Vegetables are a rich source of dietary carotenoids and tocopherols, powerful antioxidants that have the capacity to protect cells against oxidative damage caused by free radical reactions. There is evidence for a negative correlation between the incidence of certain types of cancer, age-related macular degeneration, cataract development, and cardiovascular disease with increased carotenoid and tocopherol intake. Development of elite vegetable germplasm with enhanced levels of these phytochemicals will potentially promote health among the consuming public. To assess the feasibility for genetic improvement in phytochemical content, it is necessary to partition the phenotypic variability into its component sources (genotype, environment, and genotype by environment interaction). To provide data for comparison and partition of phenotypic variation, 41 sweet corn and 13 broccoli genotypes were grown and harvested in one location for 3 years and analyzed for phytochemical content by HPLC. The most abundant form of carotenoids and tocopherols were lutein and gamma-tocopherol in sweet corn and beta-carotene and alpha-tocopherol in broccoli. Analysis of variance showed that, in sweet corn, the differences among genotypes described most of the phenotypic variation (76% for lutein, and 78% for gamma-tocopherol). Genotype by year interaction was a second significant factor, while variation affiliated with the year was found to be a minor component. In contrast, in broccoli, the three sources of variability contributed equally to describe the total phenotypic variation for beta-carotene and alpha-tocopherol. These results suggest that elite sweet corn and broccoli germplasm with improved carotenoid and tocopherol levels can be developed using conventional breeding protocols.
Khalid Ibrahim and John Juvik
Aly M. Ibrahim and Khalid A. Al-Zeir
Kanta Kobira, Khalid Ibrahim, Elizabeth Jefferey, and John Juvik
Considerable epidemiological evidence exists on the association between consumption of antioxidant-rich vegetables and incidence of chronic diseases, including cancer and cardiovascular disease. Broccoli (Brassica oleracea L. sp. italica) florets are relatively abundant sources of antioxidants, and potentially amenable to genetic manipulation to enhance this vegetable's health-promoting properties. This investigation focuses on the identification of chromosomal segments in the nuclear genome of broccoli associated with antioxidant carotenoid and tocopherol variability. A broccoli F2:3 population consisting of 163 families derived from a cross between two parents (VI-158 and BNC) and previously mapped with 62 polymorphic SSR and SRAP marker loci was evaluated for carotenoid and tocopherol concentration in floret tissue over two growing seasons. Significant differences were observed among F2:3 family means for concentrations of lutein (10-fold difference between the lowest and highest family), beta-carotene 17-fold), alpha-tocopherol (8-fold) and gamma-tocopherol (6-fold). On a concentration basis, beta-carotene, lutein, alpha-tocopherol, and gamma-tocopherol were the most abundant antioxidant forms in broccoli. Heritability estimates of primary phytochemicals ranged from 0.35 to 0.38, 0.40, and 0.44 for beta-carotene, alpha-tocopherol, gamma-tocopherol, and lutein, respectively. Composite interval mapping (CIM) identified two quantitative trait loci (QTL) associated with carotenoid variability on two linkage groups and five QTL associated with tocopherol variability on four linkage groups. The QTL identified in this study have potential for use in marker-assisted crop improvement programs to develop elite germplasm designed to promote health among the consuming public.
Aly M. Ibrahim, Khalid A. AlZeir, and Mohammed A. Majeed
Squash is grown in the field and in tunnel type greenhouses in Saudi Arabia. To satisfy the demand for squash, additional production in controlled greenhouses would be desirable. The Jedida cultivar was treated with growth regulators. Seedlings were sprayed with Ethrel at 400 ppm. At flowering, six treatments were made: Agriton (60g/100L), sprayed at 10 day intervals; IAA (1%), IBA (1%), and Rootone, dusted on stigmas; hand pollination; and control. Fruits were harvested when they were 12 cm long. Ethrel increased the number of female flowers by 96% and changed the female: male ratio from 1:2 to 8:1. Highest marketable yield was obtained with the hand pollination, IBA, and IAA treatments. Yield in the Control treatment was low due to low insect activity. The results suggest that treatment with IAA or IBA will permit production of squash on a commercial scale in controlled greenhouses.
Khalid E. Ibrahim, Kanta Kobira, and John A. Juvik
Genotype-by-environment interaction (G×E) is a fundamental concern in plant breeding since it hinders developing genotypes with wide geographical usefulness. Analysis of variance (ANOVA) has been widely used to interpret G×E, but it does not elucidate the nature and causes of the interaction. Stability analysis provides a summary of the response patterns of genotypes to different growing environments. Two classes of phytochemicals with putative health promoting activity are carotenoids and tocopherols that are relatively abundant in broccoli. Growing clinical and epidemiological evidence suggests that vegetables with enhanced levels of these phytochemicals can reduce the risk of cancer, cardiovascular, and eye diseases. The objective of this study is to have better understanding of the genetic, environmental and G×E interaction effects of these phytochemicals in broccoli to determine the feasibility of the genetic enhancement. The ANOVA and Shukla's stability test were applied to a set of data generated by the HPLC analysis of different carotenoid and tocopherol forms for six broccoli accessions grown over three environments. The ANOVA results show a significant G×E for both phytochemicals that ranged from 22.6% of the total phenotypic variation for beta-carotene to 54.0% for delta-tocopherol while the environmental effects were nonsignificant. The genotypic effects ranged from as low as 1% for alpha-tocopherol to 31.5% and 36.0% for beta-carotene and gamma-tocopherol, respectively. Stability analysis illustrated that the most stable genotype for all phytochemicals is Brigadier. The results suggest that feasibility of the genetic enhancement for major carotenoids and tocopherols. A second experiment that includes a larger set of genotypes and environments was conducted to confirm the results of this study.
Allan Brown, Khalid Ibrahim, Sultana Islam, Elizabeth Jeffery, and John Juvik
A set of 216 PCR-based molecular markers was screened for polymorphisms using two morphologically dissimilar broccoli lines, `VI-158' and `BNC'. Fifty-nine of these markers, representing 69 detected polymorphisms and two morphological markers, were used to construct a genetic linkage map of broccoli [Brassicaoleracea (L.) var. italica] from a population of 162 F2:3 families generated from the cross between these two lines. Ten genetic linkage groups were generated that spanned a distance of 468 cM with an average interval width of 9.4 cm. This map represents the first combined SSR and SRAP map of Brassica oleracea. Comparisons are made to existing maps of Brassicanapus and to inter-specific maps of Brassicaoleracea. To our knowledge this is the first linkage map of broccoli [Brassicaoleracea (L.) var. italica] and should provide a useful tool for the genetic analysis of traits specific to the italica subspecies.
Ji Yeon Kang, Khalid E. Ibrahim, John A. Juvik, Doo Hwan Kim, and Wha Jeung Kang
Strong evidence exists to suggest that increased consumption of glucosinolates from Brassica vegetables is associated with reduced risk of cancer induction and development. Development of elite germplasm of these vegetables with enhanced levels of glucosinolates will putatively enhance health promotion among the consuming public. To evaluate levels of glucosinolate phenotypic variation in Chinese cabbage tissue and partition the total phenotypic variation into component sources (genotype, environment, and genotype-by-environment interaction), a set of 23 Brassica rapa L. var. pekinensis genotypes were grown in two different environments (field plots and greenhouse ground beds). Gluconasturtiin and glucobrassicin were found to account for ≈80% of total head glucosinolate content. Significant differences were found in glucosinolate concentrations between the lowest and highest genotypes for glucobrassicin (6-fold) and for gluconasturtiin (2.5-fold). Analysis of variance showed that for the three major glucosinolates (gluconasturtiin, glucobrassicin, and progoitrin), the genotypic effects described most of the phenotypic variation (62% averaged over the three compounds). The next most important factor was genotype × environment interaction (29%), whereas variation affiliated with the environment was found to be relatively minor (8%). These results suggest that genetic manipulation and selection can be conducted to increase glucosinolate content and the putative health promotion associated with consumption of Chinese cabbage.
Ji Yeon Kang, Khalid E. Ibrahim, Doo Hwan Kim, Wha-Jeung Kang, and John A. Juvik
Gluconasturtiin is a glucosinolate (GS) present in Chinese cabbage and its breakdown product, phenelethyl isothiocyanate (PEITC), inhibits phase I enzyme activation of endogenous carcinogenic compounds and enhances phase II enzyme detoxication, reducing cancer risk and promoting health in humans. This study was conducted to evaluate the interaction between the genotype and the environment to influence GSs in Chinese cabbage. Twenty-five accessions were grown in three environments and tissue quantified for GS levels by HPLC. While gluconasturtiin was observed to be the most abundant GS form, 3-indolylmethyl GS (glucobrassicin) and 1-methoxy-3-indolylmethyl-GS (neoglucobrassicin) were also found. Significant differences were observed among tissues, genotypes and environments in GS concentration and composition. Gluconasturtiin ranged from 0.56 μmol·g-1
DW in leaf tissue of Hau No. 2 to 11.89 μmol·g-1 DW in Chilsung. There were dramatic differences among different tissues of the same genotype with young leaf and root tissues having significantly higher concentrations of gluconasturtiin than other tissues. Gluconasturtiin in Sandong No. 5 ranged from 1.69 μmol·g-1 DW in mature leaves to 18.69 μmol·g-1 DW in root tissue. GS content of the same genotypes in three different environments indicated that plants grown in the greenhouse had higher GS content compared to field grown plants. Results of this study indicate that genotypic variation and the growing environment have substantial effects on GS content in Chinese cabbage. This investigation provides important information for future genetic and molecular studies and has identified Chinese cabbage genotypes that offer superior health benefits to consumers.