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Keywords:

  • Sycamore;
  • Norway maple;
  • seed development;
  • seed germination;
  • desiccation tolerance

SUMMARY

Differences in maturation drying and desiccation tolerance during seed development were detected between the two contrasting Acer spp., Norway maple (Acer platanoides L.), which shows orthodox seed storage behaviour, and sycamore (A. pseudoplatanus L.), which shows recalcitrant seed storage behaviour. In both species, the onset of germinability (150 d tests at 5 °C) occurred after percentage seed moisture content had begun to decline, but before net loss in seed moisture. The onset of germinability in Norway maple occurred 4 wk before physiological maturity (i.e. 4 wk before the end of the increase in seed dry matter), whereas in sycamore it occurred some ten weeks before physiological maturity when the seeds were only 60 % filled. Seeds of Norway maple were able to tolerate enforced rapid desiccation to 10% moisture content (f. wt) at physiological maturity, when maturation-drying had reduced seed moisture content to 54 %. Between 2 and 4 wk later seed moisture content rapidly declined naturally to 25 %, at which value the fruits were shed. In contrast, a constant rate of maturation-drying was observed in sycamore. The seeds were shed at 58 % moisture content and, in almost all cases, the seeds were intolerant of rapid desiccation to c. 10 % moisture content throughout seed development. A very small proportion of sycamore seeds did survive rapid desiccation when harvested between 6 September and 4 October, but no seeds survived desiccation to 5 % moisture content or below. A comparison of the germination of sycamore seeds harvested on four dates and dried to various moisture contents showed that the seeds tolerated greater desiccation as they matured between 12 July and 20 September, but there was no further change thereafter. The results are therefore compatible with previous classifications of seed storage behaviour in each species, and with the view that the initial decline in seed moisture content stimulates the developmental switch which results in the onset of germinability in both orthodox and recalcitrant seeds.