The Annonaceae comprise roughly 600 species of trees and shrubs in 40 to 50 genera which provide edible fruits (e.g. Annona squamosa L., sugar apple). In some genera the fruits are fleshy, but in others the fruits are dry. The seeds show orthodox storage behaviour.
SEED DORMANCY AND GERMINATION
Seed dormancy can be a considerable problem. Detailed information on seed germination is provided for the genus Annona in this chapter. A limited number of other recommended germination test procedures is provided in Table 22.1.
TABLE 22.1 Summary of germination test recommendations for species within the Annonaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Asimina triloba Dunal |
|
|
90d |
scarify, abrade with sharp sand, or file or nick seed coat,
then pre-chill, 1°-5°C, 30-60d |
Riley |
|
Rollinia deliciosa |
|
|
21d |
pre-soak, 24h |
Riley |
ANNONA
|
A. cherimola Mill. [A. cherimolia
Mill.] |
cherimoya |
|
A. crassiflora Mart. |
|
|
A. diversifolia Safford |
ilama |
|
A. muricata L. |
soursop, guanabara |
|
A. reticulata L. |
common custard-apple, bullocks-heart |
|
A. squamosa L. |
sweetsop, sugar-apple |
I. Evidence of dormancy
Seeds of A. muricata, A. reticulata and A. squamosa are reported not to exhibit dormancy (3,4,5), but may, nevertheless, take up to 3 months to germinate (3). However, freshly harvested seeds of A. cherimola, A. crassiflora and A. diversifolia may exhibit considerable dormancy (1,2,4,6): several months after-ripening at room temperature may be required for full germination (1).
II. Germination regimes for non-dormant seeds
A. cherimola
Constant temperatures: 25°C, 75d (6)
A. reticulata, A. squamosa
Constant temperatures: 30°C, 100d (4)
III. Unsuccessful dormancy-breaking treatments
A. cherimola
Scarification: mechanical (6); mechanical, then pre-soak, 24h (6)
Pre-soak: 24h (2,6); 100°C, then allow to cool, 24h (2)
GA3: pre-applied, 24h, 10-1000 ppm (2)
A. crassiflora
Constant temperatures: 35°C (4); 30°C, 200d (4)
Scarification: (4)
Pre-soak: 7d (4)
Hydrogen peroxide: pre-applied, 7,14d, 1% (4)
Glucose: (4)
A. squamosa
Scarification: (3)
A. diversifolia
Pre-soak: 24h (1)
IV. Partly-successful dormancy-breaking treatments
A. cherimola
GA3: pre-applied, 24h, 10000 ppm, test for 3m (2); pre-applied, 24h, 20, 200, 750, 1000 ppm, test for 10w (6)
A. diversifolia
GA3: pre-applied, 24h, 3.5, 35, 350, 3500, 35000 ppm (1)
V. Successful dormancy-breaking treatments
A. cherimola
GA3: pre-applied, 24h, 500 ppm, test for 75d (6)
A. crassiflora
Constant temperatures: 30°C, in diffuse light, 300d (4)
A. muricata
Alternating temperatures: 25°/30°C, light, 24h/d, 46d, after heat treatment, 40°C, 5d (7)
VI. Comment
Despite the seed coats of Annona spp. being thick and heavily lignified the seeds imbibe without difficulty (3,4,6). Consequently scarification or pre-soaking treatments are not beneficial (2,3,4,6). The major germination problems appear to result, in A. squamosa at least, from the fact that the embryo is small, only partly developed, and embedded in a large endosperm (3); the embryo continues to develop after being shed from the mother plant (3). It has been suggested that non-dormant seeds of Annona spp. be tested for germination in moist sand or between moist paper towels at a constant temperature of 30°C for 100 to 300 days (4). It is suggested here that, in addition, GA3 be pre-applied for 24 hours at 350 to 500 ppm to promote the germination of dormant seeds. Pre-application of GA3 for 1 day at concentrations between 3.5 and 35000 ppm showed maximum promotion of germination at 350 ppm for 5 lots of A. diversifolia (1). Do not exceed 350 to 500 ppm because GA3 at higher concentrations, 1000 ppm (6), 3500 ppm (1), may reduce germination and, moreover, affect seedling growth: treatment at 350 ppm did not cause abnormal seedling development whereas treatment at 3500 ppm and higher did (1).
VII. References
1. Campbell, C.W. and Popenoe, J. (1968). Effect of gibberellic acid on seed dormancy of Annona diversifolia Saff. Proceedings of the Tropical Region, American Society for Horticultural Science, 11, 33-36.
2. Duarte, O., Villagarcia, J. and Franciosi, R. (1974). [The effect of different treatments on the propagation of cherimoya by seeds, cuttings and grafting.] Proceedings of the Tropical Region, American Society for Horticultural Science, 18, 41-48.
3. Hayat, M.A. (1963). Morphology of seed germination and seedlings in Annona squamosa. Botanical Gazette, 124, 360-362.
4. Rizzini, C.T. (1973). Dormancy in seeds of Annona crassiflora Mart. Journal of Experimental Botany, 24, 117-123.
5. Stephens, S.E. (1936). Some tropical fruits. No. 11. The soursop. Queensland Agricultural Journal, 46, 409-412.
6. Toll-Jubes, T., Martinez, H., Padilla, E. and Oste, C.A. (1975). [Effects of mechanical scarification, substrate, seed position and gibberellic acid on germination in cherimoya.] Revista Agronomica del Noroeste Argentino, 12, 161-172.
7. Chin, H.F., Hor, Y.L. and Mohd Lassim, M.B. (1984). Identification of recalcitrant seeds. Seed Science and Technology, 12, 429-436
