma radiation. The mixoploid mutants exhibit increased thickness of leaf, stem and root tissues, short internodes, a modified leaf lamina shape and a strong resistance to Spilocaea oleagina (Cast.) Hugh. In addition, they produce a mixture of normal drupes and some abnormally large ones, almost twice normal size. The variation in the nuclear DNA content of the mixoploid mutants is closely correlated with variation in their pollen size, crop capacity and the production of large fruit. Triploid genotypes with 69 chromosomes were isolated by germinating the seeds of these large fruits, collected from both the mixoploid mutants. Tetraploid plantlets, with 92 chromosomes, were obtained from cv. ‘Frantoio’ by selecting in vitro, during several proliferation phases, the shoots with obvate leaf shape which occurred among the shoots with normal lanceolate or intermediate leaf shape.

Fruit Characteristics of Hybrid Triploid Melons

Thirteen triploid lines of melon (Cucumis melo L.) were derived from crosses involving five tetraploid and seven diploid lines. Fruit characters were assessed. When allowed to open pollinate in field plots with adjacent diploid pollinators, eight triploid genotypes were sterile or nearly sterile (&lt;1% viable seed). Five triploid genotypes were partially fertile, indicating viable pollen grains were present. Cytological analysis performed on progeny of a partially fertile triploid plant fertilized by open pollination indicated euploid female gametes were common. Triploid hybrids between tetraploid `Miniloup' and several other diploid parents had vegetative and fruit characteristics intermediate to the parents. Most triploid genotypes yielded round fruit in contrast to their diploid parent whose fruit were oval to oblong and the tetraploid parent that had oblate fruit. Sugar levels of some triploid hybrids were as high as diploid parents.

Fruit Characteristics of Hybrid Triploid Melons

Thirteen triploid lines of melon (Cucumis melo L.) were derived from crosses involving five tetraploid and seven diploid lines. Fruit characters were assessed. When allowed to open pollinate in field plots with adjacent diploid pollinators, eight triploid genotypes were sterile or nearly sterile (&lt;1% viable seed). Five triploid genotypes were partially fertile, indicating viable pollen grains were present. Cytological analysis performed on progeny of a partially fertile triploid plant fertilized by open pollination indicated euploid female gametes were common. Triploid hybrids between tetraploid `Miniloup' and several other diploid parents had vegetative and fruit characteristics intermediate to the parents. Most triploid genotypes yielded round fruit in contrast to their diploid parent whose fruit were oval to oblong and the tetraploid parent that had oblate fruit. Sugar levels of some triploid hybrids were as high as diploid parents.