Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2015
Publication Date: 6/1/2015
Citation: Stansell, Z.J., Cory, W., Couillard, D.M., Farnham, M.W. 2015. Collard land races are novel sources of glucoraphanin and other aliphatic glucosinolates. Plant Breeding. 134:350-355.
Interpretive Summary: Collard is a non-heading, leafy green cole crop that is grown mostly during fall, winter and spring in the southeastern United States. Collard is especially important as a vegetable that can be harvested throughout the cool southern winter. Traditional collard patches and even early commercial fields of collard were planted with heirloom varieties perpetuated by individual seed savers; however, many of those heirlooms have been lost or replaced in recent decades by hybrids and other commercial varieties. From 2003 to 2006, an ARS scientist in cooperation with University colleagues explored the coastal plain region of North and South Carolina in search of collard gardens containing heirloom varieties, and about 80 of them were obtained from seed savers during that search. In the current work, ARS scientists at the U.S. Vegetable Laboratory and a scientist at the College of Charleston in South Carolina undertook a study to assay leaves of the collected heirloom collards for their makeup of compounds called glucosinolates, some of which are known to impart good health when consumed by humans. The scientists found that certain collard heirlooms contain high levels of glucoraphanin, a well-studied glucosinolate of broccoli that breaks down into a substance called sulforaphane, which in turn protects mammalian cells against carcinogens. The finding of relatively high levels of glucoraphanin in collard is of great interest to plant scientists, human nutritionists and medical professionals who previously thought that only broccoli contained high levels of glucoraphanin, but can now recognize some collard varieties as containing it as well. It is possible that some of the examined collard heirlooms will prove valuable as genetic resources in efforts by plant breeders to develop new cultivated varieties with higher levels of glucoraphanin as has been done in broccoli.
Technical Abstract: Glucosinolates form an important class of metabolites in Brassicas whose cognate isothiocyanates may provide chemoprotective effects in humans. Although certain B. oleracea crops have well documented glucosinolate profiles, collard (Brassica oleracea L. subsp. oleracea convar. acephala var. viridis) remains relatively unexplored. In the last few decades, the diversity of cultivated collards has been diminished due to the wide scale adoption of a few commercial F1 hybrid cultivars. In response to this, 81 neglected collard landraces were collected from the coastal plain region of the southeastern United States during the early 2000's from seed savers and small farmers. The objectives of this study were to: [a] compare glucosinolate profiles within collard cultivars against the recently conserved collard landraces; [b] identify any accessions with a particularly distinct or abundant glucosinolate profile (i.e. elevated glucoraphanin); and [c] determine the potential of B. oleracea var. viridis as a target for chemoprotective based plant breeding. During the winter of 2010/2011, the 81 collard landraces, four other var. viridis, and four commercial collard cultivars were evaluated in the field and harvested leaves assayed for glucosinolates. In a subsequent study, 19 selected landraces plus the cultivars were included in a repeat trial in the fall and winter 2012/2013. The highest glucoraphanin concentration in leaves of a commercial cultivar (Blue Max) averaged across both environments was 1.8 µmol/g dry mass, and glucoraphanin was often undetectable in most cultivar samples. However, 18 collard landraces contained significant levels of glucoraphanin in leaves in both years, and three were found to repeatedly contain glucoraphanin in excess of 9.5 µmol/g dry leaf-tissue mass under both field environments. These landraces are rich sources of important glucosinolates, previously thought to be most abundant in other B. oleracea vegetables.