GENETICS AND GENETIC IMPROVEMENT OF DISEASE RESISTANCE AND QUALITY TRAITS IN WATERMELON, BROCCOLI, AND LEAFY GREEN BRASSICAS
Location: Vegetable Research
Title: Mineral concentration of broccoli florets in relation to year of cultivar release
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 6, 2011
Publication Date: November 1, 2011
Citation: Farnham, M.W., Keinath, A.P., Grusak, M.A. 2011. Mineral concentration of broccoli florets in relation to year of cultivar release. Crop Science. 51:2721-2727.
Interpretive Summary: It has been suggested by some scientists that concentrations of minerals like calcium, magnesium, and potassium in our food crops have decreased over time as these crops have been improved by plant breeders. For most crops, any current evidence indicating changes in mineral concentration is circumstantial at best, and there is a need to conduct appropriate field studies to directly compare mineral concentrations in fruits and vegetables harvested from “old” versus “new” crop varieties. Such studies can verify if changes have truly occurred over a span of years. Using broccoli as a test crop, USDA scientists at the U.S. Vegetable Laboratory in Charleston, South Carolina, grew 14 varieties developed over a span of years from 1950 to the present in two field trials, harvested and processed broccoli heads from those varieties, and then USDA scientists at the Children’s Nutrition Research Center in Houston measured mineral concentrations in the sampled heads. The oldest broccoli varieties tested in this study had high concentrations of most minerals assayed but they produced inferior quality heads that are not saleable in the current marketplace. There was no evidence that mineral concentrations of varieties released and grown over more than thirty years from the 1970s have changed. This is an interesting outcome because there is no indication that breeders have been monitoring mineral concentrations of broccoli during a time when the crop has been improved for numerous horticultural traits. Data from this study will provide a useful guide in helping broccoli breeders understand the variation in mineral concentrations they should expect among their breeding stocks and also provide a realistic baseline that should be maintained as other characteristics are improved in the future.
Recent reports have proposed that breeding for yield in agronomic and horticultural crops has resulted in decreases in mineral nutrient (e.g., calcium, magnesium) concentration of the harvested part of these crops. Data used to support such claims are taken from historical food nutrient databases that represent samples taken and assayed over many years from unidentified environments and cultivars, using variable analytical methods. A more appropriate way to examine nutrient changes over time is to conduct field tests of cultivars released over a period of years in the same environment(s). Thus, we undertook a study to evaluate mineral concentration of broccoli heads harvested from field-grown cultivars released over more than 50 years. Our specific objectives were to: 1) evaluate variation in concentrations of Ca, Cu, Fe, K, Mg, Mn, Mo, Na, P, S, and Zn among the cultivars tested; 2) compare our values with those from the USDA Nutrient Database; and 3) determine if there is a relationship between date of cultivar release and different concentrations. Fourteen broccoli cultivars (13 hybrids and one open pollinated population) were grown in replicated trials in two fall environments at Charleston, SC, and florets were sampled from harvested heads and assayed for mineral content by ICP-OES. Results indicated there were significant cultivar differences in mineral concentrations of sampled broccoli florets for Ca, Cu, Fe, K, Mg, Na, P, and Zn, but not for Mn, Mo, or S. With most minerals, there was no clear relationship between floret concentration and year of cultivar release. Although, the oldest cultivar studied tended to exhibit some of the higher concentrations for most minerals, from 1975 to the current time, no significant changes appear to have occurred. We propose that it is most relevant to examine possible nutritional changes for cultivars that were grown in this country during that latter period when the phenotype of broccoli changed dramatically and the vegetable grew in prominence as a component in the U.S. diet. Results of this work provide a guide for mineral levels in broccoli that should be maintained as other characteristics are manipulated in the future.