Starch Accumulation in Leaves of Potato (Solanum tuberosum L.) during the First 18 Days of Photoperiod Treatment

Abstract

Potato (Solanum tuberosum L.) plants were grown under long days (LD) of 18 h 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). Temperature was constant at 21 degrees C. Leaves were sampled at the beginning and end of the high density light period for starch analyses. Potato leaves accumulated starch more rapidly under SD than under LD; and this difference continued after a second major sink, the tuber, began to develop. Starch accumulation over 10 h in SD leaves was three times higher than in LD leaves, even after 17 d of treatment. By this time SD gave higher whole plant relative growth rates than LD, and the tuber mass of SD plants exceeded 30% of their total plant biomass. The DE treatment resulted in starch accumulation intermediate to the LD and SD treatments. Genotypes likewise differed: the earlier genotype, more strongly induced to tuberize, had higher leaf starch accumulation than the later genotype. The effects of photoperiod and genotype were also present when potatoes were grown at 27 degrees C, a temperature unfavourable for tuberization under LD. Thus the formation of a strong tuber sink was consistently associated with more rapid leaf starch accumulation.