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  • Author or Editor: John R. Stommel x
  • Journal of the American Society for Horticultural Science x
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Genetic characterization of anthracnose resistance in tomato (Lycopersicon esculentum Mill.) caused by Colletotrichum coccodes (Wallr.) Hughes was accomplished using populations developed from crosses between the anthracnose susceptible cultivar US28 and three resistant breeding lines (115-4, 625-3, and 88B147) that varied in their degree of anthracnose resistance and relative stage of adaptation for commercial use. These lines were of common parental lineage with resistance derived from the small-fruited L. esculentum USDA PI 272636. Anthracnose lesion diameters and fruit weight were measured in puncture inoculated fruit of parental, F1, F2, and backcross generations within each cross. Correlation coefficients between fruit size and lesion diameter were low and generally nonsignificant. Estimates of broad and narrow sense heritabilities for resistance were moderate and declined as relative anthracnose susceptibility of the resistant parent increased coincident with increasing horticultural adaptation. A simple additive dominance model, m[d][h], was adequate to explain the genetic variance for anthracnose resistance in all crosses. Genetic variance for anthracnose resistance was primarily additive. The minimum number of effective factors or loci conditioning anthracnose resistance declined during attempts to transfer high levels of resistance from PI 272636 into adapted breeding lines.

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Solanum ochranthum Dunal is a nontuber bearing wild relative of the cultivated tomato (Lycopersicon esculentum Mill.), and a potential source of new genes for disease and pest resistance. Because S. ochranthum is sexually isolated from tomato, somatic hybrids between tomato (PI 367942; L. esculentum Mill. var. cerasiforme (Dunal) A. Gray VFNT cherry × L. peruvianum (L.) Mill. backcrossed to VFNT cherry) and S. ochranthum (LA2117) were developed previously to overcome these crossing barriers. Attempts to backcross these hybrids to tomato have been unsuccessful. Pollen fertility and mitotic and meiotic studies in tomato + S. ochranthum somatic hybrids determined the cause of the sterility of the somatic hybrids and identified hybrids with moderate fertility. Chromosome counts of dividing root tip cells delineated tetraploid (2n = 4x = 48) and hexaploid (2n = 6x = 72) genotypes and aneuploidy in these hybrids. Meiotic analysis of developing microspores confirmed the presence of precocious division and laggard chromosomes at anaphase in both hexaploid and tetraploid hybrids. Bridges were observed in hexaploids at anaphase I and II and multivalent configurations were observed at diakinesis. Multivalents and univalents were evident in nearly all cells examined, proving that the two genomes are homoeologous. Aberrant microsporocytes with five to six developing microspores were noted in hexaploid hybrids. The occurrence of homoeologous pairing between chromosomes of both fusion parents is advantageous to effect recombination between these isolated species. However, the negative effects of multivalent formation and univalents likely contributed to observed sterility in these first generation fusion hybrids. Low to moderate levels of pollen fertility (0% to 52%) were found in tetraploid hybrids, while little or no viable pollen (0% to 4%) was observed in hexaploid somatic hybrids.

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Eggplant (Solanum melongena L.) is ranked among the top ten vegetables in terms of oxygen radical absorbance capacity due to its fruit's phenolic constituents. Several potential health promoting effects have been ascribed to plant phenolic phytochemicals. We report here a first evaluation of phenolic acid constituents in eggplant fruit from accessions in the USDA eggplant core subset. The core subset includes 101 accessions of the cultivated eggplant, S. melongena, and 14 accessions representing four related eggplant species, S. aethiopicum L., S. anguivi Lam., S. incanum L., and S. macrocarpon L. Significant differences in phenolic acid content and composition were evident among the five eggplant species and among genotypes within species. Fourteen compounds separated by HPLC, that were present in many but not all accessions, were identified or tentatively identified as hydroxycinnamic acid (HCA) derivatives based on HPLC elution times, UV absorbance spectra, ES-—MS mass spectra, and in some cases proton NMR data. These phenolics were grouped into five classes: chlorogenic acid isomers, isochlorogenic acid isomers, hydroxycinnamic acid amide conjugates, unidentified caffeic acid conjugates, and acetylated chlorogenic acid isomers. Among S. melongena accessions, there was a nearly 20-fold range in total HCA content. Total HCA content in S. aethiopicum and S. macrocarpon was low relative to S. melongena. A S. anguivi accession had the highest HCA content among core subset accessions. Chlorogenic acid isomers ranged from 63.4% to 96% of total HCAs in most core accessions. Two atypical accessions, S. anguivi PI 319855 and S. incanum PI500922, exhibited strikingly different HCA conjugate profiles, which differed from those of all other core subset accessions by the presence of several unique phenolic compounds. Our findings on eggplant fruit phenolic content provide opportunities to improve eggplant fruit quality and nutritive value.

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Inheritance of resistance to tomato anthracnose caused by Colletotrichum coccodes (Wallr.) S.J. Hughes was evaluated in parental, F1, F2, and backcross populations developed from crosses between adapted resistant (88B147) and susceptible (90L24) tomato (Lycopersicon esculentum Mill.) breeding lines. Resistance was evaluated via measurement of lesion diameters in fruit collected from field-grown plants and puncture inoculated in a shaded greenhouse. Backcross and F2 populations exhibited continuous distributions suggesting multigenic control of anthracnose resistance. Anthracnose resistance was partially dominant to susceptibility. Using generation means analysis, gene action in these populations was best explained by an additive-dominance model with additive × additive epistatic effects. A broad-sense heritability (H) of 0.42 and narrow-sense heritability (h2) of 0.004 was estimated for resistance to C. coccodes. One gene or linkage group was estimated to control segregation for anthracnose resistance in the cross of 90L24 × 88B147.

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Fruit of the cultivated tomato (Lycopersicon esculentum Mill.) store predominantly glucose and fructose whereas fruit of the wild species L. hirsutum Humb. & Bonpl. characteristically accumulate sucrose. Reducing sugar and sucrose concentrations were measured in mature fruit of parental, F1, F2, and backcross (BC1) populations derived from an initial cross of L. esculentum `Floradade' × L. hirsutum PI 390514. Generational means analysis demonstrated that additive effects were equal to dominance effects for percentage of reducing sugar. It was determined that a single major gene, dominant for a high percentage of reducing sugar, regulates the percentage of reducing sugar in tomatoes. We propose that this gene be designated sucr. Only additive effects were demonstrated to be important for glucose: fructose ratios. Using L. hirsutum as a donor parent for increasing total soluble solids concentration in the cultivated tomato is discussed.

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Violet to black pigmentation of eggplant (Solanum melongena L.) fruit is caused by anthocyanin accumulation. Model systems demonstrate the role of regulatory genes in the control of anthocyanin biosynthesis. Anthocyanin structural gene transcription requires the expression of at least one member of each of three transcription factor families: MYB, MYC, and WD. To determine the molecular genetic basis for anthocyanin pigmentation in eggplant fruit, we used real-time polymerase chain reaction (PCR) to evaluate the expression of anthocyanin biosynthetic (Chs, Dfr, Ans) and regulatory (Myc, Myb B , Myb C , Wd) genes in S. melongena genotypes that produce fruit with dark violet (‘Classic’) or white (‘Ghostbuster’) coloration, respectively. Transcript levels and anthocyanin content were evaluated in fruit at various stages of development ranging from small post-anthesis fruit to full-sized marketable fruit. Anthocyanin content increased 9-fold in developing violet-colored ‘Classic’ fruit, whereas low but detectable concentrations were found in white ‘Ghostbuster’ fruit. Chs, Dfr, and Ans as well as Myb C and Myc transcript levels were significantly higher in ‘Classic’ in comparison with ‘Ghostbuster’ fruit at comparable stages of fruit development with greatest differences observed for Ans transcript levels. Myb C and Myc transcript levels increased in developing ‘Classic’ fruit coincident with increasing anthocyanin content. Myb B and Wd transcript levels were not coordinated with changes in biosynthetic transcript levels or anthocyanin concentration.

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Abstract

Five cycles of phenotypic recurrent selection for total dissolved solids and sugar type (reducing vs. nonreducing) were performed on four carrot (Daucus carota L.) populations of common background. The populations contained high or low percentage of total dissolved solids (HTDS and LTDS, respectively) with high or low levels of reducing sugar (HRS and LRS, respectively). Effective selection for total dissolved solids (TDS) and sugar type was indicated by significant gains over five cycles of selection. TDS decreased in LTDS/HRS and LTDS/LRS populations by 21.9% and 15.9%, respectively. Corresponding increases of 22.4% and 28.2% were observed in HTDS/HRS and HTDS/LRS populations. Mean reducing sugar levels in HRS roots after five cycles of selection were limited to 2.0% of root fresh weight; sucrose was the primary storage carbohydrate. Reducing sugars were not detected in LRS roots. Mean total sugar levels in the HTDS and LTDS populations were 7.1% and 3.1% of root fresh weight, respectively. Realized heritability estimates ranged from 0.40 to 0.45 for the four populations. The onset of flowering was markedly delayed in plants of the two HTDS populations after five cycles of selection.

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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During the past 40 years, the US fresh-cut product market has experienced a consistent increase in demand because consumers prioritize health and convenience. Increased interest in fresh-cut products and ready-to-eat vegetables has led to innovations in breeding, product selection, and packaging. However, despite the increased popularity of bell pepper and chile pepper (Capsicum annuum L.), research of fresh-cut jalapeño pepper is limited. This study was conducted to identify jalapeño cultivars that could be suitable as a raw fresh-cut product and explore measures beyond tissue membrane electrolyte leakage (EL) of processed products that may be useful for the identification of cultivars suitable for fresh-cut applications. A total of 22 fresh-cut parameters were examined across five cultivars of jalapeño peppers and 10 intercrosses of these cultivars, including visual quality based on an image analysis via a computer vision system, package headspace gas composition, tissue membrane EL, and texture. Based on our results, the genotypes were grouped into five clusters using a cluster analysis. Variables including tissue softening (r2 = 0.95), EL (r2 = 0.95), total energy of the mesocarp (r2 = 0.95), and package headspace carbon dioxide (CO2) partial pressure (r2 = 0.94) had strong associations with the cluster. A principal component analysis with biplots further confirmed the results. Cultivars Goliath and Emerald Fire and their hybrids in the first and second clusters showed good quality for fresh-cut applications. The fifth cluster, represented by a single cultivar, Jalapeño M, had the smallest physical size, rapid shelf-life decline, accumulated CO2 partial pressures, increased EL, and rapid tissue softening in comparison with the other genotypes. All jalapeño cultivars except Jalapeño M maintained good quality until day 14 postprocessing, and some maintained good quality until 21 days postprocessing. Hybrid crosses suggested that two of the cultivars evaluated, Goliath and Emerald Fire, were useful as parents when transferring superior fresh-cut quality traits to progeny. Traditionally, the EL level has been used as an index of freshness (or tissue deterioration). Our results showed that other quality analyses, including measurements of tissue softening via an imaging analysis, and physical analyses of tissue firmness can also be used as indices for the freshness of fresh-cut jalapeños. The results suggest that fruit size, wall thickness, and skin toughness might be useful as predictive measures in the field for the selection of jalapeño genotypes with superior fresh-cut quality.

Open Access

Fresh pepper (Capsicum) fruit that are sliced and/or diced are referred to as fresh-cut products. The current report evaluates the inheritance of postharvest attributes that contribute to pepper fresh-cut quality. Marketable green fruit of large-fruited Capsicum annuum accessions with bell and related pod types (Class 1), C. annuum accessions with jalapeno and serrano pod types (Class 2), and thin-walled “aji”-like tabasco pod types from Capsicum baccatum, Capsicum frutescens, and Capsicum chinense (Class 3) were processed and stored up to 14 days in selective oxygen transmission rate packaging. Fresh-cut attributes were influenced by genotype as well as year. For all pod types, O2 and CO2 partial pressures in storage packages, tissue weight loss, and electrolyte leakage differed among accessions, days of storage, and years of testing. Percent O2 declined and CO2 and electrolyte leakage generally increased during storage. Some accessions in Class 1 and Class 2 maintained acceptable product quality during storage. Changes in fruit weight loss were small with greater weight loss observed in Class 1 accessions relative to weight loss for Class 2 and Class 3. Broad-sense heritability for fresh-cut attributes was moderate to low indicating that it will be difficult to breed for fresh-cut quality.

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