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  • Author or Editor: David Francis x
  • Journal of the American Society for Horticultural Science x
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The lack of resistance to bacterial diseases increases both the financial cost and environmental impact of tomato (Lycopersicon esculentum Mill.) production while reducing yield and quality. Because several bacterial diseases can be present in the same field, developing varieties with resistance to multiple diseases is a desirable goal. Bacterial spot (caused by four Xanthomonas Dowson species) and bacterial speck (caused by Pseudomonas syringae pv. tomato Young, Dye and Wilkie) are two economically important diseases of tomato with a worldwide distribution. The resistance gene Pto confers a hypersensitive response (HR) to race 0 strains of the bacterial speck pathogen. The locus Rx3 explains up to 41% of the variation for resistance to bacterial spot race T1 in field trials, and is associated with HR following infiltration. Both Pto and Rx3 are linked in repulsion phase on chromosome 5. We made a cross between two elite breeding lines, Ohio 981205 carrying Pto and Ohio 9834 carrying Rx3, to develop an F2 population and subsequent inbred generations. Marker-assisted selection (MAS) was applied to the F2 progeny and to F2:3 families in order to select for coupling-phase resistance. Thirteen homozygous progeny from 419 F2 plants and 20 homozygous families from 3716 F3 plants were obtained. Resistance was confirmed in all selected families based on HR in greenhouse screens using bacterial speck race 0 and bacterial spot race T1 isolates. Resistance to bacterial spot race T1 was confirmed in the field for 33 of the selected families. All selected families were also resistant to bacterial speck in the field. MAS was an efficient tool to select for desirable recombination events and pyramid resistance.

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The genetic and environmental variation for flesh color of tomato (Lycopersicon esculentum Mill.) fruit was quantified using 41 red-fruited breeding lines, open-pollinated cultivars, and hybrids that are representative of the diversity of tomatoes grown for whole-peel processing in the midwestern and eastern United States and Ontario, Canada. Objective color measurements were made for 2 years from replicated experiments with 2 to 4 blocks per year. Genotypes differed significantly in lightness value (L*), saturation (chroma), and hue angle. Variation within fruit and among fruit in plots accounted for more than 75% of the environmental variation for the color traits. The crimson locus (ogc) accounted for less than one-third of the variation in fruit color among genotypic means, and explained 18% to 27% of the genotypic variation for L*, chroma, and hue. Estimates of variance components were used to develop sampling strategies for improving selection efficiency. Genotypes were identified that may be useful for studying genetic differences that lead to quantitative variation for fruit color in red-fruited populations of tomato.

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An inbred backcross (IBC) population derived from Lycopersicon hirsutum LA407 and L. esculentum was evaluated in replicated field trials to assess its potential for the improvement of red-fruited tomatoes. Significant phenotypic variation among genotypes was detected for the hue (tint), L (darkness), and chroma (saturation) of color. Significant effects due to environment and genotype × environment interactions also were observed. One superior inbred backcross line from this population, IBL 2349, was used to develop an F2 population and to explore the genetic basis of color. Two independent L. esculentum quantitative trait loci (QTL) associated with improved color were identified based on linkage to markers mapping to chromosome 4 and chromosome 11. Epistatic interactions were identified between the two L. esculentum loci. Unexpected epistatic interactions also were identified between L. esculentum loci and an LA407 introgression on chromosome 7 present within IBL 2349. The two L. esculentum QTL and the epistatic interactions were confirmed in replicated trials with F3 and F4 families. The loci identified in this study and their epistatic interactions may provide additional tools for the improvement of red-fruited tomatoes in breeding programs.

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Abstract

The effectiveness of gamma radiation as an enhancer of anthocyanin and flavonol pigment synthesis in cranberries was determined. Three different maturities of cranberries, based on their degree of coloration, and radiation levels of 150 and 300 krad were employed. The changes in the anthocyanin and flavonol pigments were measured quantitatively at regular intervals during storage. Radiation had a beneficial effect on the pigmentation of full-red cranberries and resulted in a significant increase in the anthocyanin and flavonol pigment contents. Effects on the less colored berries were not as great and in some cases flavonoid synthesis was reduced. The radiation induced changes were strictly quantitative in nature and there were no qualitative changes in the anthocyanins and flavonols. The visual effects of radiation on cranberries were minor softening and a stimulation of pigment production in the endocarp area of the fruit, resulting in internal coloration of the fruit. It was concluded that gamma radiation has an effect on the biosynthesis of the pigments involved and that the maturity stage of the cranberries was the controlling factor in determining the degree of response to radiation treatment. A possible mode of action of radiation on flavonoid synthesis was postulated.

Open Access

Fruit firmness is a key quality component of tomatoes (Lycopersicon esculentum Mill.) for fresh-market and processed product applications. We characterized inheritance of firmness in processing tomato germplasm developed from interspecific L. esculentum Mill. × L. cheesmanii f. minor (Hook. f.) C.H. Mull. and intraspecific L. esculentum crosses. Although firmness is a key quality attribute of tomato, there is no standard method for measuring it. We measured the elastic portion of firmness by compression (compression Fmax) and puncture (puncture Fmax), and the viscoelastic portion by force-relaxation. The experimental design incorporated six genotypes in a complete 6 × 6 diallel. Compression Fmax and force measurements recorded at 0.5, 1.0, 5.0, and 10.0 seconds of relaxation were strongly related to each other, while relaxation parameters (A, B, C) describing relaxation curve shape were generally independent. Compression Fmax, relaxation curve parameter A, and puncture Fmax were significantly different among hybrids. Significant differences between Maryland and Ohio environments were evident for compression Fmax and relaxation curve parameter A. The patterns of firmness means differed among firmness measurement methods, namely for compression Fmax and puncture Fmax, indicating that they measure different aspects of tomato fruit firmness. Soft-fruited parents generally exerted a negative effect on compression Fmax, whereas firm-fruited parents most often exerted a positive effect on compression Fmax. The force required for fruit compression best approximated subjective assessment of fruit firmness. Force required for fruit puncture was subject to a significant environmental × hybrid influence in the genotypes evaluated. Shape of the force relaxation curve (i.e., parameter A) was not predictive of relative fruit firmness. General combining ability (GCA) and specific combining ability were both significant with GCA being the principal source of genetic variation. In agreement with combining ability estimates, narrow-sense heritability estimates for compression Fmax and puncture Fmax were relatively high.

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Breeding and development of ornamental woody plants for specific ideotypes will provide diverse choices to meet specific needs for natural and constructed landscapes. An F1 half-sib family analysis of Magnolia virginiana generated from controlled pollinations was implemented to identify potential juvenile selection strategies for two mature ideotypes: a compact and rounded shrub form (to 2.5 m tall and wide) and a single-stemmed, small tree form (to 4 m tall), both with abundant flowering. The 2-year test was conducted in a container nursery. Fourteen traits were measured in 2007 and 2008, including height at three intervals (July, August, and September), mean branch length and branch count, early and late flower production, collar sprout formation, stem diameter, and branch angle. There were significant differences between F1 half-sib families (P ≤ 0.0001) for all traits. Phenotypic and genetic correlations and narrow sense heritability were estimated for these traits. Phenotypic and genetic correlations showed favorable associations among branch count, caliper, and early flower production. These traits were used to form a selection index for a shrub ideotype. Also, there were positive phenotypic and genetic correlations between height and late flower production, which were both negatively correlated with collar sprout formation. These traits were used to form a selection index for the single-stemmed, small tree ideotype. Narrow sense heritabilities were high for most traits in 2007 but were lower in 2008. Results suggest that selection of phenotypes ranking highest for the traits of interest may yield the desired ideotypes. However, introduction of additional genetic variation through new germplasm accessions may be necessary to maintain breeding progress.

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A broad source of Gerbera × hybrida Hort. germplasm was evaluated for vase life. Senescence mode, i.e., bending or folding of stems or wilting of ligulae was also recorded for flowers evaluated. Intensive selection was practiced to improve vase life. About 10% of the plants from a sample population were selected for having flowers with high vase life. Progeny means for vase life resulting from a topcross between these plants and `Appleblossom' were used to select five plants (about 1.5% of the sample population) whose flowers had high vase life. A diallel cross using these five plants as parents resulted in a progeny population with an increase in mean vase life of 3.4 days compared to mean vase life for the initial sample population. Increases in vase life means for days to bending, folding, and wilting were 0.3, 3.5, and 1.2 days, respectively. Plants with flowers which senesced due to wilting had the longest mean vase life before and after breeding. Changes in proportion of senescence modes were observed; bending decreased, folding and wilting increased. Frequencies of bending, folding, and wilting were compared to vase life means for 10 progenies. Proportion of bending generally decreased as vase life increased.

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For many horticultural crops, selection is based on quality as well as yield. To investigate the distribution of trait variation and identify those attributes appropriate for developing selection indices, we collected and organized information related to fruit size, shape, color, soluble solids, acid, and yield traits for 143 processing tomato (Solanum lycopersicum L.) lines from North America. Evaluation of the germplasm panel was conducted in a multiyear, multilocation trial. Data were stored in a flat-file format and in a trait ontology database, providing a public archive. We estimated variance components and proportion of variance resulting from genetics for each trait. Genetic variance was low to moderate (range, 0.03–0.51) for most traits, indicating high environmental influence on trait expression and/or complex genetic architecture. Phenotypic values for each line were estimated across environments as best linear unbiased predictors (BLUPs). Principal components (PC) analysis using the trait BLUPs provided a means to assess which traits explained variation in the germplasm. The first two PCs explained 28.0% and 16.2% of the variance and were heavily weighted by measures of fruit shape and size. The third PC explained 12.9% of the phenotypic variance and was determined by fruit color and yield components. Trait BLUPs and the first three PCs were also used to explore the relationship between phenotypes and the origin of the accessions. We were able to differentiate germplasm for fruit size, fruit shape, yield, soluble solids, and color based on origin, indicating regional breeding programs provide a source of trait variation. These analyses suggest that multitrait selection indices could be established that encompass quality traits in addition to yield. However, such indices will need to balance trait correlations and be consistent with market valuation.

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