The Bixaceae comprise several species of trees and shrubs within two genera. Bixa orellana L. (annatto) provides a dye. The fruits are dehiscent capsules and seed storage behaviour is orthodox. Detailed information on seed germination is provided here for Bixa orellana only.
BIXA
B. orellana L. achiote, annatto
I. Evidence of dormancy
Without treatment some seeds of B. orellana may take more than a year to germinate (2). Hardseededness, induced by drying seeds below 40% moisture content, is the main cause of this slow germination (2).
II. Germination regimes for non-dormant seeds
Constant temperatures: 30°C, 15d (2)
Alternating temperatures: 25°/30°C, light, 24h/d, 23d (1)
III. Unsuccessful dormancy-breaking treatments
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IV. Partly-successful dormancy-breaking treatments
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V. Successful dormancy-breaking treatments
Removal of seed covering structures: chip at radicle end (2)
VI. Comment
B. orellana shows orthodox seed storage behaviour - tolerating desiccation to 10% moisture content (2), but problems have arisen with seeds dried to 4% or stored at low temperatures (5°C, -20°C) when subsequently tested for germination at 30°C in a 15 day test after chipping the testae (2). Further investigations with very dry seeds are required. It is suggested that the dry seeds be humidified for several days after chipping to avoid the possibility of imbibition injury and that before storing seeds at low temperatures moisture should be allowed to equilibrate throughout each seed. Further work may show advantage in testing the seeds for germination in alternating temperature environments. In the meantime it is suggested that chipping, humidification and testing at 25° to 30°C be practised but note that the seeds - particularly the very dry seeds - may require considerably more than 15 to 23 days to germinate.
VII. References
1. Chin, H.F., Hor, Y.L. and Mohd Lassim, M.B. (1984). Identification of recalcitrant seeds. Seed Science and Technology, 12, 429-436.
2. Goldbach, H. (1979). Germination and storage of Bixa orellana seeds. Seed Science and Technology, 7, 399-402.
