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  • Author or Editor: Khalid E. Ibrahim x
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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.

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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.

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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.

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