The Myrtaceae comprise 3000 species of woody plants within about 75 genera which provide edible fruits (e.g. Feijoa sellowiana Berg., feijoa), spices (e.g. Pimenta dioica (L.) Merr., pimento), oils (e.g. Pimenta racemosa (Mill.) J.W. Moore, bay), and timber and firewood (e.g. Eucalyptus spp.). The fruits vary from a pulpy berry or drupe to a woody capsule or nut. The seeds generally show orthodox storage behaviour. For example, Callistemon and Melaleuca spp. are maintained in the long-term seed store at the Wakehurst Place Gene Bank. Eugenia brasiliensis Lam., however, is reported to show recalcitrant seed storage behaviour.
SEED DORMANCY AND GERMINATION
The embryos are either curved or linear, the cotyledons generally large, and the seed coats hard - thereby delaying or preventing germination. Dormancy per se (that is innate dormancy, see Chapter 5, Volume I) can also prevent or delay germination. Treatments to overcome the barrier provided by the hard seed coat (see Chapter 7, Volume I), gibberellins and warm germination test temperatures (roughly 25°C) tend to result in the promotion of seed germination. Detailed information on seed dormancy and germination is provided in this chapter for the genera Eugenia (including synonyms within Syzygium and Myrtus) and Psidium, and information on recommended germination test procedures and dormancy-breaking treatments for other species is summarised in Table 50.1. In addition the algorithm below may be helpful in developing suitable germination test procedures for other species.
RBG Kew Wakehurst Place algorithm
The first step in the algorithm is to test seeds at constant temperatures of 21°C and 26°C with light applied for 12h/d. If the results of these tests indicate a trend in the response of germination to constant temperatures then a further sample of seeds is tested at a more extreme constant temperature. For example, if germination at 26°C is greater than at 21°C then test a further sample of seeds at a constant temperature of 31°C with light applied for 12h/d.
If the above constant temperature regimes do not result in full germination then the second step in the algorithm is to test further samples of seeds at an alternating-temperature regime of 23°-26°/9°-11°C (12h/12h) with light applied for 12h/d during the period spent at the upper temperature.
TABLE 50.1 Summary of germination test recommendations for species within the Myrtaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Eucalyptus deglupta Blume |
TP; BP |
20°/30°C |
14d |
|
AOSA |
|
Eucalyptus grandis Sieber ex Benth. |
TP; BP |
25°C |
14d |
light |
AOSA |
|
Eucalyptus spp.
|
|
|
|
rules state that seed replicates should be weighed |
ISTA |
|
|
|
|
out for testing rather than being counted |
|
|
|
|
|
|
pre-chill, 1°-5°C, 4w |
G&R |
|
|
Feijoa sellowiana Berg. |
|
|
21d |
pre-chill, 1°-5°C, 30-60d |
Riley |
|
Myrciaria cauliflora Berg. |
|
|
21d |
pre-soak, 24h |
Riley |
|
Myrtus communis L. |
|
|
21d |
pre-chill, 1°-5°C, 30-60d |
Riley |
|
Rhodomyrtus tomentosa |
|
|
21d |
pre-soak, 24h |
Riley |
|
Syzygium spp. |
|
|
21d |
pre-soak, 24h |
Riley |
EUGENIA
|
E. brasiliensis Lam. [E. dombeyi (Spreng.)
Skeels] |
|
|
E. jambolana Lam. [E. cuminii Druce.; E.
jambolanum DC.; Syzygium cuminii Skeels; Myrtus cuminii
L.] |
jambolan, jambolan-plum |
|
E. jambos |
|
I. Evidence of dormancy
Poor and delayed germination has been reported for seeds of E. jambolana (2,3). Freshly harvested seeds of E. brasiliensis germinate readily, although it is reported to be possible to induce secondary dormancy (1). E. brasiliensis is reported to show recalcitrant seed storage behaviour (1).
II. Germination regimes for non-dormant seeds
E. brasiliensis
Constant temperatures: 25°C, 14d (1)
E. jambos
Alternating temperatures: 25°/30°C, light, 24h/d, 22d (4)
III. Unsuccessful dormancy-breaking treatments
-
IV. Partly-successful dormancy-breaking treatments
E. jambolana
GA3: pre-applied, 48h, 100-400 ppm (2)
V. Successful dormancy-breaking treatments
E. brasiliensis
GA3: co-applied, 10-4 M, plus kinetin, co-applied, 10-4 M (1)
E. jambolana
GA3: pre-applied, 48h, 500 ppm (2)
Eugenia spp.
Pre-soak: 24h (5)
VI. Comment
It is suggested that seeds of Eugenia spp. be tested for germination at 25°C; at 15°C secondary dormancy may be induced (1). A 60-day germination test period may be required. Treatment with gibberellins is an effective dormancy-breaking treatment (1,2) and is suggested as an additional treatment where dormancy is a problem.
VII. References
1. Goldbach, H. (1979). Imbibed storage of Melicoccus bijugatus and Eugenia brasiliensis (E. dombeyi) using abscisic acid as a germination inhibitor. Seed Science and Technology, 7, 403-406.
2. Shanmugavelu, K.G. (1970). Effect of gibberellic acid on seed germination and development of seedlings of some tree plant species. Madras Agricultural Journal, 57, 311-314.
3. Singh, R.K. and Thakur, S. (1977). Seed germination and seedling growth of jamum (Syzygium [Eugenia] cuminii Skeels) types. Proceedings of the Bihar Academy of Agricultural Sciences, 25, 139-142.
4. Chin, H.F., Hor, Y.L. and Mohd Lassim, M.B. (1984). Identification of recalcitrant seeds. Seed Science and Technology, 12, 429-436.
5. Riley, J.M. (1981). Growing rare fruit from seed. California Rare Fruit Growers Yearbook, 13, 1-47.
PSIDIUM
|
P. araca |
|
|
P. cattleianum Sabine [P. littorale
Raddi] |
strawberry guava |
|
P. guajava L. |
guava |
|
P. pumilum |
|
I. Evidence of dormancy
P. guajava and P. cattleianum show orthodox seed storage behaviour (1,2,9). Poor and delayed germination has been reported in P. araca (8), P. cattleianum (8), P. guajava (3,5-8), and P. pumilum (8). The cause of this problematic germination has been ascribed to the hard seed coat characteristic (6). Dormancy can be removed by after-ripening for 4 months (9).
II. Germination regimes for non-dormant seeds
P. cattleianum
Alternating temperatures: 20°/30°C (12h/12h) (1)
P. guajava
Constant temperatures: 28°-30°C (2)
Alternating temperatures: 20°/30°C (12h/12h) (1); 25°/30°C, light, 24h/d, 14d (10)
III. Unsuccessful dormancy-breaking treatments
P. guajava
Pre-soak: 24h (4); 14d (7); 100°C (3); 100°C, 5 min (7)
Scarification: concentrated nitric acid, 6-12 min (6); concentrated sulphuric acid, 5 min (7)
Hydroxylamine: pre-applied, 24h, 10-3 M (4)
Indoleacetic acid: pre-applied, 8h, 500, 1500 ppm (7)
IV. Partly-successful dormancy-breaking treatments
P. guajava
Pre-soak: (3)
Potassium cyanide: pre-applied, 24h, 10-3 M (4)
Sodium azide: pre-applied, 24h, 10-3 M (4)
Ethrel: pre-applied, 8h, 500-1500 ppm (7)
Indoleacetic acid: pre-applied, 8h, 1000 ppm (7)
Scarification: concentrated sulphuric acid, 3-12 min (6); concentrated hydrochloric acid, 6-12 min (6); concentrated nitric acid, 3 min (6)
V. Successful dormancy-breaking treatments
P. guajava
Pre-soak: 12-72h (6)
Scarification: concentrated hydrochloric acid, 3 min (6)
Psidium spp.
Pre-soak: 24h (11)
VI. Comment
Scarification of the seeds with subsequent testing in an alternating temperature regime are required for germination to occur. It is suggested for hard-seeded accessions of Psidium spp. that the seeds be scarified for 3 minutes only in either concentrated sulphuric acid or concentrated hydrochloric acid. All accessions can be tested at 20°/30°C (16h/8h), but a test duration of at least 3 months is necessary. Details of a suitable tetrazolium staining procedure for assessing seed viability have been provided by reference (5) - bisected seeds should be stained for 12-14 hours at room temperature in a 1% solution.
VII. References
1. Becwar, M.R., Stanwood, P.C. and Leonhardt, K.W. (1983). Dehydration effects on freezing characteristics and survival in liquid nitrogen of desiccation-tolerant and desiccation-sensitive seeds. Journal of the American Society for Horticultural Science, 108, 613-618.
2. Chacko, E.K. and Singh, R.N. (1971). Studies on the longevity of papaya, phalsa, guava and mango seeds. Proceedings of the International Seed Testing Association, 36, 147-158.
3. Haq, F., Khan, M.S. and Faridullah, I. (1973). Germination trial on guava seed. Journal of Agricultural Research, Pakistan, 11, 121.
4. Roberts, E.H. (1964). The distribution of oxidation-reduction enzymes and the effects of respiratory inhibitors and oxidising agents on dormancy in rice seeds. Physiologia Plantarum, 17, 14-29.
5. Shanker, G. and Ranganathi, A.S. (1974). A quick test for aonla, ber and guava seed viability. Current Research, 3 18-19.
6. Singh, S. and Soni, S.L. (1974). Effect of water and acid soaking periods on seed germination in guava. Punjab Horticultural Journal, 14, 122-124.
7. Sinha, M.M., Verma, J.P. and Koranga, D.S. (1973). Studies on the seed germination of guava (Psidium guajava L.) I. Effect of scarification and plant growth regulation treatments. Progressive Horticulture, 5, 37-40.
8. Teaotia, S.S. and Singh, R.D. (1973). Standardization of rootstocks of guava. I. Studies on seed germination, congeniality and vigour of various guava species and varieties. Progressive Horticulture, 4, 23-24.
9. Teng, Y.T. and Hor, Y.L. (1976). Storage of tropical fruit, seeds. In Seed Technology in the Tropics (eds. H.F. Chin, I.C. Enoch and R.M. Raja Harun) pp. 135-146. Universiti Pertanian Malaysia, Serdang, Selangor, Malaysia.
10. Chin, H.F., Hor, Y.L. and Mohd Lassim, M.B. (1984). Identification of recalcitrant seeds. Seed Science and Technology, 12, 429-436.
11. Riley, J.M. (1981). Growing rare fruit from seed. California Rare Fruit Growers Yearbook, 13, 1-47.
