Seed age: background
- Seed age influences the potential performance of the progeny crop.
- Seed age may be measured as chronological or physiological age.
- Pre-sprouting (“chitting”) seed tubers is often described as physiological ageing but is only part of the ageing process.
- This is the age of seed in calendar days, e.g.
- from initiation of the seed tubers to re-planting or
- from haulm killing of the seed crop to re-planting.
- Chronological age may be modified by times of planting (or haulm killing) and re-planting and has been used commercially in an attempt to produce seed of high or low prolificacy.
- A very low chronological age may result in physiologically young seed tubers, which produce low numbers of stems and tubers.
- A very high chronological age may result in physiologically old seed tubers, which produce high numbers of stems and progeny tubers.
- In practice, very early planting of the seed crop and very late planting of the progeny crop is required to have an appreciable affect on seed prolificacy.
- There may be limitations to yield potential from both very low and very high chronological ages and effects may be confounded by other factors such as temperature during growth of the seed crop.
- This is defined as “the physiological stage of the tuber which influences its productive capacity” (defined by the European Association for Potato Research, [Reust, 1986]).
- Physiological age may be modified by growth and storage times and conditions.
- The term physiological age is most commonly used to quantify pre-sprouting (chitting) conditions.
- Biologically, physiological age represents the conditions experienced from initiation of the seed tuber until its replanting. Hot growing conditions therefore result in higher physiological age then do cool growing conditions.
- Chronological and physiological age of seed tubers are often linked.
Advantages of pre-sprouting
- Pre-sprouting of seed tubers can result in early crop emergence, early onset of tuber bulking and relatively high yields at early harvests.
- Pre-sprouting may be advantageous for production of “early” potatoes.
- Pre-sprouting could be used to manipulate the development of maincrop potatoes but the disadvantages of pre-sprouting should be considered.
Disadvantages of pre-sprouting
- Pre-sprouting of seed tubers has the potential to reduce root growth, number of progeny tubers, rate of tuber bulking, duration of tuber bulking and potential tuber yield.
- Pre-sprouting at high temperatures may result in apically dominant seed with a low yield potential.
- Removing sprouts (e.g. by damage during handling) delays plant development and alters the relationship between number of progeny tubers and rate of tuber bulking.
When is pre-sprouting necessary and how long should sprouts be?
- There appears to be little advantage from producing sprouts of more than 10 mm length but a greater danger of damaging sprouts during handling.
- As the time from planting to harvest increases, the advantage of, and requirement for, pre-sprouting declines.
- Maincrops with at least 4 – 5 months from planting to harvest, are unlikely to require pre-sprouting.
Pre-sprouting in practice
- The response to pre-sprouting varies between cultivars.
- For the same accumulated temperature, sprouts produced in the dark are longer than those produced in the light and are more prone to damage during handling.
- The time from planting to emergence decreases as mean sprout length increases to 10 mm but there is little advantage of longer sprouts.
- Seed tubers may be returned to cold store after pre-sprouting, without apparent detrimental effects. This should prevent excessive sprout growth if there is to be a delay before planting.
- Allow sufficient pre-sprouting in the light to produce a mean sprout length of no more than 10 mm, then if necessary return seed tubers to cold storage until shortly before planting.
Controlled atmosphere treatment of seed
- The aim is to increase the number of progeny produced by each seed.
- Seed is held in a controlled temperature and gaseous atmosphere for a period of time. The temperature is increased and oxygen levels are reduced (if oxygen levels were normal and temperatures were increased then seed would simply physiologically age). Typical conditions for this treatment are 20 oC, 3% O2 and 0% CO2 for 2 weeks
- Effects on number of progeny tubers have been variable.
- A more consistent effect has been an increase in seed decay (Pectobacterium soft rot, primarily). Removing oxygen causes anaerobic conditions similar to water logging and increased risk of soft rot is inevitable.
Use of cut seed
- Seed of some cultivars, or seed which is in short supply, may be supplied as cut seed.
- The distribution of tuber “eyes”, and thus of potential stems, varies from end to end of a tuber.
- The potential of apical and basal halves of seed tuber differs: apical halves can produce earlier emergence and higher yields per plant than do basal halves.
- Differences between apical and basal tuber halves may be exacerbated by poor growing conditions.
- It can be expected that cut seed will produce less uniform plant development than will whole seed. It is likely that differences between seed pieces will become more apparent as conditions at planting become poorer.
- Curing the cut surfaces of seed is important to reduce the risk of rotting diseases.
- Use of cut seed is not recommended but if only cut seed is available (e.g. for a particular cultivar) the seed should be planted in as good conditions as possible.
Seed age and manipulation notes
Seed 2020 (Includes an introduction to / review of the importance of seed)
Seed age 2005 (Definitions and effects of chronological and physiological age)
Physiological age 2001 (Summary of effects of physiological age)
Cut seed 2001 (Further information on problems associated with cut seed)
Cut seed 1999 (The problems associated with cut seed)
Controlled atmosphere seed treatment 2000 (Manipulation of store atmosphere increases risk of poor emergence)
Seed age 1999 (Potential advantages and disadvantages of physiological age; appropriate sprout growth)
Seed age 1997 (Principles of physiological age, PRG research)