Assessing potato canopy growth and development at the individual leaf level to improve the understanding of the plant source-sink relations

Seed potato (Solanum tuberosum L.) physiological age (PA; defined as the developmental stage of a potato seed) and genotype are known to influence potato yield and final tuber yield distribution. We investigated the impacts of PA of two contrasting cultivars ('Bondi' and 'Fraser') on growth and development of individual canopy organs and their linkage with the source-sink process that regulates final tuber yield distribution. Differences in tuber yield distribution were associated with key morphological and phenological changes in the potato canopy. The beginning of the tuber growth phase was marked by a change in phyllochron across cultivars. PA influenced individual leaf expansion rate and time of flowering, which impacted the final tuber yield distribution. Time of flowering, or, number of leaves produced prior to first flower appearance, reflected the PA and could be used to indicate potential 'sink strength' or sink limitations (associated with tuber yield distribution) later in the tuber growing phase. The results suggest crop source limitations might arise in indeterminate main potato cultivars that rely on physiologically older leaves (or early emerged large leaves) for green leaf area at the end of the tuber growing phase, which may shift the yield distribution towards smaller tuber grades.