Performance and Characteristics:

Pages in tuber aging section:

Plants growing from seed tubers of different physiological age perform differently (van der Zaag and van Loon, 1987). Differences are summarized in Table 1. Aging in storage can affect tuber set and seed handling (Chase, 1995; Chase et al., 1989; McKeown, 1990). Figure 1 presents data on Russet Burbank (Iritani et al., 1983). Storage temperature regimes were converted into heat accumulation units [p-days = (daily storage temperature in oF - 39oF) x number of days stored]. The data presented is based on seed purchase on October 31 and planting on March 31, and underestimates the actual exposure of tubers to physiological days. Figure 2 adapts unpublished data from Australia on cv. Kennebec (Grice, 1993). It demonstrates that aged seed emerges earlier, grows faster, yields higher early, and yields less later than unaged seed. Figures 3 and 4 illustrates the shift in tuber size distribution in relation to stem number per plant as affected by seed tuber aging in storage (Knowles et al., 2003; Knowles and Knowles, 2006).

Table 1. Performance Characteristics Associated with Physiological Age of Seed Tubers. (Iritani and Thornton, 1984)

CharacteristicYoung SeedOld Seed
emergence slowerfaster
early vigorgreaterlesser
tuber formation laterearlier
formation periodlongermore uniform
tuber numberlessmore
tuber bulkinglongershorter
tuber sizinglargersmaller
early harvest yield lowergreater
late harvest yieldgreaterlower

Bioassays and Age Estimations

The simplest bioassay is to take sample tubers from a lot and place them in the dark at room temperature. After a few weeks, observe the sprouting pattern and match this with their sprouting (Bohl et al., 2003 van der Zaag and van Loon, 1987). Another determination is called the physiological age index (Caldiz et al., 2001) but this method can take several months. It is not practical for growers but may be useful for research. A laboratory test that takes a month involves weighting and counting sprouts (van Ittersum et al., 1990). There is no current method to quantify aging. However, in the future it is hoped that physiological aging of tubers can be measured biochemically. One potential age marker is 2-methyl butanol (Knowles et al., 2003).

Since bioassays take time at least a few weeks, they present a kind of “delayed exposure snap shot” of aging. For an immediate estimate on the relative physiological age of seed lots, a heat accumulation calculation is commonly used (Jenkins et al., 1993; Knowles and Botar, 1991). This method is based primarily on temperature exposure over time. The equation is p-age (oF) = (average daily storage temperature minus 39oF) times number of days between dormancy break and planting. [In oC, replace 39oF with 4oC.] One weakness of this method is that it does not take into account chronological aging, i.e., no aging at the base temperature, which, however, does occur (Caldiz et al., 2001). The time-temperature data reported by Iritani et al., 1983 and used for Figure 1 were transformed into physiological (oF) day units for comparisons.

Figure 1:

Physiological age related to stem number and yield

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Figure 2:

Relation of physiological age and plant height

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Relation of stem length, tuber numbers

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Figure 4:

Relation of plant stem length, tuber distribution


Bohl, W.H., Olsen N., Love, S.L., and Nolte, P. 2003. Seed and planting management. pp. 91-114. Chap. 7. In Potato Production Systems. Stark, J.C. and Love, S.L (Eds.). Publ. Univ. Idaho Extension.

Caldiz, D.O., Fernandez, L.V. and Struik, P. 2001. Physiological age index: A new, simple and reliable index to assess the physiological age of seed potato tubers based on haulm killing date and length of the incubation period. Field Crops Res 69:69-79.

Chase, R.W. 1995. Tuber set and its influencing factors. pp. 19-23. National Crisping Potato Industry Workshop, Proceedings. A.J.Myers (Ed.) Publ. Victorian Potato Crisping Research Group, Warragul, Victoria, Austr.

Chase, R.W., Silva, G.H. and Kitchen, R.B. 1989. Pre-cutting of seed potatoes. Amer Potato J 66:723-729.

Grice, M.S. 1993. Physiological age of seed potatoes, its effect on growth and yield of subsequent crops. Peelings 38:8-10.

Iritani, W.M. and Thornton, R.E. 1984. Potatoes: Influencing seed tuber behavior. Pacific North West # 248.

Iritani, W.M., Weller, L.D. and Knowles, N.R. 1983. Relationship between stem number, tuber set and yield of Russet Burbank potatoes. Amer Potato J 60:423-431.

Jenkins, P.D., Gillison, T.C. and Al-saidi, A.D. 1993. Temperature accumulation and physiological ageing of seed potato tubers. Ann Appl Biol 122:345-356.

Knowles, N.R. and Botar, G.I. 1991. Modeling the effect of potato seed-tuber age on plant establishment. Can J Plant Sci 71:1219-1232.

Knowles, N.R. and Knowles, L.O. 2006. Manipulating stem number, tuber set, and yield relationship for northern- and southern-grown potato seed lots. Crop Sci 46:284-296.

Knowles, R., Knowles, L. and Kumar, G.N.M. 2003. Stem number & tuber set relationships for Russet Burbank, Ranger & Umatilla Russet potatoes in the Columbia Basin. Potato Progress 3(13). (

McKeown, A.W. 1990. Growth of early potatoes from different portions of seed tubers I. Emergence and plant stand. Amer Potato J 67:751-759.

van Ittersum, M.K., Scholte, K. and Kujpers, L.J.P. 1990. A method to assess cultivar differences in rate of physiological ageing of seed tubers. Amer Potato J 67:603-613.

van der Zaag, D.E., and van Loon, C.D. 1987. Effect of physiological age on growth vigour of seed potatoes of two cultivars. 5. Review of literature and integration of some experimental results. Potato Res 30:451-472.