The Rubiaceae comprise about 5000 species of mainly trees and shrubs within about 400 genera. The two most important genera are Coffea which provides beverages and Cinchona which provides medicinal products. The fruits are capsules, berries or drupes. Seed storage behaviour in the Rubiaceae is now believed to be orthodox. For example, Crucianella, Hymenopogon, and Phyllis spp. are maintained in the long-term seed store at the Wakehurst Place Gene Bank. Information on seed storage behaviour in Cinchona and Coffea spp. is discussed in subsequent sections of this chapter.
SEED DORMANCY AND GERMINATION
The seeds are usually non-endospermic; seed size varies considerably from very small in the Cinchonoideae tribe to the very much larger "bean" of the Coffeoideae tribe; dormancy is a common problem. Detailed information on seed dormancy and germination is provided in this chapter for the genera Cinchona and Coffea, and a brief summary of further information on dormancy and germination in the Rubiaceae is provided in Table 63.1. In addition the algorithm below may be helpful in developing suitable germination test procedures.
RBG Kew Wakehurst Place algorithm
The first step in the algorithm is to test seeds at constant temperatures of 16°C and 26°C with light applied for 12h/d. If full germination does not occur and a trend in germination response to constant temperatures is apparent then test further samples of seeds at more extreme constant temperatures. For example, if a greater proportion of seeds germinates at 16°C than at 26°C then test further samples of seeds at constant temperatures of 6°C and 11°C with light applied for 12h/d. If full germination does not occur and there is no significant difference between the proportions of seeds germinating at 16°C and 26°C then test a further sample of seeds at a constant temperature of 21°C with light applied for 12h/d.
If the above constant temperature regimes do not result in full germination then the second step of the algorithm is to test a further sample of seeds in an alternating temperature regime of 23°/9°C (12h/12h) with light applied for 12h/d during the period spent at the upper temperature of each cycle.
TABLE 63.1 Summary of germination test recommendations for species within the Rubiaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Galium boreale L. |
TP |
20°/30°C |
|
light, pre-chill, 4w |
M&O |
|
Ixora javanica L. |
S |
25°-30°C |
42d |
light, continuous |
CHML |
CINCHONA
|
C. josephiana Wedd. |
quinine |
|
C. ledgeriana Moens ex. Tremen |
quinine |
I. Evidence of dormancy
Although seeds of Cinchona spp. are reported to germinate readily in nursery or glasshouse sowings (1,3-6), in some cases seeds continue to germinate and emerge 2 years after sowing (5) suggesting that the seeds are dormant. Moreover in laboratory tests it is reported that the seeds only germinate in particular environments (3,6). Attempts cannot be made to remove dormancy by after-ripening since the seeds are reported to lose viability rapidly at room temperature (2,3,5,6), though at 5-8% moisture content and -4°C no loss in viability was observed over a 4 year storage period (3).
II. Germination regimes for non-dormant seeds
-
III. Unsuccessful dormancy-breaking treatments
C. josephiana
Light: dark (6)
C. ledgeriana
Constant temperatures: 15°C (3)
Light: sunlight (4)
IV. Partly-successful dormancy-breaking treatments
C. ledgeriana
Constant temperatures: 30°C (3)
V. Successful dormancy-breaking treatments
C. josephiana
Light: diffuse light (6)
C. ledgeriana
Constant temperatures: 20°C, 25°C (3); 22°C (4)
Alternating temperatures: 10°/30°C, 15°/30°C, 20°/30°C (16h/8h) (3)
VI. Comment
Germination of seeds of Cinchona spp. requires light (6), but at low illuminance (4). It is suggested that the seeds be tested for germination on top of filter papers in petri dishes at 25°C (3) in diffuse light - see Chapter 6. An alternating temperature regime of 20°/30°C (16h/8h) can be used as an alternative to a constant 25°C: both regimes were equally successful in promoting germination (3) with no advantage of the alternating temperature regime (3). Germination tests should be continued for at least 42 days (6).
VII. References
1. Anonymous (1939). Quinine seed was germinated readily at the experiment station. Puerto Rico Agricultural Experiment Station, Report 1938, 27-29.
2. Anonymous (1940). Cinchona seeds lose viability rapidly. Puerto Rico Agricultural Experiment Station, Report 1940, 18-19.
3. Barton, L.V. (1947). Effect of different storage conditions on the germination of seeds of Cinchona ledgeriana Moens. Contributions from the Boyce Thompson Institute, 15, 1-10.
4. Morrison, B.Y. (1943). Quinine from seed. Agriculture in the Americas, 3, 131-133. (From Horticultural Abstracts, 1943, 13, 1533.)
5. Portères, R. (1948). Competition ou entr'aide au sein de l'espèce et de la race. Le cas des germinations de Cinchona. Comptes Rendus de l'Académie des Sciences, 227, 1114-1115.
6. Thomas, A.S. (1946). Cinchona in Uganda. Empire Journal of Experimental Agriculture, 14, 75-84.
COFFEA
|
C. arabica L. arabica |
coffee |
|
C. canephora Pierre ex Froehner [C. robusta
Linden; C. laurentii De Wild.; C. maclaudii A.Chev.; |
robusta coffee |
|
C. arabica L. var. stuhlmannii Warb.; C.
bukobensis Zimm.; C. welwitschii Pierre ex De Wild.; |
|
|
C. ugandae Cramer; [C. kouilouensis Pierre ex De
Wild.; C. quillou Wester] |
|
|
C. excelsa A.Chev. [C. dewevrei De Wild. &
Th. Dur. var. excelsa A. Chev.] |
|
|
C. liberica Bull ex Hiern [C. abeokutae Cramer;
C. klainei Pierre ex De Wild.] |
liberica coffee |
|
C. racemosa Lour |
racemosa coffee |
|
C. stenophylla G. Don |
|
I. Evidence of dormancy
A discussion of the seed storage characteristics (orthodox) of Coffee spp. is provided in the comment since these have provide substantial problem in the past. Delayed and/or low germination of under-ripe or freshly harvested seeds (3,9,30) or intact seeds (1-3,14,16-19,22,33,34) is reported frequently. A short period of after-ripening at room temperature (8-32 days) can increase the proportion of seeds germinating and reduce the time taken to germinate (18,19). Dried seeds can show particularly delayed and erratic germination (10,15,29,31). The delay to germination caused by drying has been described as secondary dormancy in Coffea spp. (29). An inhibitor to germination is reported to be present in the endocarps of the seeds (29), but others disagree (19).
II. Germination regimes for non-dormant seeds
Coffea spp.
Constant temperatures: 25°C (14,18,19,32); 30°C (6,8,20,22,26,28,33,34)
Alternating temperatures: 18°/30°C (20)
III. Unsuccessful dormancy-breaking treatments
C. arabica
Removal of seed covering structures: exocarp, mesocarp, endocarp and testa (12)
Pre-soak: 40°-45°C, 5h (16)
GA3: pre-applied, 48h, 10-1000 ppm (24); pre-applied, 48h, 0.5 x 10-3, 10-3 M, germinate at 30°C in light, 5400 lux (26); pre-applied, 48h, 10-4 M (28)
Light: white, continuous (28)
Biuret: co-applied, 2.5% (25); pre-applied, 0.5-2.5% (25)
Abscisic acid: pre-applied, 48h, 10-4 M (28)
IV. Partly-successful dormancy-breaking treatments
C. arabica
Pre-soak: 48h (16)
Pre-wash: (29)
Hydrochloric acid: pre-applied, 48h, 1 N (16)
Sulphuric acid: pre-applied, 48h, 1 N (16)
Boric acid: pre-applied, 48h, B at 10 ppm (16)
Pentothenic acid: pre-applied, 48h, 0.1% (16)
Ascorbic acid: pre-applied, 48h, 0.1% (16)
Nicotinic acid: pre-applied, 48h, 0.1% (16)
Riboflavin: pre-applied, 48h, 0.1% (16)
Inositol: pre-applied, 48h, 0.1% (16)
Thiourea: pre-applied, 48h, 1% (16)
Indoleacetic acid: pre-applied, 48h, 100 ppm (16)
Indolepropionic acid: pre-applied, 48h, 100 ppm (16)
Naphthaleneacetic acid: pre-applied, 48h, 100 ppm (16)
GA3: pre-applied, 48h, 100 ppm (16)
Copper sulphate: pre-applied, 48h, Cu at 10 ppm (16)
Manganese chloride: pre-applied, 48h, Mn at 10 ppm (16)
Zinc sulphate: pre-applied, 48h, Zn at 10 ppm (16)
Pyridoxine: pre-applied, 48h, 0.1% (16)
Removal of seed covering structures: endocarp, test for 18d (29); endocarp, test for 28d (1)
C. canephora pH: 4-6 (18,20)
Removal of seed covering structures: part of endocarp over embryo (19); part of endocarp from distal half of seed (19); part of endocarp from flat side of seed (19)
V. Successful dormancy-breaking treatments
C. arabica
Constant temperatures: 28°-30°C (33); 30°C (22,34); 30°C in dark (28)
Pre-soak: 2,4d, at 24°C (18); 24h, then warm stratification (35)
Pre-wash: 6h (16)
Light: dark, continuous (28)
Removal of seed covering structures: endocarp (2,3,5,9,17,18, 19,22,24,28,29,31,33,34); endocarp, then pre-soak, 24h (32)
Kinetin: pre-applied, 48h, 10-4, 10-5 M (28)
Thiamine: pre-applied, 48h, 0.1% (16)
Folic acid: pre-applied, 48h, 0.1% (16)
Ferrous sulphate: pre-applied, 48h, Fe at 10 ppm (16)
C. canephora
Constant temperatures: 24°-34°C in dark (20); 28°-33°C (33); 30°C (22)
Alternating temperatures: 18°/30°C (20)
Oxygen: above 21% (19)
Removal of seed covering structures: endocarp (10,18,19,21,22,23,33); endocarp, then pre-soak, 24h (32)
Pre-soak: 2,4d, at 24°C, germinate at 30°C (18)
C. excelsa
Removal of seed covering structures: endocarp, germinate at 28°-33°C (33)
C. liberica
Pre-soak: 24h, then warm stratification (35)
Removal of seed covering structures: endocarp, germinate at 28°-33°C (33)
C. stenophylla
Removal of seed covering structures: endocarp, germinate at 28°-33°C (33)
VI. Comment
Sand, paper towels (test between papers) and filter papers (test on top in petri dishes) are all suitable substrata for germination tests of Coffea spp. (4,5,8,10,14,17,19,21,22,29,31,33). A high level of moisture in the germination test substratum can delay germination (22), although coffee seeds will germinate satisfactorily in aerated water provided their endocarps have been removed (18,19). This suggests that oxygen can be a limiting factor in germination tests. If sand is used for germination tests a suitable moisture content for the sand is 10% by volume (22).
Fresh, intact, coffee seeds require between 60 and 110 days to germinate (14,18,19). The removal of the endocarps increases the proportion of seeds which will germinate and reduces the time taken to germinate by between 14 to 21 days (2,24,31) and 28 to 42 days (18,19,21). The endocarp is reported to be impermeable to water (9), but it seems more likely that the endocarp delays the uptake of moisture rather than preventing it completely. Minimum germination test periods for fresh seeds from which the endocarps have been removed is 21 days for C. arabica, 43 days for C. canephora, 46 days for C. excelsa and C. Stenophylla, and 53 days for C. liberica (33). Endocarps should be removed by hand: mechanical removal is damaging (12).
Drying the seeds results in erratic germination in subsequent tests (10,15,29,31). Even with endocarp removal dried seeds take longer to germinate than fresh seeds (15,31): the cause of this appears to be a delay to imbibition in the dried seeds (14). Dried seeds from which endocarps have been removed require 90 days for germination (5,7). Even so, the total proportions of seeds germinating may be low. The previously dried seeds which remain ungerminated at the end of germination tests are reported to be dormant (29). Treatment with kinetin can be promotory in such cases (28), but gibberellin and light treatments are reported to inhibit coffee seed germination (24,26,28). 29°C is reported to be the most suitable constant temperature for seed germination (20).
Consequently it is suggested here that coffee seeds be tested for germination, after the endocarps have been removed, at 30°C in the dark for approximately 100 days, or more. Where dormancy is a problem it is suggested that a 48 hour pre-treatment in 10-4 or 10-5 M kinetin be provided.
It seems necessary to add some notes at this point concerning the seed storage behaviour of Coffea spp. Despite a number of reports to the contrary, Coffea spp. show orthodox seed storage behaviour. That is, for air-dry seeds longevity is increased by reducing seed moisture content (3-8,11,18,20,21,31,33) - although of course, as with seeds of other orthodox species, in the presence of sufficient oxygen coffee seed survival periods at moisture contents close to fully imbibed can be substantial and greater than those at intermediate moisture contents (31) - see Chapter 1. One way in which we are able to demonstrate orthodox seed storage behaviour in Coffea spp. is to calculate the value of the constant CW of the improved viability equation - see the 1982 Report - which describes the relative improvement to longevity obtained by reducing seed moisture content. The value obtained (3.5, calculated from reference 7) is similar to that for onion (Allium cepa L.).
Nevertheless there are a number of problems. Although one report has shown that seed moisture content can be reduced to 5% without damage to the seeds (8), certain other reports suggest damage to seeds dried below 8% moisture content (5,6,21,27). It is possible that many of these reports are due to failure of the very dry seeds to imbibe and germinate within the duration of the germination test; that is germination test periods may be adequate for fresh and partly-dried seeds but inadequate for the very dry seeds. For example, within the range of 5 to 10% seed moisture content storage at the highest moisture content was reported to be preferable to storage at lower moisture contents in one investigation, but this conclusion was based on germination tests which were concluded after only 8 days (8).
Problems, however, have also been reported at low storage temperatures. For example, for coffee seeds at 13 to 15% moisture content a storage temperature of 2° to 5°C has been reported to result in poorer germination than storage at 10°C (8,31). Moreover, dry seeds stored at -18°C for 2 months or -10° to -16°C for 10 days showed reduced germination (33), whilst seeds dried to 5 to 7% moisture content and stored at -19° to -15°C for 5 months failed to germinate at all in a subsequent germination test (21).
Thus whilst we are confident that Coffea spp. show orthodox seed storage behaviour, storage under IBPGR preferred conditions cannot be recommended until the above problems have been satisfactorily resolved. We suggest that the following factors should be taken into account when attempting to resolve these problems. First, germination test environment and duration must be sufficient to enable the very dry seeds to germinate. This means that endocarp removal and a very long test duration are essential. Secondly, when seeds are dried and moisture content determined the experimeter must ensure that embryo moisture content (that is, not just moisture content of the whole seed) is below the levels at which freezing damage would be expected. Either allow seed moisture content to equilibrate throughout the seeds after drying by maintaining at around 15°C for some time before storing at sub-zero temperatures, or remove the seed covering structures before drying and dry and store the embryos only. Finally, it may be advisable to humidify the very dry seeds prior to germination tests.
VII. References
1. Anonymous (1951). Studies in the germination of coffee seeds. Fourth Annual Report of the Research Department of the Indian Coffee Board (1950-1951), Bulletin No. 4, 30-32.
2. Anonymous (1952). Studies in the germination of coffee seeds. Fifth Annual Report of the Research Department of the Indian Coffee Board (1951-1952), Bulletin No. 5, 46-49.
3. Anonymous (1953). A semente de café. Bol. Super. Serv Café Sao Paulo, 28, 27-28. (From Horticultural Abstracts, 1953, 23, 4603.)
4. Arcila-Pulgarin, J. (1977). Influence of drying temperature on the germination of coffee seeds. Indian Coffee, 41, 261,264.
5. Bacchi, O. (1955). [Sun-drying of coffee seeds.] Bragantia, 14, 225-236.
6. Bacchi, O. (1956). [Further experiments on sun-drying coffee seed.]
Bragantia, 15, 83-91.
7. Bacchi, O. (1958). [Seed storage study. IV. Coffee.] Bragantia, 17, 261-270.
8. Bendana, F.E. (1962). The physiology of coffee seeds. I. Problems related to storage. Coffee, Turrialba, 4, 73-75.
9. Bendana, F.E. (1962). The physiology of coffee seeds. II. Factors retarding germination, parchment. Coffee, Turrialba, 4, 76-79.
10. Bouharmont, P. (1971). La conservation des graines de caféiers destineés à la multiplication au Cameroun. Café Cacao Thé, 15, 202-210.
11. Carelli, M.L.C. and Monaco, L.C. (1977). [Racemosa coffee seed conservation.] Bragantia, 36, 31-34.
12. Coste, R. (1955). Les caféiers et les cafés dans le monde. In Les Caféiers, pp. 66. Larose, Paris.
13. Couturon, E. (1980). Le maintein de la viabilité des graines de caféiers par le controle de leur teneur en eau et de la temperature de stockage. Café Cacao Thé, 24, 27-32.
14. Goldbach, H. and Vizcarra, A.H. (1980). Some observations on tetrazolium-testing of coffee seed (Coffea arabica and C. canephora). Turrialba, 30, 223-226.
15. Gonzalez, J.A. (1973). Germinacion de la semilla de Coffea arabica variedades Bourbon y pacas almacenada en polietileno a distintas humedades. Instituto Salvadoreno de Investigaciones del Cafe. Boletin Informativo Suplemento No. 28, 24 pp.
16. Gopal, N.H. and Ramaiah, P.K. (1971). Studies on hastening of germination of arabica coffee seed and further growth of the seedlings. I. Hastening of germination. Indian Coffee, 35, 459-464.
17. Gopal, N.H. and Ramaiah, P.K. (1972). Studies on the physiology of germination of coffee seed. I. Observations on sprouting. Journal of Coffee Research, 2, 14-19.
18. Huxley, A. (1962). Physiological and ecological investigation with coffee seeds and seedlings in Uganda. Ph.D. Thesis, University of Reading.
19. Huxley, P.A. (1964). Some factors which can regulate germination and influence viability of coffee seeds. Proceedings of the International Seed Testing Association, 29, 33-60.
20. Huxley, P.A. (1964). The effect of hydrogen-ion concentration, temperature and seed-drying method on the germination of coffee seeds. Proceedings of the International Seed Testing Association, 29, 61-70.
21. Huxley, P.A. (1964). Investigations on the maintenance of viability of Robusta coffee seed in storage. Proceedings of the International Seed Testing Association, 29, 423-444.
22. Huxley, P.A. (1965). Coffee germination test recommendations and defective seed types. Proceedings of the International Seed Testing Association, 30, 705-714.
23. Kamau, I.N. (1975). Coffee seeds and their care. Kenya Coffee, Research Notes, 306 pp. Coffee Research Station, Ruiru, Kenya.
24. Maestri, M. and Vieira, C. (1961). [A note on the reduction of the percentage of coffee seed (Coffea arabica L. var. bourbon) by the action of gibberellic acid.] Rev. Ceres, 11, 247-249. (From Horticultural Abstracts, 1963, 33, 3995.)
25. Naik, C.S.K., Raju, T. and Rao, W.K. (1980). Effect of biuret on seed germination and growth of coffee seedlings. Journal of Coffee Research, 10, 47-52. (From Horticultural Abstracts, 1981, 51, 3107.)
26. Takaki, M. and Dietrich, S.M.C. (1980). Effects of GA3 and light on polysaccharide levels and metabolism in germinating coffee seeds. Journal of Experimental Botany, 31, 1643-1649.
27. Ultee, A.J. (1933). Storage of coffee seed. Archiv v Koffiecult Nederland Indié, 7, 75-83. (From Biological Abstracts, 10, 4111.)
28. Valio, I.F.M. (1976). Germination of coffee seeds (Coffea arabica L. cv. mundonovo). Journal of Experimental Botany, 27, 983-991.
29. Velasco, J.R. and Gutierrez, J. (1974). Germination and its inhibition in coffee. Philippine Journal of Science, 103, 1-11.
30. Visweshwara, S. and Raju, K.S.K. (1972). Seed germination in coffee. Indian Coffee, 36, 278-285, 290.
31. Vossen, H.A.M. van der (1979). Methods of preserving the viability of coffee seed in storage. Seed Science and Technology, 7, 65-74.
32. Wellman, F.L. (1961). Coffee, botany, cultivation and utilisation, pp. 122-128. Leonard Hill, London.
33. Wellman, F.L. and Toole, V.K. (1960). Coffee seed germination as affected by species, diseases and temperature. Proceedings of the Caribbean Section, American Society of Horticultural Sciences, 4, 1-6.
34. Went, F.W. (1957). The experimental control of plant growth. Chronica Botanica, 17, 164-168.
35. Riley, J.M. (1981). Growing rare fruit from seed. California Rare Fruit Growers Yearbook, 13, 1-47.
