In Situ Vernalization: A Novel Method for Accelerated Biennial Vegetable Crop Seed Production

Biennial vegetable crops, like beet (Beta vulgaris), carrot (Daucus carota) and onion (Allium cepa), have a life cycle that spans two growing seasons, and are hence time and resource-intensive to breed and to harness for seed production. We sought to determine if environmental conditions could be manipulated to shorten the life cycle of these plants, thus hastening seed production, through a novel “in situ vernalization” (ISV) method. In this method, 7-8 week old seedlings of three varieties (inbred, F1 hybrid, and OP) of each species were exposed to temperatures of 4°C for 7-8 weeks in two different settings: a controlled temperature chamber and an outdoor cold frame. The control consisted of the corresponding roots subjected to 12-16 weeks of vernalization at 4°- 10° C according to standard methods. After ISV/vernalization, all treatments were relocated to a warm (15°C) greenhouse, with 16 hour photoperiod, to promote flowering. After 13 weeks, all plants with floral structures were moved to a warmer (20°C) greenhouse for seed production. ISV treatment was successful for beets, as beet seedlings that underwent ISV flowered at rates as high as, or higher than, control beets. However, all carrot and most onions that underwent ISV failed to produce floral structures, while the control carrots and onions flowered. The flowering beets have been crossed within ISV and control groups and, later, the seed production rates and seed quality will be compared. This study has led to a better understanding of vernalization requirements in all species, and has provided a more economical and straightforward model for beet seed production.