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  • Author or Editor: John R. Stommel x
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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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Heat-tolerant and heat-sensitive tomato (Lycopersicon esculemum Mill.) genotypes were grown in the greenhouse under optimum and high temperature stress regimes. Levels of heat tolerance in the genotypes were established by determining percent fruit set under the high temperature regime. Under optimum temperature, fruit set in the heat-sensitive genotypes ranged from 41 to 54% and in the heat-tolerant genotypes from 45 to 91%. Under high temperature, no fruit set was observed in the heat-sensitive genotypes whereas, fruit set in the heat-tolerant genotypes ranged from 5 to 64 %. In vitro germination and pollen tube growth of pollen taken from genotypes grown under optimum temperature conditions were determined before and after subjecting the pollen to 45C for 1, 2, and 4 hours. Pollen viability of heat tolerant genotypes was less affected by heat treatment than that of most heat sensitive genotypes. The results suggest that environmental factors independent of temperature may also influence pollen viability.

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Heat-tolerant and heat-sensitive tomato (Lycopersicon esculentum Mill.) genotypes were grown in the greenhouse under optimum and high temperature stress regimes. Levels of heat tolerance in the genotypes were established by determining percent fruit set under the high temperature regime. Under optimum temperature, fruit set in the heat-sensitive genotypes ranged from 41 to 54% and in the heat-tolerant genotypes from 45 to 91%. Under high temperature, no fruit set was observed in the heat-sensitive genotypes whereas, fruit set in the heat-tolerant genotypes ranged from 5 to 64%. In vitro germination and pollen tube growth of pollen taken from genotypes grown under optimum temperature conditions were determined before and after subjecting the pollen to 45C for 1, 2, and 4 hours. Pollen viability of heat tolerant genotypes was less affected by heat treatment than that of most heat sensitive genotypes. The results suggest that environmental factors independent of temperature may also influence pollen viability.

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Heat-tolerant and -sensitive Lycopersicon esculentum Mill. and L. pimpinellifolium (Jusl.) Mill. genotypes were grown in the greenhouse under optimum- (27/23C, day/night) and high-temperature (35/23C) stress regimes. Heat tolerance levels in the genotypes were established by determining percent fruit set at high and optimum temperatures. Under optimum temperature, fruit set ranged from 41% to 84% and from 45% to 91% in the heat-sensitive and heat-tolerant genotypes, respectively. Under high temperature, no fruit set in the most heat-sensitive genotypes. Fruit set in the heat-tolerant genotypes ranged from 45% to 65%. In vitro germination and tube growth of pollen taken from genotypes grown under optimum temperature conditions were determined before and after subjecting the pollen to 45C for 1, 2, and 4 hours. The response of pollen to heat treatments was genotype dependent and not a general predictor of fruit set under high-temperature stress.

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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

A protocol was developed to make in vitro graft unions among Lycopercicon spp., and regenerates from cultured graft unions were evaluated for chimera formation. Young seedlings were preconditioned for 4 to 6 days in liquid 1/2-strength Murashige & Skoog (MS) basal medium supplemented with 8.9 μM benzyladenine and 1.0 μM indole-3-butyric acid. Preconditioned seedlings exhibited increased biomass and enhanced graft union survival. In particular, survival of cleft grafts increased from 37% to 95% with the seedling preconditioning. When graft unions among different genotypes were excised from apex-to-apex in vitro cleft grafts and plated on MS basal medium supplemented with 9.1 μM zeatin and 3.9 μM ancymidol, as many as 100 plantlets were regenerated from a single graft union. However, no chimeric regenerates were recovered, indicating that asymmetric responses to grafting may be a limiting factor to in vitro chimera formation.

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Colorado Potato Beetle (Leptinotarsa decemlineata Say., CPB) is a destructive pest of the cultivated potato, Solanum tuberosum L. Certain glycoalkaloids in potato leaves are effective deterrents to this insect; however, in tubers these compounds can be toxic to humans. Leptines are foliar-specific glycoalkaloids produced by the related species, S. chacoense. These compounds have been shown to confer resistance to CPB. We are studying the inheritance of leptine production in segregating F1 and F2 populations derived from two S. chacoense accessions, 55-1 and 55-3, which are (respectively) high and low leptine producers. The F1 segregates 1:1 for high (>70% of total glycoalkaloids) and low (<20% of TGA) leptine content. Segregation data from the F1 and F2 populations suggest a twogene model for leptine production: a dominant repressor and a recessive inducer. Using two bulked DNA samples composed of highand low-leptine individuals from the F1 population, we are using various types of molecular markers (RAPDs, SSRs, DS-PCR, and AFLPs) to search for markers linked to leptine production. We have identified a RAPD band that appears to be closely associated with low leptine content and supports the two-gene model. The use of such a marker in a breeding program will facilitate the development of CPB resistant potato varieties.

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