van den Herik, B.; Bergonzi, S.; Bachem, C. W. B.; Tusscher, K. H. W. J.

Yield of harvestable organs is a complex function of photosynthetic output, and sink-strength and timing of competing carbon sinks. In potato (Solanum tuberosum) the effect of tuber onset timing and post-tuberization canopy senescence on growth dynamics and tuber fresh weight are poorly understood. To advance our understanding we compared above- and belowground traits of wildtype plants (WT) with StSP6A, i.e., tuberigen, knockdown plants (SP6Ai) and developed simple computational models to aid interpretation of results. We find that SP6Ai results in a delay of approximately 2 weeks in tuber onset, yet has a 4-to-5-week delayed canopy senescence. Together this results in a prolonged tuber growth phase, with reduced synchronization in tuber onset and a resulting increased variance in tuber sizes, while overall final tuber fresh weight remains similar. Using a leaf and tuber growth model comparing various leaf senescence mechanisms, we find that resource competition, and not a shared signal for tuberization and senescence, is able to explain how delayed tuberization leads to further delayed senescence. Our results point to a role for resource competition in the correlated timing of tuber onset and canopy senescence, as well as a leading role for StSP6A in tuber onset synchronization and tuber size uniformity.