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Fiona Hay

Learn about the factors affecting seed longevity, predictions on germinability in controlled conditions, and impacts of ambient storage. Understand viability monitoring and storage strategies in genebanks. Explore data trends and potential solutions for better seed management practices.

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Fiona Hay

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  1. Fiona Hay • Current position: Senior Scientist, T.T. Chang Genetic Resources Center • Education and training: • M.Sc. 2002 Birkbeck College, University of London, UK – Applied statistics and operational research • Ph.D. 1997 King’s College, University of London, UK - The development of seed longevity in wild plant species • B.Sc. 1993 University of Manchester, UK – Applied plant science • Work experience • 2009- T.T. Chang Genetic Resources Center • 1997-2009 Millennium Seed Bank Partnership, Royal Botanic Gardens Kew, UK • Research highlights • >50 peer-reviewed journal articles on seed collecting, germination / dormancy and longevity in relation to genebank management and use of collections; Chief Editor, Seed Science and Technology;key note speaker at ISSS meetings in 2013 and 2015; adjunct appointments with UPLB and UWA.

  2. How long can rice seeds stay alive for?

  3. How long can rice seeds stay alive for? • Outline: • Definitions, prediction • Genebank viability monitoring data • Factors influencing the potential longevity of seeds • Conclusions

  4. Seed longevity: definitions, prediction A seed lot comprises many individual seeds

  5. Seed longevity: definitions, prediction High vigour Ageing symptoms Non-viable 100%, fast, uniform germination 90%, slower germination 60-70% slow uneven, germination 40-50% slow sporadic germination 20-30% abnormal germination No germination A seed lot comprises many individual seeds Storage

  6. Seed longevity: definitions, prediction Seed longevity is the length of time (period, p) during which the germinability of a sample of seeds will remain above a critical / target level (controlled, dry-storage conditions). Line fitted by probit analysis

  7. Seed longevity: definitions, prediction Seed longevity is the length of time (period, p) during which the germinability of a sample of seeds will remain above a critical / target level (controlled, dry-storage conditions). Parameters of the normal distribution: Mean, μ (= p50) Standard deviation,  Frequency of seed deaths follows a normal distribution 

  8. Seed longevity: definitions, prediction Seed longevity is the length of time (period, p) during which the germinability of a sample of seeds will remain above a critical / target level (controlled, dry-storage conditions). • Parameters of the normal distribution: • Mean, μ (= p50) • Standard deviation,  • Ellis-Roberts (1980) viability equation (in probits): • v = Ki – p/ • v = viability, Ki = initial viability • At p50, viability in probits = 0 hence, • p50 = Ki x  Ki = 3   

  9. Seed longevity: definitions, prediction Kiis the initial viability of the seed lot (in probits) • is constant for all seed lots within a species; depends on moisture content and temperature according to the equation m = moisture content, t = temperature • Species viability constants solved for 53 species in 1996, mostly crop species represented in crop genebank collections

  10. Seed longevity: definitions, prediction Question: We are storing 300 MT of paddy seed with 14% seed moisture content and 85% germination in a cold room maintained at 20-22°C with relative humidity 65 - 70%. Can you please conclude how long the seed will hold its original viability (germination) in that condition.  After taking out from this controlled condition how long seed will retain its germination in normal ambient temperature of 37-40°C and 80% relative humidity. This time duration will have to be provided for transportation and storing before finally sowing/broadcasting in field. 

  11. Seed longevity: definitions, prediction

  12. Seed longevity: definitions, prediction FAO (2013) Genebank standards: Viability monitoring intervals should be set at 1/3 of the length of time predicted for viability to fall to 85% (regeneration standard): • Medium-term: 14 years • Long-term: 49 years • How well do these predictions reflect what is happening in genebank storage? • Can we reduce the frequency of viability testing? Long-term store: -18°C Medium-term store: 2-4°C Drying room: 15% RH, 15°C = 7% moisture content (mc) Processing area: 50% RH, 22°C = 11.3% moisture content (mc)

  13. Genebank germination data: a bit messy ‘Rejuvenation’ @ ≤ 85%; testing ceases IRGC accession number Data downloaded October 2013.

  14. Alternative way of looking at the data – proportion of accessions ‘failing’ Data for seeds stored in the active and base collections. Downloaded October 2013. Proportion of seed lots from each crop season that had / hadn’t failed. ‘Failure’ = ≤85 % germination. Oldest samples showing evidence of an increasing rate of failure. Newest samples showing evidence of an increasing rate of failure. Assume it’s mainly due to reduction in Ki.

  15. Decline in the storage potential of seeds regenerated at IRRI Accessions from Laos regenerated at IRRI, stored in the active collection

  16. – not due to variation in storage moisture content

  17. – not due to workload

  18. Alternative way of looking at the data – proportion of accessions ‘failing’ What happened in the early 1990’s?

  19. What happened in the early 1990s? New genebank head: Mike Jackson Photo: E. Hettel, IRRI

  20. Review of genebank operations: changes to pre- and post-harvest factors that influence longevity Research on when and where to regenerate; when to harvest; effect of genotype on longevity. Changes to seed processing and packaging; installation of a seed drying room. Regeneration plots at IRRI, 2015 dry season

  21. i. When and where to regenerate; when to harvest = Field = Controlled environment KameswaraRao and Jackson (1996a): 3 japonica varieties (O. sativa) grown in the field (1993 DS) or in a controlled environment (24/18°C). Harvested at 28, 35 and 42 DAF. Storage experiments after routine drying. Conclusions: No significant difference in potential seed longevity depending on environment. DS field regeneration is OK.

  22. i. When and where to regenerate; when to harvest KameswaraRao and Jackson (1996b): 3 indicas, 1 japonica, planted 14 Oct, 24 Nov, 5 Jan (1993 DS). Harvested at 21-42 DAF. Storage experiments after routine drying.. Conclusions: Sow mid-October to allow ripening to coincide with cooler, drier period. Harvest at 35 DAF.

  23. i. When and where to regenerate; when to harvest = attainment of maximum dry weight (DW) KameswaraRao and Jackson (1996c): 16 O. sativa, 1 O. glaberrima (1993 DS). Harvested at 14-42 DAF. Storage experiments after routine drying. Conclusions: Maximum longevity at 33-37 DAA (after maximum DW). OK to regenerate in DS at IRRI.

  24. i. When and where to regenerate; when to harvest = attainment of maximum dry weight (DW) KameswaraRao and Jackson (1996c): 16 O. sativa, 1 O. glaberrima (1993 DS). Harvested at 14-42 DAF. Storage experiments after routine drying. Conclusions: Maximum longevity at 33-37 DAA (after maximum DW). OK to regenerate in DS at IRRI. Current practice: accessions are routinely regenerated in the dry season at IRRI, target harvest at 35 DAA.

  25. i. When and where to regenerate; when to harvest

  26. i. When and where to regenerate; when to harvest 20 accessions, harvested 24-45 DAF. Use of chlorophyll fluorescence to decide when to harvest? Data from Hay et al. (2015) 24 DAF 31 DAF 38 DAF 45 DAF

  27. i. When and where to regenerate; when to harvest; genotype KameswaraRao and Jackson (1997): 10 O. sativa, 2 O. glaberrima(1994 DS). Harvested at 21-35 DAF. Conclusions: Maximum longevity at 28-35 DAA. Aus and Boro types have greatest seed longevity. Nipponbare x kasalath (japonica x aus) Sasaki et al., 2005

  28. i. Genotype: high failure rate countries Japan, South Korea, Taiwan, Hong Kong, Bhutan, Russian Federation [Soviet Union], Kazakhstan, Tajikistan, Uzbekistan, Ethiopia, Iraq, Azerbaijan, Turkey, Bulgaria, Romania, Italy, Spain, Portugal, [Yugoslavia], Tunisia, Morocco, Switzerland, Germany, South Africa Data for seeds of accessions originally from the Philippines or Taiwan, regenerated 1985DS, stored in the active collection

  29. ii. Processing and packaging Manual seed sorting based on visual characteristics, with reference to the seed file (original sample).

  30. ii. Processing and packaging Manual seed sorting based on visual characteristics, with reference to the seed file (original sample). Pre-1993, active and base samples were in vacuum-sealed cans; post-1993, active samples were sealed in aluminium foil packets.

  31. ii. Processing and packaging Manual seed sorting based on visual characteristics, with reference to the seed file (original sample). Pre-1993, base collection stored at -10°C; post-1993, at -20°C. Pre-1993, active and base samples were in vacuum-sealed cans; post-1993, active samples were sealed in aluminium foil packets. -10°C -20°C

  32. ii. Post-harvest drying “Drying at 10-25°C and 10-15% relative humidity (r.h.) using either a desiccant or drying chamber is preferred.” FAO / IPGRI, 1994

  33. ii. Post-harvest drying “All seed samples should be dried to equilibrium in a controlled environment of 5–20 °C and 10-25 percent of relative humidity, depending upon species.” FAO , 2013

  34. ii. Post-harvest drying Genebank dry room Hot-air batch dryer Crisostomo et al. (2011): 10 O. sativa (2010 DS). Dried using a hot-air flat-bed dryer or in the genebank drying room. Controlled deterioration test. Conclusion: Seed physiological quality better if dried in the hot-air flat-bed dryer.

  35. ii. Post-harvest drying Data from Whitehouse et al. (2015): 20 O. sativa (2013 DS) harvested on one occasion, between 24 and 48 DAF, dried in drying room (‘DR’) or with heated air (‘BD’). Before 1993, seeds were initially dried at high temperature!

  36. But, ‘step changes’ in the early 1990s don’t explain the trend…! What happened in the early 1990’s?

  37. But, ‘step changes’ in the early 1990s don’t explain the trend…! Controlled-environment, reciprocal-transfer experiments with two japonica varieties: “Seed viability was most vulnerable to low or high temperature in the 7 or 14 d after anthesis…” (High temperature: 38 / 34 °C) Crop Science, 55, 354-364.

  38. Step changes don’t explain the trend… Whole year Dry season Wet season Penget al. (2004) attributed decline in rice yields to increase in night-time temperature; a 1.33°C increase between 1979-2003 over the dry season.

  39. Step changes don’t explain the trend… Seeds harvested at different days after flowering. Whitehouse et al. (2015).

  40. Step changes don’t explain the trend… Seeds harvested at different days after flowering. Increase in longevity, somewhat independent of genotype and DAF Whitehouse et al. (2015), Hay et al. (2015).

  41. Step changes don’t explain the trend… Seeds harvested at different days after flowering. Whitehouse et al. (2015), Hay et al. (2015).

  42. Step changes don’t explain the trend… Climate data from IRRI’s climate unit. Whitehouse et al. (2015), Hay et al. (2015).

  43. Step changes don’t explain the trend…

  44. ii. Post-harvest drying Data from Whitehouse et al. (2015): 20 O. sativa (2013 DS) harvested on one occasion, between 24 and 48 DAF, dried in drying room (‘DR’) or with heated air (‘BD’). Return to initially drying seeds at high temperature!

  45. Conclusions Seed longevity is important for anyone using and storing seeds (percentage and vigour of germination). Longevity depends on the storage conditions (primarily moisture content and temperature) and on the initial viability of the seeds. The storage potential of seed lots of genebank accessions regenerated at IRRI has declined since the early 1990s. Longevity can be affected by pre- and post-harvest factors; maturity at harvest and drying regime (depending on the moisture content of the seeds at harvest) are particularly important.

  46. Conclusions (ctd.) • Some of the things we need to do / have started: • Start testing base-stored seeds after the active-stored seeds reach the viability standard. • Further analysis of the genebank monitoring data (beyond 2002) – with climate data? • Still need to optimize the drying process (something we can control). • GWAS study (Jae-Sung Lee): variation in Kiand/or σ?

  47. Acknowledgements Funding: GCDT (Genebank CRP) long-term grant GCDT (Genebank CRP) IRRI RAP GRiSP ISTA Editing (SST)

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