CHAPTER 62. ROSACEAE

The Rosaceae comprise more than 3000 species of trees, shrubs and herbaceous plants within about 115 genera. The most important genera are those which provide edible fruits (e.g. Eriobotrya japonica Lindl., loquat). Fruit structure is diverse, viz: achenes, follicles, hips, pomes or drupes. Seed storage behaviour is orthodox, although the storage behaviour of loquat has not been clarified.

SEED DORMANCY AND GERMINATION

The seeds are usually non-endospermic and dormancy can be a considerable problem. B.R. Atwater classifies seed morphology as non-endospermic seeds with axile foliar embryos within a woody seed coat and an inner semi-permeable layer (see Table 17.2, Chapter 17). Although the several layers of seed covering structures can prevent or delay germination, embryo dormancy can also be a considerable problem. Typical methods of promoting germination include scarification, chipping or removing the seed covering structures and pre-chilling: considerable pre-chill durations may be necessary to promote full germination of the more dormant seed populations.

Detailed information on seed dormancy and germination is provided in this chapter for the genera Fragaria, Prunus (including synonyms within Amygdalus, Armeniaca, Cerasus, Laurocerasus, Padus and Persica), Pyrus (including synonyms within Aronia, Malus and Mespilus) and Rubus. Further recommendations for suitable germination test procedures and dormancy-breaking treatments are summarised in Table 62.1. In addition the two algorithms below (for herbaceous and woody species respectively) may be helpful in developing suitable germination test procedures.

RBG Kew Wakehurst Place algorithm for herbaceous rosaceous species

The first step in the algorithm for seeds of herbaceous species is to test at constant temperatures of 16°C, 21°C and 26°C with light applied for 12h/d. If full germination has not been achieved and the results suggest a trend of germination response to constant temperatures then further samples of seeds are tested at more extreme constant temperatures. For example, if a greater proportion of seeds germinate at 16°C than at the two higher constant temperatures, test two further samples of seeds at constant temperatures of 6°C and 11°C with light applied for 12h/d.

If full germination has not been achieved in any of the above constant temperature regimes 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 phase of each cycle spent at the upper temperature.

If full germination has not been promoted, the third step of the algorithm is to estimate viability using a tetrazolium test (see Chapter 11, Volume I).

If the result of the tetrazolium test indicates that the failure to achieve full germination is due to the presence of dead seeds and that one of the above regimes promoted the germination of all, or almost all, the viable seeds, then this regime is used for all subsequent germination tests. If, however, the result of the tetrazolium test indicates that dormancy has not been broken by the regimes applied so far in the algorithm, then experiment with modifications to the above regimes. Clues to possible satisfactory dormancy-breaking treatments and promotory germination test environments can be obtained from the information provided for four genera in this chapter and from Table 62.1.

RBG Kew Wakehurst Place algorithm for woody rosaceous species

The first step in the algorithm is to pre-chill samples of seeds for 8, 12 and 24w at 2° to 6°C and then test the pre-chilled seeds at constant temperatures of 16°C and 21°C with light applied for 12h/d.

If the first step in the algorithm does not result in full germination then the second step is to take two further samples of seeds. Remove the seed coats from one sample of seeds, but only chip the seed coats of the second sample and then subject both samples to the most successful pre-chill and constant temperature germination test regime determined from a comparison of the results of step one.

If the second step in the algorithm does not result in full germination then the third step is to estimate viability using a tetrazolium test (as described for the third step of the algorithm for herbaceous rosaceous species).

TABLE 62.1 Summary of germination test recommendations for species within the Rosaceae

Species and Authority	Substrate	Temperature	Duration	Additional directions	Source
Agrimonia eupatoria L.	TP	20°/30°C	60d	pre-soak, 24h, chip or file off fragment of testa	ISTA
Amelanchier laevis wiegand				warm stratification, 25°C, 4w, then pre-chill, 1°-5°C, 16w	G&R
Amelanchier spp.			21d	scarify, abrade with sharp sand, or file or nick seed coat, pre-chill, 1°-5°C, 30-60d	Riley
Chaenomeles japonica Lindl.				warm stratification, 25°C, 2w, then pre-chill, 1°-5°C, 8-16w	G&R
Cotoneaster spp.		20°/30°C; 10°/25°C		light, 8h/d, warm stratification, 25°C, 12w, then pre-chill, 1°-5°C, 12w	G&R
Crataegus mollis Scheele	TP; BP	20°/30°C	14d	scarify, sulphuric acid, 2h, then warm stratification, 20°C, 90d, then pre-chill, 3°-5°C, 120d	AOSA
Crataegus monogyna Jacq.	S	20°/30°C	28d	warm stratification, 25°C, 3m, then pre-chill, 3°-5°C, 9m	ISTA
Crataegus spp.				warm stratification, 25°C, 4-16w, then pre-chill, 1°-5°C, 12-16w	G&R
			40d	scarify, abrade with sharp sand, or file or nick seed coat, pre-chill, 1°-5°C, 30-60d	Riley
Cydonia oblonga Mill.				warm stratification, 25°C, 2-4w, then pre-chill, 1°-5°C, 16w	G&R
			21d	pre-chill, 1°-5°C, 90d	Riley
Eriobotrya japonica Lindl.			21d	pre-chill, 1°-5°C, 30-60d	Riley
Geum x borisii Hort.	TP; BP	20°/30°C; 20°C	21d	light	ISTA
Geum chiloense Balbis	TP; BP	20°/30°C; 20°C	21d	light	ISTA
Geum quellyon Sweet		20°/30°C	21d	keep wet	Atwater
Geum spp.	TP	20°/30°C	21d	seeds sensitive to drying out in test	AOSA
			28d	dry storage (to after-ripen seeds), test at alternating temperatures	Atwater
Potentilla anserina L.		20°/30°C	14d	light, potassium nitrate, 0.2%	Atwater
Potentilla flabelliformis	TP	20°/30°C; 20°C		light, pre-chill, 3°-5°C, 4w	M&O
Potentilla glandulosa Lindl.	soil		9d		Atwater
Potentilla tridentata Ait.		20°/30°C	45d	light, potassium nitrate, 0.2%	Atwater
Rosa multiflora Thunb.	TP	10°/30°C	28d	pre-chill, 3°-5°C, 28d	ISTA
	TP	10°/30°C	28d	light, pre-chill, 3°-5°C, 28d	AOSA
Rosa rugosa Thunb.			30d	pre-chill, 1°-5°C, 30-60d	Riley
Rosa spp. (except R. multiflora)	S	20°C	70d	pre-chill, 12m	ISTA
Rosa spp.				warm stratification, 25°C, 0-8w, then pre-chill, 1°-5°C, 8-16w	G&R
Sanguisorba minor Scop.	TP; BP	20°/30°C; 20°C	28d		ISTA
	BP	15°C	14d		AOSA
Sorbus spp.	S	20°/30°C	28d	pre-chill, 3°-5°C, 4m	ISTA
				warm stratification, 25°C, 2w, then pre-chill, 1°-5°C, 14-16w	G&R
			30d	pre-chill, 1°-5°C, 60d	Riley

FRAGARIA

Fragaria spp.

strawberry

I. Evidence of dormancy

Strawberry seed germination is generally slow and erratic (5). This is one manifestation of dormancy, germination continuing to occur, for example, between 5 and 10 weeks in germination tests at 24°C (1). After-ripening treatments of 6 months duration result in partial, but not complete, loss in dormancy (1).

Dormancy varies considerably between cultivars (1). Seeds produced by self-pollination can be much more dormant than seeds produced from cross-pollination (1). Dormancy may be substantially less in seeds extracted from rotted fruits (3), but drying seeds at room temperature (18°-20°C) may induce dormancy (3). Since much of the work on dormancy in strawberry seeds does not specify the species, the information provided here is not divided into the separate species.

II. Germination regimes for non-dormant seeds

Constant temperatures: 24°C, 36d (4); 24°C, 70d (1); 25°C, 60d (5)

III. Unsuccessful dormancy-breaking treatments

Constant temperatures: 19°-20°C, 60d (3); 31°-33°C, 22d (9)

Pre-chill: 0°-1°C, 10d (2); 0°-1°C, 2-4w (2); 0°-1°C, 6w (2); 2°C, 4w (15); 3°-5°C, 16d (7); 5°C, 10d (8); 5°C, 3w (4)

Thiourea: 0.1, 0.2% (8)

Scarification: concentrated sulphuric acid (13); concentrated sulphuric acid, 15 min (10)

Pre-soak: 8,24h (11)

Light: dark, at 25°C (12)

Coumarin: co-applied, 1-50 mg/1, at 25°C in dark (12)

2-4, Dichlorophenoxyacetic acid: co-applied, 1-10 mg/l, at 25°C in dark (12)

GA₁: co-applied, 1 mg/l, at 25°C in dark (12)

GA₃: co-applied, 1, 10 mg/l, at 25°C in dark (12)

GA_3/4: co-applied, 500 ppm, in red light (13)

GA₅: co-applied, 1-50 mg/l, at 25°C in dark (12)

GA₇: co-applied, 1-50 mg/l, at 25°C in dark (12)

GA₉: co-applied, 1-50 mg/l, at 25°C in dark (12)

Indoleacetic acid: pre-applied, 24h, 100, 200 ppm (9)

Colchicine: pre-applied, 24h, 400 ppm (9)

IV. Partly-successful dormancy-breaking treatments

Constant temperatures: 24°C, 60d (4); 25°C in light (8)

Alternating temperatures: 15°/30°C (16h/8h) in light (8)

Pre-chill: 0°-1°C, 1-5w (2); 0°-1°C, 1-5m (2); 0°-1°C, 2-8m (2); 4°C, 2-16w, germinate at 24°C, 10w (1); 4°C, 1m (3); 5°C, 6w (4); 5°C, 30-90d (8); 2°C, 18d, plus GA_3/4, co-applied, 100 ppm, in red light (13); 2°C, 18d, plus thiourea, co-applied, 25 ppm, in red light (13); 2°C, 8w (15)

Thiourea: pre-applied, 24h, 500 ppm (9); pre-applied, 24h, 0.1, 0.2%, germinate at 20°-22°C (6); 0.01, 0.05% (8); co-applied, 100, 250 mg/l, at 25°C in dark (12); co-applied, 5-250 ppm, in red light (13)

GA₁: co-applied, 10, 50 mg/l, at 25°C in dark (12)

GA₃: pre-applied, 24h, 25-75 ppm, germinate at 20°-22°C (6); pre-applied, 24h, 100, 200 ppm (9); 100-500 ppm (8); co-applied, 50 mg/l, at 25°C in dark (12)

GA_3/4: co-applied, 1-100 ppm, in red light (13)

GA₄: co-applied, 1-50 mg/l, at 25°C in dark (12)

GA₅: co-applied, 10 mg/l, at 25°C in dark (12)

2-Chloroethane phosphonic acid: pre-applied, 24h, 1000, 2500 ppm, germinate at 20°-22°C (6); 50-200 ppm (8); 500-5000 ppm (8)

Scarification: sulphuric acid, 96%, 8 min, with or without pre-chill, 3°-5°C, 16d (7); concentrated sulphuric acid, 2,3 min (8)

Ammonium nitrate: pre-applied, 24h, 0.2, 0.5% (9)

Potassium nitrate: 0.1, 0.2% (8); pre-applied, 24h, 0.2% (9)

Sodium hypochlorite: pre-applied, 8,24h, 1% (11)

Light: red, 5 min-24h, at 25°C (12); red, continuous (13); green, continuous, at 25°C (12)

Nitric acid: pre-applied, 24h, 0.15, 0.25% (9)

Malic hydrazide: pre-applied, 24h, 200-500 ppm (9)

Colchicine: pre-applied, 24h, 250 ppm (9)

Hydrogen peroxide: pre-applied, 4,14,24h (9)

V. Successful dormancy-breaking treatments

Pre-chill: 2°C, 44d, with or without GA₃, co-applied, 10, 100 ppm, or with or without GA_3/4, 1, 10 ppm, at 20°-25°C in red light (13)

2-Chloroethane phosphonic acid: pre-applied, 24h, 5000 ppm, germinate at 20°-22°C (6); pre-applied, 24h, 5000, 10000 ppm (15)

Potassium nitrate: 0.2%, at 15°/30°C (16h/8h) in light (8)

Light: red, continuous, at 25°C (12)

VI. Comment

Light is essential for promoting the germination of dormant strawberry seeds (12) - red light being promotory and far red light being inhibitory (8,14). For practical treatments white light is sufficient for the promotion of germination (8). 25°C is the most suitable constant temperature germination test regime (5). For seed lots which are only slightly dormant, testing in continuous light at 25°C is sufficient for full germination (12), but for slightly more dormant seeds an alternating temperature regime of 15°/30°C (16h/8h) gives substantially greater germination than a constant 25°C (8).

We can confirm that the germination of dormant strawberry seeds is promoted by alternating temperature regimes: within the range 11°-38°C constant temperatures between 23°-27°C are the most suitable, but alternating temperatures with similar mean temperatures give more rapid and greater germination provided the maximum temperature of the alternation is below about 34°C (A). The maximum benefit from alternating temperatures only requires a small amplitude of alternation, 3°-7°C, and there is some benefit in providing the lower temperature of the alternation for the greater part of the cycle; 23°/30°C (16h/8h) is the most suitable regime (A).

The more dormant strawberry seed lots require further dormancy-breaking treatments in addition to alternating temperatures and light (A). Pre-chill treatments have been applied widely. Optimum treatment periods are reported to vary from 4 to 12 weeks between lots (1), but 4 months' pre-chilling is reported to be a suitable compromise between conflicting optimum periods, at least in one investigation with 28 seed lots (2). Very long pre-chill treatments may be counter-productive, for example 6 months (2), and there is some suggestion that very short-duration treatments may also reduce germination, for example 16 days (7). These points minimise the usefulness of pre-chill treatments.

Of the gibberellins, GA₄ is the most successful in promoting germination (12), but the effect of gibberellins is often marginal (6) and in some cases may cause a reduction in germination (13). Ethrel (2-chloroethanephosphonic acid) can be very successful in promoting germination (6), but treatment with potassium nitrate is reported to be a more effective dormancy-breaking agent than either ethrel or gibberellins (8). The response to pre-treatment with sodium hypochlorite is variable between lots and in some cases may be injurious (11). Consequently it is not advisable to use a standard sodium hypochlorite disinfection treatment.

Scarification of strawberry seeds with concentrated sulphuric acid can be promotory and far more effective than pre-chill treatments (7). However, the treatment period is a critical factor, 8 minutes' treatment being promotory (7) whilst 15-minute treatments may reduce germination in some seed lots (10).

We found that no single dormancy-breaking agent could be applied which would promote full germination in all lots (A). Consequently we devised a germination test regime which combined a number of stimulatory factors. On the basis of this work the following regime is recommended for germinating strawberry seeds: first scarify the seeds in concentrated sulphuric acid for 10 minutes, then pre-wash for 30 minutes, then treat in 1 M hydrogen peroxide for 24 hours, and finally test for 49 days in an alternating temperature regime of 23°/30°C (16h/8h) with light during the 8h cycle and 0.2% potassium nitrate co-applied (A). The combined treatment has been found to be non-injurious to seeds (A), but the reader is reminded that the provision of an alternating temperature regime with light and potassium nitrate alone is likely to be sufficient for the less dormant seed lots (8).

For large scale sowings of seeds (regeneration or multiplication) it is important to apply light whilst preventing the seeds from drying out. This can be achieved by sowing the seeds on top of compost (that is, exposed to light) and using a mist-propagation unit to maintain a high humidity above the seeds (15).

VII. References

1. Adam, J. and Wilson, D. (1967). Factors affecting the germination of strawberry seeds. Report of the Long Ashton Research Station for 1966, 90-95.

2. Bringhurst, R.S. and Voth, V. (1957). Effect of stratification on strawberry seed germination. Proceedings of the American Society for Horticultural Science, 70, 144-149.

3. Brown, A.E. and Musa, M.J. (1980). The beneficial effect of rotting of strawberry fruit by Botrytis cinerea on subsequent germination. Seed Science and Technology, 8, 269-275.

4. Guttridge, C.G. and Bright, S. (1978). Accelerating and synchronizing germination of strawberry seeds by osmotic pre-treatments. Euphytica, 27, 843-848.

5. Henry, E.M. (1934). The germination of strawberry seeds and the technic of handling the seedlings. Proceedings of the American Society for Horticultural Science, 31, 431-433.

6. Iyer, C.P.A., Chacko, E.K. and Subramanium, M.D. (1970). Ethrel for breaking dormancy of strawberry seeds. Current Science, 39, 271-272.

7. Jonkers, H. (1958). Accelerated flowering of strawberry seedlings. Euphytica, 7, 41-46.

8. Nakamura, S. (1972). [Germination of strawberry seeds.] Journal of the Japanese Society for Horticultural Science, 41, 367-375.

9. Negi, S.P. and Singh, R. (1972). Effect of different chemicals on germination of strawberry seeds. Indian Journal of Horticulture, 29, 265-268.

10. Scott, D.H. and Ink, D.P. (1948). Germination of strawberry seed as affected by scarification treatment with sulfuric acid. Proceedings of the American Society for Horticultural Science, 51, 299-300.

11. 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.

12. Thompson, P.A. (1968). The effect of some promoters and inhibitors on the light controlled germination of strawberry seeds; Fragaria vesca semperflorens Ehr. Physiologia Plantarum, 21, 833-841.

13. Thompson, P.A. (1969). The use of chilling and chemical treatments to promote rapid germination of strawberry achenes. Journal of Horticultural Science, 44, 201-210.

14. Toole, E.H. (1961). The effect of light and other variables on the control of seed germination. Proceedings of the International Seed Testing Association, 26, 659-673.

15. Wilson, D., Goodall, A. and Reeves, J. (1973). An improved technique for the germination of strawberry seeds. Euphytica, 22, 362-366.

PRUNUS

P. americana Marsh.	wild cherry, wild yellow plum
P. amygdalus Batsch. [P. dulcis D.A. Webb]	almond
P. armeniaca L. [Armeniaca vulgaris Lam.]	apricot
P. avium L. [P. cerasus avium L.; Cerasus avium Moench.]	sweet cherry, mazzard cherry, gean, bird cherry
P. besseyi Bailey [P. prunella Daniels; P. pumila besseyi Waugh]	Bessey cherry, western sand cherry
P. cerasia Bl.	kerassi
P. cerasifera Ehrh. [P. domestica var myrobalan L.; P. myrobalana Loisel.; P. korolkowi Vilm.]	myrobalan plum, cherry plum, mariana plum
P. cerasus L. [Cerasus vulgaris Mill.]	sour cherry, pie cherry
P. domestica L. [P. damascena Dierb.; P. communis Huds.]	plum
P. fruticosa	ground cherry
P. laurocerasus L. [Laurocerasus officinalis Roem.]	common laurel, cherry laurel
P. lusitanica L. [Laurocerasus lusitanica Roem.]	Portugal laurel
P. padus L. [P. racemosa Lam.; Padus racemosa Schneid.; Cerasus padus DC.]	European bird cherry
P. pensylvanica L. [P. persicifolia Desf.; P. montana Marsh.; P. lanceolata Willd.] pin cherry, wild red cherry, fire cherry
P. persica Batsch. [Amygdalus persica L.; Persica vulgaris Mill.]	peach
P. salicina Lindl. [P. triflora Roxb.]	Japanese plum
P. sargentii Rehd.	Sargents cherry
P. serotina Ehrh. [Padus serotina Borkh.]	black cherry, rum cherry
P. spinosa L.	sloe, blackthorn
P. virginiana L. [P. nana DuRoi; P. demissa (Nutt.) D. Dietr.; Padus nana (Du Roi) Borkh.]	choke cherry

I. Evidence of dormancy

Seed dormancy in Prunus spp. is pronounced and dormancy-breaking treatments are required as a matter of routine. For general reviews of seed drying, storage, germination and dormancy in Prunus spp. see (10,20). Because of the stony endocarp seed dormancy is often thought to be the sole property of the seed coat, but this is not so since extracted embryos are dormant (e.g. 20,32). For example, in P. domestica dormancy is associated with the entire seed, viz. testa, cotyledons and embryo (30). Secondary dormancy can be induced if the seeds are set to germinate at high temperatures (19,20). For example, in P. avium 2 weeks at 25°C in darkness induces dormancy (32).

II. Germination regimes for non-dormant seeds

Prunus spp.

S: 20°/30°C (16h/8h); 20°C: 28d (ISTA)

TP; S: 18°-22°C: 10-14d (AOSA)

III. Unsuccessful dormancy-breaking treatments

P. americana

Pre-chill: 1°-10°C, 4m (17)

P. armeniaca

Warm stratification: 22°C, 1-4w (5)

Malonic acid: pre-applied, 1h, 100-500 ppm (5)

P. avium

Pre-chill: 1°C, 3w (36); 1°C, 1m, with or without GA₃, pre-applied, 24h, 100-400 ppm (16); 3°C, 30w (42)

Warm stratification: 20°C, 3-16w (36); 22°C, 5m (15)

Pre-soak: 19°C, 96h, then pre-dry, 30 min (49)

GA₃: pre-applied, 24h, 100-400 ppm (16)

Removal of seed covering structures: stones cracked (23); stones cracked and seed coats removed (23)

P. cerasia

Warm stratification: 25°C, 2-4m (12)

Pre-soak: 24h, then sun dry (12)

Scarification: sulphuric acid, 15,30 min (12)

P. cerasus

Pre-chill: 3°C, 27w (42)

P. domestica

GA₃: 16 ppm, plus N-6-benzyladenine, 8 ppm (30)

Removal of seed covering structures: testa (30); excise embryo (30)

P. laurocerasus

Pre-chill: 6°C, 1,2m, with or without GA₃, pre-applied, 24h, 100 ppm (39)

Warm stratification: 18°-21°C, 1-12m (39)

GA₃: pre-applied, 24h, 100 ppm, with or without warm stratification, 18°-21°C, 1-12m (39)

P. pensylvanica

Pre-chill:.5°C, 150d (29)

Warm stratification: 20°C, 30d, then pre-chill, 5°C, 120d (29)

Potassium nitrate: pre-applied, 48h, 0.05 M, 20°C (29)

P. persica

Pre-chill: 4.4°C, 1-4w, germinate at 20°C (46); 5°C, 2w (7); 7°C, 15d, with or without seed coat (38); 10°C, 15d (38)

Warm stratification: 24°C, 15-60d (38); 24°C, 15,30d, after seed coat removal (38); 31°C (7)

Pre-wash: 5d, germinate at 20°C (46)

Removal of seed covering structures: excise embryo (46); endocarp (46)

GA₃: pre-applied, 0.3-3g/1 (7); pre-applied, 24h, 500, 1000 ppm, to pre-chilled seeds (9); co-applied, 0.02 ppm, plus benzyladenine, 1 ppm (8); co-applied, 2 ppm, plus benzyladenine, 100 ppm (8); pre-applied, 24h, 50, 100 ppm (37)

GA_4/7: pre-applied, 24h, 50, 100 ppm (37)

GA₇: (7)

Malonic acid: pre-applied, 1h, 100-5000 ppm (5)

Urea: pre-applied, 6h, 10^-3-3x10^-1 M, after 2d at 20°C (35)

Mercaptoethanol: pre-applied, 6h, 10^-4-10^-1 M, after 2d at 20°C (35)

Mercaptoethylamine: pre-applied, 6h, 10^-4-10^-1 M, after 2d at 20°C (35)

6-Benzylaminopurine: (7)

2-Chloroethylphosphonic acid: (7)

P. spinosa

Pre-chill: 3°C, 32w (34)

IV. Partly-successful dormancy-breaking treatments

P. americana

Pre-chill: 1°-10°C, 5-7m (17)

P. amygdalus

Constant temperatures: 2°C, 10°C, 15°C, 40d (45); 10°C, 19-27w (28) Removal of seed covering structures: endocarp, germinate at 10°C, 15°C, 30d (45)

P. amygdalus x P. persica

Constant temperatures: 10°C, 19-27w (28)

P. armeniaca

Pre-chill: 0°C, 10°C, 1-4w (5); 3°C, 1-3w (5); 4.5°C, 1w (5); 3°C, 27w (42)

Removal of seed covering structures: seedcoats (5)

GA₃: pre-applied, 30 min, 20-20000 ppm (5)

P. avium

Pre-chill: 1°C, 8w (36); 1°C, 2-6m, with or without GA₃, pre-applied, 24h, 100-400 ppm (16); 1°-2°C, 20-80d (22); 2°-3°C,' 5-8m (23); 2°-5°C, 120d (49); 2°-7°C, 3-6m (18); 3°C, 2-8m (15); 3°-5°C, 4m (24)

Warm stratification: 20°C, 2w, then pre-chill, 3°-5°C, 3.5m (24); 20°C, 2w, then 3°C, 27-33w (33,40,41,42,43); 20°C, 2w, then 1-3 cycles of 3°/25°C (2w/2w or 4w/2w), then 3°C, 32w (33)

GA₃: pre-applied, 24h, 100 ppm (15)

Removal of seed covering structures: crack stones (16); crack stones, then GA₃, pre-applied, 24h, 400 ppm (16)

Scarification: notch stone with emery wheel, then with or without hydrogen peroxide, pre-applied, 24h, 0.5%, then pre-chill, 2°-5°C, 120d (49)

P. besseyi

Pre-chill: 7m (1)

P. cerasia

Pre-chill: 5°C, 2-4m (12)

P. cerasifera

Pre-chill: 3°C, 27-32w (34,42)

Warm stratification: 20°C, 2w, then 3°C, 27-32w (34,42)

P. cerasus

Pre-chill: 2°-7°C, 3-7m (18)

Warm stratification: 20°C, 3w, then pre-chill, 2°-7°C, 7m (18); 20°C, 2w, then 3°C, 27w (42)

P. domestica

Pre-chill: 3°C, 27-35w (34,42)

Warm stratification: 20°C, 2w, then 3°C, 27-35w (34,42) Removal of seed covering structures: testa (30); crack stones (3); crack stones, then pre-chill, 3°-6°C, 35d (3); crack stones, then pre-chill, 3°-6°C, 28d, then GA₃, co-applied, 20-100 ppm (3); crack stones, then pre-chill, 3°-6°C, 28d, then thiourea, co-applied, 2500-10000 ppm (3); crack stones, then pre-chill, 3°-6°C, 28d, then GA₃, co-applied, 50 ppm plus thiourea, co-applied, 5000 ppm (3)

P. fruticosa

Pre-chill: 3°C, 27w (42)

Warm stratification: 20°C, 2w, then 3°C, 27w (42)

P. laurocerasus

Pre-chill: 6°C, 4-12m (39)

Warm stratification: 18°-21°C, 1,2m, then pre-chill, 6°C, 3-4m (39)

GA₃: pre-applied, 24h, 100 ppm, then pre-chill, 6°C, 4-6m (39)

P. mahaleb

Pre-chill: 3°C, 27w (42)

Warm stratification: 20°C, 2w, then 3°C, 27w (42)

P. padus

Pre-chill: 3°C, 30w (42)

Warm stratification: 20°C, 2w, then 3°C, 30w (42)

P. pensylvanica

Alternating temperatures: 5°/20°C, 5°/30°C (1d/1d, 5d/5d), 30d, then pre-chill, 5°C, 120d (29)

Warm stratification: 30°C, 30d, then pre-chill, 5°C, 120d (29)

Calcium nitrate: (2); pre-applied, 24h, 20°C, 0.02 M (29)

Ammonium sulphate: (2)

Urea: (2)

P. persica

Constant temperatures: 1°-10°C, 3.5m (6); 10°C, 19-27w (28)

Pre-chill: 35d, then GA₃, pre-applied, 24h, 20-200 ppm (9); 1°-2°C, 20-80d (22); 3°C, 2-10w (8); 3°C, 27w (42); 3°C, 2-6w, plus GA₃, co-applied, 2 ppm, plus benzyladenine, 100 ppm (8); 4.4°C, 8w, germinate at 20°C (46); 4.4°C, 1,2,4w, excise embryos or remove endocarps, germinate at 20°C (46); 5°C, 6w (7); 5°C, 34w (42); 7°C, 30-75d, with or without seed coat (38); 10°C, 30-75d (38); 10°C, 15-75d, after seed coat removal (38); 5°C, 5-20d (37)

Warm stratification: 24°C, 75d (38); 24°C, 45-75d, after seed coat removal (38); 20°C, 2w, then 3°C, 27w (42); 20°C, 2w, then 5°C, 34w (42)

Pre-wash: 5d, then excise embryos, germinate at 20°C (46)

Removal of seed covering structures: pericarp, germinate at 1°C, 10°C, 3.5m (6); endocarp, then pre-chill, 6°C, 16-83d (4); endocarp, with or without GA₃, pre-applied, 24h, 0.3, 1 g/1 (7); endocarp, then pre-chill, 5°C, 2w (7); seed coats (5); endocarp, then pre-chill, 20d (11); endocarp, then GA₃, pre-applied, 1000 ppm, then pre-chill, 20d (11)

GA₃: pre-applied, 30 min, 100-20000 ppm (5); pre-applied, 6h, 10^-3 -3x10^-1 M, after 2d at 20°C (35); pre-applied, 24h, 100-200 ppm, germinate at 4°-6°C, 8w (26)

Thiourea: pre-applied, 6h, 10^-3 -3x10^-2, 3x10^-1 M, after 2d at 20°C (35); pre-applied, 24h, 2500-7500 ppm, germinate at 4°-6°C, 8w (26)

6-Benzyl-amino-purine: pre-applied, 24h, 60-100 ppm (37)

P. persica x P. amygdalus

Constant temperatures: 10°C, 19-27w (28)

P. serotina

Pre-chill: 3°C, 27w (42)

Storage: room temperature (dry), 37d, then pre-chill, 0°-3°C, 120d (21)

P. spinosa

Warm stratification: 20°-25°C, 2w, then pre-chill, 1°-5°C, 18w (19); 20°C, 2w, then 3°C, 32w (34)

P. virginiana

Pre-chill: 3°C, 10,16,24w, germinate at 10°/16°C, 16°/21°C, 21°/27°C, dark/light (10h/14h) (31)

V. Successful dormancy-breaking treatments

P. amygdalus

Pre-soak: 16h, then pre-chill, 0°-10°C, 3-4w (27)

Removal of seed covering structures: endocarps, germinate at 2°C, 40d (45)

P. armeniaca

Pre-chill: 3°C, 4w (5); 4°-5°C, 2-4w (5)

Warm stratification: 20°C, 2w, then 3°C, 27w (42)

Removal of seed covering structures: seed coat, then GA₃, pre-applied, 30 min, 4000, 12000 ppm (5)

P. avium

Pre-chill: 1°C, 16w (36)

Warm stratification: 20°C, 3w, then pre-chill, 2°-7°C, 6m (18); 20°C, 2w, then 3°C, 2,4,6w, then 25°C, 2w, then 3°C, 30w (42); 20°C, 2w, then 4-10 cycles of 3°/25°C (2w/2w), then 3°C, 32w (33); 20°C, 2w, then 4-8 cycles of 3°/25°C (4w/2w), then 3°C, 32w (33); 20°C, 2w, then 2 cycles of 3°/25°C (8w/2w) or (14w/2w), then 3°C, 12-16w (33)

P. domestica

Removal of seed covering structures: testa, plus GA₃, 4 ppm and N-6-benzyladenine, 2 ppm (30); testa, plus GA₃, 16 ppm and N-6-benzyladenine, 8 ppm (30); excise embryo, plus GA₃, 16 ppm and N-6-benzyladenine, 8 ppm (30)

P. persica

Pre-chill: 4.5°C, 8w (5); 5°C, 10w (7); 5°C, 30-70d, germinate at 25°C, dark (37)

Removal of seed covering structures: pericarp, then pre-soak, 16h, then remove inner seed coat, germinate at 25°C (13); pericarp, germinate at 5°C, 3.5m (6); endocarp, then warm stratification, 20°C, 2d, then pre-chill, 6°C, 25d, germinate at 20°C in light, 800 fc, 12h/d (4); endocarp, plus GA₃, pre-applied, 24h, 3 g/1 (7); endocarp, then pre-chill, 5°C, 6, 10w (7); endocarp (37); endocarp, then pre-chill, 5°C, 10-30d (37)

Thiourea: pre-applied, 6h, 10^-1 M, after 2d at 20°C (35)

6-Benzyl-amino-purine: pre-applied, 24h, 150-250 ppm (37); pre-applied, 24h, 200 ppm, plus GA₃, 100 ppm (37); pre-applied, 24h, 200 ppm plus GA_4/7, 100 ppm (37)

P. serotina

Warm stratification: 20°C, 2w, then 3°C, 27w (42)

Prunus spp.

Excise embryo, or Pre-chill (ISTA)

Excise embryo (AOSA)

VI. Comment

An indication of the degree of dormancy within seeds of Prunus spp. is provided by the fact that the preferred method of determining viability in ISTA rules is the tetrazolium test and the second preference is the excised embryo test; germination tests following a 3 to 4 month pre-chill at 3°-5°C is the least preferred ISTA procedure. Similarly AOSA rules suggest the use of either the excised embryo test or the tetrazolium test. Details of tetrazolium and excised embryo test procedures are provided in Chapter 11. In addition, references (47) and (25) provide details of embryo culture procedures for P. americana, P. avium, P. cerasus, P. persica, and P. amygdalus, P. avium, P. domestica, P. persica, P. salicina respectively. If sufficient expertise is available (and this is essential) then gene banks may decide to follow AOSA/ISTA rules and use either tetrazolium or excised embryo tests to monitor the viability of Prunus accessions in long-term storage. Even so, it is essential that the bank is able to promote the germination of dormant seeds when this is required. There are problems with embryo culture: seedlings obtained from excised embryo culture have a very low survival percentage in field sowings (49).

Before considering germination it is necessary to point out a further problem for gene banks. In many of the references cited here the seeds were not dried: they were extracted from the fruits and then immediately placed under conditions designed to remove dormancy. Dry intact seeds, however, may take between 40 and 60 days to become fully imbibed (46); removing the endocarp halves this time (46); soaking the seeds in water further reduces this period (46). When removing the endocarp it is possible to damage the seed mechanically which results in microbial damage in subsequent germination tests (23). However, such injury can be avoided if the seeds are dried before endocarp removal (23). In most reports endocarp removal and pre-soaking or pre-washing (to increase moisture content and/or to remove possible inhibitors to germination) were used as routine preliminary seed treatments, e.g. (8), and are suggested for gene bank use. Incidentally, it is desirable to clean seeds of all pulp and juice - by washing - as soon as possible at seed extraction (19).

Pre-chill treatments have been widely used to break dormancy, but treatment periods of six months may be necessary to promote germination. Endocarp removal can substantially reduce the pre-chill periods required for full germination, but without a long pre-chill treatment dwarf seedlings may result (14,48). A short exposure of such seedlings to low temperatures, however, overcomes this problem (14). Although pre-chill treatments between 1° and 10°C have been effective, e.g. (6,17), 3° to 5°C appear to be the most suitable constant pre-chill temperatures (5,17). A fluctuation of the pre-chill temperature between 2° and 5°C may be more promotory than a constant temperature of 3°C (49). Seeds will in fact germinate under the pre-chill treatment conditions, for example, at 2°C (45) and 10°C (28) for P. amygdalus, at 3°C for P. virginiana (31), between 1° and 10°C for P. americana (17), and at 3°C for P. armeniaca, P. avium, P. cerasifera, P. cerasus, P. domestica, P. fruticosa, P. mahaleb, P. padus, P. persica, and P. serotina (42). For this reason it is suggested that seeds undergoing pre-chill treatments be checked and seedlings removed regularly - just as in germination tests. Subsequent germination tests should not be at too high a temperature, 20°C is suggested, otherwise secondary dormancy may be induced. However, after very long pre-chill treatments the risk of secondary dormancy is reduced, in which case higher temperatures, such as an alternating temperature regime of 21°/27°C (10h/14h) (31), appear to result in greater germination than lower temperatures - 10°/16°C, 16°/21°C (10h/14h) (31), and wide amplitude alternating temperatures are also promotory - for example, 5°/25°C (16h/8h) (42). Nevertheless, since it cannot be guaranteed in advance that a pre-chill treatment has been sufficient to remove the risk of secondary dormancy being induced, germination test temperatures of 20°C or below are recommended. Of course, one alternative is to use an extended pre-chilling treatment, 3°-5°C, throughout and treat it as a very long germination test.

Although there is seldom any benefit from warm stratification treatments alone, a short treatment prior to a pre-chill treatment can be of benefit (4,19,29,32-34,39-44). The temperature recommended for the warm stratification is usually 20° to 25°C, but for P. pensylvanica 30°C has been suggested (29). The following pre-treatments have been recommended for breaking dormancy: 2 weeks' warm stratification then 11 to 27 weeks' pre-chill for P. armeniaca, P. cerasifera, P. mahaleb, and P. serotina, (42); 2 weeks' warm stratification then 12 to 34 weeks' pre-chill for P. persica (42); 2 weeks' warm stratification then 13 to 30 weeks' pre-chill for P. domestica (42); 2 weeks' warm stratification then 15 to 27 weeks' pre-chill for P. cerasus (42); 2 weeks' warm stratification then 15 to 33 weeks' pre-chill for P. avium (42); 2 weeks' warm stratification then 27 weeks' pre-chill for P. fruticosa (42); 2 weeks' warm stratification then 8 to 12 weeks' pre-chill for P. avium (44); 2 weeks' warm stratification then 11 to 18 weeks' pre-chill for P. armeniaca (19); 2 weeks' warm stratification then 18 weeks' pre-chill for P. avium, P. cerasifera, P. persica, P. spinosa and P. virginiana (19); 2 to 4 weeks' warm stratification then 18 weeks' pre-chill for P. padus, P. sargentii and P. serotina (19); 9 weeks' pre-chill for P. amygdalus, P. lusitanica (19); a 2 day pre-soak in 0.05 M calcium nitrate, then alternate between 30°C and 5°C for 30 days with 3 cycles of 5 days at each temperature, then pre-chill for 60 days at 5°C with a further 30 days at 1°-2°C, then pre-soak in 0.05% GA₃ for 1 day, then pre-chill for a further 5 days at 5°C, and then move to 30°C for germination for 10 days, cycling between these two later regimes for as long as necessary for P. pensylvanica (29); pre-soak in 400 ppm GA₃ for 1 day, then pre-chill for 5 to 6 months for P. avium (16). If treatment with gibberellic acid is contemplated then it is worth considering treatment with thiourea as an alternative, since thiourea is reported to be a more successful dormancy-breaking agent than gibberellic acid (35). It is worth pointing out that many of the above treatments were devised for nursery sowings where uniform, rapid, germination is desired after, but not during, the pre-chill treatment. In one case (42), however, the range of pre-chill periods given above indicate the variation in time, taken to germinate at 3°C after a warm stratification treatment for the first and last seeds to germinate. A more detailed summary of these procedures has been provided elsewhere (10).

In addition to the promotion to germination which results from warm stratification prior to pre-chilling, further promotion can occur in P. avium when the pre-chilling treatment is interrupted by one or more warm stratification treatments (33,42). For the second (and any subsequent) warm stratification treatment a temperature of 25°C is more promotory than 20°C (42). The most promotory alternating warm stratification/pre-chill treatments reported are 2 weeks at 20°C, then 2 weeks at 3°C, then 2 weeks at 25°C, then 3°C until germination was complete (42), and 2 weeks at 20°C, then 4 cycles of 2 weeks at 3°C and 2 weeks at 25°C, then 3°C until germination was complete (33). In the latter case full germination was achieved after 9 months in all (33), but it is worth noting that although the intermediate treatments at 25°C increased the total proporation of seeds germinating (that is they further promoted the germination of dormant seeds) the germination of the least dormant seeds in the population was delayed (33). Similar treatments with P. cerasifera, P. domestica, and P. spinosa, however, failed to promote germination (34), although the treatments increased the proportions of viable (but ungerminated) seeds of P. cerasifera and P. spinosa at the end of the tests (34).

Although the two preceding paragraphs provide some help in suggesting suitable germination test regimes, differences between seed lots within species (42) will make it difficult for gene banks to choose an appropriate germination test regime for each Prunus accession. The following preliminary investigation at accession receipt has been suggested where sufficient seeds (and staff to carry out the work) are available (10). When the accession has been dried and placed under long-term storage conditions, randomly sample 350 seeds. Randomly divide the sub-sample into 7 groups of 50 seeds and test as follows.

1. Estimate viability using the excised embryo test or a staining test.

2. Test for germination at 3° to 5°C for up to 6 months.

3. Treat the imbibed seeds at 20°C for 2 weeks, and then test for germination at 3° to 5°C for up to 6 months.

4. Treat the imbibed seeds at 20°C for 2 weeks, then subject to 4 cycles of 2 weeks at 3° to 5°C and 2 weeks at 25°C, and then test for germination at 3° to 5°C for up to 6 months.

5,6,7. As for 2,3,4 respectively but first remove the endocarps from the dry seeds.

VII. References

1. Adams, J. (1927). The germination of the seeds of some plants with fleshy fruits. American Journal of Botany, 14, 415-428.

2. Auchmoody, L.R. (1979). Nitrogen fertilization stimulates germination of dormant pin cherry seed. Canadian Journal of Forest Research, 9, 514-516.

3. Bajwa, G.S., Sandhu, A.S. and Khajuria, H.N. (1980). Seed germination studies in plum. Research Bulletin of Marathwada Agricultural University, 4, 6-7. (From Seed Abstracts, 1981, 4, 3132.)

4. Biggs, R.H. (1966). Germination of "Okinawa" peach seeds under conditions of Florida. Proceedings of the Florida State Horticultural Society, 79, 370-373.

5. Chao, L. and Walker, D.R. (1966). Effects of temperature, chemicals, and seed coat on apricot and peach seed germination and growth. Proceedings of the American Society for Horticultural Science, 88, 232-238.

6. Crocker, W. and Barton, L.V. (1931). After-ripening, germination, and storage of certain rosaceous seeds. Contributions from the Boyce Thompson Institute, 3, 385-404.

7. Davies, F.T. (1983). Breaking seed dormancy of "Nemaguard" peach. HortScience, 18, 959.

8. Diaz, D.H. and Martin, G.C. (1972). Peach seed dormancy in relation to endogenous inhibitors and applied growth substances. Journal of the American Society for Horticultural Science, 97, 651-654.

9. Donoho, C.W. and Walker, D.R. (1957). Effect of gibberellic acid on breaking of rest period in Elberta peach. Science, 126, 1178-1179.

10. Ellis, R.H. and Hong, T.D. (1984). Prunus seed germination and storage. In Maintenance of temperate fruit collections by long-term seed storage, IBPGR, Rome (in press).

11. El-Tomi, A.L., Shawky, I., Rawash, M.A. and Makrem, M. (1978). Effect of cold stratification and gibberellic acid on seed germination of Mit Ghamr peach. Research Bulletin of the Faculty of Agriculture, Ain Shams University, 834, 1-13. (From Seed Abstracts, 1981, 4, 569.)

12. Evenari, M., Konis, E. and Zirkin, D. (1948). On the germination of some rosaceous seeds. II. The germination of Kerassi seeds. Palestine Journal of Botany, 4, 166-170.

13. Flemion, F. (1934). Dwarf seedlings from non-after-ripened embryos of peach, apple, and hawthorn. Contributions from the Boyce Thompson Institute, 6, 205-209.

14. Flemion, F. and Waterbury, E. (1945). Further studies with dwarf seedlings of non-after-ripened peach seeds. Contributions from the Boyce Thompson Institute, 13, 415-422.

15. Fogle, H.W. (1958). Effects of duration of after-ripening, gibberellin and other pretreatments on sweet cherry germination and seedling growth. Proceedings of the American Society for Horticultural Science, 72, 129-133.

16. Fogle, H.W. and McCrory, C.S. (1960). Effect of cracking, after-ripening and gibberellin on germination of Lambert cherry seeds. Proceedings of the American Society for Horticultural Science, 76, 134-138.

17. Giersbach, J. and Crocker, W. (1932). Germination and storage of wild plum seeds. Contributions from the Boyce Thompson Institute, 4, 39-52.

18. Gil, S., Guerra, D.R. and Lavandero, R.R. (1979). [Germination of cherry seeds in relation to stratification conditions.] Ciencia e Investigación Agraria, 6, 95-98. (From Seed Abstracts, 1980, 3, 2342.)

19. Gordon, A.G. and Rowe, D.C.F. (1982). Seed Manual for Ornamental Trees and Shrubs. Forestry Commission Bulletin 59, 132 pp., HMSO, London.

20. Grisez, T.J. (1974). Prunus L. Cherry, peach, and plum. In Seeds of Woody Plants in the United States, pp. 658-673. Agricultural Handbook 450, Forest Service, U.S.D.A., Washington DC.

21. Grisez, T.J. (1976). Black cherry seeds stored 8 years. USDA Forest Service Tree Planters Notes, 27, 20-21, 24.

22. Haut, I.C. (1933). The influence of drying on the after-ripening and germination of fruit tree seeds. Proceedings of the American Society for Horticultural Science, 29, 371-374.

23. Havis, L. and Gilkeson, A.L. (1949). Starting seedlings of Montmorency cherry. Proceedings of the American Society for Horticultural Science, 53, 216-218.

24. Herrero, J. (1980). [Stratification of cherry stones.] Anales de la Estación Experimental de Aula Dei, 15, 46-53. (From Seed Abstracts, 1982, 5, 2217.)

25. Hesse, C.O. and Kester, D.E. (1955). Germination of embryos of Prunus related to degree of embryo development and method of handling. Proceedings of the American Society for Horticultural Science, 65, 251-264.

26. Hundal, P.S. and Khajuria, H.N. (1979). Effect of GA₃ and thiourea on seed germination of different varieties of peach. Indian Journal of Agricultural Sciences, 49, 417-419.

27. Kester, D.E. (1969). Almonds. In Handbook of North American Nut Trees (ed. R.A. Jaynes), pp. 309, Northern Nut Growers Association.

28. Kester, D.E. (1969). Pollen effects on chilling requirements of almond and almond-peach hybrid seeds. Journal of the American Society for Horticultural Science, 94, 318-321.

29. Laidlaw, T.F. (1983). Studies on pin cherry germination. II. The impact of temperature and temperature fluctuation in a 30 day initial treatment period preceding continuous cold stratification. Internal NOVA Report, pp. 1-61, Laidlaw Vegetation Consulting Ltd., Tofield, Alberta. (In preparation.)

30. Lin, C.F. and Boe, A.A. (1972). Effects of some endogenous and exogenous growth regulators on plum seed dormancy. Journal of the American Society for Horticultural Science, 97, 41-44.

31. Lockley, G.C. (1980). Germination of chokecherry (Prunus virginiana) seeds. Seed Science and Technology, 8, 237-244.

32. Michalska, S. (1982). Embryonal dormancy and induction of secondary dormancy in seeds of Mazzard cherry (Prunus avium L.). Arboretum Kórnickie, 27, 311-332.

33. Michalska, S. and Suszka, B. (1980). The effect of multiple induction of dormancy in Prunus avium L. seed. In Secondary dormancy of seeds of Prunus species, pp. 13-24, Polish Academy of Sciences, Institute of Dendrology, Kórnik near Poznañ, Poland.

34. Michalska, S. and Suszka, B. (1980). Effects of multiple induction of dormancy on germination of seeds of various Prunus L. species. In Secondary dormancy of seeds of Prunus species, pp. 27-40, Polish Academy of Sciences, Institute of Dendrology, Kórnik near Poznañ

35. Paul, J.R. and Biggs, R.H. (1963). Influence of gibberellic acid, mercaptoethanol, mercaptoethylamine, thiourea, and urea on the germination of 'Okinawa' peach seeds. Proceedings of the Florida State Horticultural Society, 76, 393-397.

36. Proctor, J.T.A. and Dennis, F.G. (1968). Gibberellin-like substances in after-ripening seeds of Prunus avium L. and their possible role in dormancy. Proceedings of the American Society for Horticultural Science, 93, 110-114.

37. Rouskas, D. and Hugard, J. (1982). Possibilité d'utilisation d'une cytokinine seule ou associeé à d'autres regulateurs de croissance pour lever la dormance des graines de rosaceés fruitierès du genre Prunus. Fruits, 37, 195-202.

38. Sharma, H.C. and Singh, R.N. (1978). Effect of stratification temperature, stratification period and seed coat on seed germination of peach cultivar 'Sharbati'. Scientia Horticulturae, 9, 47-53.

39. Simancik, F. (1970). Germination of seeds of Prunus laurocerasus L. after gibberellic acid treatment at warm, cold and warm-followed-by-cold stratifications. Proceedings of the International Seed Testing Association, 35, 393-403.

40. Suszka, B. (1962). [Influence of the temperature factors on the breaking of dormancy in mazzard seeds (Prunus avium L.).] Arboretum Kórnickie, 7, 189-275.

41. Suszka, B. (1964). [The influence of method and duration of stone storage on the germination capacity of mazzard cherry (Prunus avium L.).] Arboretum Kórnickie, 9, 223-235.

42. Suszka, B. (1967). [Studies on dormancy and germination of seeds from various species of the genus Prunus L.] Arboretum Kórnickie, 12, 221-282.

43. Suszka, B. (1970). [Storage of mazzard cherry (Prunus avium L.) seeds over many years.] Arboretum Kórnickie, 15, 129-137.

44. Suszka, B. (1978). Germination of tree seed stored in a partially afterripened condition. Acta Horticulturae, 83, 181-187.

45. Therios, I.N. (1982). Effects of temperature, moisture stress and pH on the germination of seeds of almond (Prunus amygdalus 'Truoito'). Seed Science and Technology, 10, 585-594.

46. Toit, H.J.du, Jacobs, G. and Strydom, D.K. (1979). Role of the various seed parts in peach seed dormancy and initial seedling growth. Journal of the American Society for Horticultural Science, 104, 490-492.

47. Tukey, H.B. (1934). Artificial culture methods for isolated embryos of deciduous fruits. Proceedings of the American Society for Horticultural Science, 32, 313-322.

48. Tukey, H.B. and Carlson, R.F. (1945). Morphological changes in peach seedlings following after-ripening treatments of the seeds. Botanical Gazette, 106, 431-440.

49. Zielinski, Q.B. (1958). Some factors affecting seed germination in sweet cherries. Proceedings of the American Society for Horticultural Science, 72, 123-128.

PYRUS

P. amygdaliformis Vill.	wild pear
P. arbutifolia L. [Aronia arbutifolia Ell.; Mespilus arbutifolia L.]	red chokeberry
P. betulaefolia Bnge.	wild pear
P. Calleryana Decne.	wild pear
P. communis L. [P. pyraster Borkh.; P. caucasica]	cultivated pear
P. dimorphophylla Makino	wild pear
P. elaeagrifolia Pall.	wild pear
P. P. Fauriei Scheidweiler	wild pear
P. gharbiana Trabut.	wild pear
P. hondoensis Nakai & Kikuchi	wild pear
P. malus L. [Malus domestica Borkh.; Malus communis DC.; Malus sylvestris Mill.]	apple
P. mamorensis Trabut.	wild pear
P. pashia Hamet	wild pear
P. pyrifolia (Burm.) Nakai [P. serotina Rehd.; P. sinensis Hort.]	Japanese pear, Chinese pear, sand pear
P. syriaca Boiss.	wild pear
P. ussuriensis Maxim. [P. sinensis Lindl.; P. Lindleyi; P. amurensis; P. ovoidea]	Harbin pear

I. Evidence of dormancy

Seeds of Pyrus spp. extracted from fresh, mature fruits are, almost without exception, dormant and fail to germinate unless specific treatments to remove dormancy are applied (2,32). If partly dormant seeds of Pyrus spp. are tested for germination or dried at temperatures of about 20°C or above secondary dormancy is likely to be induced and prevent germination (1,11-13,16,30). This secondary dormancy may be more difficult to remove than the innate dormancy of freshly extracted seeds (13).

II. Germination regimes for non-dormant seeds

P. communis

TP; S: 18°-22°C: 10-14d (AOSA)

P. malus

TP; S: 18°-22°C: 7-10d (AOSA)

Constant temperatures: 15°C (20,25)

Potassium cyanide: co-applied, 10^-5-10^-2 M, 20°C (18)

Pyrus spp.

S: 20°/30°C (16h/8h): 28d (ISTA)

III. Unsuccessful dormancy-breaking treatments

P. arbutifolia

Constant temperatures: 15°-30°C, 150d (5)

Alternating temperatures: 10°/30°C, 20°/30°C (5)

Pre-chill: 10°C, 60-120d (5)

P. betulaefolia

Pre-chill: -1°C (32); 5°C, 32d (32); -15°C, 10d (32)

P. Calleryana

Pre-chill: -6°C, 22d (32); 4°C, 4-44d, then GA₃, pre-applied, 24h, 250-1000 ppm (34)

GA₃: pre-applied, 24h, 250-1000 ppm, then pre-chill, 4°C, 4-44d (34)

P. communis

Pre-chill: 5°C, 32d (32)

P. elaeagrifolia

Pre-chill: -1°C (32); 5°C, 32d (32)

P. Fauriei

Pre-chill: -1°C (32)

P. malus

Alternating temperatures: 10°/25°C, with or without pre-soak, 20h (2)

GA₃: pre-applied, 3d, 5-200 ppm, germinate at 15°C (20); co-applied, 5-200 ppm, germinate at 15°C (20)

Removal of seed covering structures: outer coat (11); embryo, germinate at 20°/24°C in light, 10000 lux, 12h/d (35)

Kinetin: pre-applied, 3d, 1-100 ppm, germinate at 15°C (20); co-applied, 1-100 ppm, germinate at 15°C (20)

Hydrogen peroxide: pre-applied, 3d, 1-10%, germinate at 15°C (20); co-applied, 1-10%, germinate at 15°C (20)

Thiourea: pre-applied, 3d, 0.05-1%, germinate at 15°C (20); co-applied, 0.05-1%, germinate at 15°C (20)

Potassium nitrate: pre-applied, 3d, 0.05-1%, germinate at 15°C (20); co-applied, 0.05-1%, germinate at 15°C (20)

Ethephon: pre-applied, 100-1000 ppm (31); pre-applied, 3d, 0.1-1%, germinate at 15°C (20); co-applied, 0.1-1%, germinate at 15°C (20)

8-Hydroxyquinoline sulphate: pre-applied, 4-9w, 200 ppm (31)

Silver nitrate: pre-applied, 4-6w, 50-100 ppm (31)

Storage: room temperature, with or without pre-soak, 20h (2)

P. pashia

Pre-chill: -1°C (32)

P. pyrifolia

Pre-chill: 5°C, 32d (32)

P. ussuriensis

Pre-chill: -1°C, 2°C (32)

IV. Partly-successful dormancy-breaking treatments

P. amygdaliformis

Pre-chill: 2°C, 5°C, 10°C (32)

P. arbutifolia

Pre-chill: 1°C, 5°C, 60-120d (5)

P. betulaefolia

Pre-chill: 2°-10°C (32); 5°C, 32d (32)

P. Calleryana

Pre-chill: -1° to 10°C (32); -6°C, 22d, then 7°C, 10d (32); 7°C, 10d (32); 4°C, 4-24d, germinate at 20°C in light, 0.2 W m^-2, or dark (34); 4°C, 28-44d, germinate at 20°C, dark (34)

P. communis

Pre-chill: -1° to 7°C (32); 5°C, 32d (32)

Pre-soak: 24h, after pre-chill (32)

GA₃: pre-applied, 24h, 500 ppm, then pre-chill, 5°C, 69d (32); pre-applied, 24h, 500 ppm, then pre-chill, 5°C, 90d (23)

Dimethylsulphoxide: pre-applied, 24h, 10-100 ppm (32)

P. elaeagrifolia

Pre-chill: 2°-7°C (32)

GA₃: pre-applied, 24h, 500 ppm, then pre-chill, 5°C, 30-40d (32)

P. Fauriei

Pre-chill: 2°-10°C (32); 5°C, 32d (32)

P. hondoensis

Pre-chill: -1°C, 7°C (32)

P. malus

Constant temperatures: 1°-5°C, stored seeds (5); 5°-10°C, 10w (11)

Pre-chill: 1°-5°C, 4,10w (5); 0°C, 6w (3); 3°C, 80-120d, germinate at 20°C, 25°C, 20d (26); 5°C, 6d, germinate at 5°-28°C, 46d (1); 5°-10°C, 10w, germinate at 20°C (11); -2° to 10°C (2); in fruit, 10°-20°C, 21-112d, remove seed coats, germinate at 20°C (25); in fruit, 0°-5°C, 21,35,56d, remove seed coats, germinate at 20°C (25); in fruit, 0°C, 120d, remove seed coats, germinate at 20°C, 25°C (25); in fruit, 0°C, 8w, germinate at 15°C (19)

Warm stratification: 30°-35°C, 5d or more, germinate at 20°C (24)

Pre-soak: 48h, then pre-chill, 2°-5°C, 14-60d, germinate at 25°C (13)

Ethephon: 250-1000 ppm, after pre-chill (22)

Hydrogen cyanide: 10^-3 -10^-5 M (8)

GA₃: 125-500 ppm, after pre-chill (22)

Removal of seed covering structures: inner and outer coats (10); inner and outer coats, germinate at 15°C (19,20);

Scarification: concentrated sulphuric acid, 30 min, 30°C, germinate at 15°C (20); concentrated sulphuric acid, 30 min, 30°C, germinate at 15°C with GA₃, co-applied, 5-200 ppm (20); sulphuric acid, 0.8-100% (2)

P. pashia

Pre-chill: 5°-10°C (32); 4.4°C, 7-28d (7)

GA₃: pre-applied, 36h, 50, 100 mg/l, then pre-chill, 4°C, 7d (7)

Thiourea: pre-applied, 36h, 1, 2.5 g/l, then pre-chill, 4°C, 7d (7)

P. pyrifolia

Pre-chill: 2°-7°C (32); 5°C, 5m, germinate at 13°-18°C (15)

P. syriaca

Pre-chill: 5°C, 32d (32)

P. ussuriensis

Pre-chill: 5°C (32)

V. Successful dormancy-breaking teatments

P. amygdaliformis

Pre-chill: 5°C, 25d (32); 7°C (32)

P. arbutifolia

Pre-chill: 1°C, 90d, germinate at 20°C (5)

P. betulaefolia

Pre-chill: 5°C, 85d (32)

P. Calleryana

Pre-chill: 5°C, 80d (32); 5°C, 32d (32); 4°C, 28-44d, germinate at 20°C, in light, continuous, 0.2 W m^-2 (34)

P. communis

Embryo excision (AOSA)

Pre-chill: 5°C, 130d (32); 60-90d (27)

Removal of seed covering structures: inner and outer coats, after pre-chill (32)

GA₃: pre-applied, 24h, 500 ppm, then pre-chill, 5°C, 95d (32)

P. dimorphophylla

Pre-chill: 5°C, 90d (32)

P. elaeagrifolia

Pre-chill: 5°C, 130d (32)

P. Fauriei

Pre-chill: 5°C, 80d (32)

P. gharbiana

Pre-chill: 5°C, 80d (32)

P. hondoensis

Pre-chill: 5°C, 170d (32); 2°C, 5°C (32)

P. malus

Embryo excision (AOSA, ISTA)

Constant temperatures: 5°C, 52d (1)

Pre-chill: 75-100d (27); 0°-10°C, 8-10w (4); 3°C, 80d, germinate at 15°C, 20d (26); 5°-10°C, 180d (6); 5°C, 75d, germinate at 15°C (20); 5°C, 100d, germinate at 25°C (1); 5°C, 45d, then remove seed coats, germinate at 25°C (1); 4°C, 68d, germinate at 25°C (14); 5°C, 21d, germinate at 5°C, 28d (1); 0°C, 127-190d, germinate at 5°-10°C, 24d (11); 0°C, 160-190d, germinate at 20°C, 13d (11); 1°-2°C, 56d (12); 5°C, 21d, then remove seed coats, germinate at 15°-17°C (9); in fruit, 0°C, 5°C, 112d, then remove seed coats, germinate at 20°C (25); in fruit, 0°C, 120d, then remove seed coats, germinate at 5°C, 10°C, 15°C (25); in fruit, 0°C, 11w, germinate at 15°C (19); in fruit, 0°C, 8-40w, then remove seed coats, germinate at 15°C (19)

Removal of seed covering structures: inner and outer coats, germinate at 15°C with GA₃, co-applied, 5-200 ppm (20) Storage: 20°C, 50d, then remove seed coats, pre-chill, 5°-10°C, 68d, germinate at 19°C, 4d (11)

Ethephon: co-applied, 100 mg/l, pre-chill, 40d, then excise embryo, germinate at 20°/24°C (night/day) in light, 10000 lux, 12h/d (35)

P. mamorensis

Pre-chill: 5°C, 60d (32)

P. pashia

Pre-chill: 5°C, 40d (32)

GA₃: pre-applied, 36h, 150 mg/l, then pre-chill, 4°C, 7-28d (7); pre-applied, 36h, 50, 100 mg/l, then pre-chill, 4°C, 14-28d (7)

Thiourea: pre-applied, 36h, 5 g/l, then pre-chill, 4°C, 7-28d (7); pre-applied, 36h, 1-2.5 g/l, then pre-chill, 4°C, 14-28d (7)

P. pyrifolia

Pre-chill: 5°C, 160d (32)

P. syriaca

Pre-chill: 5°C, 80d (32); 5°C, 9d (32)

P. ussuriensis

Pre-chill: 5°C, 100d (32); 7°C (32)

Pyrus spp.

Excise embryo, Pre-chill (ISTA)

VI. Comment

Seed storage and germination of apple and pear for genetic resources conservation has recently been reviewed elsewhere (9). The preferred ISTA and AOSA methods for testing viability are the tetrazolium or excised embryo tests. Chapter 11 provides details of these procedures. From the above it is apparent that pre-chill treatments have been widely applied to promote the germination of dormant seeds of Pyrus spp. In addition to conventional pre-chill treatments to the seeds, Pyrus seed dormancy can be removed by pre-chill treatments whilst the seeds remain within the fruits (19,21). However, the longer that seeds remain within fruits under such conditions the longer they take to germinate (33). There is also some evidence that pre-chilled seeds subsequently dried and stored require additional pre-chill treatments after storage before they will germinate (12). In fact this is because drying the seeds at warm temperatures induces secondary dormancy (1,11-13,16,30). It is recommended that the seeds be extracted from the fruits as soon as possible after harvest and dried at around 15°C with a high airflow rate and low relative humidity (about 10%) (9). Some intermediate storage of fruits is probably unavoidable. During this period the fruits should be stored at 5°C (9).

Although optimum temperatures for pre-chilling may vary between species (32), a common pre-chill temperature of about 5°C can be used for all species provided the treatment period is allowed to vary (32). Unfortunately the pre-chill treatment periods required to promote germination of the most dormant seed are substantial, for example 170-180 days (6,32). In general seeds of pear species require shorter pre-chill treatments than those of apple (27).

Seeds will eventually germinate during a pre-chill treatment at 5°C, for example, after 15 weeks (1) or 17-19 weeks (5). In fact the germination of dormant seeds is higher the lower the temperature, at least down to about 5°-10°C (1,11,25,26). The range of 15°-17°C has been described as the compensation temperature (1). If seeds are tested for germination at temperatures below this range germination may be reduced because of secondary dormancy. If seeds are tested for germination at temperatures below this range dormancy is likely to continue to be broken during the germination tests (1). However, the mean time to germinate will also increase (25). Thus 15°C is a sensible germination test temperature for Pyrus spp. provided seed dormancy is removed by another treatment.

Seed coats of Pyrus spp. remain permeable to moisture after drying (28). Seed coat removal aids germination of dormant seeds and is preferable to 15 or 30 minutes concentrated sulphuric acid scarification (20). However, if seed coats are removed from fresh seeds and these seeds tested for germination at 25°C then the resulting seedlings are dwarf (10). Thus a germination test temperature of 15°C should be used even if seedcoats are removed. Seed coat removal is rarely completely effective on its own, but pre-chill treatment periods can be reduced if seed coats are removed (28). There is no effect of the seed coat during the pre-chill treatment (29), and it is both easier and preferable (to avoid fungal decay during the pre-chill) to remove seed coats from the moist seeds after the pre-chill treatment but before the germination test (29).

The following general procedure has been recommended and found to be satisfactory. Pre-chill the seeds on top of moist filter paper at 5°C for 21 days; then remove all three seed coats from each seed and place the seeds on clean moist filter paper and test for germination at 15°-17°C for 21 days; return non-deteriorated seeds which fail to germinate within this period to 5°C for a further (21 day) pre-chill treatment and then return to 15°-17°C (9).

At 15°C radicle growth may be substantially greater than hypocotyl growth (9). The optimum temperature for the former is 15°C whereas that for the latter is 25°C (17). Within the range 5°-25°C, the temperature at which embryo germination occurs does not affect subsequent radicle or hypocotyl growth rates in other environments (17). Thus to aid normal seedling development it is advisable to transfer germinating seedlings from 15°C to 20°C to enable more balanced growth of both radicle and hypocotyl (9).

Gibberellins could be provided as an additional stimulus to promoting the germination of the more dormant seeds. Pre-applied GA₃ - 24h, 500 ppm (23,32) - is suggested. This is more promotory if applied prior to the pre-chill treatment (32).

VII. References

1. Abbott, D.L. (1955). Temperature and the dormancy of apple seeds. Proceedings of the XIVth International Congress, Scheveningen, 1, 746-753.

2. Bakke, A.L., Richey, H.W. and Reeves, K. (1926). Germination and storage of apple seeds. Iowa Agricultural Experimental Station Research Bulletin, 97, 241-255.

3. Connor, H.C. (1947). The storage and germination of apple seed. Agricultural Gazette of New South Wales, 58, 414-416.

4. Crocker, W. (1928). Storage, after-ripening, and germination of apple seeds. American Journal of Botany, 15, 625-626.

5. Crocker, W. and Barton, L.V. (1931). After-ripening, germination and storage of certain rosaceous seeds. Contributions from the Boyce Thompson Institute, 3, 385-404.

6. Dall'Orto, F.A.C., Ojima, M., Rigitano, O., Scaranari, H.J. and Martins, F.P. (1978). [Germination of apple seeds.] Bragantia, 37, 83-91. (From Seed Abstracts, 1979, 2, 2645, 2885.)

7. Dhillon, B.S. and Sharma, M.R. (1978). Note on the effect of growth-regulators on the germination of wild pear seeds. Indian Journal of Agricultural Sciences, 48, 370-372.

8. Dziewanowska, K., NiedŸwiedŸI., Chodelska, I. and Lewak, S. (1979). Hydrogen cyanide and cyanogenic compounds in seeds. I. Influence of hydrogen cyanide on germination of apple embryos. Physiologie Végétale, 17, 297-303.

9. Ellis, R.H. (1982). Seed storage and germination of apple and pear. Plant Genetic Resources Newsletter, 50, 53-61.

10. Flemion, F. (1934). Dwarf seedlings from non-after-ripened embryos of peach, apple and hawthorn. Contributions from the Boyce Thompson Institute, 6, 205-209.

11. Harrington, G.T. (1923). After-ripening and germination of apple seeds. Journal of Agricultural Research, 23, 153-161.

12. Haut, I.C. (1932). The influence of drying on the after-ripening and germination of fruit tree seeds. Proceedings of the American Society for Horticultural Science, 29, 371-374.

13. Kamiñski, W. and Zagaja, S.W. (1974). [Secondary dormancy of apple seeds. Part I. The effect of raised temperature.] Prace Instytutu Sadownictwa w Skierniewicach, A, 18, 3-8.

14. Luckwill, L.C. (1952). Growth-inhibiting and growth-promoting substances in relation to the dormancy and after-ripening of apple seeds. Journal of Horticultural Science, 27, 53-67.

15. Omura, M., Sato, Y. and Seike, K. (1978). Long term preservation of Japanese pear seeds under extra-low temperatures. In Long Term Preservation of Favourable Germ Plasm in Arboreal Crops (eds. T. Akihama and K. Nakajima), pp. 26-30, Fruit Tree Research Station, M.A.F., Fujimoto, Japan.

16. Perino, C. and Côme, D. (1977). Influence de la température sur les phases de la germination de l'embryon de pommier (Pirus malus L.). Physiologie Végétale, 15, 469-474.

17. Perino, C. and Côme, D. (1979). Conditions de germination de l'embryon de pommier et croissance de la racine et de l'hypocotyle de la plantule. Physiologie Végétale, 17, 829-838.

18. Perino, C. and Côme, D. (1981). Influence du cyanure de potassium sur la germination de l'embryon de pommier (Pirus malus L.) non dormant. Physiologie Végétale, 19, 219-227.

19. Sanada, T., Yoshida, Y. and Haniuda, T. (1980). [Studies on the method of seed storage in apple breeding. I. Suitable method for short-term storage.] Bulletin of the Fruit Tree Research Station, Series C, Morioka, 7, 1-14.

20. Sanada, T., Yoshida, Y. and Haniuda, T. (1980). [Studies on the method of seed storage in apple breeding. II. Effective method for breaking dormancy of dry stored seed.] Bulletin of the Fruit Tree Research Station, Series C, Morioka, 7, 15-31.

21. Sanada, T., Yoshida, Y. and Haniuda, T. (1981). [Studies on the method of seed storage in apple breeding. III. Differences in storage using early to late maturing cultivars and wild species.] Bulletin of the Fruit Tree Research Station, Series C, Morioka, 8, 15-29.

22. Sinha, M.M., Pal, R.S. and Awasthi, D.N. (1977). Effect of stratification and plant growth regulating substances on seed germination and seedling growth in apples. Progressive Horticulture, 9 (2), 27-30.

23. Shawky, I., Tomi, A. El., Rawash, M.A. and Makanem, M. (1978). Preliminary studies on the germination of Pyrus communis seeds. Research Bulletin, Ain Shams University, Faculty of Agriculture, 826, 12 pp. (From Seed Abstracts, 1980, 3, 1030.)

24. Thévenot, C. and Côme, D. (1978). Levée de dormance des embryons de pommier (Pirus malus L.) par traitement des graines à des températures élevées. Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences, D, 287, 1127-1129.

25. Thévenot, C., Perino, C. and Côme, D. (1983). Influence of temperature on breaking of dormancy, germination sensu stricto and growth of apple embryo: thermal optimum of these phenomena. Israel Journal of Botany, 32, 139-145.

26. Tylkowski, T. (1978). [New method for evaluating germinability of common antonovka apple seeds in a cold-warm thermal regime.] Arboretum Kórnickie, 23, 153-159.

27. United States Department of Agriculture. Some characteristics of seeds of species used as rootstocks for tree fruits and nuts. In Seeds: The Yearbook of Agriculture 1961 (ed. A. Stefferud), pp. 550-551, USDA, Washington D.C.

28. Visser, T., (1954). After-ripening and germination of apple seeds in relation to the seed coats. Proceedings Koninklijke Nederlandse Akademie van Wetenschappen, 57, 175-185.

29. Visser, T. (1956). The role of seed coats and temperature in after-ripening, germination and respiration of apple seeds. Proceedings Koninklijke Nederlandse Akademie van Wetenschappen, 59, 211-222.

30. Visser, T. (1956). Some observations on respiration and secondary dormancy in apple seeds. Proceedings Koninklijke Nederlandse Akademie van Wetenschappen, 59, 314-324.

31. Wan, C.K. (1980). The role of ethylene in seed dormancy with particular reference to apple (Malus domestica Bork H.) seeds. Pertanika, 3, 78-81. (From Seed Abstracts, 1981, 4, 3721.)

32. Westwood, M.N. and Bjornstad, H.O. (1968). Chilling requirements of dormant seeds of 14 pear species as related to their climatic adaptation. Proceedings of the American Society for Horticultural Science, 92, 141-149.

33. Wills, R.B.H. and Scriven, F.M. (1983). Relation between germination of apple seeds and susceptibility of fruit to storage breakdown. Journal of Horticultural Science, 58, 191-195.

34. Shen, X.-S. and Mullins, M.G. (1983). Seed germination in pear rootstock. Australian Horticulture, 81, 50-51.

35. Sinska, I. and Gladon, R.J. (1984). Ethylene and the removal of embryonal apple seed dormancy. HortScience, 19, 73-75.

RUBUS

R. allegheniensis Porter	blackberry, mountain blackberry
R. axillaris Lej.	blackberry
R. bellardii Weihe & Nees [R. glandulosus Bellardi]	blackberry
R. caesius L.	dewberry
R. chamaemorus L.	bakeapple, cloudberry
R. corylifolius (Sm.)	blackberry
R. fuscus Weihe & Nees	blackberry
R. harmannii Sudre	blackberry
R. idaeus L.	European raspberry, red and yellow garden raspberry
R. insularis F. Aresch.	blackberry
R. laciniatus Willd.	cut-leaved blackberry, evergreen blackberry
R. lindebergii P.J. Muell.	blackberry
R. neglectus Peck	purple raspberry
R. nessensis W. Hall	blackberry
R. nitidus Weihe & Nees [R. divaricatus P.J. Muell.]	blackberry
R. occidentalis L.	black raspberry, black cap raspberry
R. odoratus L.	flowering raspberry, thimbleberry
R. phoenicolasius Maxim.	wineberry
R. plicatus Weihe & Nees	blackberry
R. radula Weihe ex.Boenn.	blackberry
R. scheutzii Lindeb.
R. scissus W. Wats.	blackberry
R. sprengelii Weihe
R. sulcatus Tratt.
R. taeniarum Lindeb.	blackberry
R. thyrsanthus Focke	blackberry
R. vestitus Weihe & Nees	blackberry

I. Evidence of dormancy

Seeds of Rubus spp. show delayed and poor germination thereby causing substantial problems for breeders (5,7,13-15,18). Dormancy is not limited to that imposed by the seed coat alone (7,8,10,11,14). Many authors have failed to indicate the species. Where the species has been identified it is given here; the remaining information is classified as blackberry, dewberry or raspberry.

II. Germination regimes for non-dormant seeds

-

III. Unsuccessful dormancy-breaking treatments

R. allegheniensis

Pre-chill: 0°-3°C, 5°-8°C, 10°C, 1-8m (7); plus potassium nitrate, co-applied, 0.2% (7)

Vitamin B₁: pre-applied (7)

Acetic acid: pre-applied, 6, 12h (7)

R. chamaemorus

Pre-chill: 1°C, 3-5m (15); 4°C, 7m (22); 4°C, 7m, then pre-soak, 8m (22); 4°C, 7m, then remove endocarp (22); 4°C, 7m, then kinetin, co-applied, 4.6x10^-7 M (22)

Scarification: concentrated sulphuric acid, 0.5-2h (15)

R. corylifolius, R. fuscus

Scarification: concentrated sulphuric acid, 60 min, then calcium hypochlorite, pre-applied, 5d, 1% in saturated calcium hydroxide (14)

R. idaeus

Pre-chill: 4-5m (1); 5°C, 3m (10)

Pre-soak: (16)

Oxygen: (16)

Ether: (16)

Scarification: acid (16)

R. insularis, R. lindebergii

Scarification: concentrated sulphuric acid, 60 min, then calcium hypochlorite, pre-applied, 5d, 1% in saturated calcium hydroxide (14)

R. neglectus

Pre-chill: 2°-4°C, 5m (21)

Scarification: concentrated sulphuric acid, 4h (21)

R. phoenicolasius

Pre-chill: 2°-4°C, 5m (21)

Scarification: concentrated sulphuric acid, 1,4,5.5h (21)

R. vestitus

Scarification: concentrated sulphuric acid, 60 min, then calcium hypochlorite, pre-applied, 5d, 1% in saturated calcium hydroxide (14)

Rubus spp. - blackberry

Pre-chill: 5°C, 3m (10); 2°-4°C, 5m (21); 5°-7°C, 3m, germinate in dark (17)

Pre-soak: 1,2,3w (18)

Removal of seed covering structures: excise embryo (11)

Sodium hypochlorite: pre-applied, 1,2,3w, 1% (18)

Scarification: concentrated sulphuric acid, 30 min (18,23); concentrated sulphuric acid, 1,2,5.5h (21); concentrated sulphuric acid, 30 min, then pre-chill, 2°C, 4m (13)

Thiourea: pre-applied, 6d, 1% (23)

Rubus spp. - dewberry

Pre-chill: 2°-4°C, 5m (21)

Scarification: concentrated sulphuric acid, 1,5h (21)

Rubus spp. - raspberry

Pre-chill: 2°-4°C, 5m (21); 5°-7°C, 3m, germinate in dark (17)

Calcium chloride: (12)

IV. Partly-successful dormancy-breaking treatments

R. allegheniensis

Warm stratification: 3.5m, then pre-chill, 3°-5°C, 4m (7)

Scarification: concentrated sulphuric acid, 0.5,1,1.5h (7); concentrated sulphuric acid, 10-60 min, then pre-chill, 3°-5°C, 3m (7); concentrated sulphuric acid, 50,60 min, then pre-chill, 1°-5°C, 1-3m (6)

R. axillaris, R. bellardii, R. caesius

Scarification: concentrated sulphuric acid, 60 min, then calcium hypochlorite, pre-applied, 5d, 1% in saturated calcium hydroxide (14)

R. chamaemorus

Pre-chill: 1°C, 6-13m (15); 4°C, 7m, then remove endocarp and nick seed coat (22); 4°C, 7m, then GA₃, co-applied, 5.7x10^-7-5.7x10^-5 M (22); 4°C, 7m, then kinetin, co-applied, 4.6x10^-6, 4.6x10^-5 M (22); 4°C, 7m, then pre-soak, 6h, 23°C, then remove endocarp and nick seed coat (22)

Light: 665 lux, 12h/d, at 18°C (22)

R. hartmannii

Scarification: concentrated sulphuric acid, 60 min, then calcium hypochlorite, pre-applied, 5d, 1% in saturated calcium hydroxide (14)

R. idaeus

Warm stratification: 25°C, 4-6w, then pre-chill, 0°C, 7-8w (4); 15°-20°C, 140d (16)

Calcium hypochlorite: pre-applied, 4d, 1% (4)

Removal of seed covering structures: endocarp, then scarify, concentrated sulphuric acid, 2h, germinate at 18°-23°C in dark (16)

Scarification: concentrated sulphuric acid, 15-30 min, then pre-chill, 1°-4°C, 1-3m (6); concentrated sulphuric acid, 20 min, then calcium hypochlorite, pre-applied, 7d, 3% (20)

R. laciniatus

Pre-chill: 4-5m (1)

R. neglectus

Scarification: concentrated sulphuric acid, 1,2h (21)

R. nessensis, R. nitidus

Scarification: concentrated sulphuric acid, 60 min, then calcium hypochlorite, pre-applied, 5d, 1% in saturated calcium hydroxide (14)

R. occidentalis

Warm stratification: 20°/30°C (night/day), 3m, then pre-chill, 5°C, 3m (10)

Sodium hypochlorite: pre-applied, 6d, 1%, then pre-chill, 2°-3°C, 5m (18)

Scarification: concentrated sulphuric acid, 15,20 min, then pre-chill, 1°-4°C, 1-3m (6); concentrated sulphuric acid, 20 min, then pre-chill, 2°-3°C, 5m (18)

R. odoratus

Pre-chill: 4-5m (1)

R. phoenicolasius

Scarification: concentrated sulphuric acid, 2h (21)

R. plicatus, R. radula, R. scheutzii, R. scissus, R. sprengelii, R. sulcatus, R. taeniarum, R. thyrsanthus

Scarification: concentrated sulphuric acid, 60 min, then calcium hypochlorite, pre-applied, 5d, 1% in saturated calcium hydroxide (14)

Rubus spp. - blackberry

Pre-chill: 0°-2°C, 5-6m (2); 3°C, 4-5m (11); 4°-7°C, 3m, light, germinate in light (17)

Warm stratification: 20°/30°C (16h/8h), 3m, then pre-chill, 5°C, 3m (10)

Potassium hydroxide: pre-applied, 30-60 min, 2 M (14)

Sodium hypochlorite: pre-applied, 1,2w, 1%, then warm stratification, 21°-24°C, 7w, then pre-chill, 2°-3°C, 3m (18) Calcium hypochlorite: pre-applied, 6d, 1% (23)

Scarification: concentrated sulphuric acid, 30 min (14); concentrated sulphuric acid, 2-4h (2); concentrated sulphuric acid, 4h (21); concentrated sulphuric acid, 1,3h, at 0°C, then pre-chill, 2°C, 4m (13); concentrated sulphuric acid, 0.5h, then warm stratification, 21°-24°C, 7w, then pre-chill, 2°-3°C, 3m (18); concentrated sulphuric acid, 0.5-2h, then calcium hypochlorite, pre-applied, 5d, 0.5, 1% in saturated calcium hydroxide (14); concentrated sulphuric acid, 30 min, then calcium hypochlorite, pre-applied, 6d, 1%, then pre-chill, 2°-4°C, 6w (23); concentrated sulphuric acid, 3h, then pre-soak, 30 min, oxygenated water, germinate at 20°/10°C in light, 14h/d (25); concentrated sulphuric acid, 3h, then pre-soak, 30 min, oxygenated 10^-5 M GA, germinate at 20°/10°C in light, 14h/d (25); concentrated sulphuric acid, 3h, then pre-soak, 30 min, oxygenated 10^-7 M benzyladenine, germinate at 20°/10°C in light, 14h/d (25)

Rubus spp. - dewberry

Scarification: concentrated sulphuric acid, 2,4h (21)

Rubus spp. - dewberry

Rubus spp. - raspberry

Pre-chill: -2°C, 6m (5); 5°-7°C, 3m, light, germinate in light (17); 3°-4°C, 8w (8); 6m, then calcium hypochlorite, pre-applied, 4d, 1% in saturated calcium hydroxide (19)

Warm stratification: 15°C, 8w, light, 16h/d (8); 15°C, 6w, light, 16h/d, then pre-chill, 3°-4°C, 2w (8); 15°C, 4w, light, 16h/d, then pre-chill, 3°-4°C, 4w (8); 15°C, 2w, light, 16h/d, then pre-chill, 3°-4°C, 6w (8); 21°-24°C, 2m, then pre-chill, 2°-3°C, 3m (18)

Pre-soak: 1w, then pre-chill, 2°-3°C, 3m (18); 1w, then warm stratification, 21°-24°C, 2m, then pre-chill, 2°-3°C, 3m (18)

Light: daylight supplemented by mercury vapour lamp, 16h/d (8)

Sodium hypochlorite: pre-applied, 6,9d, 0.5, 1% (8); pre-applied, 1w, then pre-chill, 2°-3°C, 3m (18); pre-applied, 1w, then warm stratification, 21°-24°C, 2m, then pre-chill, 2°-3°C, 3m (18)

Potassium hydroxide: (12)

GA₃: (12)

Scarification: notch (3); sandpaper (5); sulphuric acid (12); concentrated sulphuric acid, 20-50 min (5); concentrated sulphuric acid, 10-30 min (8); concentrated sulphuric acid, 50 min (24); concentrated sulphuric acid, 1-4h (21); concentrated sulphuric acid, 20 min, then pre-chill, 2°-3°C, 3m (18); concentrated sulphuric acid, 20 min, then warm stratification, 21°-24°C, 2m, then pre-chill, 2°-3°C, 3m (18); concentrated sulphuric acid, 10,20 min, then sodium hypochlorite, pre-applied, 6,9d, 0.5, 1% (8); concentrated sulphuric acid, 20 min, then sodium hypochlorite, pre-applied, 6d, 0.5%, then pre-chill, 3°-4°C, 4-10w (8); concentrated sulphuric acid, 20 min, then sodium hypochlorite, pre-applied, 6d, 1%, then GA₃, co-applied, 100-1000 ppm (8); concentrated sulphuric acid, 20 min, then sodium hypochlorite, pre-applied, 6d, 1%, then pre-chill, 3°-4°C, 4,6w, then GA₃, co-applied, 100-1000 ppm (8); concentrated sulphuric acid, 20 min, then calcium hypochlorite, pre-applied, 6d, 1, 2% in saturated calcium hydroxide (8); concentrated sulphuric acid, 20 min, then calcium hypochlorite, pre-applied, 6d, 1, 2% in saturated calcium hydroxide, then pre-chill, 3°-4°C, 4,6w (8); concentrated sulphuric acid, 20 min, then thiourea, pre-applied, 6d, 0.5-2% (8); concentrated sulphuric acid, 20 min, then thiourea, pre-applied, 6d, 0.5-2% in saturated calcium hydroxide (8); concentrated sulphuric acid, 20 min, then thiourea, pre-applied, 6d, 1% in saturated calcium hydroxide, then GA₃, co-applied, 500 ppm (8)

V. Successful dormancy-breaking treatments

R. idaeus

Warm stratification: 20°/30°C (night/day), 3m, then pre-chill, 5°C, 3m, germinate at 20°/30°C (night/day) (10)

R. occidentalis

Warm stratification: 21°-24°C, 2m, then pre-chill, 2°-3°C, 3m (18)

Sodium hypochlorite: pre-applied, 6d, 1%, then warm stratification, 21°-24°C, 2m, then pre-chill, 2°-3°C, 3m (18)

Scarification: concentrated sulphuric acid, 20 min, then warm stratification, 21°-24°C, 2m, then pre-chill, 2°-3°C, 3m (18)

Rubus spp. - blackberry

Removal of seed covering structures: endocarp, then pre-chill, 2°-3°C, 5m (9)

VI. Comment

It should be clear from the long list of only partly successful dormancy-breaking treatments which incorporate several stimulatory treatments that the promotion of germination of dormant seeds of Rubus spp. is difficult and rarely sufficient to promote full germination. For this reason the topographical tetrazolium test has been recommended as essential for assessing seed viability in Rubus spp. (19): no combined dormancy-breaking and germination test procedure has yet been devised which will promote the germination of all seeds of all Rubus spp., or which will promote the germination of all seeds of all cultivars within a single species.

Single application of many dormancy-breaking agents such as pre-chilling, alternating temperatures, light, potassium nitrate, thiourea and kinetin are generally ineffective (7,8,10,17,21,22), but have some effect when applied to seeds previously scarified (4,6-9,13,18,20,22,23). Gibberellins, sodium hypochlorite, calcium hypochlorite or prolonged warm stratification applied singly can promote the germination of intact seeds of Rubus spp. (4,7,8,22), but their effectiveness is greatly increased when applied to seeds previously scarified (8,14,18,20,23). However, scarification alone is either unsuccessful (11,13,15,16,22,23) or has only limited effect (2,5-8,14,16,18,20,21,24). Sulphuric acid (concentrated) scarification gives variable results depending upon treatment duration, seed lots, and species. For the majority of raspberry species a 20-30 minute treatment is safe and partly effective (5,6,8,18,20), but some seed lots have a requirement for 1-4 hours treatment for maximum promotion (21). For the majority of blackberry species 30 minute to 2 hour treatments are optimal (6,7,14), although some require 2-4 hours (2,13,21) whilst 3 hour duration treatments may kill seeds in other blackberry seed lots (13). Consequently, to avoid damage to the seeds, it is suggested that the duration of the concentrated sulphuric acid scarification should not exceed 20 minutes.

It is quite clear that gene banks will have to use multifactor dormancy-breaking treatments to promote the germination of seeds of Robus spp. The following multifactor treatment has been recommended and, though not completely successful, is suggested as the most satisfactory treatment currently available. Scarify the seeds in concentrated sulphuric acid for 20 minutes, then soak for 6 days in a 1% solution of calcium hypochlorite dissolved in saturated calcium hydroxide, then pre-chill the seeds at 3°-5°C for 6 weeks, and finally test for germination at 20°/30°C (16h/8h) in the light on the top of filter papers moistened with 500 ppm GA₃ (8).

The following investigations are suggested to those attempting to improve this procedure: the effect of replacing the calcium hypochlorite treatment with a shorter duration hydrogen peroxide treatment; the effect of an additional warm stratification treatment prior to pre-chilling; the effect of alternating warm stratification/pre-chilling treatments - see section on Prunus; and the effect of co-application of gibberellins during pre-chilling as well as during the germination test.

VII. References

1. Adams, J. (1927). The germination of the seeds of some plants with fleshy fruits. American Journal of Botany, 14, 415-428.

2. Afanasiev, M. (1942). Propagation of trees and shrubs by seeds. Oklahoma Agricultural Experiment Station, Circular 106, 43 pp.

3. Baumeister, G. (1959). [A method for accelerating germination in Rubus seed. Short communication.] Zuchter, 29, 185-187. (From Horticultural Abstracts, 1959, 29, 3324.)

4. Cadman, C.H. and Anderson, K.S. (1954). Report of the Scottish Horticulture Research Institute for 1953-1954, pp. 17-19.

5. Fejer, S.O. and Spangelo, L.P.S. (1971). Seed germination in the red raspberry. Fruit Varieties and Horticultural Digest, 25, 75-76.

6. Heit, C.E. (1966). Propagation from seed. VII. Germinating six hardseeded groups. American Nurseryman, 125, 10-12, 37, 39-41, 44-45.

7. Heit, C.E. and Slate, G.L. (1950). Treatment of blackberry seed to secure first year germination. Proceedings of the American Society for Horticultural Science, 55, 297-301.

8. Jennings, D.L. and Tulloch, B.M.M. (1965). Studies on factors which promote germination of raspberry seeds. Journal of Experimental Botany, 16, 329-340.

9. Kerr, E.A. (1954). Seed development in blackberries. Canadian Journal of Botany, 32, 654-672.

10. Krepting, L.W. and Roe, E.I. (1949). The role of some birds and mammals in seed germination. Ecological Monographs, 19, 269-286.

11. Lasheen, A.M. and Blackhurst, H.T. (1956). Biochemical changes associated with dormancy and after-ripening of blackberry seed. Proceedings of the American Society for Horticultural Science, 67, 331-340.

12. Misic, P.D. and Belic, M.V. (1973). [Methods for improving the germination of red raspberry seeds.] Jugoslovensko Vocarstvo, 7, 153-156. (From Horticultural Abstracts, 1975, 45, 1562.)

13. Moore, J.N., Brown, G.R. and Lundergan, C. (1974). Effect of duration of acid scarification on endocarp thickness and seedling emergence of blackberries. HortScience, 9, 204-205.

14. Nybom, H. (1980). Germination in swedish blackberries (Rubus L. subgen. Rubus). Botaniska Notiser, 133, 619-631.

15. Rantala, E.-M. (1976). Sexual reproduction in the cloudberry. Annales Agriculturae Fenniae, 15, 295-303.

16. Rose, R.C. (1919). After-ripening and germination of seeds of Tilia, Sambucus, and Rubus. Botanical Gazette, 67, 281-308.

17. Scott, D.H. and Draper, A.D. (1967). Light in relation to seed germination of blueberry, strawberries and Rubus. HortScience, 2, 107-108.

18. Scott, D.H. and Ink, D.P. (1957). Treatment of Rubus seeds prior to after-ripening to improve germination. Proceedings of the American Society for Horticultural Science, 69, 261-267.

19. Sokolova, V.A. and Kichina, V.V. (1971). [Increasing the germination rate of raspberry seeds.] Vestnik Sel'skokhozyaistvennoi Nauki, 16, 87-90. (From Horticultural Abstracts, 1972, 42, 3289.)

20. Topham, P.B. and Carmichael, E. (1972). The improvement of seedling production in two subfertile raspberry crosses following the application of growth substances. Journal of Horticultural Science, 47, 5-9.

21. Tukey, H.B. (1924). Studies of fruit seed storage and germination. New York State Agricultural Experiment Station Bulletin, 509, 3-19.

22. Warr, H.J., Savory, D.R. and Bal. A.K. (1979). Germination studies of bakeapple (cloudberry) seeds. Canadian Journal of Plant Science, 59, 69-74.

23. Wenzel, W.G. and Smith, C.W.J. (1975). Germination tests with blackberry seeds. Angewandte Botanik, 49, 11-14.

24. Williams, D.D. (1956). Sulphuric acid treatment of raspberry seed. Canadian Horticulture Council Report 1955, 60 pp.

25. Lundergan, C.A. and Carlisi, J.A. (1984). Acceleration of the reproductive cycle of the cultivated blackberry. HortScience, 19, 102-103.