Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 29, 2006
Publication Date: May 1, 2007
Citation: Farnham, M.W., Hale, A.L., Grusak, M.A., Finley, J.W. 2007. Genotypic and environmental effects on selenium concentration of broccoli heads grown without supplemental selenium fertilizer. Plant Breeding. 126:195-200. Interpretive Summary: Broccoli heads contain relatively high concentrations of the mineral selenium. This nutrient is now known to be essential to good human health. Moreover, accumulating evidence indicates that the unique form that selenium takes in broccoli may protect humans that consume it from cancer. It is possible that plant scientists could improve the selenium content of broccoli through breeding and genetics to make it an even healthier vegetable. However, nothing is known about the influence of genetics and environment on affecting selenium concentrations in broccoli heads. This is something that must be understood before systematic improvement can be attempted. Thus, the goal of this research was to determine if different varieties of broccoli exhibit different concentrations of selenium and if the environment in which the varieties are grown influences the concentration of selenium in their heads. Our results, which are based on growing 35 different broccoli varieties in three different environments, indicate that both the variety and the environment influence the selenium concentration of heads. It is clear however, that environment appears to have a much greater effect than the variety. Importantly, results indicate that it should be feasible to develop new broccoli varieties that exhibit relatively high selenium concentration combined with a high quality, dense head. Alternatively, it may also be possible to manipulate the environment in which broccoli is grown to stimulate greater uptake of selenium from the soil, in turn raising the levels in the harvested heads. Such efforts will ultimately lead to the enhancement of broccoli as an even more nutritious vegetable for human consumption.
Technical Abstract: Selenium (Se) is an important trace element in human nutrition that is essential to normal health. Broccoli (Brassica oleracea L.) is known to accumulate relatively high concentrations of Se, and there is strong evidence that consumption of Se-enriched broccoli florets decreases cancer risk. In light of the above, this study was conducted to evaluate differences in Se concentration per head and total Se head content for a collection of broccoli hybrids (20) and inbreds (15) grown in field environments and to assess the relative importance of genotype versus environment in affecting Se levels. When analyzed over three environments, there was a significant genotype effect for Se head concentration with hybrids, but not inbreds, but the environmental effect was about ten times larger than that for genotype. Total Se content (ng/head) was significant for hybrids and inbreds, but as with concentration, environmental effects were much larger for this trait. Head Se concentrations for hybrids ranged from 52.7 to 84.7 ng/g and total Se accumulation ranged from 563 to 885 ng/head. These same respective traits ranged from 49.3 to 80.0 ng/g and 678 to 876 ng/head for inbreds. There was no correlation between Se head concentration and head dry mass or days from transplant to maturity for either hybrids or inbreds. There was no evidence that Se might be diluted in broccoli heads as mass increases with cultivars that produce dense heads. Results indicate that it should be feasible to combine relatively high Se concentration or content with high head dry matter (DM), a phenotype that broccoli breeders tend to strive toward.