The wild tomato Lycopersicon pennellii is resistant to numerous important pests of cultivated tomato, L. esculentum, including armyworm, fruitworm, aphids, leafminers, and whitefly. The pest resistance of L. pennellii is mediated by the presence of acylsugars, which constitute 90% of L. pennelliitype IV trichome exudate. Transfer of the ability to accumulate acylsugars could result in pest-resistant tomato cultivars, and thus, a reduction in the dependence on synthetic chemicals for insect control for this crop. Initial tomato lines bred for acylsugar production possessed the desired insect resistance, but were of poor horticultural quality due to linkage drag. These tomato lines possessed seven or eight L. pennellii introgressions, some of which were quite large. As a result, about 25% to 30% of the genomes of these acylsugar lines were comprised of L. pennellii DNA. A set of 20 molecular markers was created, providing markers throughout each introgression. The acylsugar breeding program then combined use of a biochemical assay for acylsugars and genomic analyses using these molecular markers to determine which of the introgressions were involved in the linkage drag, and to select plants that either eliminated or shortened those introgressions. Introgressions on chromosomes 2, 3, 5, and 10 were found to be associated with negative characteristics, such as delayed germination, reduced fruit set or size, delayed maturity, or reduced seed set. New acylsugar lines that eliminate or reduce some of these introgressions were created. The new lines show marked improvement in some of the affected traits, while also producing acylsugars. Hybrids created using these lines show marked improvement in horticultural type.
Martha A. Mutschler, Jian Hua Xiong, Ahmed Wally and Ricardo Lobato-Ortiz
Cristián Vela-Hinojosa, Héctor B. Escalona-Buendía, José A. Mendoza-Espinoza, Juan M. Villa-Hernández, Ricardo Lobato-Ortíz, Juan E. Rodríguez-Pérez and Laura J. Pérez-Flores
Antioxidants, antioxidant capacity, and the expression of isoprenoid metabolism–related genes and two pigmentation-related transcription factors were studied in four native and four hybrid tomato (Solanum lycopersicum) genotypes with different-colored fruit. Red fruit genotypes were associated with greater lycopene, β-carotene, lipophilic antioxidant capacity, and greater chromoplast-specific lycopene β-cyclase (CYC-B) transcript levels. Orange fruit genotypes had greater concentrations of tocopherols and greater transcript levels of homogentisate phytyl transferase (VTE-2), 1-deoxy-D-xylulose phosphate synthase (DXS), and 4-hydroxyphenylpyruvate dioxygenase (HPPD). The yellow fruit genotype was greater in total polyphenol and hydrophilic antioxidant capacity with greater expression of geranylgeranyl reductase (GGDR), phytol kinase (VTE-5), phytoene synthase (PSY) 2, lycopene β-cyclase (LCY-B), SlNAC1, and SINAC4. Greater levels of individual antioxidants were associated with specific coloration of tomato fruit. Moreover, the negative correlations between the expression of PSY1 and VTE-5, and between lycopene and chlorophyll, suggest a balance between carotenoids, tocopherols, and chlorophylls. The results of this study support either the direct commercialization of tomatoes with different color fruit or use of their genotypes in breeding programs to increase antioxidant levels among existing cultivars.