Prof. Dr. Paul Struik

Already during the 1950s, researchers started unravelling the impact of environmental factors on dormancy and physiological age of seed tubers and providing recommendations how to grow, store and use seed tubers. World-wide, research on dormancy and physiological age was prominent during the 1980s and 1990s, with ample attention for variation in behaviour among cultivars. Physiological age became important with global trade of seed tubers, disconnecting the production and storage of seed from it use. Seed management also became increasingly complicated when potatoes started to become widely grown in areas with several potato growing seasons per year. While long dormancy and slow ageing are required in regions with one crop per year, short dormancy and rapid sprouting are desired in areas with multiple potato crops per year. Knowing the seed’s physiological age is required to optimize crop management for various market outlets.

Nowadays, there is consensus on the following: older seed gives earlier emergence, with more stems, earlier tuberization, more tubers per plant, smaller but more uniform tuber size, and earlier senescence. But recently all this was challenged. Chunmei Zou et al. conducted a multi-annual, multi-location research project on the impact of physiological age of seed tubers. They produced seed lots of four cultivars on the same site during three subsequent years: Lady Claire (slow-ageing and early), Agria (slow-ageing and late), Innovator (fast-ageing and early), and Festien (fast-ageing and very late). These lots were stored at three temperatures until the next planting season with detailed monitoring of the variation in physiological age created. Storage temperatures were 4, 7, and 10 ºC, but in the last cycle the 7 ºC was replaced by 17 ºC for more dramatic effects. Subsequently, seed lots were planted at different locations. In total, there were eight field experiments, each with 36 plots (4 cultivars × 3 physiolo­gical ages × 3 replicates), intensively phenotyped throughout the growing season.

The researchers analysed and modelled the sprouting behaviour over time and quantified the temperature effects on the model parameters. Despite some year effects, their results were consistent with existing literature from the 1980s and 1990s: higher storage temperature advanced sprouting and physiological ageing of the seed tubers, but the lowest storage temperature produced the
highest sprout weight after incubation assessed at the same temperature sum. The vigour declined after long storage at higher temperature. Effects were most pronounced in fast agers.

Seeds stored at high temperatures was in poor shape at planting; very long sprouts needed to be removed. Nevertheless, all seed lots stored at 4, 7 or 10 ºC performed well in all eight experiments. In general, there were small effects during early phases of crop growth, but at final harvest there were hardly any significant effects in number of stems per plant, number of tubers per plant, tuber yield per hectare or tuber-size distribution, in any of the eight experiments differing in site and year. Even the seeds that were stored at 17 ºC performed much better than expected, although their emergence and yield were somewhat reduced.

The findings suggest revisiting earlier research, with a focus on the cultivar-specific range of physiological age that allows good seed performance. Moreover, good agricultural practice and environmental factors can apparently mask effects of physiological age within this range. Does this mean that we can ignore the impact of physiological age? Recently, very late planting because of extremely wet springs, caused use of old seed resulting in various problems with crop growth in northwest Europe. Nevertheless, yields were often better than expected. ●