2019 ASHS Annual Conference

Phytonutrients may play a key role in prevention of certain slow to progress diseases like cancer. Epidemiological evidence supports the inverse relationship between certain cancers and the consumption of cruciferous vegetables which contain glucosinolates – phytonutrients produced almost exclusively in the Brassicaceae family. Furthermore, lab studies have demonstrated chemopreventive roles of certain glucosinolates. Production systems that enhance phytonutrient concentrations could deliver products that benefit producers and consumers. The red to far-red (R:FR) light ratio is known to affect glucosinolates; although how it impacts individual glucosinolates within specific cultivars is not well understood. R:FR is important in a field setting as it can be dramatically influenced by shading and reflectance from nearby plants as well as in controlled environments where the light source can be attuned to maximize phytonutrient concentrations.

This research examines R:FR effects on the concentration of the particularly chemopreventive indole glucosinolate, glucobrassicin. We grew ‘Ruby Ball’ and ‘Tiara’ cabbage (Brassica oleracea var. capitata) in a split-plot design in a high-tunnel in spring and fall of 2016 and 2017 in Grand Rapids, MN. Plants were subjected to various durations of weed competition (consisting of eight different treatments) which altered R:FR within the canopy. Light spectra were taken weekly in order to relate the treatments to changes in R:FR. Soil moisture was never limiting and nitrogen was applied as a split application to minimize nutrient competition. Glucobrassicin concentration in ‘Ruby Ball’ was maximized in treatments of high competition, which was in part driven by R:FR reduction caused by dense vegetation (R² = 0.51; p<0.001). Analysis of variance showed treatment differences (p<0.001), and the treatment with the longest duration of weed competition resulted in the highest glucobrassicin concentration in the head tissue compared to a weed-free control (89.0 vs 43.8 µmol 100g^-1 fresh weight respectively). Other treatments resulted in intermediate concentrations and displayed a general positive relationship between competition and glucobrassicin concentration. Growth rate was not a significant contributing factor. Similarly, ‘Ruby Ball’ grown in a growth chamber under R:FR of 5.0, 1.1, and 0.3 showed that glucobrassicin concentration was highest in head tissue in the 0.3 R:FR treatment which resulted in over two times the concentration compared to the other two treatments (24 vs 10 and 9 µmol 100g^-1 fresh weight for 0.3, 1.1, and 5.0 R:FR treatments respectively). This data suggests that R:FR manipulation affects glucobrassicin in ‘Ruby Ball’ cabbage heads in high-tunnels and controlled environments.