The Saxifragaceae comprise more than 1000 species of herbaceous plants and shrubs within about 70 to 100 genera. The most important genus is Ribes which provides edible fruits (currants and gooseberries); some authorities classify the genus Ribes in the Grossulariaceae. The fruits are capsules or many-seeded berries. Seed storage behaviour is orthodox. For example, Ribes spp. are maintained in the long-term seed store at the Wakehurst Place Gene Bank.
SEED DORMANCY AND GERMINATION
The seeds contain abundant endosperm and dormancy can be a considerable problem. B.R. Atwater classifies seed morphology as endospermic seeds with axillary miniature embryos (see Table 17.1, Chapter 17). Pre-chill treatments and alternating temperature test regimes (particularly when combined) tend to promote seed germination provided the test duration is sufficient.
Detailed information on seed dormancy and germination is provided in this chapter for the genus Ribes (including synonyms within Chrysobotrya and Grossularia). A brief summary of suggested germination test procedures and dormancy-breaking treatments for other species is provided in Table 66.1. In addition the algorithm below for the Grossulariaceae may be helpful in developing suitable germination test procedures for species which can be so classified.
RBG Kew Wakehurst Place algorithm (Grossulariaceae)
The first step in the algorithm is to test seeds at constant temperatures of 11°C and 16°C with light applied for 12h/d. If neither constant temperature regime promotes full germination and there is a trend in germination response to constant temperatures then test further samples of seeds at more extreme constant temperatures. For example, if the proportion of seeds germinating at 11°C is greater than that at 16°C then test a further sample of seeds at a constant temperature of 6°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 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.
If the second step of the algorithm does not result in full germination then the third step is to pre-chill a further sample of seeds at 2° to 6°C for 8w and then test in the most appropriate temperature regime determined from a comparison of the results of steps one and two.
TABLE 66.1 Summary of germination test recommendations for species within the Saxifragaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Heuchera sanguinea Engelm.
|
TP |
20°/30°C; 20°C |
21d |
potassium nitrate, pre-chill |
ISTA |
|
TP |
20°/30°C |
18d |
light, potassium nitrate |
AOSA |
|
|
|
20°C |
21d |
light, potassium nitrate, 0.2% |
Atwater |
RIBES
|
R. americanum Mill. [R. floridum
L'Her.] |
American blackcurrant |
|
R. aureum Pursh [R. tenuiflorum Lindl.;
Chrysobotrya aurea Rydb.] |
golden currant |
|
R. cynosbati L. [R. gracile Michx.;
Grossularia cynosbati (L.) Mill.] |
pasture gooseberry, prickly gooseberry |
|
R. Grossularia L. [R. reclinatum L.;
Grossularia reclinata Mill.] |
English gooseberry |
|
R. missouriense Nutt. [R. gracile Pursh not
Michx.; Grossularia missouriensis (Nutt.) Cov. & Britt.] |
Missouri gooseberry |
|
R. multiflorum Kid. |
white currant |
|
R. nigrum L. |
European blackcurrant |
|
R. odoratum Wendl. [R. fragrans Lodd.;
Chrysobotrya odorata Rydb.] |
Missouri currant, buffalo currant, golden currant, flowering
currant |
|
R. Roezli Regel |
|
|
R. rotundifolium Michx. [Grossularia
rotundifolia (Michx.) Cov. & Britt.] |
round-leaf gooseberry |
|
R. sativum Syme [R. vulgare Jancz. not Lam.;
R. rubrum Auth. not L.; R. rubrum var sativum
Reichb.] |
common currant, garden currant |
I. Evidence of dormancy
The germination of seeds of Ribes spp. is often irregular, unpredictable, and substantially delayed as a result of dormancy (1,2,5-7,11). Consequently seed dormancy is a major problem for breeders (1). Dormancy in R. aureum has been described as extreme (6). In R. missouriense seed germination problems are reported to result from both a seed coat effect and from dormancy within the extracted seeds (9).
II. Germination regimes for non-dormant seeds
R. americanum
Alternating temperatures: 20°/30°C (night/day) (3)
R. aureum
Alternating temperatures: 20°/30°C (night/day) (3,6)
R. cynosbati
Alternating temperatures: 20°/30°C (night/day) (3)
R. missouriense
Alternating temperatures: 20°/30°C (night/day) (3,9)
R. odoratum
Alternating temperatures: 20°/30°C (night/day) (3)
R. rotundifolium
Alternating temperatures: 10°/25°C (night/day) (3,5)
III. Unsuccessful dormancy-breaking treatments
R. americanum
Constant temperatures: 15°C (5)
R. aureum
Constant temperatures: 20°C (6)
Alternating temperatures: 20°/30°C (night/day) (6)
R. cynosbati
Constant temperatures: 20°C (5)
Alternating temperatures: 15°/32°C, 20°/32°C (night/day) (5)
R. multiflorum
Scarification: concentrated sulphuric acid, 1,2h (12)
R. nigrum
Constant temperatures: 24°C, dark (1)
Alternating temperatures: 10°/4°C (12h/12h) (1)
Scarification: concentrated sulphuric acid, 1,2h (12)
R. rotundifolium
Constant temperatures: 20°C (5)
Alternating temperatures: 20°/32°C (night/day) (5)
R. sativum
Scarification: concentrated sulphuric acid, 1,2h (12)
Ribes spp.
Scarification: concentrated sulphuric acid, 15 min-2h (12)
IV. Partly-successful dormancy-breaking treatments
R. americanum
Pre-chill: 5m (2); 5°-7°C, 200d, germinate at 20°/30°C (night/day) (3)
Warm stratification: 20°/30°C (night/day), 60d, then pre-chill, 5°C, 90-120d, germinate at 20°/30°C (night/day) (3)
R. aureum
Constant temperatures: 25°C (6)
Pre-chill: 5°C, 90d, germinate at 20°/30°C (night/day) (3); 2°-4°C, 2m, germinate at 20°/30°C (night/day) (6)
R. cynosbati
Constant temperatures: 5°C, 10°C, 15°C (5)
Alternating temperatures: 10°/25°C (night/day) (5)
Pre-chill: 5°C, 90d, germinate at 20°/30°C (night/day) (3)
Warm stratification: 25°C, 32°C, 2m, germinate at 10°/25°C (5)
R. missouriense
Constant temperatures: 15°C (5)
Pre-chill: 5°C, 90d, germinate at 20°/30°C (night/day) (9)
Warm stratification: 20°/30°C (night/day), 90d, then pre-chill, 5°C, 90d, germinate at 20°/30°C (night/day) (9)
R. nigrum
Alternating temperatures: 24°/4°C (12h/12h, 16h/8h, 8h/16h) (1); 18°/4°C, 30°/4°C, 24°/15°C, 24°/18°C (12h/12h) (1); 24°/4°C (12h/12h, 24h/24h, 48h/48h, 72h/72h, 48h/24h, 24h/48h, 72h/24h, 24h/72h), 12w, then 24°/4°C (12h/12h) (1)
Pre-chill: 4°C, 2-28w, germinate at 24°/4°C (12h/12h) (1); 4°C, 2-28w, then scarify, notch, germinate at 24°/4°C (12h/12h) (1); 4°C, 12w, then scarify, 50% sulphuric acid, 5 min, germinate at 24°/4°C (12h/12h) (1)
Warm stratification: 24°C, 12w, germinate at 24°/4°C (12h/12h) (1)
GA3: pre-applied, 0.02-0.1%, then pre-chill 2°-3°C, 140d (8) Removal of seed covering structures: notch seed coat with razor (1)
R. odoratum
Warm stratification: 20°/30°C (night/day), 60d, then pre-chill, 5°C, 60-90d, germinate at 20°/30°C (night/day) (3)
R. rotundifolium
Constant temperatures: 5°C, 10°C, 15°C (5)
Alternating temperatures: 10°/25°C, 15°/32°C (night/day) (5)
Warm stratification: 25°C, 32°C, 2m, germinate at 10°/25°C (night/day) (5)
Scarification: concentrated sulphuric acid, 35 min (5)
V. Successful dormancy-breaking treatments
R. aureum
Warm stratification: c. 2w, then pre-chill, 2°-4°C, 2m, germinate at 20°/30°C (night/day) (6)
R. cynosbati
Pre-chill: 5m (2)
R. Grossularia
Pre-chill: 0°-10°C, 90-120d (4); 3°C, 3-4m (7)
R. missouriense
Pre-chill: 5°C, 90d, germinate at 20°/30°C (night/day) (3)
R. Roezli
Pre-chill: 2.5°C, 3.5m (11)
R. sativum
Pre-chill: (10); 3°C, 3-4m (7)
VI. Comment
Seed dormancy in Ribes spp. can vary considerably between accessions produced in different years (1). Although a number of treatments have been reported as successful (above), the reports derive mainly from glasshouse sowings and we suspect that the most dormant seeds failed to germinate. Prolonged pre-chilling and alternating temperature germination test regimes are the most effective dormancy-breaking treatments (1-7,9,10,11). Alternating temperatures of 24°-25°/4°-10°C are the most effective in promoting germination (1,3,5); the higher temperature should be applied for the greater part - 16 hours - of the diurnal cycle (1). Although prolonged pre-chilling - 3 to 5 months at between 2° and 4°C - may be sufficient for some seed lots of Ribes spp. (2,7,10,11), it fails to promote complete germination in accessions of R. americanum, R. aureum, R. cynosbati, R. nigrum and R. odoratum (1,3,6,9).
There appears to be no satisfactory procedure at present for promoting the germination of all dormant seeds within Ribes spp., and it has been suggested that viability can only be determined by using a tetrazolium test (6), but the authors provided no details of the procedures to be followed. More work is required before a completely satisfactory procedure can be advised. We suggest that investigations should concentrate on alternating temperature regimes. Three different types of treatment may be useful when combined; warm stratification, then pre-chill, then an alternating temperature for germination. Alternatively a single alternating temperature regime may be sufficient.
In the meantime the following general procedure is suggested. First notch the seed coat using a razor, then pre-chill at 3°-5°C for 2-4 months, and finally transfer to an alternating temperature regime of 24°/4°C (16h/8h) - for at least a further 6 to 8 weeks. For the least dormant accessions, or where some germination is required in a short period of time, the above alternating temperature regime alone can be provided.
VII. References
1. Adam, J. and Wilson, D. (1967). Factors affecting the germination of black currant seed. Report of the Long Ashton Research Station for 1966, pp. 96-103.
2. Adams, J. (1927). The germination of the seeds of some plants with fleshy fruits. American Journal of Botany, 14, 415-428.
3. Anonymous (1948). Ribes L. Currant, gooseberry. In Woody Plant Seed Manual, pp. 317-320. USDA Forest Service, Miscellaneous Publication No. 654.
4. Barton, L.V. (1939). Experiments at Boyce Thompson Institute on germination and dormancy in seeds. Scientific Horticulture, 7, 186-193.
5. Fivaz, A.E. (1931). Longevity and germination of seeds of Ribes, particularly R. rotundifolium, under laboratory and natural conditions. USDA, Technical Bulletin No. 261, 40 pp.
6. Heit, C.E. (1971). Propagation from seed. Part 22: Testing and growing western desert and mountain shrub species. American Nurseryman, 133, 10-12, 76-89.
7. Keep, E. (1975). Currants and gooseberries. In Advances in fruit breeding (eds. J. Janick and J.N. Moore), pp. 197-268, Purdue University Press, Indiana.
8. Khokhlova, V.V. (1979). [Effect of gibberellin on black currant seed germination.] Fiziologiya i Biokhimiya Kul'turnykh Rastenii, 11, 605-610. (From Seed Abstracts, 1980, 3, 3114.)
9. Krepting, L.W. and Roe, E.I. (1949). The role of some birds and mammals in seed germination. Ecological Monographs, 19, 269-286.
10. Pammel, L.H. and King, C.M. (1929). Germination of trees and shrubs. Proceedings of the Iowa Academy of Science, 36, 201-211.
11. Quick, C.R. (1936). Chemical control of harmful fungi during stratification and germination of seeds of Ribes roezli. Phytopathology, 26, 694-697.
12. Tukey, H.B. (1924). Studies of fruit seed storage and germination. New York State Agricultural Experiment Station Bulletin 509, 19 pp.
