Collard Landraces are Novel Sources of Glucoraphanin and other Aliphatic Glucosinolates

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 L.) remains relatively unexplored. Recently, 86 neglected collard landraces were collected from the coastal plain region of the southeastern United States from seed savers and small farmers. In the last few decades, the diversity of cultivated collards has likely been diminished due to the wide scale adoption of a few commercial F1 hybrid cultivars. The objectives of this study were to: [a] compare glucosinolate profiles within collard cultivars against the of 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 Brassica oleracea L. viridis as a target for chemoprotective based plant breeding. During the winter of 2010/2011, 86 collard landraces and also four common commercial 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. Average glucoraphanin content of leaves in the commercial cultivars in both environments was never found above a threshold of 1.83 µmol / g dry leaf-tissue weight and usually was undetectable. Among the collard landraces, 18 accessions contained detectable levels of glucoraphanin and three were found to repeatedly contain glucoraphanin in excess of 11 µmol / g DW under both growth environments. These landraces are rich sources of important glucosinolates, previously thought to be unique to broccoli.