Search Results

You are looking at 1 - 3 of 3 items for :

  • Author or Editor: Joanne A. Labate x
  • Journal of the American Society for Horticultural Science x
Clear All Modify Search

A diversity panel of 190 National Plant Germplasm System (NPGS) tomato (Solanum lycopersicum) accessions was genotyped using genotyping by sequencing. These originated from 31 countries and included fresh market, ornamental, processing, breeders’ lines, landraces, and home gardening types, as well as six different accessions of the economically valuable cultivar San Marzano. Most of the 34,531 discovered single nucleotide polymorphisms were rare and therefore excluded from downstream analyses. A total of 3713 high-quality, mapped single nucleotide polymorphisms that were present in at least two accessions were used to estimate genetic distances and population structure. Results showed that these phenotypically and geographically diverse NPGS tomato accessions were closely related to each other. However, a subset of divergent genotypes was identified that included landraces from primary centers of diversity (South America), secondary centers of diversity (Italy, Taiwan, and France), and genotypes that originated from wild species through 20th century breeding for disease resistance (e.g., ‘VFNT Cherry’). Extreme variant accessions produce cultivated fruit traits in a background that contains many wild or primitive genes. These accessions are promising sources of novel genes for continued crop improvement.

Open Access

Broccoli (Brassica oleracea L. var. italica Plenck) and cauliflower (B. oleracea var. botrytis DC) are closely related botanical varieties. The underlying genetic bases of their phenotypic differences from each other are not well understood. A molecular genetic marker enabling B. oleracea germplasm curators and breeders to predict phenotype from seeds or seedlings would be a valuable tool. Mutant alleles at flower developmental pathway loci BoAP1-a, Bo-CAL-a, and glucosinolate biosynthetic pathway locus BoGSL-ELONG have been reported to be associated with a cauliflower phenotype. We surveyed mutant alleles at these three loci in a genetically diverse sample of broccoli and cauliflower accessions from the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS) Plant Genetic Resources Unit (PGRU) and the University of Warwick, Genetic Resources Unit of Warwick HRI (HRI). Phenotypic and genotypic data were collected for multiple plants per accession during two field seasons. Simple genetic models assuming dominance or codominance of alleles were analyzed. Goodness-of-fit tests rejected the null model that the mutant genotype was associated with a cauliflower phenotype. A correlation analysis showed that BoAP1-a and BoCAL-a alleles or loci were significantly correlated with phenotype but the fraction of variation explained was low, 4.4% to 6.3%. Adding BoGSL-ELONG to the analysis improved predictive power using the linear regression procedure, Maximum R-square Improvement (max R 2). In the best three-variable model, only 24.8% of observed phenotypic variation was explained. Because tested genetic models did not hold robustly for the surveyed accessions, it is likely that there are multiple genetic mechanisms that influence whether the phenotype is broccoli or cauliflower. Our results in commercial cultivars indicate that other genetic mechanisms are more important in determining the horticultural type than are BoAP1-a and BoCAL-a.

Free access

Fusarium wilt of tomato (Solanum lycopersicum), caused by fungal pathogen Fusarium oxysporum f. sp. lycopersici (Fol), is one of the most important diseases in tomato production. Three races of the pathogen are described, and race-specific resistance genes have been applied in commercial tomato cultivars for controlling the disease. Race 3 (Fol3) threatens tomato production in many regions around the world, and novel resistance resources could expand the diversity and durability of Fol resistance. The wild tomato species, Solanum pennellii, is reported to harbor broad resistance to Fol and was the source of two known Fol3 resistance genes. In this study, we evaluated 42 S. pennellii accessions for resistance to each fusarium wilt race. F1 plants, developed from crossing each accession with the Fol3 susceptible line ‘Suncoast’, were evaluated for Fol3 resistance, and BC1F1 plants were screened to determine the likelihood that Fol3 resistance was based on a novel locus (loci). Nearly all accessions showed resistance to Fol3, and many accessions were resistant to all races. Evaluation of F1 plants indicated a dominant resistance effect to Fol3 from most accessions. Genetic analysis indicated 24 accessions are expected to contain one or more novel Fol3 resistance loci other than an allele near the I-3 locus. To investigate genetic structure of the S. pennellii accessions used in this study, we genotyped all 42 accessions using genotyping by sequencing. Approximately 20% of the single nucleotide polymorphism (SNP) loci were heterozygous across accessions, likely due to the outcrossing nature of the species. Genetic structure analysis at 49,120 unique SNP loci across accessions identified small but obvious genetic differentiations.

Open Access