Glucobrassicin Enhancement Using Low Red To Far-Red Light Ratio In ‘Ruby Ball’ Cabbage And High-Throughput Glucobrassicin Estimation Using Near-Infrared Reflectance Spectroscopy

Abstract

Brassica vegetables produce glucobrassicin (GBS) and gluconasturtiin (GNST), important precursors of chemopreventive compounds. Consuming vegetables with greater GBS and GNST concentrations can lead to enhanced chemoprevention. These vegetables could be produced using GBS- and GNST-enhancing practices, for example, by manipulating light quality. We studied the effect of the red to far-red light (R:FR) ratio on GBS concentration in ‘Ruby Ball’ (red) and ‘Tiara’ (green) cabbage (Brassica oleracea) heads across four seasons. R:FR variation was induced with foliar shading using weed surrogates that competed with cabbage plants for 0, 2, 4, 6 weeks or all season. ‘Ruby Ball’ GBS concentrations were greatest when competition lasted 6 or more weeks; the associated R:FR ratio was lowest in these treatments. ‘Tiara’ was unaffected by competition. Light quality around cabbage plants was recorded using a spectroradiometer (Supplemental Table 1). Confirmation of GBS accumulation in ‘Ruby Ball’ from a low R:FR ratio was observed in controlled experiments. In two replicate studies, a R:FR=0.3 treatment resulted in 2.5- and 1.4-fold greater GBS concentration compared to R:FR=1.1 and R:FR=5.0 treatments combined. In watercress (Nasturtium officinale) subjected to end-of-day (EOD) 10-min R and/or 15-min FR pulses supplied after the main photoperiod, we observed lowest GNST concentrations after an EOD FR pulse, but highest concentrations after a R followed by FR pulse (figure 3.8). Together, these studies demonstrate the role of phytochrome in GBS and GNST accumulation. Fast, inexpensive GBS quantification methods are needed in breeding programs and for growers to verify vegetable quality. Such methods could be developed by pairing near-infrared reflectance spectroscopy (NIRS) with partial least squares regression (PLSR) to create prediction models. We developed a model to estimate GBS concentration in freeze-dried cabbage and Brussels sprout leaf tissue. Our cross-validated models predicted GBS concentration sufficiently for screening purposes (R2=0.75, RPD=2.3 and R2=0.80, RPD=2.4, fresh weight and dry weight basis, respectively). Cultivar selection, R, and FR light manipulation should be considered when developing GBS and GNST-enhancing production systems. GBS quantification is possible using NIRS with PLSR. Such high-throughput phenotyping methods could support breeding programs and provide an inexpensive tool to quantify vegetable chemopreventive value.