Changes in Tuberization and Assimilate Partitioning in Potato (Solanum tuberosum) During the First 18 Days of Photoperiod Treatment

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Abstract
Potato (Solanum tuberosum L.) plants were equilibrated under 18-h days (LD) before a subset of the plants was transferred to 10-h photosynthetic periods with either a dark night (SD) or an 8-h dim photoperiod extension with incandescent lamps (DE). Plants were harvested at regular intervals for growth analysis during the 18 d after transfer. Leaf area increased rapidly under SD and LD but was inhibited under DE. Internode elongation was similar under SD and LD, but much higher under DE. Stem d. wts were lowest under SD. Axillary branching was generally greatest under LD. Total shoot weights were greatest under LD. Total shoot weights were similar under SD to those under DE, even though within 18 d of transfer as much as one-third of the biomass of SD plants was in tubers. Tuber initiation was later under LD than under SD, and was delayed even more by DE. High temperature increased the delay in tuberization from LD. The early tuber initiation under SD was concurrent with a rapid increase in leaf area under SD, not with an early cessation of leaf growth. This was contrary to assumptions based upon studies of long-term effects of photoperiod. The resultant high sink strength under SD contributed to the greater efficiency of biomass production.