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Gad G. Yousef, Shyh-Shyan Wang and John J. Juvik

A segment from chromosome 7 of the wild tomato species, Lycopersicon chmielewskii has been introgressed through backcrossing into the processing cultivar, VF145B-7879. This segment was previously shown to carry a gene or genes that increase the soluble solids content in ripe red tomato fruits. To study the allelic interaction of this gene(s) and ascertain its performance in different genetic backgrounds, this line, homozygous for the L. chmielewskii segment, was crossed to its isogenic parent (VF145B-7879) and three other commercial cultivars (UC204c, E6203, and ChicoIII). The recurrent parent VF145B-7879 was also crossed to the other cultivars to generate two sets of hybrids, one heterozygous for the L. chmielewskii segment and the other homozygous for the L. esculentum segment on chromosome 7. Results from two years of field study revealed that the L. chmielewskii fragment, when either homozygous or heterozygous in the VF145B-7879 background, comparably increased soluble solids concentration in red fruit, suggesting dominant allelic interaction. This increase ranged from 8%–10% higher soluble solids content in these lines compared to the levels found in the recurrent parent (VF145B-7879). The F1 hybrids containing one dosage of this gene(s) showed a significant increase in the soluble solids content compared to the commercial parents. However, due to F1 heterosis observed in all the hybrid combinations, soluble solids content in the hybrids with this gene were not significantly greater than that of the hybrids without this gene. This gene was found to exert no significant influence on fruit pH, weight, and yield.

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Diana M. Cheng, Gad G. Yousef and Mary Ann Lila

Spinach (Spinacea oleracea L.) is a valuable agricultural crop that accumulates phytoecdysteroids, polyhydroxylated triterpenoids, which may play a role in plant defense and have purported health benefits for human consumers. In this study, phytoecdysteroid accumulation was measured in seeds and shoots of 15 spinach accessions to determine whether phytoecdysteroid levels vary between spinach varieties and whether seed content could reliably predict relative levels in the edible foliage. Additionally, phytosterols, precursors to phytoecdysteroids, were examined to determine potential points of regulation of spinach phytoecdysteroid biosynthesis. Significant variations in phytoecdysteroid levels between accessions were observed (P < 0.05), suggesting the potential for genetic manipulation through traditional breeding or genetic engineering to increase phytoecdysteroid levels in spinach. However, results suggest that estimation of phytoecdysteroid levels in shoots may not be achieved by measuring levels in the seeds. Levels of phytoecdysteroids in spinach ranged from 19.9 to 44.1 μg per shoot, 0.7 to 1.2 μg·mg−1 dry mass shoot, 3.2 to 9.6 μg per seed, and 0.5 to 1.1 μg·mg−1 seed. Several phytosterols connected to the phytoecdysteroid biosynthetic pathway were identified by gas chromatography–mass spectroscopy, predominantly spinasterol, 5-dihydroergosterol, and 22-dihydrospinasterol, which comprised 79.8%, 6.3%, and 4.6% of the total phytosterol content, respectively. Detection of the phytosterols cycloartenol and lanosterol in spinach suggests that spinach may also have dual biosynthetic pathways to phytosterols that contribute to the production of phytoecdysteroids.

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Gad G. Yousef, Mary A. Lila, Ivette Guzman, James R. Ballington and Allan F. Brown

Blueberry (Vaccinium L. section Cyanococcus Gray), a rich source of polyphenolics with important implications for human health and chronic diseases, has become a major fruit commodity in the United States. This study was designed to assess the impact of introgression through interspecific hybridization on anthocyanin (ANC) profiles among blueberry species. Southern highbush blueberry (V. corymbosum L.) and rabbiteye blueberry (V. virgatum Ait.) commercial cultivars, North Carolina blueberry breeding selections, and blueberry breeding populations with varying degrees of introgression from multiple species were used to address this question. The breeding selections and populations were created and selected for traits not directly related to their ANC profiles and are therefore likely representative of the current selection objectives of most public and private breeding programs. Ripe fruit at a uniform stage of maturity were evaluated for ANC concentration and profile in 2 consecutive years (2010 and 2011) from all plants. Total ANC ranged from 189 to 464, 74 to 421, and 227 to 537 mg/100 g (frozen fruit) in the commercial cultivars, breeding selections, and breeding populations, respectively. Significant increases in total ANC were observed among material that represents an expanded gene pool in southern highbush blueberry (introgression from V. angustifolium Ait., V. elliottii Chap., V. myrsinites Lam., V. pallidum Ait., V. tenellum Ait., V. fuscatum Ait., V. constablaei Gray, and V. arboreum Mar.). Differences in acylation and glycosylation patterns were also observed in the same material, which may condition relative stability, absorption, and bioavailability of ANC. Results suggest that the expansion of the gene base through interspecific hybridization can have both a positive and negative impact on ANC accumulation and that breeders need to be aware of these issues early in the breeding program.

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Christine M. Bradish, Gad G. Yousef, Guoying Ma, Penelope Perkins-Veazie and Gina E. Fernandez

High tunnels have been widely adopted for red raspberry (Rubus idaeus) production in the United States to extend the harvest season and increase yields. In this study, effects of high tunnel production on contents of plant secondary metabolites (anthocyanins, carotenoids, tocopherols, and ellagitannins) in red raspberry fruit were determined for three fall-fruiting cultivars (Autumn Britten, Caroline, and Nantahala) grown at three locations in North Carolina under field and high tunnel cultivation systems. Cultivar was the primary contributing factor to variation in phytochemicals, with minor effects of location and production system. The anthocyanin cyanidin-3-glucoside and the carotenoids α-carotene, β-carotene, lutein, and zeaxanthin were higher in fruit produced in field compared with tunnel cultivation (P < 0.01). Accumulation of total anthocyanins and tocopherols in fruit were unaffected by high tunnel cultivation in comparison with traditional field cultivation. Carotenoid content varied by genotype and production system. ‘Autumn Britten’ and ‘Caroline’ showed no difference, but were higher than ‘Nantahala’ for α-carotene, β-carotene, 9-cis-β-carotene, and lutein + zeaxanthin (P < 0.0001). Phytochemical differences among field and tunnel produced fruit have important implications for breeding with increased nutritional value in mind, and also the understanding of the relationships of plant pigments to light and temperature.

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Allan F. Brown, Gad G. Yousef, Ivette Guzman, Kranthi K. Chebrolu, Dennis J. Werner, Mike Parker, Ksenija Gasic and Penelope Perkins-Veazie

The objective of this study was to examine the relative impact of genetics and environment on phenolic and carotenoid profiles in peach (Prunus persica) germplasm. Fully mature, (“ready-to-eat” stage) firm fruit of peach cultivars China Pearl, Contender, and Carolina Gold were collected from established trees at two North Carolina locations in 2009 and 2010. Advanced breeding selections NC Yellow and NC 97-48 were collected from a single location in both years. Using tandem extractions and chromatography analyses, 10 carotenoids and 24 phenolic compounds were quantified separately in the peel and flesh. Statistically significant differences were noted among peach cultivars and advanced selections for β-carotene, cyanidin-3-glucoside, cyanidin-3-rutinoside, cholorogenic acid, quercetin-3-glucoside, and individual procyanidins. Peel anthocyanin (ANC) concentration ranged from 183 mg/100 g in ‘Contender’ to non-detectable levels in NC97-48 and NC Yellow. ‘China Pearl’ and ‘Carolina Gold’ produced ANC levels approximately half of ‘Contender’. Chlorogenic acid concentration also fit a discrete pattern of accumulation but was not related to the accumulation of ANC. ‘China Pearl’, NC 97-48, and NC Yellow contained the highest levels of chlorogenic acid (105 to 136 mg/100 g), ‘Carolina Gold’ contained the lowest (52 mg/100 g), and ‘Contender’ represented an intermediate phenotype (70 mg/100 g). Statistically significant genetic variation was found for almost all compounds identified, whereas location and year effects tended to be compound-specific. For chlorogenic acid, 28% of the phenotypic variance was explained by location (year = nonsignificant), whereas 40% of the phenotypic variation of ANC was explained by differences in years (location = nonsignificant). Analyzing fruit from the same environment over 2 years or from two locations in the same year would not have adequately accounted for the variation associated with environment. The detailed phytochemical profile of peach reported here demonstrates the importance of multiyear, multilocation analysis in revealing accurate measures of phytochemical genetic variation and provides a comprehensive baseline analysis of phytochemicals in commonly grown peach cultivars that can be used to evaluate novel germplasm.

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Allan F. Brown, Gad G. Yousef, Elizabeth H. Jeffery, Barbara P. Klein, Mathew A. Wallig, Mosbah M. Kushad and John A. Juvik

Ten broccoli [Brassica oleracea L. (Botrytis Group)] accessions were grown in several environments to estimate glucosinolate (GS) variability associated with genotype, environment, and genotype × environment interaction and to identify differences in the stability of GSs in broccoli florets. Significant differences in genetic variability were identified for aliphatic GSs but not for indolyl GSs. The percentage of GS variability attributable to genotype for individual aliphatic compounds ranged from 54.2% for glucoraphanin to 71.0% for progoitrin. For total indolyl GSs, the percentage of variability attributable to genotype was only 12%. Both qualitative and quantitative differences in GSs were detected among the genotypes. Ten-fold differences in progoitrin, glucoraphanin, and total aliphatic GS levels were observed between the highest and lowest genotypes. Only two lines, Eu8-1 and VI-158, produced aliphatic GSs other than glucoraphanin in appreciable amounts. Differences in stability of these compounds among the cultivars were also observed between fall and spring plantings. Results suggest that genetic factors necessary for altering the qualitative and quantitative aliphatic GS profiles are present within existing broccoli germplasm, which makes breeding for enhanced cancer chemoprotectant activity feasible.

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John A. Juvik, Gad G. Yousef, Tae-Ho Han, Yaacov Tadmor, Fermin Azanza, William F. Tracy, Avri Barzur and Torbert R. Rocheford

This study was conducted to identify the chromosomal location and magnitude of effect of quantitative trait loci (QTL) controlling sweet corn (Zea mays L.) stand establishment and investigate the impact of dry kernel characteristics on seedling emergence under field conditions. Genetic and chemical analysis was performed on two F2:3 populations (one homozygous for su1 and segregating for se1, the other homozygous for sh2 endosperm carbohydrate mutations) derived from crosses between parental inbreds that differed in field emergence and kernel chemical composition. A series of restriction fragment-length polymorphism (RFLP) and phenotypic markers distributed throughout the sweet corn genome were used to construct a genetic linkage map for each population. F2:3 families from the two populations were evaluated for seedling emergence and growth rate at four locations. Mature dry kernels of each family were assayed for kernel chemical and physiological parameters. Composite interval analysis revealed significant QTL associations with emergence and kernel chemical and physiological variables. Improved emergence was positively correlated with lower seed leachate conductivity, greater embryo dry weight, and higher kernel starch content. QTL affecting both field emergence and kernel characteristics were detected in both populations. In the su1 se1 population genomic regions significantly influencing emergence across all four environments were found associated with the se1 gene on chromosome 2 and the RFLP loci php200020 on chromosome 7 and umc160 on chromosome 8. In the sh2 population the RFLP loci umc131 on chromosome 2 and bnl9.08 on chromosome 8 were linked to QTL significantly affecting emergence. Since seedling emergence and kernel sugar content have been shown to be negatively correlated, undesirable effects on sweet corn eating quality associated with each emergence QTL is discussed. Segregating QTL linked to RFLP loci in these populations that exert significant effects on the studied traits are candidates for molecular marker-assisted selection to improve sweet corn seed quality.