2019 ASHS Annual Conference

Brassica rapa contains several morphologically distinct subspecies. To optimize production in controlled environments, it is important to maximize resource allocation to marketable tissues, which may be achievable through environmental manipulation. Despite their genetic similarity, dry matter allocation among B. rapa subspecies differs but there are no baseline comparative studies. Obvious morphological differences among subspecies indicate physiological differences in resource partitioning during growth, which may be especially pronounced during different developmental stages. ‘Niseko’ turnip, ‘Asian Delight’ pakchoi, and mizuna were grown from seed in a greenhouse using arcilite media. Five harvests were performed at one-week intervals starting 26 days after planting (DAP). There was no difference in total biomass among subspecies at the first harvest; however, biomass of the subspecies diverged over time. Mizuna had highest biomass in all four subsequent harvests, while pakchoi had the lowest biomass. Mizuna likely outperformed turnip and pakchoi due to its large leaf area capturing more light for photosynthesis. Relative biomass of tissues were initially similar among subspecies; leaf blades, petioles, and roots comprised about 60, 25, and 15% of total biomass at first harvest, respectively. Biomass allocation shifted over time as plants developed stronger sinks. Sink filling in turnip roots initiated between 34 and 42 DAP and roots comprised 52% of total biomass at final harvest while leaves and petioles decreased to 29% and 19%, respectively. In both mizuna and pakchoi, relative biomass of leaves and roots decreased as petioles gradually increased over time. Leaves accounted for the largest fraction of biomass in mizuna during all harvests. The relative biomass of petiole tissue gradually exceeded that of leaf tissue in pakchoi. Root tissue comprised the smallest biomass fraction during all harvests for both mizuna and pakchoi. Specific leaf area (SLA) initially was similar for all three subspecies (372 cm² g^-1) and decreased over time. Final turnip, mizuna, and pakchoi SLAs were 280, 212, and 249 cm² g^-1, respectively. The decrease in SLA was associated with an increase in chlorophyll content index (CCI) among all three subspecies over time. Pakchoi had the highest CCI across all five harvests, peaking at 36 DAP and leveling off. CCI values in turnip and mizuna were similar to each other during all harvests. These patterns of biomass accumulation in turnip, mizuna, and pakchoi reflect distinct developmental and morphological changes that diverge as plants age, and may provide opportunities for improving harvest index by manipulating sink strength of targeted tissues