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Xiaofeng Yang and Carlos F. Quiros

Celery cultivars (Apium graveolens var. dulce) in North America have a narrow genetic base. Twenty-two celery, one celeriac and one annual cultivar were screened for polymorphic RAPD (Random Amplified Polymorphic DNA) markers with 28 arbitrary 10-mer primers. Among the total 231 bands obtained, 28 (12%) of the bands were polymorphic among the 24 accessions screened, but only 18 (7.8%) were polymorphic within the 22 celery cultivars. These markers are sufficient to distinguish each of the cultivars used. The average number of marker differences is 6.2 between two celery cultivars, 13.5 between the celeriac and the remaining cultivars, and 16.5 between the annual and the other cultivars. The relationship among the celery cultivars disclosed from this study is basically consistent with that observed using total protein and isozyme markers. RAPD technology provides a new alternative for cultivar identification in celery.

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Genyi Li and Carlos F. Quiros

DNA samples from 21 cultivars of celery (Apium graveolens L. var. dulce) were subjected to amplified fragment length polymorphism (AFLP) analysis. The most informative adapter combination was EcoRI-TaqI. All cultivars could be distinguished from each other by their unique fingerprints based on 73 markers. The program NTSYS grouped the cultivars in three main clusters according to their origin. The groupings observed agreed, with a few exceptions, with those expected by historical accounts and previous analyses based on biochemical and ramdomly amplified polymorphic DNA (RAPD) markers.

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Xiaofeng Yang and Carlos F. Quiros

To characterize the celery (Apium graveolens L. var. dulce, 2n = 2x = 22) genome, 126 celery cDNA clones and 340 random 10-mer primers were used to generate restriction fragment-length polymorphism (RFLP) and randomly amplified polymorphic DNA (RAPD) markers between two cultivated types. Different abundance classes of the genomic sequences represented by the cDNA clones and the RAPD markers were observed. Most of the cDNA clones were single-copy sequences, suggesting the true diploid nature of the celery genome. Nearly half of the 39 RAPD markers tested by Southern hybridization were multiple-copy sequences. Of the RAPD markers tested, 28% was single- and low-copy, and 26% was high-copy sequences. The polymorphism level of the cDNA clones was 23% when tested with four restriction enzymes (Eco RI, Eco RV, Hin dIII, and Hae III). A positive association was observed between RFLP level and the size of cDNA inserts or hybridized restriction fragments. Deletion, insertion, and base substitution were important in the formation of the RFLP markers. Eighty-two (23%) of the 340 primers tested yielded useful RAPD markers, but only 3.8% of the amplified products were polymorphic. Base substitution may be the most important mechanism for the RAPD markers in celery. The RAPD fragments revealed no RFLP markers when tested by Southern hybridization, implying that RAPD markers are an important complement to RFLP markers in genomic mapping in celery. Random methylation of cytosine was determined in 5S rDNA on Bam HI and Hin dIII cutting sites that produced ladder patterns characteristic of tandem repeats.

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J. Mitchell McGrath and Carlos F. Quiros

Morphology and fertility were characterized for 22 intersubspecies hybrids within B. campestris L. Nine subspecies, representing crop types from different geographical areas, were used as pollen donors on three different seed parents. Stability of scored morphological characters was divided into four classes based on their appearance in F1 hybrids; i) constant (present in all hybrids when the character was present in one of the parents, e.g., enlarged hypocotyl, divided leaf), ii) variable (present in some hybrids when the character was present in parent types, e.g., petiole color, pubescence), iii) novel (appearing in hybrids but not present in parents, e.g., anther tip spot, self-compatibility), and iv) reciprocal differences. Constant characters are assumed to have a strong genetic component, variable characters may result from heterozygosity in parents, an allelic series, or polygenic inheritance, and novel characters may arise through mutation or altered gene or physiological interactions. Reciprocal crosses revealed morphological components controlled by the maternal parent, and were most striking in pak-choi (ssp. chinensis) by turnip [ssp. rapifera (Metzg.) Sinsk.] hybrids. Pollen and seed fertility of hybrids was generally reduced when Indian oilseeds [ssp. dichomata (Roxb.) Olsson; ssp. trilecularis (Roxb.) Olsson] were used as parents. Inheritance of the enlarged hypocotyl character was tested in one F2 population. Segregation of the enlarged hypocotyl trait was consistent with a hypothesis of a dominant Mendelian locus. Various novel characters appeared in this F2 population that were not evident in the parents of the hybrid, some of which also showed Mendelian segregation. Genetic differentiation of nuclear or plastid genomes may account for these observations.

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Gordon M. Huestis and Carlos F. Quiros

Phylogenetic relationships of seven Apium species, including three horticultural types of A. graveolens, were assayed for RFLPs using cDNA, chloroplast DNA, and rDNA probes. Most of the probes had been previously mapped in celery. The three horticultural types of A. graveolens were found to be less polymorphic than the wild species and in phylogenetic analysis they clustered together. The wild species formed a cluster on the dendrogram corresponding to their origin in the southern hemisphere. A. nodiflorum, a wild species from Ethiopia formed a branch on the phylogenetic tree apart from all other species. This, along with morphological considerations, suggests that A. nodiflorum should be reclassified outside the genus Apium.

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Juan J. Ruiz, Belen Pico, Genyi Li, Vincent D'Antonio, Bryce Falk and Carlos F. Quiros

Resistance to Celery mosaic virus (CeMV) in celery [Apium graveolens L. var. dulce (Mill.) Pers.] is recessive and determined by the single gene, cmv. We report discovery of two polymerase chain reaction-based dominant markers tightly linked to cmv in segregating F2 and BC1 populations. Marker me1em2 is associated to the dominant (susceptibility allele) and the second marker, me8em2, to the recessive (resistance allele). Simultaneous screening for both markers in segregating populations allows for identification of both homozygous and heterozygous genotypes for disease resistance. This marker system can be used for early seedling selection, which will simplify and speed development of celery cultivars resistant to CeMV.

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Juan J. Ruiz, Santiago García-Martínez, Belén Picó, Muquiang Gao and Carlos F. Quiros

We studied the genetic variability of some traditional tomato (Lycopersicon esculentum L. Mill.) cultivars of Spain, and established their relationships using both simple sequence repeats (SSR) and sequence related amplified polymorphism (SRAP) markers. These included cultivars from different locations of three main types, Muchamiel, De la pera, and Moruno. Additionally we tested two other local cultivars, `Valenciano' and `Flor de Baladre', plus a small sample of commercial cultivars and a few wild species. Both types of markers resolved the cultivars from different groups, but SSR failed to distinguish some of those classified under the same group. All the De la pera cultivars clustered together by genetic similarity with the SRAP markers. The other traditional cultivars, which are grown in a wider geographic range, formed a more diffuse group, which included the commercial cultivar Roma. The Mexican cultivar Zapotec, a breeding line, and the virus-resistant commercial hybrid `Anastasia' were the most distant of all the cultivars. The latter hybrid had higher similarity to the wild species due to introgressed segments from them carrying the resistance genes. Similar results were observed for SSR markers but with a lower level of resolution. This information would be useful to facilitate tomato germplasm conservation and management efforts.

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Ruby Valdez-Ojeda, José Luis Hernández-Stefanoni, Margarita Aguilar-Espinosa, Renata Rivera-Madrid, Rodomiro Ortiz and Carlos F. Quiros

Annatto (Bixa orellana L.) is the sole source of bixin, a seed-specific red apocarotenoid pigment used worldwide. Genetic improvement of annatto has focused on increasing bixin content as well as fostering traits that favor higher content such as pod indehiscence and flower color, among others. Eighty-seven samples collected from two separate important agricultural regions of the southeast of Mexico were characterized morphologically and analyzed genetically for the first time. The sequence-related amplified polymorphism was used for genetic analysis. Two-step cluster analysis of the individuals based on morphological traits produced three groups: one containing individuals with desired morphological characteristics and two others with complementary traits. Like the morphological analysis, the genetic analysis indicated high genetic variation, although the dendrogram based on Nei and Li's similarity coefficient showed them to be dispersed by collection site. However, calculated similarity index values indicated all individuals exhibited high genetic variation. The results are an important advance toward a more effective genetic improvement of annatto because crosses between the different morphological and/or genetic groups described here have the potential to produce a recombination of desired traits in hybrid offspring.