Translocation of the Reproductive Stimulus in Sugar Beets

Abstract

1. Separate shoots of annual beets having more than one shoot were subjected to differential photoperiods as follows: long days or continuous illumination, short days, and continuous darkness. The parts exposed to long days or continuous illumination developed seedstalks. The parts exposed to short days, even though connected to parts exposed to long days or continuous illumination, remained vegetative. The parts kept in continuous darkness and connected to parts exposed to long days or continuous illumination developed seedstalks, even when they were also connected to shortday exposed parts that remained vegetative. 2. These results indicate that substances conducive to reproductive development may be translocated with the carbohydrates. Exposure of a part to short photoperiods produced sufficient carbohydrates for that part, and hence none was translocated to it from the long-day part. Keeping a part in continuous darkness made that part dependent on the long-day exposed part, and hence food, and with it reproductive-inducing substances, were translocated to the darkened part. 3. Continuously illuminated biennial parts of annual-biennial grafted beets failed to develop seedstalks when they were not also subjected to cool-temperature exposure. Neither did the continuously darkened annual parts of the same beets develop seedstalks. 4. About one month was required to initiate seedstalks in continuously illuminated annual parts of annual-biennial grafted beets. The continuously darkened biennial parts of most of the same beets also developed seedstalks during the following month. 5. These results indicate that the biennial is not able to synthesize reproductive-inducing substances as a result of photoperiod alone, as annuals do, but also requires cool-temperature exposure. The reproductive-inducing substances produced by biennials as a result of thermal and photoperiodic induction, and those produced in annuals as a result of photoperiodic induction alone, appear to be in effect similar. 6. A simple and effective method of grafting such material is described.