The Ericaceae comprise roughly 1500 species of trees and shrubs within about 70 genera, several of which provide edible fruits (e.g. Vaccinium oxycoccus L., European cranberry). Some authorities classify Vaccinium and related genera as Vacciniaceae. The fruits are either capsules, berries or drupes. Seed storage behaviour is orthodox.
SEED DORMANCY AND GERMINATION
B.R. Atwater classifies seed morphology as endospermic seeds with axillary linear embryos (see Table 17.1, Chapter 17). Dormancy can be a severe problem: sometimes very long pre-chill treatments may be given, but light and GA3 are alternative treatments. Detailed information is provided for the genus Vaccinium in this chapter (including synonyms within Cyanococcus and Oxycoccus). A limited number of additional recommendations for germination test conditions and dormancy-breaking treatments are summarised in Table 36.1. The algorithm below may be helpful in developing suitable seed germination test regimes for other species.
RBG Kew Wakehurst Place algorithm
The first step of the algorithm is to test the seeds at constant temperatures of 16°C and 26°C with light applied for 12h/d in each case.
If this is not successful in promoting full germination then the second step of the algorithm is to pre-chill the seeds at 2° to 6°C for 8w and then test for germination at the constant temperature which resulted in the greater proportion of seeds germinating in step one.
TABLE 36.1 Summary of germination test recommendations for species within the Ericaceae
|
Species and Authority |
Substrate |
Temperature |
Duration |
Additional directions |
Source |
|
Arbutus unedo L. |
|
|
30d |
pre-chill, 1°-5°C, 30-60d |
Riley |
|
Calluna vulgaris (L.) Hull |
|
20°C |
28d |
potassium nitrate, 0.2% |
Atwater |
|
Gaultheria shallon |
|
|
30d |
pre-chill, 1°-5°C, 30-60d |
Riley |
|
Gaylussacia spp. |
|
|
30d |
pre-soak, 24h, then pre-chill/warm stratification,
cycle |
Riley |
|
Rhododendron ferrugineum L. |
|
20°C |
28d |
GA, 800ppm |
Atwater |
|
Rhododendron spp. |
TP; BP |
20°/30°C; 25°C |
21d |
light |
AOSA |
VACCINIUM
|
V. angustifolium Ait. [V. pensylvanicum var
angustifolium Gray] |
lowbush blueberry |
|
V. ashei Reade |
rabbiteye blueberry |
|
V. canadense Kalm |
|
|
V. corymbosum L. [Cyanococcus corymbosus
Rydb.] |
highbush or swamp blueberry |
|
V. macrocarpon Ait. [Oxycoccus macrocarpus
Pers.] |
large or American cranberry |
|
V. oxycoccus L. [Oxycoccus palustris Pers.;
Oxycoccus oxycoccus MacM.] |
small or European cranberry |
|
V. uliginosum |
|
|
V. vitis-idaea L. var minus Lodd. |
foxberry, mountain cranberry |
I. Evidence of dormancy
Seed dormancy in Vaccinium spp. is often manifested by low, slow and erratic germination, as observed in V. angustifolium (1), V. ashei (5,16), V. canadense (3), V. corymbosum (7,16,19), V. macrocarpon (9,10,18) and V. oxycoccus (18). In particular, seed dormancy in V. macrocarpon has been the subject of much attention (9-12). Although seeds of Vaccinium spp. have often been stored moist (at freezing or sub-freezing temperatures) for short-term storage (1,5,8,13,17,20), the seeds are orthodox and can thus be stored satisfactorily at a low moisture content at low temperatures for long-term storage (7).
II. Germination regimes for non-dormant seeds
-
III. Unsuccessful dormancy-breaking treatments
V. ashei
Constant temperatures: 16°C in fluorescent and incandescent light, 73 x 10-6 mol m-2 s-1, 12h/d (4)
Pre-chill: 4°C, dark, 1-4w (4)
GA3: pre-applied, 24,48h, 100-1000 ppm, to seeds pre-chilled in fruits, 4°C, 75d (5)
GA4/7: pre-applied, 48h, 100 ppm (4); pre-applied, 24,48h, 100-1000 ppm, to seeds pre-chilled in fruits, 4°C, 75d (5); pre-applied, 48h, 100 ppm plus 100 ppm benzyladenine (4)
V. canadense
Pre-chill: over winter (3)
V. corymbosum
Alternating temperatures: 0°/21°C (4d/4d), 16,32,64d, then 17°C (21)
Pre-chill: 0°C, 8-64d (21); 2°C, 3m (20); 2°C, 3m, then pre-soak, 48h (20); 2°C, 3m, then sodium hypochlorite, pre-applied, 4-48h, 1% (20)
Light: dark, at 18°/21°-27°C (night/day) (19); dark, at 17°C, 24°C (21); white, continuous, at 17°C, 24°C (21); white, 24h, then dark, at 24°C (21); red, continuous, at 17°C, 24°C (21); red, 24h, then dark, at 24°C (21)
Potassium nitrate: co-applied, 0.2% (21)
Coumarin: co-applied, 10-5 M (21)
V. macrocarpon
Pre-chill: 3°-4°C, 8w (18); 3°-4°C, 8w, in fruit (18)
Light: dark, at 25°C (9,10,11)
GA3: pre-applied, 20h, 300 ppm, germinate at 25°C in dark (10)
Scarification: concentrated sulphuric acid, 5-20 min, germinate at 25°C in dark (10)
Removal of seed covering structures: prick (12); seed coat (18); seedcoat, then pre-chill, 3°-4°C, 8w (18)
V. oxycoccus
Pre-chill: 3°-4°C, 8w (18); 3°-4°C, 8w, in fruit (18)
Removal of seed covering structures: seed coat (18); seed coat, then pre-chill, 3°-4°C, 8w (18)
V. uliginosum pH: 3-9 (6)
V. vitis-idaea var minus
Pre-chill: -2°C, 37d (14)
Scarification: sulphuric acid, 0.1 N, 5 min (14)
IV. Partly-successful dormancy-breaking treatments
V. angustifolium
Constant temperatures: 19°-21°C (1); 21°C, in soil (15)
Alternating temperatures: 16°/18°C, dark/light (16h/8h) (2)
V. ashei
Alternating temperatures: 18°/21°-27°C, dark/light (night/day) (16)
Pre-chill: 100d (7)
Light: 18x10-6 mol m-2 s-1, 30-60 min/d, at 16°C (4)
Pre-soak: 48h, germinate at 16°C in light, 1h/d, 18x10-6 mol m-2 s-1
V. canadense
Light: test in soil (3)
V. corymbosum
Alternating temperatures: 10°/25°-32°C (night/day) in light or dark (21); 18°/21°-27°C, dark/light (night/day) (16,19); 0°/21°C (4d/4d), 16-64d, then 10°/25°-32°C in light (21)
Pre-chill: 100d (7)
Light: white, continuous, at 10°/25°-32°C (21); white, 24h, then dark, at 17°C or 10°/25°-32°C (21); red, continuous, at 10°/25°-32°C (21); red, 24h, then dark, at 17°C or 10°/25°-32°C (21)
V. macrocarpon
Pre-chill: 3°-5°C, 3m, in fruit, germinate at 15.5°C (8)
Light: white, 1000 fc, 1,3d, then dark, at 25°C (9); white, continuous, 4.3, 43 lux, at 25°C (11); white, 4300 lux, 1,3d, then dark, at 25°C (10)
GA3: pre-applied, 20h, 300 ppm, germinate at 25°C in light, 1,3d, 4300 lux, then dark (10); pre-applied, 20h, 10-100 ppm, germinate at 25°C in dark (11)
Scarification: concentrated sulphuric acid, 25-35 min, germinate at 25°C in dark (10); concentrated sulphuric acid, 5-35 min, then GA3, pre-applied, 20h, 300 ppm, germinate at 25°C in dark (10) Removal of seed covering structures: prick, germinate at 25°C in dark (11); prick, then GA3, pre-applied, 20h, 10-1000 ppm, germinate at 25°C in dark (11); prick, then kinetin, pre-applied, 20h, 10 ppm, germinate at 25°C in dark (11) Ether: pre-applied, 20 min, 100% atmosphere (18)
V. oxycoccus
Ether: pre-applied, 20 min, 100% atmosphere (18)
V. uliginosum
Pre-chill: 3m, germinate at 25°C in light (6)
Light: (6)
V. vitis-idaea var minus
Constant temperatures: 21°C in light, in soil (14)
V. Successful dormancy-breaking treatments
V. macrocarpon
Pre-chill: 3°-5°C, 3m, in fruit, germinate at 21°C, 26.5°C (8); 2°C, 3m, in fruit, germinate at 18°/24°C, dark/light (night/day) (13); 1°C, 5°C, 30-60d, germinate at room temperature in diffuse light (17)
Light: 1000 fc, 5-20d, then dark, at 25°C (9); 4300 lux, 5-20d, then dark, at 25°C (10); continuous, 430, 4300 lux, at 25°C (11); 4300 lux, 10d, then dark, at 25°C (12); diffuse, at room temperature (17)
GA3: pre-applied, 20h, 300, 500 ppm, germinate at 25°C in light (10, 11); pre-applied, 20h, 1000 ppm, germinate at 25°C in dark (11)
Removal of seed covering structures: seed coat, germinate on agar (18); prick, germinate at 25°C in light, continuous, 4300 lux (11)
V. oxycoccus
Removal of seed covering structures: seed coat, germinate on agar (18)
VI. Comment
Light is an essential component of any successful dormancy-breaking regime for seeds of Vaccinium spp. (2,4,6,9-12,17,19,21), but high light intensities may reduce germination - for example, 73x10-6 mol m-2 s-1 applied for 12 hours per day (4). The second essential component is an alternating temperature regime (16,19,21). These two factors account for the observations that seeds of Vaccinium spp. germinate readily in glasshouse sowings (2,15,17) - despite the reports of low, slow and erratic germination already noted.
Although 3 month pre-chill treatments had been thought to be effective in promoting loss in dormancy and had consequently been advocated as suitable short-term storage environments (5,7,8,13,20), they have subsequently been shown to be either comparatively ineffective in breaking dormancy (3,18,21) - for example, only increasing germination by 0-8% (17) - or damaging to germination (4,14,20). Chemical treatments - such as potassium nitrate (21), GA4/7 (4,5) or coumarin (21) - are generally ineffective in breaking dormancy, but GA3 can, apparently, substitute for the effect of light when pre-applied for 20 hours at 1000 ppm (11).
From limited investigations it would appear that 18°/27°C is a suitable alternating temperature germination test regime (16,19). This is sufficiently close to the widely used laboratory germination test regime of 20°/30°C (16h/8h) to suggest that seeds of Vaccinium spp. be tested for germination on top of filter paper in this regime with light applied in the manner described in Chapter 6. For the most dormant seeds, a 20 hour pre-treatment with 500 ppm GA3 is satisfactory (10,11) and is suggested as an additional treatment.
VII. References
1. Aalders, L.E. and Hall, I.V. (1975). Germination of lowbush blueberry seeds stored dry and in fruit at different temperatures. HortScience, 10, 525-526.
2. Aalders, L.E. and Hall, I.V. (1979). Germination of lowbush blueberry seeds as affected by sizing, planting cover, storage, and pelleting. Canadian Journal of Plant Science, 59, 527-530.
3. Adams, J. (1927). The germination of the seeds of some plants with fleshy fruits. American Journal of Botany, 14, 415-428.
4. Austin, M.E. and Cundiff, J.S. (1978). Factors affecting rabbiteye blueberry seed germination. Journal of the American Society for Horticultural Science, 103, 530-533.
5. Ballington, J.R., Galletta, G.J. and Pharr, D.M. (1976). Gibberellin effects on rabbiteye blueberry seed germination. HortScience, 11, 410-411.
6. Butkene, Z.P. and Butkus, V.F. (1980). [Biological and biochemical characteristics of blueberry. 2. Effect of the duration and method of stratification, time of seed harvest, temperature, light, substrate and medium pH on seed germination.] Trudy Akad. Nauk. Lit. SSR, C, 3, 45-55. (From Seed Abstracts, 1981, 4, 1197.)
7. Darrow, G.M. and Scott, D.H. (1954). Longevity of blueberry seed in cool storage. Proceedings of the American Society for Horticultural Science, 63, 271.
8. Demoranville, I.E. (1974). The effect of temperature on germination of cranberry seeds. Cranberries, 38, 7.
9. Devlin, R.M. and Karczmarczyk, S.J. (1974). The effect of light on cranberry seed germination. Cranberries, 38, 3, 16.
10. Devlin, R.M. and Karczmarczyk, S.J. (1975). Effect of light and gibberellic acid on the germination of 'Early Black' cranberry seeds. Horticultural Research, 15, 19-22.
11. Devlin, R.M. and Karczmarczyk, S.J. (1977). Influence of light and growth regulators on cranberry seed dormancy. Journal of Horticultural Science, 52, 283-288.
12. Devlin, R.M., Karczmarczyk, S.J. and Deubert, K.H. (1976). The influence of abscisic acid in cranberry seed dormancy. HortScience, 11, 412-413.
13. Greidanus, T., Rigby, J.B.F. and Dana, M.N. (1971). Seed germination in cranberry. Cranberries, 36, 13.
14. Hall, I.V. and Beil, C.E. (1970). Seed germination, pollination, and growth of Vaccinium vitis-idaea var. minus Lodd. Canadian Journal of Plant Science, 50, 731-732.
15. Hall, I.V., Forsyth, F.R., Aalders, L.E. and Jackson, L.P. (1972). Physiology of the lowbush blueberry. Economic Botany, 26, 68-73.
16. Hellman, E.W. and Moore, J.N. (1983). Effect of genetic relationship to pollinizer on fruit, seed, and seedling parameters in highbush and rabbiteye blueberries. Journal of the American Society for Horticultural Science, 108, 401-405.
17. Paglietta, R. (1977). Cranberry seed storage trials. Acta Horticulturae, 61, 211-215.
18. Rayner, M.C. (1929). The biology of fungus infection in the genus Vaccinium. Annals of Botany, 43, 56-70.
19. Scott, D.H. and Draper, A.D. (1967). Light in relation to seed germination of blueberries, strawberries and Rubus. HortScience, 2, 107-108.
20. Scott, D.H. and Ink, D.P. (1955). Treatments to hasten the emergence of seedlings of blueberry and strawberry. Proceedings of the American Society for Horticultural Science, 66, 237-242.
21. Stushnoff, C. and Hough, L.F. (1968). Response of blueberry seed germination to temperature, light, potassium nitrate and coumarin. Proceedings of the American Society for Horticultural Science, 93, 260-266.
