Improving seed quality through seed priming
Seed priming improves germination and seedling establishment through reducing dormancy, improving desiccation tolerance and enhancing seedling growth. This technology, which has been used in the seed industry for decades, can be applied to wild species for use in in situ restoration.
Germinated seeds of Tabebuia impetiginosa survive desiccation subsequent to completion of germination through survival of the protruded radicle (left). Survival of the germinated seeds even occurs if the protruded radicle turns necrotic (right; arrow), th
Germination progresses through a series of potentially reversible steps as the physiology of the seed (embryo) gradually changes (Pinto et al., 2007). In situ restoration is hampered by aspects of seed quality that interfere with the establishment of seedlings. The level of seed dormancy in the population is one such problem with implications for the number of seedlings emerging from a cohort and the vigour of the responders. Reduction of dormancy and enhanced capability for rapid germination prior to sowing seeds for restoration will benefit the speed of restoration. We have investigated how pre-hydration, including through priming, alters the physiological competency of seeds.
Seed priming is a treatment applied before sowing seeds, which typically includes application of osmotic stress to the seeds prior to drying back. These dried back seeds can then be sowed and usually display reduced dormancy and improved seedling quality. This technology is widely used in the seed industry for crops, but has the potential to also benefit in situ restoration. Upon characterization of germination and dormancy of a Brazilian Cerrado species, the response of these seeds to priming was investigated. Final germination was higher, while germination speed and uniformity were greatly improved. An interesting observation was that not only dormancy was reduced, but that also seedling quality was improved (Anese et al., 2011). In addition, altered gene expression as a result of priming is under investigation, to understand which genes play a role in the improved germination performance (Antunes et al., 2011).
If pre-hydration / priming occurs under conditions too close to the water potential for germination, then the seed physiology can change; not just in terms of germination per se, but also desiccation tolerance, in which case drying back becomes a challenge. For nine neo-tropical species studied, we observed that all seeds in a seed lot lost desiccation tolerance after the same fixed proportion of their hydration time to germination, and this proportion was fairly constant across the species (0.63–0.70) (Daws et al., 2007). Nonetheless, it is possible in some species to re-induce desiccation tolerance in seeds as long as treatment is applied shortly after radicle emergence, upon exposure to osmotic stress similar to that applied during seed priming. Studying this phenomenon creates further understanding of the seedling development program. In Tabebuia impetiginosa, a member of the Bignoniaceae family and a native tree of the tropical Americas, an improved survival response of the germinated seeds was demonstrated upon cold shock, heat shock and exogenous abscisic acid in addition to the applied osmotic stress (Vieira et al., 2010). The degree of survival depends on the origin of the accession; those from drier habitats display more post-germination desiccation tolerance than accessions from wetter habitats. These results indicate that natural variation exists for this physiological phenomenon, serving a role in adaptation to irregular precipitation patterns at the start of the wet season. Research is underway to understand how seed priming and environmental stress factors could benefit in situ restoration efforts.
Project partners and collaborators
Universidade Estadual Paulista (UNESP)
Universidade Federal de Lavras (UFLA)
Universidade Federal da Bahia (UFBA)
Universidade Estadual de Feira de Santana (UEFS)
Universidade Federal de Mato Grosso (UFMT)
Instituto Federal de Alagoas (IFAL)
Key papers published since 2006
1. Daws, M.I., Bolton, S., Burslem, D.F.R.P., Garwood, N.C., Mullins, C.E. (2007). Loss of desiccation tolerance during germination in neo-tropcial pioneer seeds: implications for seed mortality and germination characteristics. Seed Science Research 17: 273-281. (IF 1.25, times cited = 4)
2. Pinto, L.V.A., Amaral da Silva, E.A., Davide, A.C., Mendes de Jesus, V.A., Toorop, P.E., Hilhorst, H.W.M. (2007). Mechanism and control of Solanum lycocarpum St. Hill seed germination. Annals of Botany 100: 1175–1187. (IF 3.39, times cited = 7)
3. Vieira, C.V., Amaral da Silva, E.A., Alves de Alvarenga, A., Mauro de Castro, E., Toorop, P.E. (2010). Stress-associated factors increase after desiccation of germinated seeds of Tabebuia impetiginosa Mart. Plant Growth Regulation 62: 257–263. (IF 1.63, times cited = 1)
4. Anese, S., Amaral da Silva, E.A., Davide, A.C., Rocha Faria, J.M., Soares, G.C.M., Matos, C.B., Toorop, P.E. (2011). Seed priming improves endosperm weakening, germination, and subsequent seedling development of Solanum lycocarpum St. Hil. Seed Science and Technology 39: 125–139. (IF 0.61)
5. Antunes, C.G.C., Ligterink, W., Pelacani, C.R., Aflitos, S.A., De Castro, R.D., Toorop, P.E., Hilhorst, H.W.M. (2011). Differentially expressed genes in Caesalpinia pyramidalis L. seeds during osmopriming. Revista Brasileira de Sementes: in press.
Conferences and workshops
10th Conference of the International Society for Seed Science, Salvador, 2011