Effects of storage under low temperature, room temperature and in the soil on viability and vigour of Leucospermum cordifolium (Proteaceae) seeds

Published Date
South African Journal of Botany
March 2015, Vol.97:1–8, doi:10.1016/j.sajb.2014.11.003

• Author 

• G.J. Brits ^a,,
• N.A.C. Brown ^b,
• F.J. Calitz ^c,
• J. Van Staden ^d,

• aHorticultural Division, Institute for Fruit Research, Agricultural Research Council, P.O. Box 5026, Stellenbosch 7599, South Africa
• bConservation Biology Research Unit, National Botanical Institute, Kirstenbosch, P/Bag X7, Claremont 7735, South Africa
• cBiometry Services, Agricultural Research Council, P.O. Box 8783, Pretoria 0001, South Africa
• dResearch Centre for Plant Growth and Development, School of Biological and Conservation Sciences, University of Kwazulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa

Received 20 July 2014. Revised 10 November 2014. Accepted 12 November 2014. Available online 29 December 2014. Edited by MI Daws

Highlights

• •
  Leucospermum seed storage was investigated, including 4 years of soil-storage in fynbos.
• •
  Dry, open shelf-stored seeds declined quickly (2–4 years) whereas soil-stored seeds remained viable.
• •
  Seeds sown under simulated fynbos conditions spread (strategically extended) germination over 5 years.
• •
  Combined results indicate extended germination in fynbos for the freshly dispersed seed cohort.
• •
  Testa-scarified old-cohort seeds are implicated to germinate early, evenly, en masse.
• •
  Long term wet–dry cycling due to rainfall may regulate cellular repair and longevity.

Abstract

Seed longevity, the control of dormancy and the eventual fate of seeds were studied in two experiments simulating conditions in natural fynbos. In one experiment a batch of mature, freshly harvested, intact achenes (“seeds”) of the myrmecochorous species Leucospermum cordifolium was divided into lots, of which one was buried in mesic mountain fynbos (experiencing a mediterranean-type climate with hot summers). Other seed lots were stored open at room temperature and in closed nitrogen filled containers at 3 °C, respectively. Stored seeds were sampled and germinated under optimal laboratory (viability estimate) and seed bed (vigour estimate in fynbos) conditions, during autumn, after 0 (control), 1, 2 and 4 years. Low temperature stored seeds maintained a high viability and vigour for c. two years but ambient temperature storage led to a marked decline after 1 year ending in almost complete mortality after 4 years of shelf storage. Four year soil-stored seeds, by contrast, maintained a high viability and vigour, of 80% and 60% respectively of the original seed source values. The soft pericarp/elaiosome in soil-stored seeds disappeared completely whilst the testa became progressively scarified over time. The strongly increased germination rate (velocity) in soil-stored seeds was attributed to natural oxygenation mediated by testa scarification. In another experiment freshly matured intact achenes were oxygenated with 1% H₂O₂ and the pericarps removed. Disinfection and benzyladenine growth regulator soaking (200 mg L^{− 1} for 24 h) were applied as separate treatments. The seeds were then sown at 1 cm depth in a standard seed bed in autumn and germination was recorded in the first winter season and, in the undisturbed seed bed, in each subsequent winter for 5 germination seasons. H₂O₂ oxygenated seeds gave a much higher germination percentage and rate than non-oxygenated seeds, although sporadic germination continued over five germination seasons in all treatments. Seeds germinated only during autumn and early winter each year.

The results of the combined experiments suggest that, in nature, Leucospermumseeds can persist underground for long periods. We propose a model of soil-stored seeds in which the intact testa of freshly dispersed seeds is gradually scarified, leading to uneven, extended germination of the young (mainly current season) seed cohort over the first (and possibly several) post-fire germination seasons; and the synchronous germination of the older (scarified), larger, portion of the seed bank, leading to massive species recruitment during the early stages of the first post-fire winter germination season. The numerous wet–dry cycles due to natural rainfall, over prolonged periods in fynbos, may contribute to seed longevity via cellular repair processes.

Keywords

Leucospermum

Dormancy

Germination

Persistent seed bank

Soil-storage

Viability

Vigour

Wet–dry cycling

---

Fig. 1.

 Table 1

Table 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.

• ⁎ 
  Corresponding author at: Brits Nursery, 28 Flamingo Rd, Stellenbosch 7600, South Africa. Tel./fax: + 27 21 8864710.

Copyright © 2014 South African Association of Botanists. Published by Elsevier B.V. All rights reserved.

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0254629914001951