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  • Author or Editor: John R. Stommel x
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Cultured leaf explants obtained from 36 accessions of the wild tomato Lycopersicon hirsutum were evaluated for morphogenic capacity in response to 3 cytokinins [zeatin, benzylamino purine (BA) and kinetin] in combination with indoleacetic acid (IAA). Morphogenic responses within this wild species were accession-dependent, Cotyledon tissue, in comparison to true leaf explants, were superior for callus and shoot formation. Optimal callus induction medium varied with accession, but most often contained 13.3 μM BA plus 1.7 μM IAA. Media containing 4.6 or 9.2 μM zeatin plus 0.1 μM iaa were optimal shoot induction media. Explants of L. hirsutum f. typicum accessions 126445, 127826, 128644, and 390663 and L. hirsutum f. glabratum accessions 365904, 365905, and 365906 exhibited the highest levels of shoot formation.

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Cultured leaf explants obtained from 36 accessions of the wild tomato Lycopersicon hirsutum were evaluated for morphogenic capacity in response to 3 cytokinins [zeatin, benzylamino purine (BA) and kinetin] in combination with indoleacetic acid (IAA). Morphogenic responses within this wild species were accession-dependent, Cotyledon tissue, in comparison to true leaf explants, were superior for callus and shoot formation. Optimal callus induction medium varied with accession, but most often contained 13.3 μM BA plus 1.7 μM IAA. Media containing 4.6 or 9.2 μM zeatin plus 0.1 μM iaa were optimal shoot induction media. Explants of L. hirsutum f. typicum accessions 126445, 127826, 128644, and 390663 and L. hirsutum f. glabratum accessions 365904, 365905, and 365906 exhibited the highest levels of shoot formation.

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Sugar accumulation throughout fruit development in the cultivated tomato (Lycopersicon esculentum) and a wild green-fruited species (L. peruvianum) are being examined. Results obtained using HPLC demonstrate that the fruit of L. peruvianum accessions accumulate the disaccharide, sucrose, in addition to the monosaccharides, glucose and fructose, common to L. esculentum. When detectable, sucrose in the L. esculentum cultivar FM6203 was present at very low levels throughout development. Analysis of mature fruit of L. esculentum var. cerasiforme, L. pimpinellifolium, and L. cheesmanii accessions indicate glucose and fructose as the primary storage sugars. Similar to L. peruvianum, mature fruit of the green-fruited species, L. hirsutum f. typicum and L. hirsutum f. glabratum, accumulate sucrose in addition to glucose and fructose.

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Small/miniature sweet and hot peppers (Capsicum annuum L.), such as snack peppers, are a rapidly growing class of specialty peppers. Low seed count is an important attribute for consumer acceptance of small-fruited specialty peppers. Four inbred U.S. Department of Agriculture (USDA) C. annuum breeding lines exhibiting uniformity for pod type and size and normal or reduced seed count were selected for producing F1 and segregating F2 and backcross generations. Seed content of F1 hybrids and progeny produced from the backcross of F1 hybrids to normal seed count parents exhibited unimodal frequency distributions and skewed toward the parent with normal seed count. Progeny produced from backcrosses to the reduced seed count parent exhibited bimodal population distributions representative of the respective parental phenotypes. F2 populations approximated 3:1 frequency distributions skewed toward normal-seeded parental phenotypes. Chi-square tests supported a single recessive gene model with potential modifiers controlling inheritance of reduced seed count. Genetic variants with reduced seed count facilitate seed production and propagation of specialty market class peppers.

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Tomato fruit carotenoid content was measured in mature fruit of parental, F1, F2 and backcross populations derived from an initial cross of L. esculentum, cv. Floradade, with the orange fruited L. cheesmanii, LA 317. Segregation patterns for orange flesh color and percent β-carotene in F1, F2 and backcross populations fit expected models for a single dominant gene conditioning a high percentage β-carotene content and resultant orange fruit pigmentation. The inheritance of β-carotene in L. cheesmanii paralleled that of the B gene described in L. hirsutum. β-carotene was generally accumulated at the expense of lycopene in orange-fleshed individuals. Correlations between carotenoid type and total carotenoid content were not evident. Variation observed in segregating F2 and backcross populations for total carotenoid content suggested that gains in selection for increased β-carotene and lycopene content may be realized.

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Cultured leaf explants obtained from 36 accessions of the wild tomato species, Lycopersicon hirsutum Humb. and Bonpl., were evaluated for morphogenic capacity in response to three cytokinins (zeatin, BA, and kinetin) in combination with IAA. Media containing 0.1 μm IAA plus 4.6 or 9.2 μm zeatin were optimal for shoot induction. Cotyledon explants were superior to true leaf explants for obtaining shoot formation. Morphogenic responses of L. hirsutum f. typicum and L. hirsutum f. glabratum were clearly accession-dependent and ranged from exceptional with numerous shoots produced to recalcitrant with no shoots produced. The high morphogenetic capacity of leaf explants from L. hirsutum f. typicum accession 128644 was also evident in protoplast-derived calli that readily regenerated shoots. Chemical names used (E)-2-methyl-4-(1H-purin-6-ylamino)-2-buten-1-ol (zeatin), N-(phenylmethyl) -1H-purin-6-amine (BA), N- (2-furanylmethyl) -1H- purin-6-amine (kinetin), 1H- indole-3-acetic acid (IAA).

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Anthocyanins contribute to color development in economically important vegetables, fruits and floral crops. Their expression is critical to product sensory quality attributes, potential nutritive value, and stress response. Anthocyanins are synthesized in response to numerous environmental factors including temperature and light stress and pathogen attack. We have developed several Capsicum lines, including `02C27', expressing anthocyanin pigmentation differentially in various tissues (leaf, stem, fruit and flower). HPLC analysis demonstrated that the anthocyanins within the fruit, flower and leaves of Capsicum `02C27' were identical and that the major anthocyanidin was a delphinidin glycoside. Line `02C27' exhibits anthocyanin foliar pigmentation that is accumulated differentially in response to temperature stress. Under unfavorable low temperature (20 °C day/18 °C night), mature Capsicum leaves contained 4.6 times less anthocyanin per gram fresh weight than under high (30 °C day/28 °C; day/night) temperatures. Besides containing less anthocyanin in mature leaves, young immature leaves did not develop color as quickly under the lower temperature. Utilizing cloned and sequenced gene fragments of pepper chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR), and anthocyanidin synthase (ANS), we evaluated the role of transcription in regulation of flavonol biosynthesis. Analysis of anthocyanin composition and gene expression data indicated that the block in anthocyanin formation in less pigmented leaves occurred at anthocyanin synthase. In contrast to wild tupe plants, this mutant also exhibited reduced flowering and failed to set fruit under high temperature, long day conditions.

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The carotenoids have an important influence on tomato fruit quality and enhance the fruit contribution to human nutrition. Expression of the high pigment (hp) locus in tomato results in increased total carotenoids and increased efficiency of utilization of the polyenes. A similar mutant, dark green (dg), contains higher level of chlorophyll in immature fruit and results in darker red pigmentation, both externally and internally in ripe fruit. Random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) analyses were performed using two pairs of near isogenic lines (NILs) designed to be isogenic at the hp and dg loci. Sixty-four AFLP primer pairs and more than 1000 RAPD 10-mer primers were screened for polymorphism between each pair of the NILs. One RAPD marker was identified to be linked to the hp gene, and two AFLP primer pairs showed polymorphic fragments which distinguished the dg NILs. The markers identified in this study will be converted to allele specific SCAR (sequence characterized amplified region) markers, which are more useful in marker-assisted selection breeding programs.

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Anthracnose, caused by Colletotrichum coccodes, is a serious ripe tomato fruit rot disease. Genetic resistance to anthracnose is not available in commercial tomato cultivars, but has been reported in small-fruited Plant Introductions (P.I.), and with lesser intensity in a number of breeding lines. Transfer of high levels of resistance from these breeding lines or P.I.s to elite materials has proven difficult. Inheritance of resistance has been described as complex with at least six loci influencing resistance reactions. Segregating populations originating from a cross between a susceptible tomato breeding line and a large-fruited breeding line (88B147) with resistance derived from Lycopersicon esculentum var. cerasiforme P.I. 272636, were evaluated for anthracnose resistance. Analysis of anthracnose resistance in puncture-inoculated fruit indicated small, but significant, additive genetic effects for resistance. Additional populations were developed from crosses of a susceptible inbred processing tomato cultivar with: 1) the resistant P.I. 272636, 2) an unadapted small-fruited resistant line developed from P.I. 272636, and 3) the large-fruited breeding line 88B147, also with resistance derived from P.I. 272636. Small additive effects identified in large-fruited material, in comparison to the resistant P.I., suggests that resistance loci have been lost during germplasm development. This is consistent with the relatively larger lesions observed in large-fruited lines derived from P.I. 272636. Positive correlations were noted between small fruit size and high levels of anthracnose resistance. Identification of molecular markers linked to resistance genes in the respective populations will be discussed.

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