Seed size and rate: background
- The aim is to achieve a suitable number of progeny tubers to meet the market requirements.
- The potential number of progeny tubers will be determined by:
- seed quality (growing conditions, health, damage etc)
- seed size
- seed population
- The actual number of progeny tubers will be determined by:
- storage conditions of the seed
- environment from planting until tuber production
Target number of progeny tubers
- A population of 40 progeny tubers m-2 may be suitable for “baker” crops or short duration crops.
- A population of 60 progeny tubers m-2 should be suitable for most maincrop situations.
- A population of 80 progeny tubers m-2 is suitable for “punnet” or “salad” crops or requires a very high potential, long duration site.
- Seed of 40-45 mm should allow 40 progeny tubers ha-1 to be achieved; it may also be possible to achieve this from 35-40 mm seed.
- Seed of 50-55 mm should allow 60 progeny tubers ha-1 to be achieved; it may also be possible to achieve this from 45-50 mm seed.
- These seed rate / seed size relationships also appear to be true for cut seed of the same size as whole seed and planted under good conditions (for further information on cut seed see: Use of cut seed).
Achieving the potential number of progeny tubers
- PRG experimentation and published work has shown considerable variation in the number of tubers produced by seed from a single seed lot, grown in a range of environments.
- If standard or historic seed rates do not produce an appropriate number of progeny tubers, on-farm research is required to determine suitable seed rates for the growing conditions:
- plant seed at the standard seed rate and at higher and lower rates
- monitor the number of progeny tubers >10 mm produced (the biological potential) and those in the target size grade
- repeat in successive seasons and make adjustments to the commercial seed rate according to the results
- Remember that achieving the required size of progeny tubers also depends on the rate and duration of tuber bulking achieved.
- The accuracy of seed rate calculations can be further increased by removing constraints and so reducing variation in the number of progeny tubers produced and their rates of bulking.
Influences on the number of progeny tubers produced
- Performance of crops, including number of progeny tubers, can be influenced by the conditions in which the seed crop is grown.
- In particular, high temperatures during seed crop growth can reduce number of progeny tubers and yield potential in the next generation, as a result of a high physiological age of the seed produced.
- The potential number of progeny tubers increases with increasing seed size.
- Maximum seed size is the largest which can be planted accurately.
- Large seed has the largest amount of reserves per growing stem and thus the greatest “buffering capacity” for poor conditions after planting.
- Medium sized seed may produce the greatest variation in the number of progeny tubers.
- Small seed performs uniformly poorly and needs ideal conditions to produce its potential.
Seed physiological age
- There can be a 4 % reduction in number of progeny tubers for every 100 day degree increase in physiological age.
For more information see: Seed age.
Availability of water
- There can be a 1.89 % loss in number of tubers for each day drought stressed after emergence.
- Drought stress = soil moisture potential drier than -25 kPa.
- The earlier after emergence drought stress begins, the greater is the effect.
- One influence of drought is to reduce the number of stolons, and thus tubers, which are produced. Most stolons have formed by approximately 30 days after emergence but may begin to form before emergence. Dry soil before emergence may thus reduce the number of tubers produced.
- Phosphorus nutrition influences the number of tubers produced, rather than the proportion retained.
For unsprouted seed:
- There can be a 2.08 % increase in number of progeny tubers for every 1 ppm increase in soil phosphorus concentration in the range 12 – 32 ppm P.
- Sprouted seed does not follow this relationship, as pre-sprouting reduces the potential to form tubers. In this context “sprouted” means sprouts longer than 10 mm of > 500 day degrees > 4oC.
For unsprouted seed:
- There can be a 1.64 % increase in mean number of progeny tubers for every 0.01 % increase in plant phosphorus concentration between 0.25 and 0.50% P (measured 25 days after emergence).
For more information see: Phosphorus.
- Early availability of carbohydrate is important.
- Planting at low temperature can restrict the availability of carbohydrate from seed tubers.
- Some experiments with application of “Fulcrum” (a source of sugars) have shown an increase in the number of progeny tubers, where cold conditions at and after planting would have restricted carbohydrate supply from seed.
- During early growth the supply of carbohydrates from photosynthesis is limited and damage to the canopy or poor conditions may reduce photosynthesis.
- Experiments in which plants were shaded during tuber formation (restricting photosynthesis) have shown a reduction in number of progeny tubers.
Numbers of progeny tubers may also be reduced by:
- deficiency of magnesium at emergence (13 % in one experiment)
- excess potassium or other salts in the ridge (difficult to quantify at present)
- foliar applications during Os, e.g. zinc (9 % in one experiment), seaweed extract (17 % in one experiment).
- seed or soil borne diseases (difficult to quantify)
Seed and tuber number notes
Seed 2020 (Includes an introduction to / review of the importance of seed)
Seed prolificacy 2010 (Conclusions on relationships between seed planted and progeny tubers produced)
Potato prolificacy 2009 (A protocol for a prolificacy study)
Number of progeny tubers review 2009 (Includes influence of seed)
Seed potato review 2008 (Includes the importance of seed size)
Seed rate and water supply 2007 (Influence of water on seed prolificacy)
Seed size and spacing 2005 (Larger seed are more robust; growing conditions can influence performance of the same seed lot at different sites)
Seed provenance 2005 (Growing conditions can influence seed prolificacy)
Seed size and rate 2003 (PRG research: includes the difficulty of trying to produce seed size / rate tables)
Seed size and rate 2001 (PRG research; influence of early environment)
Cut seed 2001 (Further information on problems associated with cut seed)
Cut seed 1999 (The problems associated with cut seed)
Seed size and rate 1997 (PRG research)
Seed rate and size 1996 (PRG research)
Seed rate and size 1995 (PRG research)
Seed size and rate 1994 (PRG research)
Seed prolificacy 1994 (PRG research)
Notes for 1993 (Chapter 6: Seed size and rate; data from the literature shows higher yield from large than small seed at the same population; start of PRG research)
Seminar 3 Notes 1992 (Chapter 3: Plant population; published data indicates a higher yield potential from large than small seed)